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A field experiment was conducted to work out relationship between heat unit requirement and phenophases of two wheat cultivars (PBW-343 and WH-542) under different dates of sowing (2 November, 1 December and 4 January). Growth duration and heat unit requirement of different phenophases was distinct for two cultivars, and showed a decline with delay in sowing. High temperature during reproductive development in late-sown crop forced the plants to attain maturity. For all phenological stages, plants of timely-sown crop accumulated more heat units in both cultivars than late-sown crop. The pheno-thermal indices decreased during vegetative stages but increased during reproductive phenophase with delay in sowing. The cultivar, PBW-343 took more number of days, accumulated more heat units and used heat more efficiently; and thus produced higher grain yield than WH-542. The timely-sown crop used …