senna salt stress
TRANSCRIPT
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Journal
of
Experimental Botany, Vol. 28, No. 103, pp. 4 84-492, April 1977
Some Primary Featuresof Salt Tolerancein Senna
Cassia acutifolia)
ALI T. AYOUB
Hudeiba
Research
Station, P.O. Box
31,
Ed-Damer, Sudan
Received 1March1976
A B S T R A C T
Studies
on the
germination
of
Cassia acutifolia (senna) seeds indicated that they were highly
tolera nt of salinities up to 160 m mhos cm
1
, and50per cent reduction in germination occu rred
at about 20-0 mmhos cm
1
.Airtemperaturehad a significant effect onsenna germinationat
substrate salinities between 10-0and25-0 mm hos cm
1
.
Seedling growth was more sensitivetosalinityandalkalinity tha nthegermination stage.
Yo ung pla nt surv ival an d tota l pod yield were significantly reduced insoilsalinities higher th an
11-0 minhoa cm
1
, an d this was more pronounced when plan ts were irrigatedatshort intervals
with salinewaters.The sensitivity of senna to higher levels of salinities was correlated with the
higher rate of chloride accum ulation in the tissue resulting in specific chloride injury. However,
the possibilityofsodium injury cannot be excluded.
I N T R O D U C T I O N
In a previous paper (Ayoub, 1975), the importance of senna Cassia acutifolia)as a
promising irrigated cash crop was put forward. The crop requires high temperatures
and an abundance of sunlight (Gupta, 1971), and these conditions prevail in the
more arid parts of the Sudan where soil salinity and alkalinity problems may be
important. A study was, therefore, undertaken on the effects of salt levels, salt
types, and soil alkalinity on senna germination, vegetative growth, yield, and
mineral composition. Some environmental factors which may effect salt tolerance
by senna, such as watering interval and air temperature, were also included in
these studies. The present paper reports some primary features of these studies.
MATERIALS AND METHODS
Germination
studies
Germ Lnation expe rimen ts were carried out i n 10 -cm-diameter P etri dishes in asinglerandomized
design with 11 levelsof NaCl solutions (0-40-0 mmhos cm
1
) replicated four times.Ineach
sterilized Petr i dish, 10 hea lthy surface-disinfected (HgCla) senna seeds were placed on
a
filter
paper bed, covered with another sheetoffilter paper,andsoaked with 10 mlof the specified
solution. This volume was sufficient to satu ratethefilter papers a ndtopartially immersethe
seeds.ThePe tri dishes were coveredandplacedin thedarkin an incubator maintainedat
30 2
C.
The germination coim t was taken every 24h.
Interaction o f
temperature
an d salinity
on germination
The germination tests were carried out
in
Petri dishes
as
described above. Salt levels used
were 0,5 0, 8-3,
16-3,
24-5,and33-6mmhos cm
1
NaClat25 Cand each testwasreplicated four
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Ayoub Salt
Tolerance
in Senna 485
t imes.
Replicates were incubated at 12-15, 28-30,
3235,
and 40-45
C
and germ ination counts
were made on the 7th day.
ESP tolerancestudies
Hud eiba Research Station Farm he avy claysoil(Vertisols) was air-dried, crushed, a nd sieved
throug h 2 mm mesh. Soils of different exchangeable sodium perce ntage (ESP) levels were pro-
duced following the method of Chang and Dregne (1955). Final ESP levels obtained were
approximately 5, 15, 24, 35, 45, and 55.
These soils were again air-dried, sieved, and 5'5 kg of each soil placed in 21-cm-diameter
plastic pots and randomized on a ventilated greenhouse bench. Each soil test was replicated
five times. Ten seeds of senna were sown in each pot and irrigated when necessary with low-
salt tap water (0-20 mmhos).
Germination counts were recorded and after a period of 30 d plants were harvested for dry
matter determinations.
Effect of
salt
types and
levels on
plant
growth
About 5
5 kg
of washed san dy loam
soil were
put in
60
plastic pots
21 cm
diameter) with drain-
age holes and 10 seeds of senna were sown in each pot. For a period of
2
weeks the pots w ere
irrigated a lternately w ith tap w ater and Hoagland nutrie nt solution after which the seedlings
were thinned to four plants per pot and 45 pots of uniformly growing plants were selected for
salt treatments.
