Abstract:
Present study on wheat was an attempt to study the genetic diversity in 187 wheat
landraces/cultivars at different growth stages and to identify the most salinity sensitive
growth stage in wheat. Total 187 genotypes included 130 landraces/cultivars from
Pakistan, 24 from Iran, 13 from Syria, six from Egypt, six from Italy, two from USA, one
from Brazil, one from Cyprus and four from Mexico were evaluated. In first experiment
all (187) genotypes were tested at germination stage under 200 mM NaCl stress. On the
basis of salt tolerance trait indices (STTIs) of various traits studied at germination stage
and vegetative stage 48 landraces/cultivars were selected. These 48 genotypes were tested
under 250 and 300 mM NaCl stress at germination stage. Genotypes showed greater
reduction in germination rate index, plumule and radicle fresh and dry weights under high
salinity stress.
In 2nd experiment all (187) landraces/cultivars were tested at vegetative stage in
hydroponic under 200 mM NaCl stress. Eighty nine landraces/cultivars were selected
including 48 landraces/cultivars of first experiment. These landraces/cultivars were
selected based on STTIs of root and shoot length, tillers plant -1 , and root and shoot fresh
and dry weights. These 89 genotypes were tested under 250 mM NaCl stress. Root
length, root and shoot dry weights showed considerable decline under NaCl stress
compared to controlled conditions. These traits were also positively correlated with each
other and other growth parameters studied indicating that these traits were strongly
associated with salinity tolerance. In 3 rd experiment 150 genotypes were evaluated at two
locations in saline field conditions during 2007-08. Previously selected 48 genotypes
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were evaluated during 2008-09 at both salt affected locations. Total biomass, spikelets
spike -1 , tillers plant -1 and yield were the most salt susceptible traits in studied wheat
landraces/cultivars. In 4th experiment six cultivars (Local white, Pavon, Pasban 90,
Frontana, Tobari 66 and Chakwal 97) differing in salinity tolerance were crossed in half
diallel format to study the inheritance mechanism of wheat genotypes under salinity
stress.
Broad sense heritability estimates indicated that improvement in wheat genotypes
for salinity tolerance does exist. Additive genetic effects were significant for days to
heading and maturity, fertile tillers plant -1 , and plant height indicating that selection in
early segregating generations could be useful. Dominance effects were significant for
yield and yield contributing traits, indicating that selection for yield under NaCl stress
would be effective in later generations. All the yield attributing traits had positive
correlation at both genotypic and phenotypic level with yield plant -1 , indicating that all
these traits contributed towards yield and yield can be used as selection criteria under
NaCl stress. In experiment No. 5, 26 RAPD and 240 SSR markers were utilized to study
salt tolerance at molecular level. Twelve SSR markers (cfd 1, cfd 9, cfd 18, cfd 46, cfd
49, cfd 183, wmc 11, wmc 17, wmc 18, wmc 154, wmc 432, and wmc 503) detected
specific alleles in salt tolerant genotypes only. Genotypes 10807, 11299, 11383, Local
white, Pasban 90 (Pak) Sakha-92 (Egypt) and Roushan (Iran) proved to be most salt
tolerant. These genotypes can therefore, serve as donor parents for developing salt
tolerant wheat varieties.
It can be concluded that salinity stress had significant inhibitory effects on early
germination, vegetative growth, grain yield and yield attributing traits. Morphological3
and molecular analysis revealed that considerable genetic diversity present in tested
wheat genotypes for salinity tolerance. Survival rate and STTI values revealed that
vegetative stage was most salt sensitive. Heritability estimates and gene action under 200
mM NaCl salinity revealed that potential for improving salinity tolerance in wheat does
exist. Germplasm studied could be utilized in future breeding program to release salt
tolerant wheat varieties.