Distribution of the potential pathogenic Alternaria on plant leaves determines foliar fungal communities around the disease spot.

Plant leaves are colonized by a remarkably diverse fungal microbiome, which contributes to host plant growth and health. However, responses of foliar fungal community to phytopathogen invasion and measures of the fungal community taken to resist or assist pathogens remain elusive. By utilizing high-throughput sequencing of internal transcribed spacer (ITS) amplicons, we studied the relationships between the foliar fungal community around the disease spot and the pathogen of brown spot disease. The pathogenic Alternaria was found to follow a dramatically decreased trend from the disease spot to its surrounding fungal communities, whose community structure also diverged substantially away from the disease spot community. With the increase of pathogenic Alternaria, diversity indexes, including Shannon, Pielou and Simpson, showed a trend of increasing first and then decreasing. Total network links and the average path distance exhibited strong negative and positive correlations with Alternaria, respectively. Five keystone members showed direct interactions with pathogenic Alternaria. Members of Botryosphaeria, Paraphoma and Plectosphaerella might act as key 'pathogen facilitators' to increase the severity and development of brown spot disease, while Pleospora and Ochrocladosporium might be important 'pathogen antagonists' to suppress the expansion of pathogenic Alternaria. Our study provides new insights in developing new strategies for leaf disease prediction or prevention.