Host plant environmental filtering drives foliar fungal community assembly in symptomatic leaves

Influence of Association Network Properties and Ecological Assembly of the Foliar Fugal Community on Crop Quality

Revealing community assembly and their impacts on ecosystem service is a core issue in microbial ecology. However, what ecological factors play dominant roles in phyllosphere fungal community assembly and how they link to crop quality are largely unknown. Here, we applied internal transcriptional spacer high-throughput sequencing to investigate foliar fungal community assembly across three cultivars of a Solanaceae crop (tobacco) and two planting regions with different climatic conditions. Network analyses were used to reveal the pattern in foliar fungal co-occurrence, and phylogenetic null model analysis was used to elucidate the ecological assembly of foliar fungal communities. We found that the sensory quality of crop leaves and the composition of foliar fungal community varied significantly across planting regions and cultivars. In Guangcun (GC), a region with relatively high humidity and low precipitation, there was a higher diversity and more unique fungal species than the region of Wuzhishan (WZS). Further, we found that the association network of foliar fungal communities in GC was more complex than that in WZS, and the network properties were closely related to the sensory quality of crop. Finally, the results of the phylogenetic analyses show that the stochastic processes played important roles in the foliar fungal community assembly, and their relative importance was significantly correlated with the sensory quality of crop leaves, which implies that ecological assembly processes could affect crop quality. Taken together, our results highlight that climatic conditions, and plant cultivars play key roles in the assembly of foliar fungal communities and crop quality, which enhances our understanding of the connections between the phyllosphere microbiome and ecosystem services, especially in agricultural production.

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.