Editor-in-chief
Wheat Information Service
Japan.
Dated: 10-03-2007
Subject: Publication of research paper entitled “Genetic Potential of Bread Wheat Genotypes
Under Water Stress Deficit Environments:
Dear Sir:
Kindly find attached herewith the above cited paper for its publication in Wheat
Information Service, Yokohoma, Japan. Kindly acknowledge us by our E-mail address when
you receive the paper. I thank you so much for your cooperation.
Sincerely Yours,
(Dr. M. J. Rind)
Associate Professor
Department of Plant Breeding and Genetics
Sindh Agriculture University, Tandojam, Sindh, Pakistan.
INFLUENCE OF WATER STRESS IMPOSED AT DIFFERENT STAGES ON GROWTH
AND YIELD ATTRIBUTES IN BREAD WHEAT GENOTYPES (TRITICUM AESTIVUM L.)
By
N. F. Veesar, A. N. Channa, M. J. Rind*
and A. S. Larik
Department of Plant Breeding & Genetics,
Sindh Agriculture University, Tandojam, Sindh, Pakistan.
.
Abstract:
The studies were carried-out so as to assess the influence of water-stress treatments on
growth and yield attributes of wheat genotypes. The water stresses were imposed at tillering,
booting and at grain formation stages of crop growth and development. The wheat genotypes
evaluated were: Sindh-81, Mutant of Sindh-81, Indus-66 and Mutant of Indus-66. The
experiment was conducted in a Randomized Complete Block Design with three replications in
a plot size of 1.0 x 3.0m. The means squares from analysis of variance revealed significant
differences among genotypes, water stress treatments and their interactions except interaction
was non-significant for seed index only. These results further suggested that genotypes not
only performed differently but also responded variably to water stress conditions, hence some
being more tolerant than the others at various growth stages. Results further revealed that, on
an average over the genotypes, taller plant heights, higher number of tillers per plant,
maximum grain yield per plant and higher seed index were recorded in Indus-66 whereas,
more number of spikelets per spike was formed in genotype Sindh-81. Since plant height,
numbers of tillers per plant, grain yield per plant and seed index are very important
parameters in wheat and also serve best indicators of water stress tolerance, therefore
genotype Indus-66 by and large proved to be more stress tolerant as compared to other
genotypes. Averages over water-stress treatments indicated that stress imposed at tillering stage
caused significant declines in plant height, number of tillers per plant and spikelets per spike
whereas maximum reductions in grain yield and seed index occurred when stress was given at
grain formation. The significance of genotype x water stress interactions for almost all the
attributes suggested differential response of genotypes to water–deficit conditions which further
implied that genotypes with relatively little declines in important characters at crucial stages may
be preferred either for general cultivation or to be used in hybridization programmes to develop
new water stress tolerant wheat genotypes.
___________________________________________________________________________
*Corresponding author
E-mail: dr_mjr@hotmail.com
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INTRODUCTION
The drought, salinity and high temperature stresses are the main environmental
constraints and are major threats to wheat crop not only in Pakistan but throughout the world,
specially in arid and semiarid regions. Abiotic stresses, notably extremes in temperature,
photon irradiance, and supplies of water and inorganic solutes, frequently limit growth and
productivity of major crop species such as wheat (Triticum aestivum L.). Furthermore, one
abiotic stress can decrease a plant's ability to resist a second stress (Mark and Antony, 2005).
However, if a single abiotic stress is to be identified as the most common in limiting the
growth of crops worldwide, it most probably is low water supply (Araus et al. 2002). The
main consequence of moisture stress is decreased plant growth and development caused by
reduced photosynthetic activity.
All phases of plant growth are not equally vulnerable to water shortage. However
some phases can cope-up with water shortage very well, while others are more vulnerable and
water shortages at such stages may result in serious yield losses. Moisture stress is known to
reduce biomass, tillering ability, grains per spike and grain size at any stage when it occurs.
So, the over all effect of the moisture stress depends on its intensity and length of stress
(Bukhat, 2005). Substantial losses in wheat grain yield have been reported due to water
deficiency depending on the developmental stages at which crop plant experiences stress.
Water stress at various stages specially before anthesis can reduce number of ear heads and
number of kernels per ear (Dencic et al. 2000 and Mary et al. 2001). While water stress
imposed during later stages might additionally cause a reduction in number of kernels /ears
and kernel weight (Gupta et al. 2001).
