past lessons and future prospects: plant breeding for yield and persistence in cool-temperate...

Past lessons and future prospects: plant breeding foryield and persistence in cool-temperate pastures

A. J. Parsons*, G. R. Edwards†, P. C. D. Newton*, D. F. Chapman‡, J. R. Caradus§,

S. Rasmussen* and J. S. Rowarth–

*AgResearch Grasslands, Palmerston North, New Zealand, †Lincoln University, Lincoln, New Zealand,

‡DairyNZ, Lincoln, Canterbury, New Zealand, §Grasslanz Technology, Palmerston North, New Zealand, and

–Massey University, Palmerston North, New Zealand

Abstract

Pastoral-based animal production systems are under

increasing pressure to provide the high quantity and

quality of feed needed for optimal ruminant perfor-

mance. The capacity of farmers to increase forage yield

further, solely by increasing fertilizer inputs or through

improved pasture management, is limited. Emerging

requirements to balance industry production targets

against the need to reduce greenhouse gas emissions

and N losses pose further challenges. Plant breeding is

being asked to deliver results more urgently than at any

time previously, and this review attempts to highlight

issues that might limit the prospects for future progress

by seeking lessons from four past examples: (i) white

clover breeding gains and the need to consider the

complexity of the grazed grass-clover mixed sward,

with its tendency for cycling in plant species composi-

tion; (ii) a systems field trial of new and old grass ⁄clover cultivars, and how the complexity of growth of

perennial forage crops, and the dynamic optimality

required for sustainable harvesting might limit our

ability to breed for ‘yield’ per se; (iii) the manipulation of

a physiological trait (low ‘maintenance’ respiration)

and the implications of such changes for plant fitness

and G · E interactions; and (iv) an hypothesis-driven

development of a trait (high-sugar grasses) and the

value of ‘proof of concept’ studies, the requirement of

scientific understanding of the mechanisms of trait

expression, and how one might in future go about

assessing breeding achievements. We discuss the general

ecological considerations around shifts in the fre-

quency distribution of traits in new populations, whether

altered conventionally or by genetic modification, and

how selection for a particular trait might inadvertently

reduce both fitness and persistence. A major priority for

breeding, we propose, might be to revisit previously

abandoned traits that affected the physiological perfor-

mance of forage species, armed now with a capacity to

monitor gene expression at the molecular level, and so

unravel ⁄ control the G · E interactions that limited

their benefits. We also discuss how a ‘loss of yield

advantage’ of new cultivars, seen when tested several

years after sowing, requires urgent investigation and

propose this might be associated with fitness costs of

perenniality. Finally, we argue for a careful reconsid-

eration of what are realistic expectations for systems

field trials and that focus on forage breeding might be

shifted more to ‘proof of concept’ studies, critical

experimental design, comparing ‘traits’ rather than

‘cultivars’, and the wider ecological assessment of

fitness and function of traits in the plant, community

and ecosystem.

Keywords: forage breeding, fitness, pasture persistence,

trait expression, respiration, cultivar evaluation, forage

quality, breeding targets, WSC, environmental impact

Introduction

An essential element of the success of the dairy industry

in many cool-temperate zones has been the efficient

use of grazed pasture to provide the major proportion of

the feed required. This has been the keystone of the

competitive advantage for dairying in countries such as

New Zealand, where, unlike within Europe, income

from pasture-based dairy production remains a major

component of national gross domestic product (GDP).

To increase the success, plant breeding attention has

focused on increasing the annual and seasonal pattern

of pasture production, tolerance and persistence

under edaphic stress, and on parameters that lead to

improved forage quality, intake and feed conversion.

Correspondence to: Dr A. J. Parsons, AgResearch Grasslands,

Private Bag 11008, Palmerston North 4442, New Zealand.

E-mail: [email protected]

Received 31 October 2010; revised 5 December 2010

doi: 10.1111/j.1365-2494.2011.00785.x � 2011 Blackwell Publishing Ltd. Grass and Forage Science, 66, 153–172 153

Grass and Forage Science The Journal of the British Grassland Society The Official Journal of the European Grassland Federation

Considerable progress has been made in realizing

greater dry-matter (DM) yields in grasses and legumes

by breeding for greater disease and pest resistance, and

(e.g. in New Zealand) from the inclusion in grasses of

foliar fungal endophytes (Easton, 2007). Although

there have been some interesting changes in emphasis

over the last few decades, the catalogue of current

industry goals for breeding (e.g. Smith et al., 1997;

Woodfield and Easton, 2004) reads not unlike one

written 30–40 years ago (Cooper and Breese, 1971; and

see Hopkins and Wilkins, 2006).

Plant breeding is, however, being asked to deliver

results more urgently than at any previous time. There

is ever-increasing pressure for germplasm with new

traits as farmers exhaust their capacity to increase yield

solely by increasing fertilizer inputs, or improved

pasture management, through defoliation and feed

allocation (Holmes, 1998; Clark et al., 2007). Further

challenges and pressures are added by the requirement

for new goals to take account of wider considerations

such as how to balance industry production targets

against the need to mitigate emissions of greenhouse

gases (GHG), reduce nitrogen (N) loss and to sequester

soil carbon (C) (ACRE, 2007; Abberton et al., 2008).

This means that the pressures are not only for enhanced

and faster selection from within existing variance but

also for totally new traits, and traits expressed at levels

outside the known range of current variation within

forage grass species. New technologies (such as marker-

assisted selection and genetic manipulation) might offer

the means of achieving a step change, but identifying

just what characteristic or trait in a forage plant offers

the prospect of meeting industry targets in an accept-

able time is still a challenge.

Although total DM yield (with appropriate metabol-

izability) remains a key goal, the emphasis of the traits

and targets pursued by plant breeders as a means to

achieve this has shifted away from studies exploring the

processes which could increase C capture and retention

by manipulating the grassland plants’ physiology.

Increasing potential production (as distinct from the

realized production) remains a challenge.

This paper is not a critique of plant breeding, nor of

what has or has not been achieved. There have been

many such analyses and, as in any such endeavours,

the conclusion can depend very much on the interpre-

tation of each of the original trials and their experi-

mental design, and the management imposed upon

those trials. Rather than repeat that process, we

endeavour here to highlight issues to do with goals,

traits, trials, design, interpretation and delivery. The

aim is to enhance prospects for future success, regard-

less of whatever past successes have been.

This task has been approached by revisiting four

examples of forage plant breeding or selection, chosen

for their capacity to reveal critical insights into problems

with the identification and delivery of past breeding

achievements. For each, we describe the findings, some

with original, some with new interpretation and then

offer lessons that might be learned for the future. We

then present some wider, and currently topical, issues

that limit the delivery of plant breeding success:

concerns over fitness, lack of persistence and the need

to study the ‘impacts’ of proposed new traits. This is

followed by a discussion for a change in emphasis, and

the need for new protocols for developing, and notably

assessing, future plant breeding efforts.

Examples revisited: seeking new insights

The outcomes of two major programmes aimed at

evaluating plant breeding success in New Zealand are

re-examined below. The first was in terms of increasing

forage DM yield and the second was in terms of the

yield of animal products including milk solids. To

maintain clear transparent objectivity what is presented

in example (1) below is the same data from the same

papers that have been used previously to demonstrate

the success, in terms of genetic advance and of plant

breeding. In the second (2) we revisit and gather

insights from one of the few, and most thorough and

controlled assessments of plant breeding gains for dairy

production benefit. We then revisit two further exam-

ples (3 and 4, from the UK and European Union, EU)

which pursued very closely defined target ⁄ traits as they

reveal some important insights into addressing prob-

lems in the delivery of the benefits of breeding aimed at

specific plant physiological traits.

Example 1: white clover breeding gains

Caradus (1993) and Woodfield and Caradus (1994)

adopted a procedure for illustrating the rate of plant

breeding gains (in white clover) by assessing the yield of

a range of cultivars at a single location, but plotting the

yield for each against its year of introduction (see axes

used in Figure 1). These early papers combined data

from within New Zealand with data from the United

Kingdom, South Africa and Czechoslovakia, to show an

increase in agronomic performance of c. 6% per decade

since the 1930s. The authors pointed out that much of

the increase was a result of the very poor agronomic

performance of the non-New Zealand (and pre-Huia)

cultivars when grown in New Zealand.

