Critical Studies on Genetic Analysis for Terminal Heat Tolerance in Bread Wheat

Heat stress is a rigorous threat and characterized by an increasing trend in average temperature
during reproductive and grain filling stages that caused the force maturity and it is one of the major
constraints of wheat productivity in arid, semiarid, tropical and subtropical regions of the world.
Reductions in dry matter accumulation and grain yield, caused by reduced plant photosynthetic
capacity through metabolic limitations and oxidative damage to chloroplasts due to heat stress.
Nature and magnitude of gene action for yield and its attributing traits and important heat tolerant
parameters in bread wheat (Triticum aestivum l em. thell) were examined to decide breeding
strategies and to identify parents and hybrids for future crop improvement. Twelve lines and four
testers were crossed in an L x T mating design. The 48 crosses and their parents were raised under
normal (21, November 2002) and late sown (1, January 2003) at the Experimental Farm of Rajasthan
College of Agriculture, Udaipur in India.). Llines K’sona, DWR 195, C 306 and K 9708 for different
heat tolerant parameters along with grain yield were found to be good combiners. The studies
revealed that combinations of Raj 3077 x Kailash under normal (E1) and late sown (E2), C 306 x PBN
51 (E1) and C 306 x HD 2189 (E2) for grain yield; had high sca effect. The crosses viz., K 9708 x PBN
51 for proline content and heat injury, DWR 195 with HD 2189, C 306 with Kailash for heat injury only;
had desirable significant sca effects. The other crosses, HD 2329 x Kailash for pollen viability, and Raj
3765 x Kailash for chlorophyll content, were the be best specific combiners. Parents like C 306,
K’sona, DWR 195, K 9708, Raj 3077, PBN 51 and Kailash could be utilised in multiple crossing
programme and further bi-parental matting for selection of high yielding progenies under terminal heat
tolerance situations.