Screening for target spot (Corynespora cassiicola) resistance in cotton (Gossypium hirsutum L.)

Abstract

A critical problem for Alabama cotton growers is the presence of target spot (Corynespora cassicola), a foliar disease which is responsible for combined annual yield losses of >$70 million in AL, GA and the FL Panhandle. Currently, there are no resistant commercial cultivars and the only management defense are fungicide applications. Timing of application and implications for resistance to the fungicides are high. A resistant variety is the only long term solution, therefore this study focuses on the inoculation method and growing conditions of C. cassiicola in order to develop a greenhouse protocol to screen for the variety response to target spot. Preliminary experiments focused on inoculation techniques and environmental conditions favoring pathogen reproduction. It was determined that a spore suspension was preferred over a mycelium broth, the temperature required for growth was 24-32°C and that the plants had to be under consistent moisture for at least 12 hours. Future experiments will compare cultivars known to be different in a field setting to validate this protocol.