Membrane thermostability, grain growth and contribution of pre-anthesis stem reserves to grain weight of wheat under late seeded conditions

In a field experiment, ten wheat (Triticum aestivum L.) varieties were exposed to two sowing conditions i.e. optimum sowing time (November 30) and late sowing (December 30). By late sowing the varieties were given high temperature treatment during reproductive growth phase in comparison to optimum sowing. The experiment was conducted to determine membrane thermostability of these wheat varieties and to find out the contribution of pre-anthesis stem reserves to grain weight under late seeded conditions. Based on membrane thermostability (MT) test four varieties (eg.Ananda, Pavon, Aghrani and Barkat) took maximum heat killing time and were classified as relatively heat tolerant, three varieties (eg. Akbar, Kanchan and Protiva) as moderately heat tolerant and the other three varieties (eg. Balaka, Sawgat and Sonora) took the lowest heat killing time and are considered as heat sensitive. In November, 30 sowing. But the heat sensitive varieties had higher pre-anthesis stem reserves contribution at December 30 sowing conditions both the tolerant and sensitive varieties had the similar grain filling duration (40 days). But in December 30 sowing, the tolerant variety had longer grain filling duration (32 days) compared to sensitive variety (28 days). In December 30 sowing both the tolerant and moderately tolerant varieties showed lower pre-anthesis stem reserves contribution to the final grain weight compared to November 30 sowing conditions. The present results suggest that the MT test would be a suitable procedure for selecting heat tolerant and sensitive varieties and the long grain filling duration with high filling rate and less dependence on pre-anthesis stem reserves could be used to determine the heat tolerance of wheat under late seeded high temperature conditions.