Yield and Yield Components Response to Defoliation of Spring Wheat Genotypes with Different Level of Resistance to Helminthosporium Leaf Blight

Abstract

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 2001-2002 and 2002- 2003 wheat-growing season at Rampur, Chitwan, Nepal. Defoliation treatments consist of removal of flag (F), penultimate (F-1), and both F and F-1 leaves were done one day after anthesis. Results showed that defoliation had significant effects on grain yield, biomass yield, thousand-kernel weight (TKW) but not on harvest index, number of grains per spike, kernel per spikelet, and spikelets per spike. All genotypes included in this study showed some degree of compensation for loss of F, F-1, and both F and F-1 leaves, which was found to be variable between years. Removal of flag leaf was compensated by the resistant genotype NL750 for both grain yield and TKW but not for both F and F-1 leaves. Loss of both F and F-1 leaves was better compensated by BL 1473, a stably tolerant genotype in both years. For other genotypes sensitivity to defoliation was found as variable as tolerance to HLB. Key words: Spot blotch, tan spot, defoliation, compensation, flag leaf removal, penultimate leaf removal J. Inst. Agric. Anim. Sci. 26:43-50 (2005)