1. Journal of Food, Agriculture & Environment, Vol.9 (3&4), July-October 2011 545
www.world-food.netJournal of Food, Agriculture & Environment Vol.9 (3&4): 545-551. 2011
WFLPublisher
Science and Technology
Meri-Rastilantie 3 B, FI-00980
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e-mail: info@world-food.net
Received 30 June 2011, accepted 2 October 2011.
Physiological responses of tolerant spring wheat lines under water stress
Sima Taheri 1
*, Jalal Saba 2
, Farid Shekari 2
and Thohirah Lee Abdullah 3
1
Department of Plant Production, Faculty of Agriculture, Islamic Azad University of Arak, Iran. 2
Department of Plant Breeding,
Faculty of Agriculture, Zanjan University, Zanjan, Iran. 3
Department of Crop Science, Faculty of Agriculture, University Putra
Malaysia, 43400 UPM Serdang, Selangor, Malaysia. *e-mail: sima_taheri65@yahoo.com
Abstract
As one of the most important ecological factors determining crop growth and development, water deficit plays a very important role in inhibiting the
yields of crops. Improving crop resistance to drought, both through traditional breeding and biotechnology- based approaches is important. Drought
leads to a variety of biochemical, physiological and metabolic changes in plants.At present, most researchers are focused on how to maintain the best
economic productivity and highest water use efficiency in arid and semi-arid areas. This study was conducted to extract the probable correlation
between different traits and stress tolerance index (STI) of wheat lines. It was also conducted to estimate the direct and indirect effects and heritability
of these traits to provide plant breeders useful information regarding drought resistance in wheat breeding. Seventeen wheat lines, with variable
responses for drought stress, were evaluated in two different levels of stress: (a) without stress and (b) with stress. Different physiological traits,
such as relative water content (RWC), stomatal conductivity, rate of water loss of excised-leaf (RWL), cell membrane stability (CMS), canopy
temperature, osmotic adjustment (OA) and water use efficiency (WUE), were measured during growth season. The experiment was conducted in a
split block design in a randomized complete block design with three replications. The normal and stress levels were the main plots and wheat lines
were the sub plots. Analysis of variance revealed significant differences of WUE, RWLand CMS among lines, showing the potential genetic variations
of the mentioned traits. In the estimation of correlation coefficients between traits and STI in both normal and stress environments, there was a
positive and significant correlation for RWC, OA, CMS and WUE. Between stomatal conductivity, RWLand canopy temperature with STI observed
a negative and significant correlation. In path analysis, only WUE had direct effect on STI. Based on these results and from a high broad sense
heritability estimated for WUE, it can be concluded that selection for water use efficiency will be effective in wheat breeding for drought resistance.
Key words: Drought resistance, broad sense heritability, path analysis, physiological traits, wheat (Triticum aestivum L.).
Introduction
Drought is a major stress which limits crop production 1
. This
problem is especially serious in arid and semi-arid areas 2
. Wheat
(Triticum aestivum L.), the world’s most widely adapted crop
mainly grown on rainfed land, is feeding one-third of the world
population. In developing countries, almost 37% of the areas are
semi-arid and the little available moisture greatly restricts wheat
production. The World demand for wheat is predicted to increase
40% by 2020 compared to its level in the latter half of the 1990’s 3
.
