Yield Trends and

Genetic Potential

Donald N. Duvick

Johnston, Iowa

Crop yields increase annually in many nations

Changes in cultural methods (e.g., fertilizer kinds and amounts, plant density, and weed control) are responsible for about 50% of yield gains

Genetic improvements are responsible for another 50% of the yield gains

The culture-to-genetics ratio varies from crop to crop and region to region

On-farm yields: corn and soybeans in North AmericaBruulsema et al, Better Crops 84 (2000): 9-13

On-farm yields: wheat in UKAustin, Crop Sci. 39:1604-1610 (1999)

On-farm yields: wheat globalCalderini and Slafer, Field Crops Research 57(1998) 335-347

Yield gains from cultural inputs may be leveling off

In industrialized countries — Environmental concerns mitigate against

further increases in application rates for fertilizers and/or herbicides and insecticides

Weed control is nearly absolute, although it could be less effective in the future as weeds develop resistance to intensively used herbicides

DEDHAM, Iowa — By the time the Raccoon River winds through the western hills here, passing corn fields and livestock pens before reaching Des Moines miles to the east, it is so polluted the city has to put it through a special nutrient filter to meet government standards for drinking water.

The culprits are not industrial plants or mines belching toxins into the river. They are Iowa farms, which send fertilizer and animal wastes into the groundwater and into the river. (New York Times, February 10, 2002)

Fertilizer N on wheat in UK Austin, Crop Sci 39:1604-1610 (1999)

Fertilizer N on corn in USASource: USDA-ERS:Fertilizer Use and Price Statistics

Nitrogen used on corn, rate per fertilized acre receiving nitrogen, selected States

y = -0.1521x2 + 603.57x - 598764R2 = 0.9009

0

20

40

60

80

100

120

140

160

1960 1965 1970 1975 1980 1985 1990 1995Year

N, lb/A

Wheat yields since 1985 Calderini and Slafer, Field Crops Research 57(1998) 335-347

Yield gains from cultural inputs may be leveling off

In developing countries — Intensive production inputs may have adverse

agro-ecological impact In high-yield regions, reduced or no yield

increase from increased applications of fertilizer

Rice yields since advent of “Green Revolution”Pingali, et al., “Asian Rice Bowls, The Returning Crisis? (IRRI, 19970

Consequently —

Plant breeding may have to bear a much greater share of responsibility for yield gains in the years to come

Genetic yield gains continue in most crops

Gains primarily are in grains and legumes grown for the commercial market

Gains primarily are for crops bred by professional breeders, public and private

Gains in yield to date have not been materially aided by biotechnology

Gains in yield are linear and show little or no sign of leveling off

Genetic gain in rice: IRRI Peng et al, Crop Sci. 39:1552-1559 (1999)

Genetic gain in wheat: UK Austin, Crop Sci. 39:1604-1610 (1999)

Genetic gain in wheat: USAAdapted from Donmez et al, Crop Sci. 41:1412-1419 (2001)

Genetic Gain: Wheat in Great Plains

y = 33.38x - 62039R2 = 0.9227

2000

2500

3000

3500

4000

4500

5000

5500

1920 1940 1960 1980 2000 2020

Year of Introduction

Genetic gain in wheat:Mexico (CIMMYT) Reynolds et al., Crop Sci. 39:1611-1621 (1999)

Genetic gain in soybeans: USA (Maturity Group II)

Wilcox, Crop Sci. 49:1711-1716 (2001)

Genetic gain in soybeans: USAWilcox, Crop Sci. 49:1711-1716 (2001)

Genetic gain in corn: USAAdapted from Duvick in, Developing drought- and low N-tolerant maize, CIMMYT (1997)

y = 0.0763x - 141.76R2 = 0.8813

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6

7

8

9

10

11

1930 1940 1950 1960 1970 1980 1990 2000

Year of Hybrid Introduction

Yield at optimum density per hybrid

Genetic gain in corn: USACastleberry et al., Crop Sci. 24: 33-36 (1983)

Genetic gain in corn: USADuvick and Cassman, Crop Sci. 39:1622-1630 (1999)

Genetic gain in corn: USA Duvick and Cassman, Crop Sci. 39:1622-1630 (1999)

