Title of Thesis

Evaluation Of Wheat Genotypes For Salt Tolerance Based On Conventional And Molecular Approaches

Author(s)

Munir Ahmad

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 3rd experiment 150 genotypes were evaluated at two locations in saline field conditions during 2007-08. Previously selected 48 genotypes
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.Morphological 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.

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2.1 Salinity
2.2 Mechanism of Salt Tolerance
2.3 Osmotic Effects
2.4 Wheat and Salinity
2.5 Wheat Breeding for Salt Tolerance
2.6 Physiology of Salt Tolerance
2.7 Screening criteria for salt tolerance
2.8 Historical background of improving salt tolerance in wheat
2.9 Evaluation of salt tolerance at germination stage
2.10 Evaluation of salt tolerance at vegetative stage in hydroponics
2.11 Evaluation of salt tolerance in field conditions
2.12 Diallel crossing and genetic basis of salt tolerance
2.13 Molecular markers
2.14 DNA fingerprinting
2.15 Evaluation based on random amplified polymorphic DNA (RAPD)
2.16 Microsatellites or simple sequenced repeats (SSRs)
2.17 Marker assisted selection

3.1 Introduction
3.2 Materials and Methods
3.3 Results
3.4 Discussion

4.1 Introduction
4.2 Materials and methods
4.3 Results
4.4 Discussion

5.1 Introduction
5.2 Materials Methods
5.3 Results
5.4 Discussion

6.1 Introduction
6.2 Materials and Methods
6.3 Results
6.4 Discussion

7.1 Introduction
7.2 Materials and Methods
7.3 Results
7.4 Discussion

8.1 Evaluation at Germination Stage
8.2 Evaluation at Vegetative Growth Stage under Hydroponic Salinity
8.3 Evaluation under Saline Field Conditions
8.4 Diallel Analysis of Quantitative Traits in Wheat under NaCl Salinity Stress
8.5 Evaluation Based on Molecular Markers

9.1 Introduction
9.2 Key distribution scheme
9.3 Security analysis
9.4 Summary