Wheat genotypes/cultivars tolerant to water stress have higher
yield in rainfed areas 4
. There are somecertainreliablephysiological
or biochemical characteristics used in the selection of genotypes/
varieties tolerant to water deficit conditions 5
. One of these
characteristics or indicators is stomatal conductance. Stomatal
conductance decreases significantly in all wheat cultivars during
water stress 6
. Stomatal closure decreases water consumption
during water stress condition and leads to photosynthesis rate
reduction 7
. Stomatal conductance is sensitive to environmental
conditions such as light, air or soil humidity, and even wind. It
also changes by plant age. Comparing irrigated and dryland wheat,
dryland varieties have less stomatal conductance (or more stomatal
resistance) than irrigated varieties 8
. Some researchers found that
stomatal conductance is not a suitable criterion in drought
tolerance screening programs 9, 10
. Relative water content (RWC),
since it is easier and less expensive to measure, is a more suitable
criterionfordroughtresistancecomparedtoleafwaterpotential11
.It
was also reported that the RWC decreases as drought stress
increases 12
. Some findings also showed significant genetic
variation in RWC of wheat with a high heritability, thereby making
RWC as a drought screening tool only in wheat and not for water
potential components 13
. It was found that under normal conditions
canopy temperature in maize, wheat and other dryland crops was
usually lower than air temperature except during noontime, and
the canopy-air temperature difference under normal conditions
was more tangible than the water-deficit conditions, especially in
the afternoon 14, 15
. In 1963, infrared thermo-detector was used to
evaluate crop canopy temperature for the first time 16
. Low canopy
temperature during grain filling period in wheat is an important
physiological aspect for high temperature stress tolerance 17
. The
cell membrane stability (CMS) is another tool which screens wheat
genotypes for drought stress 18, 19
. Extensive application of cell
membrane stability (CMS) as selection indicator of some abiotic
stresses like drought and high temperature has been reported in
different crops like wheat 20-22
, rice 23
, cotton 24, 25
and sorghum 26
.
Lower CMS value is associated with susceptibility under drought

2. 546 Journal of Food, Agriculture & Environment, Vol.9 (3&4), July-October 2011
condition, meanwhile, genotypes having higher CMS value exhibit
greater drought tolerance.
Another physiological characteristic which was investigated in
this study is osmotic adjustment (OA). OA is one of the most
important compatibility mechanisms in many crops under water
stress condition which can be applied as screening tool for
drought-resistant bread wheat genotypes 27
. When soil water
potential (WP) under water deficit condition is lowered osmotic
adjustment causes an active accumulation of solutes within the
plants 28
. Generally, OAis achieved either by absorbing ions (e.g.
Na+
, Ca2+
, Cl-
, Mg2+
,NO3
-
,K+
,SO4
-
and HPO4
-
) or by accumulating
organic solutes (e.g. sugars, free amino acids, quaternary
ammonium compounds and sugar alcohols). This results in a
decrease in the osmotic potential of the cell. It also absorbs water
into the cell and cell turgor is maintained 29
. Consequently, OA
contributes to improving, the plant’s performance with respect to
growth and productivity by maintaining the turgor and water
supply of the plant, leading to a higher photosynthetic rate and
growth 30-33
.
Previous findings have shown that six wheat genotypes differed
with respect to their rate of water loss (RWL) and initial water
content (RWC) in ear emergence and grain filling in the stress
environment 34
. Since water stress is the most important limiting
factor of wheat production in arid and semi-arid regions of the
world, producing wheat cultivars, which use available water more
efficiently and are more tolerant in drought stress condition, is a
main objective to increase production in arid regions. However,
water use efficiency (WUE) is an important part of drought
compatibility 35
. The objectives were (i) to study the reliability of
some physiological traits for screening wheat lines under water
stress and (ii) to determine probable correlation between different
physiological traits and stress tolerance index (STI).
MaterialsandMethods
A field experiment was conducted in the Department of Plant
Breeding, Faculty ofAgriculture, Zanjan University, Iran, 48°27' E
longitude,36°41'Nlatitudeand1620maslfromMarchtoSeptember
2006. Seventeen wheat lines, with variable responses to drought
stress, were evaluated under two different levels: (a) irrigated
(without stress) and (b) non-irrigated (with stress). The amount
of water in each irrigation system was measured by water meters.