Corn: Drought tolerance, USADuvick, personal communication (2002)

y = 0.0708x - 132.16R2 = 0.8867 2001

y = 0.0822x - 151.24R2 = 0.8371 1992

4

6

8

10

12

14

1920 1940 1960 1980 2000Year of Hybrid Introduction

Yield at optimum density per hybrid 1992

2001

Drought is drought

Drought tolerance, 1930s genetics

Drought tolerance, 1990s genetics

Wheat: Irrigated performance versus ...S. Rajaram, personal communication

PROGRESS IN YIELD WITH YEAR OF RELEASE IN IRRIGATED DEMONSTRATION PLOTS. SONORA 98-99

R2 = 0.7296

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9

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1940 1950 1960 1970 1980 1990 2000 2010

RELEASE YEAR

YAQUI 50

SONORA 64

UP 301

SIETE CERROS

SONALIKA

PAVON

SERI M82

DEBEIRA

BACANORA T88

ARIVECHI M92

CUMPAS T88

SHANGHAI 4

HUITES F95

R2 = 0.73

RATE OF PROGRESS:

89.6 kg/ha per yearor2% increase in yield per year

Wheat: Drought performanceS. Rajaram (CIMMYT), personal communication (2002)

Progress in yield from more than 200 trials in drought affected and semi-drought affected locations globally.

100

105

110

115

120

125

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135

140

145

150

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

Year

Yield less than 2.5 t ha-1

Yield between 2.5 and 4.5 tha-1

r2 = 0.63

r2 = 0.39

Yield < 2.5 t ha -1Rate of progress 2.27% per year

Yield 2.5 - 4.5 t ha-1Rate of progress 2.33% per year

ESWY SAWYT SAWY

Yield Ceilings?

At what point can on-farm yields go no higher?

Will theoretical “yield potential” calculations predict that point — the yield ceiling?

Corn: Yield ceiling?Duvick and Cassman, Crop Sci. 39:1622-1630 (1999)

Corn: Yield ceiling?Duvick and Cassman, Crop Sci. 39:1622-1630 (1999)

Rice: Lowered ceiling?Peng, et al., Crop Sci. 39:1552-1559 (1999)

Corn: What ceiling?Source: Iowa Soybean Association (2002)

Iowa Master Growers Champion Non-irrigated

y = 0.0099x3 - 58.854x2 + 116170x - 8E+07R2 = 0.9235

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1950 1960 1970 1980 1990 2000 2010Year of Contest

Bushels per acre

Yield potential: theoretical or practical

Theoretical calculations require assumptions that may become outdated as farming practices change

Estimates of practical yield potential require constant updating also, as farming practices change

An eternal constant: Farmers want more yield and greater stability of yield

How to increase practical yield potential?

Change plant architecture Improve “harvest index” Increase “crowding comfort” Increase efficiency in utilizing soil

nutrients Increase tolerance to disease and insect

pests Increase tolerance to abiotic stress

Plant architecture

Rice, wheat and corn now have more upright leaves

Corn has smaller tassels Rice and wheat are designing

“New Plant Type” to have larger panicles/spikes and larger stems

Corn: tassel size, leaf angle

1930s 1990s

Corn: leaf angle

1930s 1990s

Harvest Index

Rice and wheat have increased harvest index since 1960s, but no further change is expected

Corn has not increased harvest index (when genotypes are at optimum density)

Rice, wheat, soybeans, and corn currently increase yield by increasing biomass and thereby increasing the number of grains/kernels per unit area

“Crowding comfort”: Soybeans

“As the plant population increased from 33 to 50 to 100 plant m-2 the yield of new (post-1976) cultivars became increasingly greater than that of the old (pre-1976) cultivars.” (Specht, et al., Crop Sci. 39:1560-1570. 1999)

Increased efficiency in using (or supplying) soil nutrients: soybeans

Specht, et al., Crop Sci. 39:1560-1570 (1999)

Tolerance to disease and insect pests

Conventional breeding has been effective and will continue to be effective in providing resistance to most disease and insect pests

Durable resistance is the greatest need Biotechnology, e.g. with transgenics, can produce

resistance in some cases where none is found in the crop species or its near relatives

Molecular biology, longer term, will produce theory and genetics for improved durable resistance

Tolerance to corn borer (pre-Bt) 1940s genetics 1970s genetics

Tolerance to abiotic stress

For all crops, increased yield is associated with increased tolerance to abiotic stresses such as: Too hot Too cold Too wet Too dry Too much shade Too few nutrients

Tolerance to abiotic stress

There is no completely stress-free environment

Therefore to breed for more tolerance to any stress is to breed for higher yield as well as for more stable performance

No cultivar is perfect, therefore possibilities to breed for improved yield are always present

The Future

Will gains continue? Will they meet global needs? Will they be for the right crops

and right regions?

