New proposed of standard area diagram scale for assessing black sigatoka in bananas

Abstract

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 (SAD) with high-resolution digital images with six disease levels: 0 (0%), 1 (0.1–5.0%), 2 (5.01–13.0%), 3 (13.01–23.0%), 4 (23.01–40.0%), 5 (40.01–65.0%) and 6 (> 65.0%) and compare BLS severity results in banana leaves with those based on another SAD. Five evaluations were conducted by thirteen different evaluators and each evaluation was performed at seven-day intervals. The first assessment was done without a SADs. Evaluators performed two assessments with each SAD. The statistics were analyzed with linear regression and Lin’s concordance correlation. With the proposed SAD, the evaluators improved the precision, accuracy, repeatability and reproducibility and reduced the residual distribution, as compared using the other SAD. The proposed SAD is a tool that aids users in producing a disease estimate that is close to the real value of BLS in banana leaves.