The experiment was conducted in a split block design in
randomized complete block design with three replications. The
levels of irrigation were the main plots and the wheat lines were
the sub plots. Each sub plot consisted of 6 rows which were 5 m
long and 25 cm apart. The seventeen wheat lines with variable
responses to drought stress came from the Agriculture Research
Center of Zanjan province. These lines includedAlvand, Ghods,
Shahriar,Pishtaz,C-80-20,C-80-10andZarin,whichwereirrigated
lines,andSardari,Son-64,18Yeknavakht-82,B1-3,B3-2,B3-3,B3-
1, A2-3 and Nik Nejd, which were dryland lines. To identify
genotypes with high yield potential and high stress tolerance,
there were several drought stress indices or selection criteria used:
TOL = stress tolerance 36
; MP = mean productivity; GMP =
geometric mean 37
; SSI = stress susceptibity index 38
and STI stress
tolerance index 39
.
Stress tolerance index (STI): STI is the drought tolerance criteria
based on grain yield 39
:
STI=(YN
)(YS
)/(YN
)2
where YN
and YS
are genotypes yield under normal and stress
condition and YN
is genotypes mean yield under normal stress
condition.
Determination of stomatal conductance: Stomatal conductance
(mmol/m2
s) from flag leaves of six randomly selected plants in
each experimental unit 40
was assessed using a PE4 porometer
(Delta-T Devices, UK).
Determination of relative water content (RWC): To determine
theRWC,freshleavesweredetachedfromeachtreatment,replicate
and genotype and weighed immediately to record fresh weight
(FW). Half of their portion was then dipped in distilled water for
12 h. The leaves were blotted to wipe off excess water, weighed to
record fully turgid weight (TW) and were subjected to oven drying
at 70ºC for 24 h to record the dry weight (DW). The RWC were
computed using equation proposed by Turner 41
:
RWC = [WF
-WD
] ×100/ [WT
–WD
] 19
(2)
where WF, WD, and WT were fresh weight, dry weight and turgid
weight, respectively.
Determination of canopy temperature: The crop canopy
temperature was influenced not only by soil water content but
also by air temperature, therefore, the difference of canopy-air
temperatures (TL
-Ta
) could be used as an index for diagnosing the
crop water status. In this study, the canopy temperature was
measured from the difference between crop canopy temperature
and the air temperature using a BAU-I Infrared Thermo-Detector
from1-2 pm42
.
Determination of osmotic adjustment (OA): Osmotic adjustment
was measured from the differences between the osmotic potential
of lines growing without stress conditions and the osmotic
potential of the lines growing with stress conditions 31, 43
. The
osmotic potential of each sample was also measured. Five flag
leaves were selected from each experimental unit and transferred
to laboratory in plastic bags immediately.After washing them with
distilled water and drying by wiping with facial tissue, they were
frozen in -20°C in a deep freezer for 24 hours. After thawing at
room temperature (15 min), the cell sap was extracted using a hand
press, and the OP of the cell sap was measured with the help of
microvolt meter 44-46
.
Determination of cell membrane stability (CMS): To measure
cell membrane stability, 0.6 g of fully expanded young leaves in
each experimental unit was transferred to the laboratory 40 days
after they were planted. After washing with distilled water, they
were cut to pieces and, for each line, 0.3 g of leaves were transferred
into tubes with 10 ml distilled water. The other 0.3 g samples were
transferred into tubes with 10 ml polyethylene glycol (PEG)-6000
(300 g/l). The tubes were kept at 10°C in a cooled incubator for 24
h. Then the distilled water was replaced with PEG, they were kept
in an incubator for 24 h and the electrical conductivity (T1
) of the
contents was measured. The leaf samples were killed by
(1)

3. Journal of Food, Agriculture & Environment, Vol.9 (3&4), July-October 2011 547
autoclaving for 15 min in 120 °C. The electrical conductivity of the
medium was measured again (C2
). Cellular injury was determined
using the equation:
Cell membrane injury = 1-[1-)T1
/T2
)]/[1- (C1
/C2
)] (3)
where T1
andT2
are first and second EC (PEG) and C1
and C2
are
first and second EC (distilled water) 19, 47
.
