Field Resistance to Powdery Mildew in Lycium barbarum Germplasm, Associated Leaf Anatomical Traits, and Temporal Physiological Responses in Ningqi-1

Lycium barbarum L. is a characteristic agricultural crop in Ningxia. Powdery mildew is a serious fungal disease affecting Lycium barbarum. Resistance analysis of Lycium barbarum varieties is rarely reported, and comparative information on field resistance and associated anatomical and physiological responses remains limited. This study evaluated powdery mildew resistance in 26 Lycium barbarum germplasm accessions under natural field conditions over two years, compared leaf anatomical traits in eight representative accessions, and characterized early physiological responses in the genotype Ningqi-1 after inoculation. Based on the two-year mean disease index (DI), the 26 accessions were assigned to four descriptive resistance categories. Four sigmoidal equations were fitted to the observed disease-progress data; these equations were used only as descriptive curves and were not treated as independently validated predictive models. Across the eight representative accessions, the 2021 DI was negatively correlated with the number of palisade tissue layers, palisade tissue thickness, and leaf compactness, but positively correlated with spongy tissue thickness (two-tailed Pearson correlation, n = 8). In Ningqi-1, inoculation induced time-dependent changes in antioxidant-enzyme activities, malondialdehyde content, defense-related enzyme activities, lignin content, soluble protein content, and soluble sugar content during the first 48 h. The increase in malondialdehyde content suggested enhanced membrane lipid peroxidation during infection, which may reflect oxidative stress associated with powdery mildew infection. Overall, this study characterized field disease responses, candidate anatomical traits associated with DI, and early physiological responses in Ningqi-1. These findings provide preliminary information for future resistance screening, but validation in larger germplasm populations and under controlled inoculation conditions is still required.