Equal concentrations of NaCl, CaCla, Na2SO4, and an equal mixture of NaCl and CaCl2
were compared at the levels shown in Table 2. Saline waters were applied gradually to allow
for osmotic adjustment until the final specified salt level was maintained. The plants were
harvested after 8 weeks of growth in salt treatm ents and the fresh w eight of the new growth
and its mineral contents were determined. Observations such
as
plan t survival an d leaf shedding
were also taken.
On dry ashed plan t m aterial Na and K were determined by a flame photom eter, Ca and Mg
by titrating with EDTA, and Cl using the AgNOs method (Chapman and Pratt, 1961). Soil
salinity (EC) was measured following the U.S. Salinity Laboratory method (Richards, 1954).
All experiments re ported abo ve were repeated a nd com parable results were o btained.
Frequencyofirrigationwith NaCl onsenna growth
Seeds of senna were planted in metallic lysimeters with drainage holes at the bottom and
containin g ab out 130 kg of river silt. The lysimeters used were oil drum s 65 cm high and 60 cm
in diameter and painted with a sphalt. The experimental design was a factorial combination of
five concentrations of NaCl (0-2, 2-5, 5-0, 10-0, and 20-0 mmhos cm
1
) and two intervals of
watering (every
7
or 14 d with t he salt solution). These lysim eters, with three replicates, were
arranged randomly in the open air where daily tempe ratures ranged between 25 and 39 C.
They were watered w ith ta p w ater whenever necessary until the salt treatm ents were applied.
Just before applying salt treatments the plants were thinned to eight per lysimeter.
Salt was applied after
4
weeks from sowing in increm ents of
2-5
mm hos NaCl in the irrigation
water every other d ay to allow for osmotic adjustm ent until the plan ts were receiving solutions
of assigned concentration. Salt concentrations in the soils at harvest are shown in Table
3
a s
mmhos cm
1
of saturated extract. The volumes of solutions added were sufficient to allow
copious drainage and thorough flushing out of the root medium.
Observations concerning plant survival and development were recorded. Samples of dead
plants were also taken throughout the duration of the experiment. Pod yields were recorded
periodically an d a t the termination of the experiment yield com ponents and
some
plant charac-
ters were determined. Leaf samples were also taken for N a a nd Cl analysis.
R E S U L T S
Effect and NaCl levels on seed germination
Senna seed germination never exceeded 75 per cent and under field conditions the
maximum germination obtainedwasusuallylessthan60per cent. Thislowgermina-
tion percentage is mainly due to the presence of 'hard' seeds which do not imbibe
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486
Ayoub Salt Tolerance in Senna
100-
90
80 -
70-
| 6 0
I 50-
8
I 40
30-
20-
10
0
4 5 6
Days from sowing
FIG. 1. Sen na seed germination at different NaCl levels. The num bers on the g raph are NaCl
solution conductivities in mmhos cm
1
at 25 C.
water even after 10 d soaking. Laboratory tests have indicated that these seeds
have an impermeable seed coat. The da ta shown in Fig. 1, presenting germination
perce ntage in relation t o different salt levels of th e sub stra te, are therefore based on
germinable seeds.
Control seeds completed germination on the 7th day. Seed germination was
satisfactory up to a sa lt level of about 16-0 mm hos cm
1
NaCl. Between salt levels
of 20-0 and 24-0 mm hos c m
1
germination was reduced 50 per cent and beyond th e
salt level of 30-0 mm hos cm
1
germination was almost inhibited.
Interaction of salinity and
temperature
on senna germination
Fig.
2
shows the effect of salinity a t different
ah
temperatures on senna germina-
tion. Su bstr ate salinity, ah- tem pera ture, and their intera ctio n highly significantly
affected senna germ ination . U p to a salinity of6-0mmhos cm
1
the re was no differ-
ence between tem pera tures from 28 to 45 C hi germination percentage. Air tem-
perature had its greatest effect on germination at salinities between 10-0 and 25-0
mmhoa cm
1
. Fifty per cen t reduction in germ ination occurred a t salinities of abou t
10-0,
17 0, and 22-0 mm hos cm
1
when air tempe ratures were 40-4 5,32-3 5, and 28-
30 C, respectively. Senna did not germinate at temperatures below 15 C.
Effect o f ESP levelson sennagerminationandseedling groioth
The data
ha
Table
1
shows th e effect of different E S P levels on senn a seed germina -
tion and seedling growth. Seed germination was satisfactory up to an ESP level of
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Ayovb
Salt Tolerance
in
Senna
487
o o
5-0
1
3
5-0 20-0 25-0
NsCI levd (mmhos cm
1
)
F i o .