Determination of rate of water loss of excised-leaf (RWL): To
measure of RWL, six flag leaves of six random plants from each
experimental unit were selected and weighed in the laboratory.
Samples were kept in an incubator for 24 h in 22 °C, weighed again
and kept in the oven for 24 h at 70°C to get the dry weight. RWL
was determined using the formula:
RWL = W0
-W1
/T.Wd
(4)
where W0
, W1
and Wd
arefirst weight, weightafter incubator and
dry weight ofleaves, respectively, and Tis timeofkeepingsamples
in incubator 48
.
Determination of water use efficiency (WUE): To calculate water
use efficiency, all irrigated water (using water meter), rain water
and soil humidity were measured. For the wheat water requirement
in Zanjan province, the total water height was calculated by
transferring water volume into water height. Soil humidity was
measured based on soil humidity before and after planting, and
added to used water. On the whole, WUE in based on grain yield
(kg/ha) and used water height (mm) was calculated using the
formula49
:
WUE = [GY/TWU] (5)
where GY is grain yield and TWU is total water use.
Statistical methods: Statistical computing of this research was
done by MSTAT-C and SPSS software.Analysis of variance of a
split block design based on randomized complete block design
(RCBD) was done by MSTAT-C and treatments were compared
by least significant difference (LSD) at 5% probability level. A
matrix of simple correlation coefficients between STI and relative
water traits were computed by SPSS. Broad sense heritability of
relation to water content was obtained using E(MS) in tables of
analysis of variance (RCBD).
Path analysis is an extension of the regression model, used to
test the fit of the correlation matrix against two or more causal
models which are being compared. To investigate the direct and
indirect effects of traits on STI, path analysis was calculated for
relation to water traits. For this purpose, simple correlation
coefficient was obtained between all traits and partial regression
coefficient (direct effects) of traits was calculated by SPSS. Indirect
effects were calculated by multiplying direct effects in simple
correlation coefficient.
Results and Discussion
Split block analysis of variance: The results of the analysis of
variance based on the split block is shown in Table 1. In all of the
evaluated characters there was a significant difference between
stress levels. Therefore, induced stress affected the mentioned
characters significantly. Moreover, the interaction between lines
and stress level was not significant. Likewise, in this research,
there was no significant difference for RWC, stomatal conductance
and canopy temperature among wheat lines, while wheat lines
were significantly different forWUE.Also, there was no significant
differencebetweenwheatlinesforcanopytemperatureandstomatal
conductance under drought stress condition as was also observed
in previous studies 9, 40
. However, in Israel canopy temperature
was used for screening of wheat varieties successfully 50
.
Randomized complete block design (RCBD)ANOVA under non-
stress and stress conditions: Under non-stress condition, there
was a significant difference between wheat lines for RWL (Table
2). Ghods line had the highest amount of RWL. In some previous
studies significant differences were observed between tolerant
and susceptible wheat lines in fluorescence appearance stage for
RWL34, 40
, but other studies 51
did not find any significant difference
between wheat lines for RWL. Ghods and B1-3 lines had the
highest and lowest RWL, respectively.There was also a significant
difference for CMS among wheat lines, so that Zarrin and Pishtaz
lines showed the most amount of cell membrane injury while
Sardari line showed the highest CMS. Tolerant wheat genotypes
have more cell membrane stability 52
. There was also a significant
differenceintheWUEamongwheatlinesshowinggeneticvariation
amongthem.
Table 3 shows the results of analysis of variance for STI based
on RCBD. There was a significant difference in STI among wheat
lines, showing variation among lines for drought tolerance. Ghods,
Zarrin andAlvand had the highest STI and B3-3, B1-3 and B3-2
the lowest STI.
