Phenotyping for drought and heat stress tolerance in wheat

Phenotyping of core set of wheat:

A set of 145 lines was evaluated at two locations (IARI, New Delhi and Pune) and phenotyping was carried out for a number of traits. Data on germination, days to heading (DH), yield, thousand kernel weight (TKW), days to maturity (DM), canopy temperature depression (CTD), chlorophyll content, relative water content, flag leaf area, NDVI, SPAD and yield was recorded. Significant correlations were observed between DH and DM, yield and DH (negative), TKW with DH, DM and yield, CT with DM and yield (negative) and CTD with DH and yield and negative correlation with CT.

Parental polymorphism studies in wheat:

Twenty three genotypes were selected for parental polymorphism studies based on their differential response to drought and heat under glass house and field conditions. DNA was isolated from these genotypes following standard protocols. The genotypes were screened with wheat microsatellite primers - cfd, cfa, cfb, barc, gwm, gdm and wmc series. Microsatellite markers had already been mapped and information was obtained from www.pw.usda.org. Markers covering a minimum of 10cM distance and distributed over different arms of all the 21 chromosomes had been included. A total of 450 microsatellite markers had been used and approximately two hundred polymorphic markers were observed among them. These polymorphic markers will be screened on the mapping populations to identify progenies which are drought and heat tolerant. These would also be used for recovery of background genome in backcross populations.

Marker validation and development of backcross populations:

Data on all the identified QTLs in wheat was collected and more than 200 microsatellite markers were selected associated with physiological, phenological and agronomic traits. These microsatellite markers are being screened on the parents of the backcross generations for introgression of the QTLs. The identification of polymorphic markers is in progress. Five physiological traits are targeted covering 17 chromosomes for identification of known QTLs in Indian backgrounds. These include canopy temperature with known QTLs on 15 Chromosomes (1A, 1B, 2A, 2B, 3A, 3B, 4A,4B, 5A, 5B, 6A, 6B, 6D, 7A,7B), NDVI on 3 chrs (2A, 2B and 4A), chlorophyll content on15 chrs (1A,1B,1D, 2A, 2B, 3A, 3B, 4B, 5A, 5B, 6A, 6B, 6D, 7A and 7B), WSC on 17 chrs (1A,1B,1D,2A, 2B, 2D, 3A, 3B, 4A, 4B, 4D, 5A, 5B, 6B, 6D, 7A and 7B), stay-green on 3chrs (1A,3B and 7D). Apart from this, QTLs for yield traits on chromosomes 2B, 3B, 4A,4B 5A, 6A, and 6B under moisture stress and heat stress conditions were also targeted.Around sixty QTLs linked to the physiological and yield traits covering 17 chromosomes were targeted for validation in Indian parents and then their introgression through marker assisted backcross breeding. They have been genotypically screened and their phenotypic correlation is being carried out. Ten SSR markers linked to QTLs for moisture stress traits were able to differentiate the contrasting parents. The elite Indian parents are HD 2733 and GW 322 from the North Western Plains Zone and Central and North Eastern Plains Zones,representing more than 10 million hectares of the total 29 million hectares sown to wheat in India. F1s were backcrossed with Indian parents to develop BC1F1 generations. Backcrosses have been attempted with Indian as well international donor parents to introgress traits related to moisture and heat stress in the recurrent parents. Among these sixteen backcrosses and 25 new crosses, few crosses will be advanced further depending upon the population size and availability of markers in foreground selection.

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