Characterization and Pathogenicity of Fusarium Species Associated with Soybean Pods in Maize/Soybean Strip Intercropping

Intercropping has been considered as a kind of a sustainable agricultural cropping system. In southwest China, maize/soybean strip intercropping has commonly been practised under local limited agricultural land resources. However, heavy rainfall in combination with high humidity and low temperatures cause severe pod and seed deterioration in the maturity and pre-harvesting stages of intercropped soybean. Numerous Fusarium species have been reported as the dominant pathogens of soybean root rot, seedling blight, as well as pod field mold in this area. However, the diversity and pathogenicity of Fusarium species on soybean pods remain unclear. In the current study, diseased soybean pods were collected during the cropping season of 2018 from five different intercropped soybean producing areas. A total of 83 Fusarium isolates were isolated and identified as F. fujikuroi, F. graminearum, F. proliferatum, and F. incarnatum-equiseti species complex based on morphological characteristics and phylogenetic analysis of the nucleotide sequence of EF1-α and RPB2 genes. Pathogenicity tests demonstrated that all Fusarium species were pathogenic to seeds of the intercropped soybean cultivar Nandou12. Fusarium fujikuroi had the maximum disease severity, with a significant reduction of seed germination rate, root length, and seed weight, followed by F. equiseti, F. graminearum, F. proliferatum, and F. incarnatum. Additionally, the diversity of Fusarium species on soybean pods was also considerably distinct according to the geographical origin and soybean varieties. Thus, the findings of the current study will be helpful for the management and resistance breeding of soybean pod decay in the maize/soybean intercropping system.