Broad sense heritability: Broad sense
heritability of traits was calculated based
on genotype mean using theANOVAtable
for the different levels of stress in RCBD
(Table 4). So far, there are reports of
intermediate broad sense heritability for
WUE in bread wheat under water deficit
stress 35
. In this study high broad sense
heritability of WUE was observed in both
levels of stress (84.5%) and non-stress
(80%). Similarly as previous findings 53
,
heritability of stomatal conductance and
osmotic adjustment (OA) in both stress andMS Mean square; WUE Water use efficiency; RWC Relative water content **Significant at 1% probability level; *Significant at 5%
probability level.
Table 1. Analysis of variance of water relation traits in split block design.
MSSOV Df
WUE
Stomatal
conductance
Canopy
temperature
RWC
Replication 2 1.12 23282.9 9.28 301.7
Stress level 1 20.02** 282546.2* 955.4** 5144*
Expt. error (a) 2 2.79 25267.8 6.44 653.6
Line 16 215.5** 2543.5 1.33 153.5
Expt. error (b) 32 3.66 2079.3 1.94 85.1
Line ×Stress level 16 3.18 1970.3 1.59 82.6
Expt. error (ab) 32 1 1400.8 0.969 58.1
CV% 31.1 28.7 22.3 10

4. 548 Journal of Food, Agriculture & Environment, Vol.9 (3&4), July-October 2011
non-stress levels were low. Also, RWC showed a low and
intermediate heritability in non-stress and stress levels,
respectively. In this research the heritability of CMS was high
under non-stress condition (83%), related to other findings 20
.As
in previous reports 54
, a high heritability for RWL (70%) was
observed. Stress tolerance index (STI) showed an intermediate
heritability. Before this 51
, intermediate narrow sense heritability
for STI was reported, while the heritability of other tolerance
indices had a low heritability. Therefore, using STI in screening
studies for drought tolerance was advised. As a whole, high
estimates of broad sense heritability coupled with high genetic
advance indicated additive genetic effects, which provided
sufficient scope for selection of most characters.
Simple correlations between STI and
water relation traits under stress and
normal conditions: The simple
correlation coefficients between
different traits and STI under non-stress
and stress conditions are shown in
Tables 5 and 6. A positive and
significant correlation was observed
between STI with osmotic adjustment
(OA) (0.338*) and RWC (0.383**,
0.287*) in both stress levels. Previous
researches showed that tolerant
varieties in comparison to sensitive
ones have high osmotic adjustment and
higher yield 30
. Osmotic adjustment
(OA) is a major cellular stress adaptive
response in certain crop plants that
enhances dehydration avoidance and
supports yield under stress. An
increasing number of reports provide
evidence on the association between
high rate of osmotic adjustment (OA)
and sustained yield or biomass under
water-limitedconditionsacrossdifferent
cultivars of crop plants. Since OA helps
to maintain higher leaf relative water
content (RWC) at low leaf water potential (LWP), it is evident that
OA helps to sustain growth while the plant is meeting transpiration
demand by reducing its LWP. Osmotic adjustment sustained
turgor maintenance and hence the yield-forming processes during
moderate and severe water stress 55
.
When the soil dries, water uptake by the roots becomes more
difficult and uptake declines. This reduction in water use eventually
results in the development of water deficit in the shoot and
consequently RWC decreased. The decrease in RWC in stressed
plants might be due to decreased plant vigor 12
. There was a positive
and significant correlation between WUE and STI (0.845). Water
use efficiency is an index for dry matter production based on
consumed water. Usually, maximum amount of biomass leads to
maximumamountofWUE57
.WUE
is an important part for drought
compatibility 35
. This trait can be a
suitable screening criterion for
drought resistance.
There was a negative significant
correlationbetweenRWL(-0.325*)
and STI. This in agreement with
previous results and indicated that
RWLat ear emergence stage under
water stress condition may be
used as a screening technique in
drought resistant genotypes58, 59
.
Ghods and B1-3 lines had the
highest and lowest amount of
RWL, respectively.