2. Effect of NaCl levelsa t different a i rt e m p e r a t u r e s o ns e n n a s e ed g e rm i n a t i o n :
2 8 - 3 0 C ; , 3 2 - 3 5 C ; A A ,4 0 - 4 5C .
350
O
35.
Bey ond t h a t level some seeds germ inated, b ut m ost of the seedlings died sho rtly
after that. Seedlings growing
in
ESP levels
of
25
or
more were stunted
and had
bleached-yellowish (chlorotic) secondary leaves.
The
effect
of
ES P was, there-
fore, m ore pronounced
at
the seedling growth stage than during seed germination.
TABLE 1.Effect of
exchangeable
sodium
percentage
ESP)
onsenna seed
germination
an d
seedling
growth
E S P
5
15
25
35
45
55
Relative
germination (%)
100-0
96-3
88-9
88-9
48-2
33-3
Relative
growth (%)
100-0
6 0 1
45-8
32-8
25-0
1 0 0
Effect of salt types and saltlevels
P lan t grow th, survival, and mineral composition from the different tre atm ent s as
obtained
at
th e end of the
8-week
period of growth are shown in Table
2.
Plants receiving additions
ofC GI2
were affected more markedly than those re-
ceiving the correspondinglevelsof NaCl while plant s grown inNa2SO4media showed
less chan ges
in
growth than those grown in NaCl.
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00
00
T A B L E
2. Effect of
equal conductances
o f
different
salt types on senna growth,
survival,
and m ineral composition
Sftlt treatments
Type
mmhoscm
1
ITIM
Relative
growth
Plant
survival
Mineral contents (mBq per 100 g dry wt.)
N a
Mg
C a
Cl
N o
salt
NaCl
CaCla
N a
2
S O
4
CaCla+NaCl
0-2
2-5
5 0
1 0 0
20-0
2-5
5-0
10-0
20-0
2- 5
5- 0
10-0
20-0
10-0
20-0
1-4
22-0
43-9
87 8
175-6
14-6
29 3
58-0
117-2
16-5
33-0
66-0
132-0
73-2
146-4
100
96
66
29
17
100
41
23
12
79
89
61
23
46
2
100
100
88
49
19
100
86
54
14
94
97
85
25
64
25
4-6
4-4
6-9
19-9
38-0
4-5
7-1
3 1
8-2
12-3
14-1
13-6
16-7
19-9
30-1
73-9
67-5
60-9
57-0
42-7
64-5
54-5
52-4
53-2
64-7
63-4
65-2
58-1
49-9
52-4
60-9
44-4
51-0
41-9
38-7
105-3
116-0
120-0
100-3
105-3
83-9
60-0
53-5
46-1
69-9
69-9
87-3
95-8
103-8
124-8
87-3
108-3
112-3
143-7
05-9
60-4
91-3
87-3
128-7
141-2
4- 9
18-2
34-2
106-6
121-2
1 9 0
04-0
94-0
186-0
7-5
7-7
9-5
106-6
107-2
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Ayoub Salt Tolerance
in
Senna 489
There wasaprogressive reduc tioningrowth with increasing salinityofthesub-
strate. This effect
was
more apparent
in the
plants exposed
to
chloride salinity.
Fifty
per
cent reductions
in
growth were found
at 4-0
mmhos
cm
1
CaCl2,
at 7-0
mmhos cm
1
NaCl,
and at
abou t 13-0 mm hos cm
1
Na2 SO4. Da ta
on
leaf shedding
and plant survival confirmed
the
results reported
for
plant growth.
