Exploring the potential role of soil protists in predicting banana health.

Fusarium wilt is increasingly threatening banana production around the world. Investigating soil microbial communities associated with healthy and diseased banana plants is the first step to understand the potential mechanisms involved in the disease suppression. Previous research has confirmed plant-beneficial bacterial and fungal communities are key determinants of banana health. However, to what extent protists, a key component of the soil microbiome, are linked to banana health on a large scale remains largely unknown. Here, we collected soil samples from healthy and diseased plants suffering from Fusarium wilt in multiple banana plantations within China and Laos, and examined holistic soil microbial communities including bacteria, fungi and protists using high-throughput sequencing. We explored the linkage between protists and Fusarium oxysporum and investigated the effects of biotic and abiotic factors on protists. Results showed the relative abundance of Fusarium oxysporum can be highly predicted by protists. Specifically, predatory protists revealed a negative correlation with F. oxysporum, which was confirmed in pot experiments. We found the putative plant growth-promoting bacteria, positively correlated with predatory protists, were also negatively correlated with F. oxysporum. In addition, both soil abiotic factors (i.e., soil pH and ammonia nitrogen) and biotic factors (soil bacteria) played crucial roles in determining predatory protists. We highlighted that soil predatory protists might contribute to banana health via directly inhibiting soil-borne pathogens or indirectly enriching plant beneficial bacteria.