Screening wheat germplasm for heat tolerance at terminal growth stage

The germplasm comprising of 442 wheat varieties/lines was sown in one meter long row in a plastic sheet tunnel to screen the material for heat tolerance during 2004-05 and 2005-06 at Wheat Research Institute, Faisalabad. A set of the material was sown in the open adjacent to the tunnel. The material was exposed to heat shock (>320C) by covering the tunnel with plastic sheet during grain formation for two weeks in 2004-05 and for four weeks in 2005-06. Data was recorded from 25 randomly selected heads from each row for 1000 grain weight, grains per spike and yield per spike during both the years. The data regarding survival (ability to stay green under heat stress) was also recorded. Heat effect was expressed as ratio of stressed / non stressed plants. The effects of heat stress were lesser in shorter period exposure and more drastic in prolonged exposure of the genotypes to heat. The ability of lines to stay green for longer period in heat shock had no direct relationship with seed setting. Three entries CB-367 (BB#2/ PT// CC/ INIA /3/ ALD’S’) CB-333 (WL 711/3/KAL/BB//ALD ‘S’) and CB-335 (WL711/CROW ‘S’//ALD#1/CMH 77A. 917/3/HI 666/PVN ‘S’ ) showed maximum grain development and survival. This study revealed that these genotypes can be utilized in breeding programs for development of wheat varieties having heat tolerance at terminal growth stage.