Diversity and biological activity of culturable endophytic fungi isolated from turnip (Brassica rapa subsp. rapa) roots

• Endophytic fungi orders Helotiales and Eurotiales dominate turnip root microbiome. • Botrytis sp. fungus acts as a novel plant growth-promoting endophyte in turnips. • Alternaria sp. fungus reduces black rot disease from Xanthomonas campestris pathogen. • Drought-tolerant endophytes lacking, suggesting need for sampling stress-prone areas. Brassica rapa is a crop belonging to the Brasicaceae family, which is widely grown throughout the world. Cultivation of crops of the species B. rapa are subjected to stressors that cause a decrease in production, such as drought or black rot caused by the bacterium Xanthomonas campestris . The need to find more sustainable alternatives to maintain production linked to intrinsic characteristics of the Brassica genus, such as the absence of relationships with mycorrhizal fungi, make brassica crops ideal to study the impact of endophytic fungi promoting plant growth. Endophytic fungi have been shown to improve plant performance and adaptation, whether under optimal or stressful conditions. In this paper, the fungal endophytic microbiome of the roots of five varieties of B. rapa has been isolated, identified and studied. A subset of fungi was selected, and preliminary inoculation tests were performed. The bioactivity of the selected fungi has been tested under optimal conditions, against X. campestris and drought stress. The inoculation assays show that the fungus Botrytis sp. (Br421) can be potentially useful to promote growth, while the fungi Alternaria sp. (Br261) can act as biological control agent against X. campestris as it delays the onset of disease symptoms. However, none of the fungus improved plant performance under drought conditions.