In water scarcity conditions, wheat fields are usually not irrigated on the basis of crop
demand or the quantity of water required, but the crop fields are irrigated when the farmer has
its turn. Under such situations, wheat crop suffers from different degrees of stresses and leads
to great reduction in yield. One of the best solutions to resolve the issue of shortage of
irrigation water is to evolve drought or water stress tolerant varieties those could withstand
very well with water stress or require less numbers of irrigations but still produce optimum
yields.
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In wheat breeding programmes, seeking increased yields have usually attempted to improve
drought tolerance of plants. However before successful genetic manipulation could be made,
it is important to characterize the physiological parameters of known drought tolerant or
sensitive cultivars. Analyzing physiological determinants of yield responses to water stress
may also be helpful in breeding for higher yields and stability of genotypes under drought
conditions. The traits to select (either for stress escape, avoidance or tolerance) and the
framework where breeding for drought stress is addressed will depend on the level and timing
of stress in the targeted areas. However, selecting for yield itself under stress-alleviated
conditions appears to produce superior cultivars, not only for optimum environments, but also
for those characterized by frequent mild and moderate stress conditions. This implies that
broad avoidance/tolerance to mild/moderate stresses is given by constitutive traits also
expressed under stress-free conditions (Araus et al. 2002). Keeping in view the importance of
identifying water-stress tolerant wheat genotypes, the water-stress conditions were imposed to
wheat plants at various stages of crop growth and development. The stresses were given at
tillering, at booting and at grain formation stages. Thus, the objectives of present research
were to determine the effect of water stress on yield and yield contributing traits of bread
wheat genotypes.
Material and Methods:
A field experiment was undertaken to assess bread wheat genotypes (Triticum
aestivum L.) for water stress tolerance during 2005-2006 at the experimental area of Plant
Breeding and Genetics, Sindh Agriculture University, Tandojam. The water stress treatments
were created by withholding the irrigation at various stages and for specified period of time as
under:
T1 = Six irrigations, each was applied at 15 days intervals (control without water-stress at any
stage)
T2 = Five irrigations, 1st applied at 20 days after sowing and subsequent four irrigations at 15
days intervals (stress at tillering stage).
T3 = Five irrigations 1st, 2nd, 3rd irrigations were applied at 15 days intervals and 4th
irrigation after 25 days (stress at booting stage), fifth irrigation after 15 days.
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T4 = First four irrigations were applied at 15 days intervals and 5th irrigation after 30 days
(stress at grain formation stage).
The fifteen days in Pakistani conditions are considered as normal irrigation interval
without any stress. Four bread wheat genotypes i.e. Sindh- 81, Mutant of Sindh-81, Indus-66
and Mutant of Indus-66 were grown in a Randomized Complete Block Design (RCBD) with 3
replications arranged in a plot size of 1.0 x 3m, thus there were four rows, each 3 meter long.
The spacings between row to row and plant to plant were kept at 6.0 and 4.0 inches
respectively. The sowing was done on normal planting date of November 22, 2005. The seed
was sown by single coulter hand drill with the seed rate of 125 kg ha-1. The bunds and
channels were made according to experimental design so that controlled irrigations could be
applied to the experimental plots. Thus the plots were separated by leaving 1.5m space as
buffer zone to avoid water seepage from water courses. All the required cultural operations
were adopted uniformly in all the plots throughout the growing period on as and when
required basis. Fertilizer DAP was applied at the rate of 150 kg ha-1 at the time of sowing
and two bags of nitrogen ha-I as urea was applied after sowing in three split doses i.e. with
first and third irrigations and the last dose at anthesis stage. The crop was harvested on April
8, 2006 after 135 days of sowing. The observations for yield components such as plant height,
number of tillers per plant, number of spikelets per spike, grain yield per plant (g) and seed
index (100-seed wt. g) were recorded on 10 plants per replication, thus a total of 30 plants
were studied for each treatment and genotype. The data collected were subjected to analysis
of variance according to Gomez and Gomez (1984) so as to discriminate the treatment mean
differences among genotypes and water-stress conditions. Mean comparisons were also made
by using L.S.D. (5%). For these statistical calculations, MSTAT-C software package was
used.
Results and Discussion
All the growth and developmental stages of wheat plant are not equally vulnerable to
water stresses, but some stages are more critical than the others. Some wheat genotypes may
with-stand very well to water deficiencies whereas others could sustain severe yield losses in
water deficit conditions.