Following this method of presentation, a later more

extensive study focused on improvements within New

Zealand, using Huia as the benchmark (Woodfield,

1999; and see references therein). Using data from ten

white clover cultivars in eight trials under sheep

grazing, and separately nine white clover cultivars in

154 A. J. Parsons et al.

� 2011 Blackwell Publishing Ltd. Grass and Forage Science, 66, 153–172

five trials under cattle grazing, Woodfield (1999)

provided evidence that the rate of breeding gains

(forage yield) had accelerated over the decade since

the mid-1980s. ‘Genetic Improvement under sheep

grazing [had] increased from less than 0Æ4% per year

before 1985 to more than 4% per year since 1985’, with

corresponding values for cattle grazing of 0Æ6 and 2Æ5%.

The original data are plotted in Figure 1(a,b).

A subsequent analysis by Woodfield et al. (2001)

continued this approach, adding some new cultivar data

(Kopu II and Crusader) while retaining some of the

cultivars used previously as a reference. Annual and

seasonal performance was reported from ten white

clover cultivars in three trials under rotational grazing

by sheep in the Manawatu, and nine white clover

cultivars in two trials under rotational grazing by cattle

in Waikato and the Manawatu, New Zealand. In this

study, ‘Crusader was the only cultivar under rotational

grazing by sheep to have a significantly higher clover

yield than Huia’ and Pitau, Kopu II and Crusader

performed well with cattle. The study also considered

the ranking of cultivars from a Plant Variety Rights trial

(no grazing animals). A third study, again using a wide

range of cultivars and trials, with both sheep and cattle

grazing, was presented subsequently (Woodfield et al.,

2003) focusing on the cultivar Tribute.

What distinguishes these trials is that many of the

same cultivars were included throughout. When the

data published (as Tables) from the 2001 and 2003

papers are replotted on the same axes that had been

used in 1999 (see Figures 1c,d; and 1e,f respectively), it

appears that the rate of genetic improvement assessed

from these later trials (2001 ⁄ 3) is less than had been

indicated previously (1999). The rate of gain was close

to 1% p.a. under cattle grazing and c. 0Æ6% p.a. under

sheep grazing, even if it is assumed, using data from

2003, that the yield of Crusader will itself be sustained

over subsequent years. As some of the same cultivars

were included in the earlier and later trials, we can see

that the slope of gain has decreased because the yield of

several of the new cultivars, impressive at their time of

initial release, was not as great when observed in

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Year of release Year of release

Grazed by cattle

(a) (b)

(c) (d)

(e) (f)Figure 1 Estimates of the annual

dry-matter yield of new white clover

cultivars, relative to Huia (=100), plotted

in relation to their year of release. The

cultivars were grown in mixtures with

grass and grazed either by sheep (left

column) or cattle (right column). Data (a)

and (b) from Woodfield, 1999; (c) and

(d), Woodfield et al., 2001; (e) and (f),

Woodfield et al. (2003). Open symbols,

yield of cultivar ‘Crusader’.

Plant breeding for yield and persistence 155


subsequent years. This is itself a paradox often observed

and may be the outcome of successive seed production

generations of an outbreeding species resulting in

reducing the value of general combining ability exhib-

ited in early parental and subsequent crosses.

Some insights from Example 1

The suggestion that yield gains have not been consistent

can be explained by considering that the clover was, in

all cases, assessed when grown in a mixture with grass

and was grazed. Given the complexity of the balance of

grass and clover in a mixture, both spatially (the

tendency for clover to occur in moving patches) and

temporally (clover and grass have been shown both by

theory (Schwinning and Parsons, 1996a,b) and in

practice - see the Schwinning and Parsons (1996c) time

series analysis of Rickard and Mcbride (1986) to be

involved in irregular cycles of c. 4 years), then assess-

ments of yield gains based on only one component of a

mixture and for just 3 years might be expected to give

inconsistent rankings. The yield of the accompanying

grass should have been assessed in all cases, and

presented, as well as that of the clover. However,

analysing the yield potential of mixtures is complex in

itself. It has been the topic of a great deal of study in

ecology (Harper, 1977) with explanations of all manner

of phenomena from ‘over-yielding’ to competitive

suppression. Few of these phenomena remain consis-

tent over time. Furthermore, on top of the complexity

of the cycle between grass and clover (that is proposed

to take place via the capacity of one to enhance, and the

other to run down, soil mineral nitrogen) are other

complex interactions. Any additional interspecific com-

patibilities (e.g. a mycorrhizal vs. rhizobial interaction

(Crush and Caradus, 1996)) in the small-plot field trials

would mean some clover cultivars might by sheer

chance shift between being unrepresentatively and

inconsistently advantaged or disadvantaged.

Example 2: the ‘DRC ⁄ Dexcel’ systems fieldtrial

This trial attempted to analyse the breeding success

simultaneously in both grass and clover in paddock-

sized plots grazed by lactating dairy cows. It is one of

only a few trials where the advances in plant breeding

have been assessed directly in terms of animal perfor-

mance and where the treatments (and controls) were

designed specifically to test the overall level of progress,

as opposed to comparing cultivars. This 3-year farmlet

study in the Waikato of New Zealand allowed plant DM

yield and milk solids production to be measured for

pastures consisting of cultivars of perennial ryegrass and

white clover of differing decades of origin (Crush et al.,

2006). There were four pasture treatments consisting of

a 2 · 2 factorial combination of perennial ryegrasses

representative of those available to farmers in the 1980s

and in 1998, and white clovers available in the 1960s

and 1998. Pasture treatments were grown in replicated

self-contained farmlets and stocked at a nominal three

Friesian cows per ha. The trial used a written set of

decision rules, based on Macdonald and Penno (1998),

so that management decisions could be made on an

individual farmlet basis without compromising the

objectivity of the farmlets’ management or expression

of any treatment differences. Despite some preliminary

indications (Woodward et al., 2001), the published

conclusion was that there was no significant difference

in the performance assessed either by forage DM

production or by yield of milk solids between new

grass or new clover compared with old grass and old

clover, in any of the four possible combinations (Crush

et al., 2006).


It is understandable that the conclusion led to consid-

erable discussion and the suggestion that a different

result might have been obtained had the trial used

other cultivars, maybe differing only in endophyte

strain content. This is in itself revealing. Would the

same comment have been made had the trial shown

the anticipated success? How many trials would need

to be conducted to establish a consensus? What

expectations should we have for getting definitive

answers from any given protocol for assessing plant

breeding success?

Given that grasses evolved for millions of years before

deliberate breeding attempts, it is possible that ‘yield’

might be too complex a phenomenon for selection, and

so the expectations for success are too great. After the

initial benefits to New Zealand in identifying which

were best to bring from Europe, it may be that further

gains require a far deeper understanding of how the

plants function if we are to alter them to our advantage.

Although it has long been a goal for plant breeding to

increase the total yield of the ‘grass’ crop, it has been a

very long time since there has been research focused on

altering the processes that would lead to that goal

(Sinclair et al., 2004). To obtain more yield means

greater resource use efficiency, such as more photo-

synthesis per unit DM, less respiration per unit DM,

more efficient partitioning of C (e.g. between leaf, shoot

structure and root), a better trade-off between the

strategies for growth and storage (in a perennial

especially), and more growth per unit of N, P or water.

Excellent reviews of the scope for grass (and legume)

plant improvement in this context were published in

the 1980s (Robson, 1980; Robson et al., 1988) and the



impacts of management on C fluxes added, for example,

by Parsons (1994) and Parsons and Chapman (2000). In

the case of the grass crop, even the concept of an

improved harvest index is far from simple, because,

unlike in cereals, the harvestable component (the

leaves) is also the photosynthetic component and must

be harvested continually. Hence, it requires the concept

of a sustainable dynamic harvest index, which is a

trade-off between removing leaves, and yet allowing

leaves to remain in the canopy to photosynthesize

(Parsons et al., 1988). Given the number of processes

involved in growth, and the dynamic optimality

required for sustainable harvesting, one has to question

the likelihood of being able to select conventionally for

yield, whether aided by molecular-marker selection or

not.