Mineral
compositionofshoots
Mineral contentsof plant shootsas mEq per 100 g dry wt. are also shownin
Table2. The control plants contained very littleNa andC l,but theirK contents
were high. Increasing NaClin thesubs trate increasedCl and Na anddecreasedK
con tents of shoots,
Cl
being accum ulatedatmuch higher rates. Sodium accum ulated
in larger amountsin the shoots from NaCl treatments than from Na2S(>4,and Cl
T A B L E 3. Effectof irrigation frequency with different NaCl levelsonsenna yield
and yieldcomponents
Irrigation interval NaCl levels (mmhos cm-
1
at 25
C
C) of saturated soil Watering
extract effect
0-9 7-5 10-1 16-1 27-8
Pod yield (g/pot)
7d 47-0 52-0 16-1
14 d 18-2 24-3 11-6
Salt effect 32-6 38-2 12-9
S.e. means salt effect = 5-42, watering effect = 3-44.
No. of pods/pot
7 d 661-3 691-3 228-3
14 d 254-7 330-0 176-7
Salt effect 458-0 510-7 202-5
S.e. means salt effect = 67-20, watering effect = 42-49.
Final plant survival/pot
7 d 8-0 8-0 4-7
14 d 7-7 8-0 8-0
Salt effect 7-9 8-0 6-4
S.e. means salt effect = 0-86, watering effect = 0-54.
Wt/dry pod (mg)
7d 73-3 71-0 69-3
14 d 68-0 72-7 68-3
Salt effect 70-7 71-9 68-8
S.e. means salt effect = 5-07, watering effect = 3-21.
Dry wt. plant (g)
7d 13-4 111 31
14 d 11-4 7-5 3-5
Salt effect 12-4 9-3 3-3
S.e. means salt effect = 1-85, watering effect = 1-17.
Plant height (cm)
7 d 72-7 60-7 33-0
14 d 59-7 52-7 40-7
Salt effect 66-2 56-7 36-9
S.e. means salt effect = 4-55, watering effect = 2-86.
1-4
5-3
3-3
25-3
81-3
53-3
0-3
2-7
1-5
6 9 0
6 5 0
67-0
1 1
1-7
1-4
25-0
28-3
26-7
1-5
5-6
3-6
32-0
93-3
62-7
0-3
0-7
0-5
47-0
60-3
53-7
1-4
1-8
1-6
2 5 0
26-0
25-5
23-6
1 3 0
327-7
187-2
4-3
5-4
65-9
66-ft
6 0
5-2
43-3
41-6
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490 Ayoub Salt Tolerance in Senna
accum ulated in greater amo unts fromCaCl2treatm ents th an from NaCl. Increasing
su bs tra te conten t of CaCl2 increased shoot Cl, Ca, and Mg contents w ith slight de-
crease in K contents.
Effect of frequency of irrigation ivith salt water on senna yield and yield componen ts
Results of senna pod yield and yield components from different NaCl levels are
shown in Table 3.
' P od yield was significantly affected b y sa lt levels, frequency of irriga tion, an d
the ir interaction. W atering every7d with lower-salt wa ters resulted in apprec iably
higher yields th an w atering every 14 d. Con trary to this, frequent irrigation w ith
high-salt waters injured plants and resulted in lower pod yields than irrigation
every 14 d with the same water.
The number of pods per pot in the various treatments were comparable to pod
yield while increasing salt level resulted in a small but significant P < 0-05)
depression in pod weight.
Plant survival was significantly reduced by salt levels higher than 10-0 mmhos
cm
1
in the soil. This effect was more noticeable at the shorter watering interval
than at the longer watering interval, indicating that the effect of NaCl salinity on
sen na was not solely an osmotic phenom enon. Injure d p lants contained considerable
am ounts of
Cl
which was closely related to the degree of visible injury.
Po d yield was highly correlated w ith pod num ber (r = 0-9947), less with pla nt
survival (r = 0-7221), and least with pod weight (r = 0-3818).
Dry vxight per plant and plantTieight
Significant reductions in dry matter yields and plant heights occurred at soil
salinities of 10-0 mmhos cm
1
and above. W hen soil salinity was raised from 7-5
6-0-
5-0-
v
e
p
o
y
i
e
d
3 3-0-
2
eo
3 2-0-
l-0
-
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Ayoub
Salt Tolerance in Senna
491
to 10-1 mm hos cm
1
reductions of65and 35 per cent were found in dry m atte r and
pla nt height, respectively. Increasing th e watering interva l from 7 to 14 d reduced
both parameters but not significantly.
