Inoculum Level Effect of Corynespora Cassiicola on Evaluation of Cotton Resistance in a Controlled Environment

Target spot of cotton, caused by the fungus Corynespora cassiicola, was first reported by Jones in cotton in Mississippi, U.S. Recently, target spot has become an important disease in southern states of the U.S. The major characteristic of this disease is “target spot”, starting as small black spots on leaf lamina and gradually developing into large necrotic areas ringed with chlorotic areas, hence the name target spot. The overall objective of this project is to develop a controlled environment method of evaluation for resistance to target spot caused by C. cassiicola. Primary factors that will be studied will be inoculum concentration for C. cassiicola infection and disease progress at different time points. Conidial suspensions were selected for evaluation of inoculum concentration effects on cotton. The four concentrations ((zero (control), 1 × 10³, 1 × 10⁴, and 1 × 10⁵ conidia/mL)) of inoculum of C. cassiicola were applied to three cotton genotypes in a greenhouse trial. The rating results indicated a differential response among genotypes with regard to disease symptom development. The evaluation showed that treatments with 1 × 10³ and 1 × 10⁴ conidia/mL inoculums can cause different disease severity rantings among different cotton genotypes.