Notwithstanding the difficulties, there have been

substantial efforts in the past to identify useful variation

in each of many aspects of plant physiology (see reviews

by Robson et al., 1988; Parsons, 1994). Major progress

was made in selecting not so much for higher leaf

photosynthesis, but a greater capacity of the grass crop

to sustain leaf photosynthetic potential, averting the

strong tendency for this to decline with leaf age, or

notably when leaves emerge in shade, during periods of

high LAI (Wilson, 1981). Likewise, in the past, consid-

erable progress was made in selecting for lower plant

respiration (Wilson, 1975). These advances did not

persist, but given the availability now of far greater

knowledge of molecular biology and gene expression,

those very well-defined targets should perhaps be

revisited. Was anything missed? Were such valuable

traits lost? Or were results perceived as negative and so

pursuit terminated too soon?

Example 3: an initially successful physiologicaltrait?

One of the most clear-cut examples of a trait that

showed immense promise was the development of

grass lines with low (dark) respiration. Respiration

accounts for c. 50% of the carbon fixed in photosyn-

thesis (Parsons and Penning, 1988) with approxi-

mately one half of that (25%) being associated with

the stoichiometry of synthesis of new tissues (which

can be shown to be functioning already close to

theoretical maximum efficiency (Penning De Vries,

1975) and so reducing this would reduce, not

enhance, plant growth), and the other half associated

with ‘maintenance’ (as it was then conceived). ‘Main-

tenance’ includes the continuing breakdown and

resynthesis of proteins and complex molecules (Pen-

ning De Vries, 1974; Thornley and Johnson, 1990), as

well as the consumption of energy (and so mass) in

nutrient uptake. Low ‘maintenance’ respiration there-

fore became a well-focused target for improving C

resource-use efficiency. Later studies also found evi-

dence of an unusual ‘energy-wasteful’ (cyanide resis-

tant) alternative oxidative pathway respiration

(Lambers, 1980). Material was originally selected from

the natural variation in maintenance respiration in

Lolium perenne S23 (Wilson, 1975) and breeding lines

selected for high (and corresponding low) mainte-

nance respiration were produced.

The low-respiration lines out-yielded the high-respi-

ration lines by c. 25% (Figure 2), and the mean parent

material by 5–12% (Wilson and Robson, 1981; Robson,

1982a; Wilson and Jones, 1982). The yield advantage

was evident in all components of the standing

crop (Figure 2). This was shown to have arisen not

only because of the increases in net C uptake (lower

CO2 loss per unit DM), but also because of the low-

respiration plants investing more C into new tillers, and

so recovering photosynthetic C supply faster during

regrowth following defoliation (Robson, 1982a).

Despite these very substantial and well-explained

successes, the trait advantage diminished over time (see

Robson et al., 1983, 1988). Preliminary field trials using

commercial testing procedures initially showed yield

differences between the respiration lines, but the

benefits of low respiration (in one cultivar especially)

diminished greatly in subsequent field tests. It did not

appear to survive the further process of bulking for

commercial seed production. No new cultivar was

released specifically with this trait, although the mate-

rial, like that developed for improved leaf photosyn-

thetic responses to shade, entered the elite germplasm

population held now by the Institute of Biological,

Environmental and Rural Sciences (IBERS, Aber-

ystwyth University).


Clearly, the loss over time of valuable traits being

expressed effectively is a prospect that must be faced,

and one that can be recognized as offering great hopes

for the future. Effort into understanding how to ‘lock

in’ new traits would be a new avenue for increasing the

realization of breeding gains, and so offers new pros-

pects for improvement. What is not clear is whether

traits were really ‘lost’ or whether the uncertainties of

trait expression in a complex natural world resulted in a

situation where (as below) the field trial conditions

disguise the expression of the trait, which is conse-

quently ‘missed’.

The issue of ‘fitness’ of the trait in the natural

environment was explored by Robson et al. (1982a,b)

asking simply if the trait was so advantageous, why

was it not the natural mean of the population? Robson

et al. (1983, 1988) then demonstrated that the yield



advantage of the low-respiration trait depended on

high nitrogen (N) availability (Figure 3). Replicate

groups of plants of each of the high- and low-

respiration lines were grown initially at a common

high mineral N availability, and their yields are plotted

(Figure 3) for each of four successive harvests over a

period in which the N inputs were sustained to

half the plants of each group, and inputs were

withdrawn from the other half. In plants maintained

at high mineral N availability throughout (solid lines,

Figure 3), the marked difference in yield between

high- and low-respiration plants remained. In plants

experiencing (progressively) lower N availability

(dotted lines), the difference in yield between high-

and low-respiration plants diminished. This is clear

evidence of a G · E interaction in the expression of

yield advantage from this trait. It is also clear that

capacity to detect the benefits of the trait would depend

on the N environment in which any trial was

conducted. Under the wrong conditions, even valuable

successes can be missed.

Example 4: a hypothesis-driven trait?

The high-sugar grass (HSG) trait developed by IGER is

an example of a breeding programme that was well

defined from the outset, was pursued with determina-

tion and which has narrowly survived some of the

pitfalls above.

Increasing the metabolizable energy (ME) content of

grass species forage has been an undiminishing priority

for plant breeding for over six decades, because such a

change in plant composition is simultaneously an

increase in digestibility and a decrease (at least in

relative terms) in indigestible fibre content. It has also

long been presumed to bestow greater ‘palatability’ (a

(a) (b)

Figure 2 Dry weight of all plant components of lines of Lolium perenne with ‘slow’ (a) and ‘fast’ (b) respiration, growing as

simulated swards and shown here for the fourth period of regrowth after establishment. Initial and final percentages of the

totals are shown (from Robson, 1982a).

Figure 3 Harvestable yield of simulated swards of ‘slow’-(o)

and ‘fast’-(•) respiration lines of Lolium perenne, grown under

either nitrogen sufficient conditions (____) or increasing

deficiency (- - -), during four successive 3-week regrowth

periods (from Robson et al., 1983, 1988).



somewhat loose term for many aspects of altered animal

foraging behaviour: preference, instantaneous intake

rate, even low shear strength in leaves). Although

accumulating more low molecular weight sugar content

(sucrose, fructose ⁄ glucose) might be seen as deflecting

C supply from plant growth, it was well argued that

manipulating the tendency for cool perennial grasses to

accumulate substantial high molecular weight (fructan)

largely longer-term sugar stores, which were found

predominantly in non-harvested ‘sheath bases’ (pseu-

dostems) offered prospects. The trait was very well

defined as being to increase the expression of fructans

in harvestable laminae. The anticipated impact was also

well defined (that the increased supply of energy to the

rumen would rectify an energy ⁄ protein imbalance and

so capture more protein and increase the supply of

protein (not energy) to the ruminant (Miller et al.,

2001a).

Pollock and Jones (1979) demonstrated success in

creating two divergent populations with ‘high’ and

‘low’ fructan concentrations expressed in the laminae of

(diploid) perennial ryegrass. An extensive programme

of indoor and field trials using material bulked up into

breeding lines and early cultivars was instigated.

Extensive and thorough field trials were established in

several countries, notably the United Kingdom and the

Netherlands (see Edwards et al. (2007a,b) for a full

review).

