Screening Cotton for Resistance to Alternaria Leaf Spot Caused By Alternaria Alternata in New Mexico

Alternaria leaf spot (caused by Alternaria spp.) is one of the most common foliar diseases of cotton (Gossypium spp.) and occurs in most cotton-growing regions of the world. The principle causal fungal agent of the disease is A. macrospora, while the less virulent A. alternata is also commonly observed. In New Mexico, Alternaria leaf spot caused by A. alternata, is becoming prevalent due to favorable weather conditions. The objective of this study was to evaluate commercial cotton cultivars and advanced breeding lines for resistance to A. alternata under natural field conditions. A total of 192 Upland cotton genotypes were divided into six replicated tests each with 32 entries and 3-4 replications, together with 8 Pima cotton cultivars and lines with 4 replications. The analysis of variance showed that there were significant differences (P<0.0001) among Upland cotton genotypes, while no statistically significant differences (P>0.05) were detected among Pima cotton genotypes. Depending on genotypes, the overall disease incidence was between 90 and 100%, and the average disease severity index (DSI) ranged from 0.32 to 0.96.