HEAT TOLERANCE IN WHEAT UNDER LATE SEEDED CONDITIONS

Abstract

HEAT TOLERANCE IN WHEAT UNDER LATE SEEDED CONDITIONS BY Sripati Sikder In a field experiment ten recommended wheat varieties were exposed to two sowing conditions- eg. optimum sowing (November 30) and late sowing (December 30) during November 1997 to April 1998 at the research farm of the Bangabandhu Sheikh Mujibur Rahman Agricultural University, Salna, Gazipur, Bangladesh, By late sowing the varieties were given high temperature treatment during reproduction growth phase in comparison to optimum sowing. The experiment was conducted to determine the relative heat tolerance of wheat varieties and to evaluate the relative performance of heat tolerant and heat sensitive varieties 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 tolerant and the rest three varieties (eg. Balaka, Sawgat and Sonora) took the shortest heat killing time and considered as heat sensitive. In November 30 sowing both tolerant and sensitive varieties had 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 both sowing time heat tolerant variety had higher grain growth rate compared to sensitive variety. 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. But the heat sensitive varieties had higher pre-anthesis stem reserves contribution at December 30 (late sowing) conditions. The grain number per ear, 1000 grain weight and main shoot grain weight of the tolerant and moderately tolerant varieties showed higher relative performance compared to sensitive varieties. But the relative ear number per plant and relative grain yield were found to range from low to high in heat tolerant and moderately tolerant varieties. In heat sensitive varieties the relative ear number per plant and relative grain yield were moderate to high. Thus the results suggest that in addition to membrane thermostability test, the long grain filling duration with high filling rate, less dependence on pre-anthesis stem reserves, high relative grain number per ear, 1000 grain weight and main shoot grain weight can be used to determine the heat tolerance of wheat varieties under late seeded warmer conditions.