The results of those multiple experiments did not

immediately resolve the question of the efficacy of the

trait. There was no clear indication of benefits from the

United Kingdom trials, even those where the sugar or N

content differences between plant material were accen-

tuated (by harvesting at different times of day or

applying N fertilizer to only one treatment) specifically

to test the proof of concept beyond the existing cultivar

differences; the published papers were very thorough

and objective about this. The Dutch studies were

arguably even more extensive and revealed no evi-

dence within themselves of benefits to higher sugar

content. Although it was recognized that the single

most positive response had been obtained only where

the grasses had been observed under very low soil N

availability, and not at high soil N availability typical of

intensive dairying, it took further review to recognize

that the data formed a continuum. When all data were

taken together and plotted in terms of the water-soluble

carbohydrate:crude protein (WSC:CP) ratio of herbage

in the diet (Edwards et al., 2007a,b), proof of concept

was shown. Plotting this way reveals a substantial and

valuable decline in the proportion of N eaten that is

excreted as urine (Figure 4a) and a relatively small rise

in the proportion of N excreted as milk (see Edwards

et al., 2007a), provided, and only if, sufficient difference

in WSC:CP ratio could be achieved between forage

cultivars. This is why we refer to such a presentation as

a proof of ‘concept’ and not proof of efficacy of a

cultivar.

This approach can be taken farther to develop

some much more focused and quantitative ‘targets’ for

plant breeding ⁄ manipulation. From the relationships

between Nuse efficiency (NUE)and WSC:CP ratio seen in

Figure 4a, we can calculate the size of the changes

necessary in WSC or CP to create a given size of benefit.

Fitting curves (to interpolate values) from data that

are expressed as a ratio, and where the ratio is close to

1Æ0, is fraught with pitfalls, especially if some individ-

uals prefer to look at the (inverse) CP:WSC ratio. This

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Figure 4 N utilization efficiency (N excreted as urine per unit N eaten) plotted (a) in relation to the WSC:CP ratio, and (b) the

same data in relation to the inverse, CP:WSC ratio, of the diet. The two plots highlight the problem of fitting lines and interpreting

from ratios. The solid lines (equations inset) give the same statistical match regardless of which way the ratio is expressed.

Data sources: •, 2001 data from Tas et al. (2005, 2006a); s, 2000 data from Tas et al. (2005, 2006a); m, Miller et al. (2000);

¤, Miller et al. (2001a,b); j, Moorby et al. (2006). Maths courtesy of Jonathan Newman (University of Guelph).



can be seen by plotting the same data against CP:WSC

in Figure 4b. In keeping with the biological nature of

the problem, a bi-substrate Michaelis-Menten type

function was used (see inset on Figures), and statistical

fitting using this (and its inverse transformation) gives

precisely the same ‘fit’ whichever way round the ratio

of WSC and CP is described. Figure 4a gives an inter-

relationship between three dimensions: WSC, CP and

the resulting NUE. We can therefore draw a ‘graph’

(technically a ‘map’ or ‘phase plane’) with WSC on one

axis, and CP on the other (see Figure 5). Any straight

line on this map, passing from the origin, represents a

single WSC:CP ratio. We know from the fitted lines on

Figure 4a just what that single ratio would mean in

terms of the NUE. We can therefore fill in the graph

‘space’ with a series of isolines, each line indicating a

single level of NUE to be expected from that combina-

tion of WSC and CP. This enables us to see just how

much WSC a forage grass needs to contain to create a

given level or change in NUE, and to see how this

‘target’ changes depending on the level of N in the

forage.

Finally, we can superimpose onto this ‘map’ the

actual combinations of WSC and CP seen in the whole

gamut of European Union and New Zealand trials, to

see just where we are and where we need be, in terms

of achieving a given improvement in NUE. This reveals

that current cultivars, and the HSG variants, can

achieve greater NUE in low-nutrient (judged by forage

N) systems, indeed coming close to the desired WSC:CP

ratio of c. 1Æ5 but to achieve the same level of (efficient)

NUE seen at low N, now at higher N, requires a far

greater increase in WSC content. Whereas to achieve a

WSC:CP ratio of 1Æ5 at 2% N requires a WSC content of

188 g kg)1, forage at 4% N requires 376 g kg)1. This is

far in excess of the values observed even in HSG in New

Zealand (Figure 5).

The synthesis of fructans, the major storage sugars in

ryegrass, requires the expression of several fruc-

tosyltransferases. To determine the major factors con-

trolling fructan accumulation, Rasmussen et al. (2008)

looked at the expression patterns of genes putatively

coding for fructosyltransferases at various temperatures

and defoliation regimes, and in high-sugar and control

cultivars. The expression of these genes was differen-

tially regulated by temperature, and in HSGs, formed

the molecular basis for G · E interactions. A particular

isoform of one of the fructosyltransferases was discov-

ered to be associated with high fructan accumulation in

HSGs. Subsequent work showed the expression of the

trait was affected by stage of regrowth (Rasmussen

et al., 2009). These findings are critical for the molecular

breeding programmes using either genetic markers for

selection or direct genetical modification that are now

underway.


The value of this approach (from inception of trait,

through proof of concept, to analysis leading to quan-

titative targets) is that it turns plant breeding perspec-

tives from statements of ‘wish’ (e.g. a 25% reduction in

N excretion as urine), to a situation where one can

consider just what would be required to deliver this

wish, notably just what kind of research and with what

expectations of success and associated difficulties.

The graphs make clear that because the response is a

continuum (Figure 4) any improvement (even incre-

mental) in, e.g. WSC:CP ratio, will lead to correspond-

ing improvement in the desired NUE. It also makes clear

that this is of value even though it is unlikely that the

improvements will be detectable in field trials (being

within the range of error) until considerable changes in

WSC have been made. This is of no consequence as it

0

10

20

30

40

50

60

0 1 2 3 4 5

% W

SC

%N

Figure 5 Quantitative targets for breeding for high sugar

content to reduce N loss in urine. On a ‘map’ that represents

combinations of WSC (on Y axis) and crude protein (X axis,

expressed here in terms of herbage N content), we have

plotted isolines. Each line represents a single WSC:CP ratio, and

so, from Figure 4, a given N-use efficiency, shown here as the %

of N eaten that is excreted as urine. Superimposed on this

‘map’ are the combinations of WSC and CP seen in the same

trials in UK, Netherlands and NZ that were plotted in Figure 4.

At low CP (% N) current cultivars achieve low % N loss in

urine, but at high CP (e.g 4% N) sugar content would need to

be doubled to achieve the same (c. 25%) N loss in urine. Data

sources: •, 2001 data from Tas et al. (2005, 2006a); s, 2000

data from Tas et al. (2005, 2006a); m, Miller et al. (2000); ¤,

Miller et al. (2001a,b); j, Moorby et al. (2006); D, h, Tas et al.

(2006b); e, Pacheco et al., 2007.



also conveys there is no need to conduct repeated

expensive field trials to test if the result is ‘visible’,

rather it is necessary only to follow progress in changing

WSC:CP ratio, to justify announcements of breeding

success. To bring about the desired change in WSC:CP

ratio in a short time frame would, however, require a

major ‘step change’ in the trait.

The first requirement for progress is clearly to

undertake science aimed at understanding at least the

mechanisms of fructan metabolism, the most ‘basic’

biochemistry of which, and hence the control of fructan

levels in grasses, is increasingly uncertain (Cairns et al.,

2008). It is evident that a change in the kind of research

that must be funded is justified, even to achieve what is

a practical, end-user driven industry-related goal.

Industry has been willing to fund the ‘D’ of ‘R and D’,

but not the public good ‘Research’ that is needed to

create future success, let alone ‘step changes’ in success.

Decades of this emphasis on practical extension, in the

belief it leads to faster progress, may have ironically

hamstrung even that practical progress.

Increasing the chances of obtaining a more robust

and consistent level of expression of any new trait also

requires a greater recognition of the principles of

ecology, notably those regarding the success of any

new gene in a population and community. The issue

surrounds ‘fitness’ and ‘persistence’, and raises the

spectre that if we make substantial changes to an

organism’s function, by whatever means, we might

need to foresee potential negative ‘impacts’.

Some wider considerations: fitness,persistence and impacts

Fitness of new genotypes in a community

The questions raised by Robson (1982b) over how

breeding for greater expression of traits (low respiration

for example) might affect the ‘fitness’ of the new plants

in the natural population are as pertinent as ever and

remain a challenge to answer. What we attempt below

is to describe how trait expression, natural and selected

population variation, G · E interactions and (lack of)

fitness (all phenomena that have been observed in the

examples throughout this text), are inter-related. It also

describes how new biotechnologies in theory offer a

breakthrough (but one that remains difficult to realize)

in this overwhelmingly ecological area. The whole

problem is greater in perennial, persistent, outbreeding

temperate grazed grassland species, than in annual

crops.

