Leaf litter from Cynanchum auriculatum Royle ex Wight leads to root rot outbreaks by Fusarium solani, hindering continuous cropping

Abstract Cynanchum auriculatum Royle ex Wight (CA) is experiencing challenges with continuous cropping obstacle (CCO) due to soil-borne fungal pathogens. The leaf litter from CA is regularly incorporated into the soil after root harvesting, but the impact of this practice on pathogen outbreaks remains uncertain. In this study, a fungal strain D1, identified as Fusarium solani, was isolated and confirmed as a potential factor in CCO. Both leave extract (LE) and root extract (RE) were found to inhibit seed germination and the activities of plant defense-related enzymes. The combinations of extracts and D1 exacerbated these negative effects. Beyond promoting the proliferation of D1 in soil, the extracts also enhanced the hypha weight, spore number, and spore germination rate of D1. Compared to RE, LE exhibited a greater degree of promotion in the activities of pathogenesis-related enzymes in D1. Additionally, caffeic acid and ferulic acid were identified as potential active compounds. LE, particularly in combination with D1, induced a shift in the composition of fungal communities rather than bacterial communities. These findings indicate that the water extract of leaf litter stimulated the growth and proliferation of fungal strain D1, thereby augmenting its pathogenicity towards CA and ultimately contributing to the CCO process.