Verticillium wilt resistance screening and early disease detection in eggplant using leaf injection inoculation and chlorophyll fluorescence

Verticillium wilt is a major threat to eggplant production, and there is an urgent need for the rapid and accurate screening of resistant varieties to enhance breeding efficiency. Owing to the long incubation period of Verticillium wilt before visible symptoms appear, early disease detection remains challenging. In this study, a simple and efficient leaf injection method was established and optimized by evaluating key factors, such as seedling age and inoculum concentration. The results showed that the two-leaf-one-heart stage, combined with a spore concentration of 1 × 10⁷ spores/mL, provided optimal conditions for inoculation. Chlorophyll fluorescence (Chl-F) was used to monitor the early physiological changes in plants under pathogen stress. After pathogen inoculation, changes in Chl-F parameters, such as the effective quantum yield of photosystem II (Φ_PSII) and the relative electron transport rate (rETR), were negatively correlated with the genotype’s resistance. These parameters served as early indicators for resistance screening and grading. Furthermore, our findings confirmed the high correlation (R = 0.92, P < 0.01) between the leaf injection and root-dipping inoculation methods in a resistance-segregating population, validating the reliability of the leaf injection method for resistance screening. This study demonstrated the effectiveness of combining the leaf injection method with Chl-F analysis for precise and early disease detection and offered valuable insights into enhancing eggplant breeding strategies for Verticillium wilt resistance.