First, we must recapitulate that there is not only

variation within and between individuals in popula-

tions, from which plant breeders select, but there is also

variance in the environment to which the population is

subjected, and that this is an ongoing force of ‘natural’

reselection. One common explanation for why long-

adapted natural populations have wide variance in trait

expression is that this broad gene pool (in multiple

traits) enables the population to ‘shift’ (a change in

mean or mode) when faced with uncertainty (temporal

variance, e.g. sporadic drought) or longer-term changes

in the mean environment (e.g. rising temperatures or

the increased use of N fertilizer and higher stocking

rates). At first it may be just that different individuals

enjoy greater or lesser performance, although eventu-

ally consistently unsuited individuals perish. Lack of

persistence of a trait reflects its lack of ‘fitness’ in a given

changing and fluctuating environment. This helps

explain why natural selection alone has led to a

situation where ‘permanent pastures’ (20+ years old)

in the United Kingdom were shown to have yields no

different from the latest ‘improved’ cultivars in all but

the first year after sowing, even across a wide range of N

fertilizer inputs, from 0 to 900 kg N ha)1 per year

(Hopkins et al., 1990) (Figure 6). Although mineral N

fertilizer application at high levels is a relatively recent

perturbation to the ecosystem, note that even in

ancient pastures plants will have evolved to cope with

sporadic extremely high mineral-N inputs from urine.

Similar results have been reported in New Zealand

(Rowarth et al., 1996).

Plant breeding recognizes that the existence of a wide

variance in expression is an opportunity, stressing the

value of this for artificial selection. The key is to

envisage not just a single frequency distribution of

expression for a population trait, but to envisage that in

a natural population there will be a separate (plausibly

independent) distribution and variance for each and

every trait that each plant possesses. For simplicity, in

Figure 7, we picture just two of numerous traits. Any

one plant can appear at totally different places in the

frequency distribution for separate traits. A plant may

be in the top 20 percentile of one trait, but in the

bottom 20 percentile of another trait. Different forms of

selection act on, and perturb, these distributions in

fundamentally different ways.

Any highly targeted conventional plant breeding

(such as that adopted by Wilson earlier) might select

for plants with respect to one desirable trait, and so

from the ‘high’ (vs. ‘low’) end of expression of trait A

(Figure 7) in the aim to shift the mean, and create an

ultimately new (divergent) population of plants focused

around those of type ‘A’ (see upper tail of distribution).

Selection for plants of type ‘A’ could lead to an

uncontrolled, unobserved and inadvertent selection

from within the frequency distribution of a second

trait, B. This is because there is no way of knowing just

where in a second (likely unmonitored) frequency

distribution the very same plants lie. Because the plants



initially selected with good purpose from one end of

distribution A are only a subset of the total population,

there is considerable risk that the initial selection

process gives rise to a narrowing of the whole gene

pool (less variance) and ⁄ or an inappropriate mean (bad

selection) for other traits. For this very reason, of

course, selected populations are rebuilt by procedures

(involving multiple crossing between individuals)

aimed at retaining or increasing the frequency of the

chosen gene ⁄ trait, but also with the outcome, it is

intended, of restoring wide variance in multiple other

traits. The goal is to avoid ‘negative genetic drag’

(unintended co-selection of undesirable genes) and to

avoid ‘inbreeding depression’ (increasing the frequency

of deleterious genes).

In their review, Abberton et al. (2008) acknowledge

the problem of breeding simultaneously for multiple

traits and how, instead of selecting from one ‘end’ of a

Figure 6 Annual herbage dry-matter production (t ha)1) from permanent pasture (=20+ years), h———h, and from adjacent

areas resown in 1983 using new ⁄ improved Lolium perenne cultivars, j______j. Measurements were made in a common trial at 16

sites across the UK, at five levels of nitrogen fertilizer application. Replicate areas were harvested by 4 weekly cutting (left hand

column) and 8 weekly cutting (right-hand column). All data and statistics redrawn from Tables 1 and 2, Hopkins et al. (1990).



single population (the simplistic example above),

breeders go back to ‘elite’ germplasm populations and

collections (each chosen for a variety of beneficial traits)

and cross these before making initial selections. They

also state ‘The old breeders’ maxim of ‘‘crossing the best

with the best and hoping for the best’’ remains an

excellent strategy for crop improvement’. There are

many examples where the level of success has been

good testament to the skills of breeders, notably for

disease resistance, stolon density and seed yield (in

white clover) and flowering date (in grasses). In respect

of some major components of yield, we have laid out

some examples of the outcome of that approach in the

previous sections. We do not, however, feel this offers

prospects for the rapid acceleration of progress that is

becoming essential, notably where solutions require

selection for complex multiple traits.

Genetic modification is widely advocated not least for

its ‘accuracy’ of trait manipulation. First it is argued that

if and when a particular process (e.g. an enzymatic

reaction producing fructan) has been targeted, a single

gene manipulation may very precisely up-regulate this

reaction. Genetic modification may be particularly

valuable when targeting the ‘promoter’ of genes, and

so permanently and invariably ‘switching on’ the

expression of a gene (e.g. to ‘always produce more

fructan’) and so avoiding all the uncertainties of genes

being switched by complex environmental and devel-

opmental signals. Hence, gene-promoter manipulation

could potentially remove the problem of G · E inter-

actions that has dogged studies in the case examples

above. Of course, genetic manipulation also offers the

prospect of increasing trait expression above and

beyond that seen in any current individual.

In principle, genetic manipulation might offer the

unique opportunity to alter the expression of the genes

for one single trait (e.g. up-regulate the trait A) in each

and every one of a representative sample of plants

(genotypes) from across the ‘natural’ population (see

Figure 7), and in this way make that change without

any inadvertent uncontrolled selection with respect to

any other traits (Lemaux, 2008). This would preserve

the extremely valuable near-optimized outcome of

natural selection, its mean and variance, for all those

other naturally optimized traits. This may be a popular

perception, but is it practicable?

At present, for a number of reasons, GE populations

of plants such as ryegrass are built up initially from an

extremely small number of different genotypes from

the natural population. Repeated transformations are

common, but of replicate clones from very few distinct

genotypes (Gadegaard et al., 2008). This narrows the

gene pool of all traits considerably at this initial stage of

development; the adverse consequences of this for

fitness in the highly variable environment of perennial

pasture are widely understood. The outcome is that

genetically modified populations rely as much, if not

more than ever on the procedures used in conventional

plant breeding, to multiply numbers, increase the

frequency of the new trait in the population (itself

requiring back-crossing) and to re-introduce breadth in

expression of the multiple other traits (Lemaux, 2009).

Concerns have been sufficient that new procedures are

being investigated, some of which are sufficiently

different to be subject to patent.

A question remains on whether the traits required

are those of any one organism. Abberton et al. (2008)

stress how plant-breeding targets need to encompass

changes in the way the plants interact with processes,

e.g. in the rumen or soil. Likewise, many key breeding

goals (e.g. lower GHG emissions from soils, greater

N-use efficiency, C sequestration) and certainly many

aspects of ‘fitness’ for any organism are not a conse-

quence of that organism ⁄ species itself, but of the

multitude of other organisms with which it coexists.

One classic example is fungal ‘endophyte’, but others

are associations with rhizobia, mycorrhizae and bacte-

ria. In poplar (Populus spp.) trees, yield on marginal soils

Figure 7 Implications for fitness of selection in organisms with multiple traits. The same plant may be at the desirable end (e.g.

upper quartile) of the frequency distribution for one trait, but in the undesirable lower quartile of another trait, that may be

unmonitored during selection. Although well recognized by breeders, the implications for fitness have not been well explored.



can be increased by up to 40% as a consequence of an

internal root infection with Enterobacter sp. 638, which

synthesizes a plant growth hormone (Van Der Lelie

et al., 2009; Taghavi et al., 2010). Many such processes

depend on the intimate exchange of not just metabo-

lites but signals which trigger expression of multiple

organisms’ genomes. There is growing recognition in

molecular ecology of how considerable ‘specificities’

arise between plants and soil organisms (Bardgett et al.,

1999; De Deyn et al., 2008), and how biodiversity

(another major source of community gene pool and

trait breadth) can lead to substantially improved soil

function (Steinbeiss et al., 2008; Gessner et al., 2010).

