New standard area diagram set for assessing black sigatoka in bananas

Black sigatoka, or black leaf streak (BLS), is caused by Pseudocercospora fijiensis and is the most important foliar disease in Musa production. Our goal was to develop a new standard area diagram set (SADs) with high-resolution digital images to aid in visual classification using a quantitative ordinal scale representing six disease severity ranges: 0 (0%), 1 (0 - 5%], 2 (5 - 13%], 3 (13 - 23%], 4 (23 - 40%], 5 (40 - 65%] and 6 (65-100%] and compare visual estimates of BLS severity on banana leaves with those using a previously developed ordinal scale. Three evaluations were conducted by thirteen evaluators and each evaluation was performed at seven-day intervals. The first assessment was done without a SADs. Evaluators subsequently performed two assessments with each the old ordinal scale and the novel SADs. Using the new SADs, evaluators precision, accuracy, repeatability, reproducibility, and residual distributions were improved. The proposed SADs is a tool that helps users in more accurately estimating the severity of BLS.