Four wheat genotypes (BARI gom 25, BARI gom 26, BAW 1135 and Pavon 76) were sown at different dates (29 November, 5, 16, 23 and 30 December respectively) to evaluate genotypic differences imposed by late seeded heat stress condition. This open field experiment was conducted at the research farm of Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur. Sowing on 29 November was considered as normal growing period with a mean air temperature 24.08oC during the post anthesis stages. Mean temperature was as high as 28.4oC on 30 December sowing which is heat stress condition for wheat. In late seeded crop, the physiological maturity was shifted to 8 day earlier in Pavon 76 which continued upto 32 day after anthesis in early seeded crops. On the contrary, 4-day earliness was observed to reach the physiological maturity in BARI gom 25, BARI gom 26 and BAW 1135 under stressed condition. Due to post anthesis stress, higher relative spike number per m2 (92%), higher relative grain number per spike (92%) and higher relative grain yield (89%) were exhibited in BARI gom 26 compared to Pavon 76 (75%, 78% & 56% respectively). BARI gom 26 exibits higher individual grain size and harvest index than other. Higher yield reduction was recorded in Pavon 76 (78.06 kg/ha/day) compared to BARI gom 26 (19.36 kg/ha/day) on 30 December sowing. In terms of grain growth and seed yield, BARI gom 26 was found to be superior variety as supported by Heat Susceptibility Index (0.41) for growing under warmer environment.
Key words: Heat stress, wheat, grain growth, yield, sowing dates
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