This adds complexities to the aim of enhancing the

growth and persistence of an introduced trait, in

choosing which genome should be targeted ) that of

the higher plant, or those of its ‘extended phenotype’

(Whitham et al., 2003)?

The fitness consequences of altering the trait expres-

sion and variance in any one species (e.g. the grass) and

its release into the environment ⁄ ecosystem can be

considered from the theory and experience in invasion

biology in terms of what delivers the capacity to

perform, persist and spread for organisms with new

traits. The literature offers many insights into how the

success of any one organism ⁄ species is dependent on

the multitude of other organisms with which it inter-

acts.

Loss of persistence or loss of yield?

So far, ‘persistence’ has been considered in terms of (i) a

decline in the population of a newly sown species in a

community, or (ii) a decline within the population of that

species of individuals that still express the trait. In

practice, however, there is a third consideration. Are we

really seeing a loss of persistence, in this ecological

sense, in newly sown cultivars in field trials, or is it just

that in some cases we are seeing the initial benefits,

followed by a subsequent loss of the advantages, not of

the cultivars, but of resowing (tillage) per se? There have

been a few studies, with appropriate controls, which

follow the performance and fate of sown cultivars to

distinguish between these aspects of ‘persistence’. If

farmers were to perceive a loss of yield benefit of having

resown with new cultivars, it would be very important

to distinguish whether this was a loss of yield associated

with the new cultivar itself, and so worthy of expensive

redevelopment of the cultivar’s genome, or whether the

loss of yield was unrelated to the cultivar genome

altogether.

In the extensive study by Hopkins et al. (1990), there

was a clear benefit to yield in the resowing treatment

(Figure 6), but it is not possible to confirm if this was a

consequence of the new, improved ryegrass cultivars

that were sown, or simply of tillage. To make that

distinction, it would be necessary to have ploughed and

resown the permanent pasture species also, and to have

followed yield in that third treatment, too. Where

something close to this was performed, e.g. resowing

with ‘unimproved’ species in the trials by Rowarth et al.

(1996), as well as in the DRC ⁄ Dexcel field trial

described earlier, little-to-no benefits to yield were seen

of proposed improved cultivars. In the trial by Hopkins

et al. (1990), there was a clear yield advantage in the

resowing treatment with new cultivars, but this advan-

tage lasted only 1 year. It is very unlikely that the

ephemeral advantage was attributed to a disappearance

of the newly sown cultivars or their traits, and hence

unlikely that the benefit to yield was attributed to the

new cultivars. The most common explanation for a

yield advantage following resowing per se is that tillage

stimulates N mineralization and leads to greater N

availability. In Figure 6, however, the resown species

had greater yield even at 900 kg N ha applied, where N

availability was not a limitation to either the resown

plants, or permanent pasture controls. This suggests

there are other advantages to plants in the first stages of

establishment. Understanding these might lead to step

changes in progress. We speculate two possibilities.

First, during growth from seed, plants may adopt a

different strategy, maximizing immediate growth (as

survival depends on rapid establishment), and mini-

mizing the costs of, and investment in, longer-term

infrastructure and commitments, such as storage.

Although all plant growth must ultimately be

‘resource-supply limited’, this raises the question

whether growth, notably in perennials, is also at times

‘strategy-limited’. Second, newly sown plants may also

benefit from a period of freedom from community

infrastructure costs. This could be a temporary ‘enemy

release’, or a disruption of the soil trophic web, and so a

period of freedom from the costs of supply of root

exudates to soil micro-organisms, e.g. mycorrhizal and

bacterial symbionts. Although speculative, both possi-

bilities are aspects of potential advantage recognized for

the transient success of invasive plants and many annual

weeds.

This raises the question of whether we could increase

the growth of perennial grasses, in particular, by

altering their growth strategy. In many forage grasses,

the natural life cycle of tillers is still extensively annual,

each terminating in flowering. This alone might argue

for a strong commitment in those tillers, in these

species, to having a high growth rate. However, the

plant must make long-term commitments to storage of

resources, roots and meristems, to allow for perenna-

tion, which takes place via a whole new population of

tillers. This alone would argue the plants might adopt a

conservative growth strategy in all tillers in their



vegetative phase. Our perennial forage grasses suffer a

complex overlap and integration of signals controlling

what are really two alternate strategies for survival.

Given that the rate of recruitment from seedlings in our

forage grasses is low (Edwards et al., 2005), and that

reseeding is a simple option, we could speculate that it

might be possible to up-regulate growth rate in the

vegetative phase in temperate perennial grasses.

Up-regulation could make the plants less conservative,

just as major gains were made in the case of cereals by

up-regulating the reproductive phase. This would,

however, require far more than is proposed currently

in simply switching off flowering.

There are many responses to signals such as day

length and low temperature, that may be part of the

flowering induction and initiation, but which also affect

e.g. sugar storage and mobilization patterns; leaf size,

elongation and appearance rate have impacts in stim-

ulating physiological processes, and affect shoot and

root partitioning and branching (see reviews by Par-

sons, 1988, 1994). Such major changes in plant strategy

would benefit from close scrutiny of the control

mechanisms of gene expression, e.g. for storage sugar

metabolism, and its link with environmental triggers

and hormonal signals for cell division and expansion.

Recent advances in understanding the molecular role of

gibberellins in the control of plant growth processes

(Achard and Genschik, 2009), and the observation that

even exogenous applications of gibberellic acid can

increase DM accumulation, even in plants that would

previously have been identified as being N limited

(Edwards et al., unpublished data), strongly suggests

that growth rate in the vegetative phase of our

perennial grasses may be ‘strategy’-limited as much as

‘resource-limited’. In short, we can speculate with

credible evidence that our perennial grasses are ‘hold-

ing back’ and not growing to the limits of their resource

supply.

Impacts and the notion of an optimal level oftrait expression?

There have been a few concerns raised over the

potential risks to our ecosystems of new cultivars

introduced via conventional breeding. However, the

goal of plant breeding is now explicitly stated as being to

produce plants that intentionally do have major impacts

on primary C and N cycles, are perennial and have

greater persistence. If this level of impact was ever to be

achieved successfully, could we still argue our new

germplasm was totally beneficent, without having

conducted analyses of any potential downsides to a

new trait, beforehand? On what basis can we objec-

tively preclude, at the border, the entry of new

germplasm because we know nothing of its function

in New Zealand, or of GM likewise, while requiring no

study at all of the potential impacts of organisms with

intentionally unprecedentedly altered traits? A recent

article made clear that this discrimination cannot

logically be sustained on the grounds of phylogeny or

origin, but rather: ‘It’s the trait that counts not how it

got there’ (Coghlan, 2009).

A hypothetical example (Figure 8) illustrates how the

level of expression of a trait may have impacts that are

benefits (positive impacts) but also some that may be

negative, leading to the notion there may be an optimal

intermediate level of expression of a trait. In Figure 8,

the benefits of increasing trait expression are shown to

plateau, indicating a limit to the benefits for whatever

reason. In the context of NUE, there is some indication

(from Figure 4) of how NUE does not continue to

improve above a WSC:CP ratio of c. 2Æ0, for example. In

Figure 8, the fact that there may also be ‘downsides’ to

increasing trait expression is shown. At present, breed-

ing protocols do not look systematically for these when

the material is being developed by conventional means.

