Methods for seedling identification of cucumber resistance to powdery mildew and its effect on the growth of cucumber seedlings

The severity of powdery mildew in cucumbers gravely impinges upon both yield and quality. In order to probe efficacious methods for early-stage resistance determination against powdery mildew in cucumbers, we utilized Xintai mici as an experimental subject and adopted a four-factor, three-level (L9(3)4) orthogonal experimental design. This design encompassed four factors: inoculation seedling age, inoculation concentration, inoculation method, and different hydration periods post-inoculation. Through this, we sifted and discerned the most optimal indoor method for early-stage resistance determination against powdery mildew in cucumbers. Concurrently, we studied the influence of different determination methods on the accumulation of cucumber plant biomass, chlorophyll content, and leaf photosynthetic parameters to delineate the impact patterns of powdery mildew on cucumber leaf photosynthetic traits. The results underscored that disease incidence amongst different treatments were minute, all exceeding 96.67%. In contrast to other treatments, T3 (inoculating a spore suspension of powdery mildew at a concentration of 106 per mL on one-true-leaf stage using the leaf-brushing method and maintaining hydration for 12 h post-inoculation) exhibited a rapid onset of disease, with a disease index reaching 89.03, thereby proving to be the most superior method for early-stage powdery mildew determination. Various determination methods wielded a significant influence on dry and fresh weight, chlorophyll content, and leaf photosynthetic activity of cucumber seedlings. Relative to other treatments, the net photosynthetic rate (Pn) of T3, T8, and T9 was significantly suppressed post-inoculation with powdery mildew, all lingering below 3 μmol/m2/s, while the transpiration rate (E), intercellular CO2 concentration (Ci), as well as the stomatal conductance (Gs), drastically declined, the decrease fell between 25%−80%. The relative chlorophyll content maintained at a lower level, ultimately leading to a significant reduction in the accumulation of dry matter. This demonstrates that powdery mildew can significantly stifle the growth of cucumber seedlings.