Phenotyping peanut cultivars with contrasting responses to pod rot pathogens

Peanut is a major cash crop in the world. In recent years, peanut pod rot has become increasingly prevalent, resulting in significant yield and quality losses. Resistance breeding is considered a cost-effective approach for managing pod rot. Previous research in the United States identified significant anatomical differences in leaves and shells among peanut cultivars with varying responses to pod rot caused by Pythium myriotylum Drechs. and Rhizoctonia solani Kuhn. However, whether similar anatomical features correlate with resistance to peanut pod rot in Laixi, Qingdao, remained unknown, where the primary causal pathogen for the disease was F. solani . In this study, nine peanut varieties with differing disease reactions to peanut pod rot were planted in the same plots. Paraffin sections of leaves and shells were prepared and stained to evaluate anatomical features, and the main agronomic traits were assessed alongside leaf spot disease ratings. All the four anatomical features, leaf palisade cell number, palisade cell width, index (palisade cell number per mm × cell width in μm), and shell lignin staining area, were measured before the onset of pod rot and were found to be negatively correlated with pod rot scores. Given the consistent and strong correlation of these anatomical features with pod rot resistance and their high heritability estimates, the pre-existing resistance could be identified even in the absence of the disease, which is particularly valuable for fields where pod rot may not occur every year. This study provided useful anatomical indicators for selecting resistance to peanut pod rot, predominantly caused by F. solani .