Downsides to sugar content could be acidosis in animals

(precluding, in effect, a region to the top and right

corner of the targets in Figure 5). Other possibilities

currently being investigated are that at high sugar

content, although N emissions in urine may help

reduce nitrous oxide emissions from soils, the high-

energy diet may lead to increased production of

methane (Ellis et al., 2009). The negative impacts curve

might in general also need to consider impacts on other

parts of the ecosystem. An elevated C:N ratio of plant

components, and the possibility of increased exudation

of C (e.g. as sugars or reduced amino acid secretions)

into the soil from roots are recognized to have major

affects on soil function. The changes in sugar content

Net

ben

efit

Level of expression of trait

Benefit of trait

Optimal levelof expression

‘Downside’ of trait

Figure 8 Evaluation of benefits and possible ‘down-

sides’ ⁄ risks of a trait which vary with the level of expression

of a trait.



and C:N ratio being contemplated are hugely in excess

of what is observed as a consequence, already, of the

elevated CO2 in the atmosphere that is a component of

climate change. Even those small increases have given

rise to concerns over ‘priming’ and progressive nutrient

limitation (PNL). Priming and PNL refer to the effect of

an increased supply of energy below ground leading to

a stimulus of micro-organisms that may accelerate the

decomposition and so loss of stored soil C (Fontaine

et al., 2007), and ⁄ or lead to a greater amount of N tied

up in soil biomass, but with a reduction in the

availability of N for plant growth (Luo et al., 2004;

Reich et al., 2006).

Lessons and prospects

Some basic insights emerge from the examples and

wider considerations, above. We propose there is an

urgent need to establish far more focused goals for plant

breeding, plus specific translation of ‘goals’ (e.g. ‘want

more ME’) into ‘traits’ (e.g. ‘reduce respiration to get

more total DM, or alter metabolism to get more fructan,

or lipid’) and improved quantification of ‘targets’ (e.g.

‘the required level of expression of that trait is

376 g kg)1 DM in plants at 4% N¢). This requires

improved focus on the elucidation of processes ⁄ mech-

anisms that lead to a trait, of the genes involved in

delivering that trait, and their control and expression in

response to internal and external factors (to avoid, for

example, trait loss in G · E interactions). This must be

in combination with more work to assess problems with

the fitness and persistence of traits, to ensure new traits

are ‘locked in’ to the plant, into the community, and to

ensure that yield gains are directly owing to the trait

itself, and not the act simply of cultivation and

temporary disruption of a complex above- and below-

ground ecosystem. We should also look for new insights

through re-assessing whether our evolved grassland

species ‘strategies’ are over-conservative, given the way

we intend to manage them.

Do we have unrealistic expectations of fieldtrials?

The HSG trait exemplifies the huge amount of research

required to achieve any level of certainty over the value

of the trait. In addition to the decade of fundamental

studies that backed up the initial hypothesis and created

the initial populations ready for trials at a field scale, it

took 5–8 years of very expensive and thorough field

testing and indoor studies in the UK, and a parallel

4–5 years of both indoor and outdoor testing of both

animal performance and rumen metabolism in the

Netherlands. The result was ongoing debate and a close

call with reporting a ‘false negative’. Likewise, the

attempt at a definitive answer to the success of plant

breeding in New Zealand via the DRC ⁄ Dexcel field trial

has met with very understandable lack of certainty or

conviction. Given this, we must ask just what realistic

expectation can there be for any one field trial to

provide a definitive single answer.

Need greater focus on ‘proof of concept’

Clearly, field trials must take place but we propose these

should focus on proof of concept. Field trials should not

be seen as the final step, as they do not provide a

definitive answer, no matter how practical ⁄ pragmatic

conducting a field trial may seem. If the success is

immediate, consistent and, of critical importance, sus-

tained, then little more study would be conceived.

Given past experience, however, we should anticipate

that field trials need to be seen as a stage in gathering

insights for unravelling trait expression, fitness and

impacts. The field trials would become part of a cycle

back through more detailed, and better controlled

(including controlled environment), critical analyses,

and ⁄ or re-investigation of mechanisms of trait expres-

sion and its fitness consequences (as was the case with

the HSG trait). Although this seems added time and

expense, it would be well invested if, as a consequence,

more new traits, and some older ones, were better

‘locked’ in and not ‘dropped too early’.

More critical experimental design?

Greater emphasis on critical experimentation is recom-

mended on the basis that many field trials aimed at

evaluating cultivars, or plant-breeding success in gen-

eral, have failed to separate basic factors such as

whether the benefits seen were because of the cultivar

per se or the act of resowing. Considerable emphasis

must be placed in devising trials with appropriate

controls.

The fundamental difference between ‘proof of con-

cept’ and agronomic field testing lies in the nature of

experimental design. For a field trial to provide insights

(that explain a trait success or failure, and so take us

forward), it must have included sufficient ‘controls’ and

so have been designed to test the performance of

the new trait against some pre-defined hypothesis. The

antithesis would be to attempt to demonstrate the

efficacy of a new cultivar ⁄ trait by ploughing up and

resowing this into a farm setting, and comparing

performance with what was previously there, in an

adjacent paddock that had not been ploughed and

resown, and which is run at a different stock density, or

fertilizer input. This design, as shown in Figure 6, does

not separate the benefits of new cultivars per se, from

the benefits of resowing per se. More effort to introduce



critical scientific design into any field trial will greatly

add to its value, if only because it leads to evidence that

is less equivocal.

Particular attention needs to be paid where an

assessment is being made of the performance of one

species, e.g. of a legume, when this is required to grow

and perform in a mixture, given the complexity of

performance of grass-legume mixtures. Although

growth in a mixture may be the industry ‘norm’,

growing and testing legumes in monocultures, as well

as in mixtures, adds very valuably to interpreting the

extent to which pests, grazing preference, and not just

species yield potential, are responsible for the perfor-

mance of the mixture and changes in mixture compo-

sition. Where the species are grown together, reporting

the changes in contribution of each species, and of the

total, seems essential.

Need greater focus on ‘trait’ and less on‘cultivar’

Testing needs to be focused on the ‘trait’, and so the

proof of its concept, rather than ‘cultivar’. To conduct

an extensive trial of multiple cultivars and then to

conclude only that a different result might have been

gained if other cultivars had been used is to lock

developments in plant breeding into endless expensive

comparisons of given companies’ contributions (cf.,

comparing General Motors and Ford) when what is

needed for progress is to compare fundamental traits

(cf. diesel vs. petrol, or either of these vs. draft horses).

Perhaps a better general protocol would be for seed

companies, using an agreed basic national evaluation

scheme, to have ‘cultivar’ testing per se as a responsi-

bility and major government and primary industry

funding effort go into assessing the efficacy of new

traits, and new means to produce traits. Any notion of

‘Breeding Worth’ (Macdonald et al., 2008) could attend

to worth of ‘traits’ as opposed to ‘cultivars’. This might

also avert dispute ⁄ litigation over the alleged value of

respective company products.

It is the trait that counts not how it got there

The New Zealand pastoral industry relies almost exclu-

sively on exotic species and since the introduction of

the Hazardous Species and New Organisms Act, concern

has been expressed that New Zealand will lag behind

the rest of the world unless farmers are able to take

advantage of new introductions and new biotechnology

developments (Lancashire, 2004). Having a strong case,

based on substantial field testing and analyses of proof

of concept (for example all that is described here for the

HSG trait), would assist with the justification necessary

to proceed for a GM (or novel introduction) release. The

case would also be all the stronger if it were possible to

demonstrate that the possibility of any limits to those

benefits (or ‘risk’) had been explored a priori by having

foreseen possible impacts of the trait.

Under the headline ‘It’s the trait that counts, not how

it gets there’, Coghlan (2009) reported increasing

concerns in Europe over the largely unregulated intro-

duction of novel plant traits being produced by con-

ventional breeding, compared with that of cross-border

introductions or release of genetically modified organ-

isms. Having a standard procedure to explore trait

impacts, and fitness, that is applied whether the plants

are GM, cross-border, or conventional would serve well

to reduce abrupt barriers to acceptance of biotechno-

logical solutions. Canada leads the world in trialling a

trait-based system for assessing biosecurity and recog-

nizes the need to include any significant change in the

expression of a trait even if this arises within an

organism already distributed within that country. The

point is not to restrict plant breeding, or biotechnology,

but to suggest that the way a trait is created should not

be the determinant of release.