Yields can (will?) continue to climb, but ... The cost per unit of improvement has risen

consistently during the past 100 years Enthusiasm for production agriculture including

plant breeding consistently declines (in the non-farm population of the rich countries)

Funding for public sector plant breeding (and for public agricultural research in general) consistently declines worldwide

Yields can (will?) continue to climb, but ... Attitudes toward private sector plant breeding

polarize toward condemning it or assuming that “it can do it all”

Widespread fear of genetic engineering for plant breeding is transforming into a fear of plant breeding in general

Gains cost more

Thus we seem to require increasingly greater numbers of maize breeders to maintain a constant rate of improvement in yield.” (Duvick, in Genetic Contributions to Yield Gains of five Major Crop Plants. CSSA. 1984)

Higher yields not needed “The biotechnology industry claims it holds the

answer to world hunger: high technology to increase production. But according to the United Nations Food and Agriculture Organization (FAO), this badly misstates the problem. There is no shortage of food in the world. Per capita food production has never been higher.” Advertisement in New York Times, October 11, 1999, by Turning Point Project, a coalition of more than 60 non-profit organizations.

Funding declines “Expenditures on agricultural

research in the public sector, including the International Agricultural Research Centers (IARCs) have stagnated and in some cases, declined sharply in recent years.” (Maredia and Byerlee, Agricultural Economics 22:1-16. 2000)

Parasite or protector? “… government does the costly, basic and

innovative research, while big companies pick up the profits in the marketplace.” (Fowler and Mooney, “Shattering: Food Politics, and the Loss of Genetic Diversity”. 1990.”

“Some question the need for continued public funding [of agricultural research], thinking that … the private sector will do the job.” (Pardey and Beintema, Slow Magic. IFPRI Policy Statement. 2002)

Plant breeding = genetic engineering?

“Recently, in the state of Washington, usually known for its progressive policies, strawberry plots and greenhouses belonging to Washington State University have been savaged, even though they contained not one single transgenic plant! In fact, nobody at that university has ever conducted transgenic research on strawberries.” (Lurquin, The Green Phoenix, A History of Genetically Modified Organisms. 2001)

Can breeding meet the challenge?

Predicted rates of increase in food demand during the next 50 years tend to be larger than measured genetic gains in yield during the past 50 years

Future food needs are greatest in regions where breeding progress has been slowest

But with adequate political and economic support, yield gains could be greatly increased in the most needy regions

Can breeding meet the challenge?

Plant breeding cannot do the job alone

It must be preceded and under-girded by the proper political and economic climate

Tailor breeding to the place and people

Breeding techniques suited for commercial agriculture in industrial countries will work also for commercial agriculture in developing countries

But many farming people (2 billion?) in “traditional agricultural areas” (poor land, poor economy) do not farm commercially and have different and highly diverse needs for variety improvement.

Participatory plant breeding may be best suited for such “traditional” farmers

Participatory Plant Breeding Several variations, all emphasize

decentralization strong farmer participation on-farm testing

Professional breeders advise but do not dictate

Goal is to produce varieties that meet local farmers’ needs that farmers can reproduce

What about biotechnology?

Biotechnology will not enable spectacular increases in yield in the near term

Biotechnology will be essential over the long term to help yield gains keep in step with global food needs

Biotechnology in the near term will be more useful in developing countries than in industrial countries, if it can help breeders add badly needed kinds of disease and insect resistance

What about biotechnology? Biotechnology’s greatest contribution to plant

breeding will be to increase the depth of knowledge about gene action and how to modify it to suit needs of farmers

Biotechnology causes contrasting social problems at present; it arouses fears and raises hopes in two types of people: Type 1: great fear of repressive monopolies Type 2: great hope of high profit margins Both types may be wrong

In conclusion: Plant breeding, properly supported and wisely conducted,

can help to increase food production in step with diverse needs of a growing global population

Breeding must be done with care to produce products

That farmers want and can eat and/or sell That grow well where the farmers farm That respond well to the way the farmers farm

As breeders would say: Pay attention to GxE

Carpentry 101:

Plant breeding is a three-legged stool: Leg 1: National and state public

sector programs Leg 2: International public sector

programs Leg 3: A diverse assemblage of

private sector programs The stool supports the farmer