Stomatal conductance either
under stress (0.247) or in normal
conditions (0.044) showed a
positive and significant correlation
MS
SOV Df WUE
Stomata
conductance
Canopy
temperature
RWC RWL CMS OA
Replication 2 1.43 48520.1 13.43 360.53 0.90 24.70 88.98
Lines 16 3.92* 3412.9 1.13 44.53 1.18** 617.8** 156.3
Expt. error 32 0.78 2504.2 1.47 46.7 0.40 103.6 104.70
CV% 53.3 27.3 16.29 8.18 10.75 27.7 42.2
MS Mean square; WUE Water use efficiency; RWC Relative water content; RWL Rate of water loss from excised-leaf; CMS Cell membrane stability;
OA Osmotic adjustment.**Significant at 1% probability level; *Significant at 5% probability level.
Table 2.Analysis of variance of water relation traits in randomized complete block design
under non-stress condition.
N Non-stress; S Stress; h2
B Broad sense heritability.
Estimate
Stress
level
WUE
Canopy
temperature
Stomata
conductance
RWC RWL CMS OA STI
h2
B N 80 very low 26.7 low 70 83 34
% S 84.5 22 11.2 43.8 - - -
47
Table 4. Broad sense heritability of water relation traits in stress and non-stress condition.
MS
SOV Df WUE
Stomatal
conductance
Canopy
temperature
RWC STI
Replication 2 3.36 31.47 2.31 590.03 1.048
Line 16 12.14* 1101.57 1.78 168.03 3.399**
Expt. error 32 1.89 975.98 1.43 94.8 0.927
CV % 36.6 40.25 20.3 14.09 47
Table 3.Analysis of variance of water relation traits in randomized complete
block design under stress condition.
MS Mean square; WUE Water use efficiency; RWC Relative water content; STI Stress tolerance index; .**Significant at 1%
probability level; *Significant at 5% probability level.
CMS RWL WUE OA
Stomatal
conductance
Canopy
temperature
RWC
RWL -0.206
WUE 0.240 0.230
OA -0.056 -0.078 -0.228
Stomatal conductance 0.060 -0.016 0.312* -0.144
Canopy temperature -0.120 0.215 0.059 0.058 0.085
RWC -0.135 0.009 -0.188 0.162 0.265 0.105
STI 0.225 -0.325* 0.845** 0.338* 0.044 -0.060 0.383**
WUE Water use efficiency; RWC Relative water content; RWL Rate of water loss from excised-leaf; CMS Cell membrane stability; OA Osmotic adjustment.
STI Stress tolerance index;**Significant at 1% probability level; *Significant at 5% probability level.
Table 5. Correlation coefficients between STI and water relation traits under non-stress.
WUE OA
Stomatal
conductance
Canopy
temperature
RWC
OA -0.348*
Stomatal conductance 0.315* -0.303*
Canopy temperature -0.216 0.104 -0.216
RWC 0.351* 0.049 0.018 0.072
STI 0.891* 0.338* 0.247 -0.125 0.287*
Table 5. Correlation coefficients between STI and water relation traits under stress.
WUE Water use efficiency; RWC Relative water content; OA Osmotic adjustment; STI Stress tolerance index;**Significant at 1%
probability level; *Significant at 5% probability level.

5. Journal of Food, Agriculture & Environment, Vol.9 (3&4), July-October 2011 549
with STI. Under stress condition, photosynthesis efficiency of
tolerant genotypes is more than in susceptible ones. Reduction in
photosynthesis rate was accompanied by increasing
photosynthesis and water use efficiency under drought stress,
and this reduction can be related to reduction in stomatal
conductance which decreases almost 90 percent under stress
condition. Although closing of stomata decreases the water
consumption it also prevents import of CO2
resulting in
photosynthesis rate reduction to less than compensation point60
.
In spite of reduction in stomatal conductance, induced stress
increases the CO2
concentration in stomata from 186.2 to 270.1
µmol/mol61
.
