Different Disease Levels Reveal Kiwifruit Brown Spot Impacts on Fruit Yield and Quality

Kiwifruit brown spot, caused by the fungus Corynespora cassiicola, has recently emerged as a problematic foliar disease of kiwifruit, causing premature defoliation. The objective of this study was to determine the effects of kiwifruit brown spot on the yield and quality of kiwifruit. Principal component analysis (PCA) was used to conduct a comprehensive evaluation of the fruit quality of 'Hongyang' kiwifruit in the main producing regions. The first principal component for PCA included the weight of individual fruit, soluble solids content, and dry matter content, which were negative significantly correlated with disease index. The significant differences among different disease levels indicated that the impact of the disease on fruit quality was largely determined by these three intrinsic flavor indices. Due to kiwifruit brown spot, the average yield loss was 22.652%, which leads to kiwifruit quality being downgraded by one grade, resulting in an economic loss of 73,591 yuan/ha. The Pearson correlation coefficient between disease index and comprehensive score of fruit quality was -0.762 (p < 0.01), indicating a significant relationship. Accordingly, the disease loss model was constructed, and the damage threshold based on disease index for kiwifruit brown spot was calculated to be 36.14. In conclusion, this study found that kiwifruit brown spot could have a significant impact on yield and fruit quality.