Development and statistical validation of a diagrammatic scale for assessing rhizome necrosis severity in banana caused by Radopholus similis

Abstract Accurate quantification of rhizome necrosis caused by Radopholus similis is essential for resistance studies, phenotyping, epidemiological analyses, and nematode management in banana. However, visual assessment of rhizome necrosis remains poorly standardized and highly subjective. This study aimed to develop and statistically validate a diagrammatic scale to quantify the severity of rhizome necrosis in banana plants infected by R. similis. One hundred rhizomes exhibiting a wide range of necrosis levels were selected from greenhouse-grown, inoculated plants. Rhizomes were photographed, digitally processed, and the necrotic area was quantified using ImageJ software. Based on these measurements, a diagrammatic scale with eight severity levels (0, 5.4, 9.6, 20.0, 30.5, 40.1, 56.7, and 83.4%) was constructed. Scale validation was performed by ten inexperienced evaluators who estimated disease severity in two independent assessments conducted with and without the aid of the proposed scale. Accuracy, precision, and agreement were evaluated using linear regression analyses, coefficients of determination (R²), and Lin’s concordance correlation coefficient (CCC). Use of the diagrammatic scale significantly improved evaluator performance, resulting in higher R² and CCC values and a substantial reduction in systematic bias. The results demonstrate that the proposed diagrammatic scale is a robust, accurate, and reproducible tool for standardizing the assessment of banana rhizome necrosis caused by R. similis , with direct applicability to resistance screening and banana breeding programs.