Terminal heat stress and spot blotch disease (caused by Cochliobolus sativus) are the most important stresses responsible for significant yield losses every year in warm South Asian plains. Both of these stresses are very severe in late planted wheat, which is common in rice-wheat and rice-rice-wheat cropping systems. The development of genotypes tolerant to both stresses might be very useful for increasing yield and reducing yield losses. Information is limited on how different genotypes respond to both stresses (individually and combined) and on the degree of tolerance present in South Asian wheat genotypes. The study was done to evaluate the tolerance of South Asian wheat genotypes to both stresses by comparing the stress factor susceptibility index (SFSI). Eleven diverse South Asian genotypes were evaluated under spot blotch stress (non-fungicide protected plots), heat stress (late planted and fungicide protected), both stresses (non-fungicide protected and late planted) and normal planting situations (fungicide protected and normal season planted) at Rampur, Chitwan, Nepal. Both stresses reduced the grain yield and thousand-kernel weight (TKW), but not other yield components, including grains/spike and spikelets/spike. Genotypes BL 1473, Gautam and NL971 were moderately to highly tolerant to both types of stress. Generally genotypes that are tolerant or resistant to spot blotch also showed tolerance to heat stress, suggesting a common physiological mechanism to combat both stresses in tolerant genotypes.

Breeding for resistance to Helminthosporium leaf blight (HLB) caused by a complex of spot blotch (Cochliobolus sativus) and tan spot (Pyerenophora tritici-repentis Died) of wheat (Triticum aestivum L.) is difficult due to complex nature of resistance, and high influence of environment. This study was conducted to examine whether genotypes having variation in level of resistance and tolerance differ in compensation to loss of leaves. Five spring wheat genotypes with different levels of resistance and tolerance to HLB were grown under irrigated field conditions in randomized complete block design during