Also, canopy temperature showed a negative but non-significant
correlation with STI in both stress (-0.125) and normal conditions
(-0.060). The crop canopy temperature relies on energy exchange
between the crop surface and the atmosphere, which is determined
by sensible heat flux. Especially the latent heat exchange is a
primary cause leading to spatial variation of canopy temperature.
Therefore, the crop canopy temperature closely correlated to the
water deficit stress could be used to monitor crop water status 62
.
The lower soil water content resulted in smaller absolute value of
the temperature difference and lower yield, with less filled grain
numberperpanicle.
The cell membrane stability is a measurement of resistance
induced in plants exposed to desiccation created artificially by
thePEG.Cellmembranestability(CMS)alsoreferstothecapability
Figure 1. Diagram of path analysis of water relation traits and STI in non-stress condition.
RWC
Canopy
temperature
Stomatal
conductance
OA WUE RWL CMS STI
RWC -0.149 -0.01029 -0.04717 -0.022194 -0.150776 0.001413 -0.00486 0.383
Canopy temperature -0.015645 -0.098 -0.01513 -0.007946 0.047318 0.033755 -0.00432 -0.060
Stomatal conductance -0.039485 -0.00833 -0.178 0.019728 0.250224 -0.002512 -0.00216 0.044
OA -0.024138 -0.005684 0.025632 -0.137 -0.182856 -0.012246 -0.002016 0.338
WUE 0.028012 -0.005782 0.055536 0.031236 0.802 0.03611 0.00864 0.845
RWL -.001341 -0.02107 0.002848 0.0106860 0.18446 0.157 -0.007416 -0.325
CMS 0.020115 0.01176 -0.01068 0.007672 0.19248 -0.032342 0.036 0.225
Table 7. Path analysis of STI with water relation traits under non-stress condition.
*The numbers on diameter are direct effects of traits on STI.
RWC
Canopy
temperature
Stomatal
conductance
OA WUE STI
RWC 0.031 0.004752 -0.000702 -0.00196 -0.320814 0.287
Canopy temperature 0.002232 0.066 0.008424 -0.00416 -0.197424 -0.125
Stomatal conductance 0.00558 -0.014256 -0.039 0.01212 0.28791 0.247
OA 0.001519 0.006864 0.011817 -0.040 -0.318072 0.338
WUE -0.010881 -0.014256 -0.012285 0.01392 0.914 0.891
*The numbers on diameter are direct effects of traits on STI.
Table 8. Path analysis of STI with water relation traits under stress condition.
of plant cell tissues to hold electrolytes under drought condition
by retaining the cell membrane configuration undamaged 63
.There
was a positive but non-significant correlation between STI and
cell membrane stability (CMS). Sardari line showed the highest
CMS in this research. In addition to good performance of various
genotypes for morpho-physiological traits contributing towards
drought tolerance in sorghum, most of them revealed lower grain
yield per plant. This supported the soundly recognized fact that
yield of crop plants in drying soil will decline even in tolerant lines
of that crop species 64
.
Path analysis of STI with water relation traits in stress and
normal conditions: Path analysis uses standardized
regression coefficients. Standardized regression coefficients are
changes in Y variable for each one unit changes in X variable
while other X variables are fixed. The correlation coefficients
between STI and water relation under normal and stress conditions
are shown in the last line of Tables 7 and 8, respectively, and the
result of path analysis are in Fig. 1 and 2. Since water use efficiency
had the most direct effect (0.802, 0.914) on STI in both stress and
normal condition and its high broad sense heritability, it can be
concluded that between evaluated characteristics, WUE is the
best criterion for drought resistance screening. The correlation of
other traits with STI is mainly for their relation with WUE. In
regards to high broadsense heritability of RWL and CMS, these
two traits are effective in indirect breeding of STI by WUE.

6. 550 Journal of Food, Agriculture & Environment, Vol.9 (3&4), July-October 2011
Figure 2.Diagram of path analysis of water relation traits and STI under stress condition.
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