Canopy temperature depression as an indication of correlative measure of spot blotch resistance and heat stress tolerance in spring wheat

Abstract

Heat stress and spot blotch disease are most important stresses in non-traditional tropical wheat-growing areas causing significant yield losses and covering more than twenty five million hectares of land worldwide. These two stresses are supposed to be associated complicating development of tolerant genotypes. The current study was done with the objective of assessing potential application of canopy temperature depression (CTD) as an integrative trait for screening spot blotch resistance and heat stress tolerance. Ten genetically diverse genotypes with different level of resistance to spot blotch were grown both heat stressed (late sowing) and non-stressed (timely sowing) field conditions during 2002-2003 at Rampur and Bhairahawa, Nepal. Canopy temperature was measured during the different growth stages in fungicide protected and non protected plots using a hand held infrared thermometer and was used to calculate CTD and Area Under CTD Progress Curve (AUCTDPC). A strong negative correlation was observed between AUDPC per day and AUCTDP'C (r = -0.72**) indicating that foliar blight susceptibility has important role in decreasing AUCTDPC. Genetic differences were observed for both spot blotch resistance and heat stress tolerance, so that genotypes could be categorized into tolerant to either one or both stresses based on AUCTDPC and AUDPC per day readings. AUCTDPC proved to be an integrative trait for both types of stresses and has promise for further application in selection of stress tolerant genotypes in tropical environments.