A standard area diagram set for assessing severity of dragon fruit (Hylocereus spp.) stem canker caused by Neoscytalidium dimidiatum

Abstract

Dragon fruit canker (DFC) disease caused by the fungus Neoscytalidium dimidiatum poses a significant threat to yield and fruit quality in cultivating dragon fruit (Hylocereus spp.). Accurate assessment of canker severity is crucial for determining the effectiveness of management strategies for controlling this disease. We developed a standard area diagram set (SADs) consisting of nine levels of disease severity (0.5 to 60%) and subsequently validated the SADs based on the patterns and distribution of the symptoms. For the validation, eighteen raters with no prior experience in disease assessment were recruited to estimate the severity of canker symptoms on 50 stems/cladodes of dragon fruit before and after using SADs. Both accuracy and precision were improved when they used the SADs. Statistical parameters for the 18 raters were as follows: bias coefficient factor (C_b) without SADs = 0.791, with SADs = 0.982; correlation coefficient (r) without SADs = 0.884, with SADs = 0.918; Lin's concordance correlation coefficient (ρ_c) without SADs = 0.702, with SADs = 0.902. Estimates were also more reliable by using the SADs: inter-rater coefficient of determination (R²) without SADs = 0.749, with SADs = 0.810. The newly developed SADs provide a practical, standardized tool for assessing dragon fruit canker severity, aiding researchers and growers in more accurate disease monitoring, yield loss estimation, intervention planning, and control measure evaluation.