The relationship between pod yield and Cl contents of senna leaves is demon-
strated in Fig. 3. Significant yield reduction occurred when the Cl content of the
blade was above 28 m Eq per 100 g dry w t. Fifty per cent yield reduction occurred
a tClcontent of about 62 m Eq , and at Cl content of greater th an 110 m E q pod yield
was very low. The Na contents also varied with NaCl levels, but these variations
seemed to be of minor magnitude.
DISCUSSION
Senna was shown to be fairly tolerant of salinity at the germination stage. A 50
per cent reduction in germination was reached at salt levels between 20-0 and 24-0
mmhos cm
1
. By way of contra st, a 50 per cent reduction in germ ination was found
at 13-0 for groundnuts (Shalhevet, Reiniger, and Shimshi, 1969), 14-0 for tomatoes
(van H oorn, 1970), and 21-0-30-5 mm hos cm
1
for rice (Pearson, Ayers, an d E ber-
hard, 1966). The relatively higher tolerance of senna to salinity during germina-
tion is not surprising since it is a crop originating from regions with a dry climate
and where salinity problems usually exist . The optimum temperature at which
senna could germ inate satisfactorily at high salinity levels was found to be between
28 and 30 C. The significant interac tion of soil salinity an d air tem per atu re re-
ported in this study might be imp ortan t in determining optimum sowing dates on
saline soils. Senna seeds germinated in soils high in exchangeable sodium (ESP of
35),
bu t mo st of the seedlings died shortly after. T he chlorotic sym ptom s appearing
in seedlings growing in high ES P levels couldbedue to the to xic effects of bica rbo na te
ions resulting in high pH values.
Salt type effects were considered important in senna since Na2SC>4 effects were
generally less detrimental to the plant growth than were those of CaCl2 or NaCl
of the same salinity. Plants treated with chloride salts were damaged to a greater
extent indicating the more deleterious effects of chloride ion. With chloride salinity,
CaCl2 was more toxic tha n N aCl. I t w ould appear t h at t he high chloride conc entra-
tion in the plant tissue produces the dr astic decrease in plan t growth. I t is possible
that the high sodium levels in plants found in some treatments could be due to
chloride injury to mem branes giving rise to passive sodium u pta ke .
Senna very rapidly absorbed chloride from the root media and accu m ulated toxic
amounts of it in the leaves. Visible chloride injury symptoms occurred at foliar
chloride concentration of abo ut 4270 m Eq per 100 g dry w t., pla nt g row th w as
retarded at about85m Eq , and pla nt survival was highly imp aired at chloride levels
of more tha n 140 m Eq . In its sensitivity to chloride injury, senna behaves in a like
manner to avocado, citrus, and grapes but contrary to most plant species which are
more sensitive to sulphate salts (Mengel, 1973).
Fo r good pod yields of senna, NaCl salinity should not exceed ab out 8-0 m m hos
cm
1
in the soil, but satisfactory yields may be obtained up to 15-0 mmhos cm
1
,
similar to safnower and wheat (Bernstein, 1970).
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492 Ayoub Salt T olerance in Senna
More frequent irriga tion w ith saline w ater induced, earlier and more severe inju ry
than less frequent irrigation. Bernstein and Francois (1975) found that more fre-
quent sprinkling with saline waters resulted in greater osmotic shock than less
frequen t wa tering. Moreover, it was noted in this stud y th at w ater use by the crop
was reduced greatly under high salinity. It is, therefore, inadvisable to give extra
water to senna under saline conditions.
In conclusion, the following points can be mentioned. Senna is moderately toler-
ant to salinity. It seems to be more salt tolerant at germination and later growth
stages , th e seedling stage being the most sensitive. Avoiding adverse environm ental
conditions like high air temperature (Francois and Goodin, 1972), low relative
humidity (O'Leary, 1975), and bad cultural practices (Sandoval and Benz, 1973)
at that critical stage may improve the salinity tolerance by senna and its survival
in the field.
ACKNOWLEDGEMENTS
The author is grateful to the Director General, A.R.C, Sudan for permission to
publish this paper and to D r. R. H. Nieman ofU.S. Salinity Laboratory, Riverside,
for his valuable comments and encouragement.
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