The realistic expectation (from evidence above) that

no single field trial is likely to be definitive becomes a

serious concern where the new trait is genetically

engineered (or a cross-border introduction). The ques-

tion would then have to be asked ‘have we exhausted

all means to establish the benefits before calling for

release, or, are we calling for release to test if there are

any benefits?’ Again, more work on proof of concept,

and recognizing how much of this can be established

using non-GM surrogates for a trait, can only increase

society’s confidence in the prospect being a risk worth

taking.

Assess fitness and function of genes in the plant,community and ecosystem

Reinvestigating why past improvement traits have not

‘survived’ or been ‘locked in’ from initial experimental

trial populations to commercial-scale seed supplies, or

through seed multiplication, is essential for future

success, and we need a culture of critical scientific

challenge for the future.

Considerable, and ever-growing, effort is put into

introducing new beneficial traits into plants. In the

future, this effort should be matched by an equally

determined effort, founded in molecular and popula-

tion ecology, to ensure that a trait has a net fitness

benefit, and so remains expressed within the plant,

and ⁄ or the plant with the traits is sustained within the

plant community.

In the studies from IGER (in preceding sections), we

see one example of how this is performed, with

assessments being made to compare the divergent



selected population (e.g. of high respiration or high

sugar) with that of the opposite divergent population

(e.g. low respiration or low sugar). This certainly

establishes that these are two distinct new populations,

but ultimately it is far more valuable (as was the case in

both examples mentioned here) to assess how well the

desired (high sugar, low respiration) new population

compares with either the original population mean or

more appropriately (as again was performed) with the

mean of a control population. In both cases, this was at

least one widely available ‘standard ⁄ control’ cultivar.

Likewise, when field testing new cultivars or traits, it is

imperative to separate the effects of resowing per se from

the effects of the new cultivar. Resowing with the old

cultivar, and comparing the yields of both resowings

with that of the undisturbed original adapted material,

seems a minimum design. Monitoring the yields of

these over time, and the presence of not just yield

advantage, but of the sown plants themselves, and the

traits in them, is the only way to assess fitness and

establish what are the persistence issues, should any

need to be addressed. While there have been a few

examples of this approach, in very few cases was any

subsequent action taken. In GM trials in particular, we

feel it is imperative that any success in enhancing a trait

is measured against the mean of the global, non-GM

population (what could be obtained by non-GM meth-

ods) and not in terms of how far the transformed clones

differ from the original pre-transformed clone. We feel

the public, and this includes funders and industry, are

likely to feel confused unless all claims for success are

based only on the difference between the new level of

expression in the new population, and that of the

‘natural’ or unmodified population, and the extent to

which this difference is significant, and can be sustained

over time.

Combine breeding and management to deliverthe ‘trait’

Given the time taken and difficulty in altering a plant

trait through breeding ⁄ selection, whether conventional

or biotechnologically assisted, to what extent a given

level of contribution ⁄ progress towards an industry goal

could be made by other means must be considered. This

would help prioritize which traits warrant the sub-

stantial effort to pursue through breeding, and which

goals could be at least partially fulfilled more readily.

Management approaches might substitute for breeding;

though, in some cases the two will be additive. In the

case of HSG, for example, substantial benefits have

been shown, in achieving high WSC:CP ratios in the

diet and consequent improvements in NUE, simply by

altering (i) timing of feeding (allocating animals new

paddocks to focus intake late in the day when sugar

contents in forage are higher); (ii) stage of regrowth

returning animals to a paddock in a rotation at a time

when again the level of sugars has recovered greatest [a

function of both the initial severity of grazing, and the

duration of regrowth and temperature (Lee et al., 2008;

Rasmussen et al., 2009; Bryant et al., 2010)], as well as

(iii) by using current HSG cultivars. All the above

enhance WSC:CP ratio in both HSG and ‘controls’.

A second example of how management alone may

deliver a ‘trait’ that might otherwise be pursued by

breeding or GM, is ‘digestibility’. Animal science has

long justified the significance of reducing fibre content,

and the scope to do this, by relaying figures for ‘D’ value

in, e.g. Lolium perenne of c. 60–70, and stressing the

scope and benefits therefore of raising this towards 80.

One angle is to genetically suppress flowering. Certainly

such low D values as 60–70 are possible. However,

some of the emphasis arises from the tendency in

animal feed performance trials, to cut material infre-

quently from the pasture for feeding indoors. Grazing

management of pasture alone is capable of controlling

the expression of flowering (Johnson and Parsons,

1985; Orr et al., 1988) and delivering D values of 77–79

consistently, giving a D value of grass very similar to

that of white clover (Orr et al., 1995). Given ruminants

show disturbed eating behaviour when fed low-fibre

diets, notably pure clover diets (Parsons et al., 1994),

the scope for benefit of fibre reduction when D value is

already 75–80% is more limited.

In both the examples above, an increase in sugar

content within a cultivar might add to that achieved by

timing of harvest, and a reduction in fibre content

might produce benefits in situations where excellent

management of grassland cannot be achieved (e.g.

when impending dry spells demand that early-spring

growth be left standing). Note too that raising sugar

content is simultaneously (largely by dilution) improv-

ing digestibility and metabolizability (Rasmussen et al.,

2009). In weighing options, all such factors should

increasingly be considered.

Whose goals count?

Finally, many have argued that the prospects for

advancing agriculture through plant breeding are small,

simply because such a small proportion of grassland

land area is currently resown in any 1 year (typically 3–

5%, reflecting a mean ‘ley’ time >20 years). However,

we could readily argue that if there were a demonstra-

ble improvement in the performance of a new grass

germplasm, this rate of resowing would increase very

rapidly and substantially. Moreover, even if thereafter

this new germplasm were highly persistent, any

subsequent low rate of resowing would be immaterial.

Agricultural production would benefit, even if the seed



sales prospects were small. The argument of ‘no

prospects via breeding’ based on ‘resowing rate is small’

is untenable.

Conclusions

There is still great scope for future gains in primary

industry production using low-cost pasture-based feed-

ing with the kinds of highly persistent and high soil

carbon sustaining systems that are increasingly recog-

nized as attractive to consumers in global markets.

Given the size of change needed, and the fact that it is

likely that there are few processes of plant growth that

plant science has failed to recognize, there is little

prospect of coming up with totally new things to alter in

plants. Hence, revisiting past efforts, as has been

done in this paper, armed with hindsight and

new technologies, is sensible. Just as new technologies

bring previously uneconomic mines into production,

we have extracted new insights from our past efforts,

with a view to improving the likelihood of future

successes.

The last word is we must be wary. In the United

Kingdom, for instance, government research funding

was largely withdrawn from the eminently successful

grass plant breeding of the Institute of Grassland and

Environmental Research (IGER, now IBERS) on the

grounds that if its focus was commercial, then private

seed industry should support it and not the tax payer.

Defra in UK (the Department of Environment, Food

and Rural Affairs) is now providing £400 000 per

annum for four grass- and clover-breeding projects in

a LINK scheme with matched funding from industry,

although continuity of research effort may have been

lost. In New Zealand, the prominence of our pastoral

exports in the nation’s GDP argues we should see far

more acceptance of the national benefit of all grassland

research. We must also seek a better distribution of

funding support for breeding efforts, between seed

companies per se, levy-based primary industry (e.g.

Dairy), and government for public good.

Acknowledgments

This review is an updated version of an article that was

first presented at the 4th Australasian Dairy Science

Symposium, Christchurch, NZ, 2010 (Parsons et al.,

2010). The authors, Tony Parsons and Dave Chapman,

take this opportunity to acknowledge, with deepest

thanks, the considerable contribution to grassland

science, through his tireless encouragement and men-

toring on the need for critical scientific challenge and

experimental design, made by Dr Mike Robson, who

sadly passed away in 2010. The lead author also thanks

AGMARDT (NZ) for support.

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