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The statistical analysis was carried out so as to determine the differences among four
wheat genotypes in response to four water-stress conditions. The mean squares from analysis
of variance (Table-1) revealed that main effects (genotypes and water stress treatments) and
their interactions were significant for all the characters studied except seed index where
interactions were non-significant (Table-1). The significance of genotypes and water stress
treatments indicated that varieties performed differently and water stress treatments also
significantly affected the plant traits. The interactions were significant further implied that
varietal response to stress environment was also variable some being less affected than the
others, it means choice of the tolerant genotypes could be made for important attributes.
Results with respect to plant height revealed that maximum culm lengths of 98.4 and 100.5cm
were attained by genotype Mutant of Induds-66 when stresses were subjected at both tillering
and booting respectively indicated its being more water stress tolerant whereas minimum
plant heights of 74.4 and 78.4 given by genotype Sindh-81 implied its being more vulnerable
to water stresses. On an average, declines of 8.49% at tillering and 3.08% at booting were
caused by the water stress conditions against no stress control
(Table-2). Gupta et al. (2001)
and Muzammil (2003) also observed substantial decline in plant height when irrigation was
withheld at booting stage, however tolerant genotypes attained more plant height. The number
of tillers per plant has got direct contribution towards grain yield. It means, as the number of
productive tillers increase, there will be simultaneous increase in yield. On an average over
genotypes, Indus-66 produced more numbers of tillers. However, stress at tillering caused
significant declines in number of tillers, yet maximum reduction occurred in genotype
Mutant-81 (15.8 tillers) and minimum in Indus-66 (20.8 tillers) suggesting mutant-81 being
highly susceptible and Indus-66 highly tolerable to water-deficit environments. Over the
stress treatments, stress imposed at tillering caused greatest declines of 19.1% in tillers as
against no stress control. These results thus suggested that if grain yield in wheat is to be
increased via numbers of tillers, then water stress at tillering stage may be avoided. Similar to
present findings, Rana et al. (1999) and Kimutro et al. (2003) found that water stress at
tillering or at booting significantly affected the formation of tillers in wheat.
6
Generally, spikes with more number of spikelets are supposed to produce more grains
per spike, consequently higher yields per plant. Under water stress conditions, on an average,
number of spikelets per spike declined, nevertheless prominent reduction occurred (10.98%)
when stress was given at tillering stage. As regards to varietal performance, particularly at
tillering stage where maximum reduction in number of spikelets was expected, genotype
Sindh-81 by producing maximum numbers of spikelets per spike (22.6) ranked as the most
water stress tolerant genotype (Table-2). These results thus suggested that stress may be
avoided at tillering stage in order to increase the numbers of spikelets per spike. The grain
yield is the total out-put of all the yield components. The average yield of all the genotypes
dropped considerably under all the water-deficit conditions, yet the declines of 20.74, 46.85
and 101.23% were recorded when stresses were subjected at tillering, booting and at grain
formation respectively (Table-2). Averaged over all the stress environments, Indus-66
produced maximum grain yield per plant, thus less affected, thus being more water stress
tolerant genotype. Surprisingly, Indus-66 which formed less number of tillers per plant still
gave more grain yield per plant could be explained probably having more number of
productive tillers rather than having non-productive as in case of genotype Sindh-81. A large
reduction in yield with stress at grain formation suggested that water stress must be avoided at
grain filling so as to save the yield losses. Solomon et al. (2003) Ozturk and Aydin (2004)
also found yield reductions of 79.7 and 65.5% when water stress was imposed either at earlier
stages or at grain formation. Seed index is also considered as one of the most important
indicators of stress tolerance via kernel weight. In all the stress environments, seed index
declined subsequently as 26.90% at tillering, 51.89% at booting and 81.45% at grain
formation (Table-2). On an average over genotypes, the maximum seed index was noted in
Indus-66, hence being highly tolerant to water stress conditions. Seed index results therefore
suggested that stress may be avoided at grain formation and genotype Induss-66 may be
preferred in water deficit environments.
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Conclusions:
For growth parameters like plant height, tillers per plant and spikelets per spike,
considerable declines were observed when stress was imposed at tillering stage, nonetheless,
maximum reductions in grain yield per plant and seed index (100-seed wt. g.) occurred when
stresses were subjected at grain filling stage. Generally, genotype Indus-66 performed well in
water stress conditions as it attained a reasonable plant height, produced more tillers, gave
higher grain yields and seed index as compared to other genotypes.
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