High microbial diversity in the rhizosphere and soil improves carrot (Daucus carota L.) postharvest storability.

Postharvest diseases can cause significant losses in carrot (Daucus carota) yield during storage. In this study, the effects of soil quality and microbial diversity in bulk field soil and the rhizosphere on carrot postharvest storability were investigated. Microbial genera in bulk soil and rhizosphere samples were identified by Illumina MiSeq amplicon sequencing of the bacterial 16S rRNA gene and fungal ITS regions. Disease symptoms in the stored carrots were monitored after 6 months of cold storage, and the main pathogens were identified. Field sites with mineral soils, which had higher pH values, had greater bacterial and fungal diversity than sites with organic soils. Organically farmed fields had greater bacterial diversity than conventionally farmed fields. The community structures of both bacteria and fungi were largely driven by field site, including its main chemical characteristics, with rhizosphere and bulk soil samples from the same site displaying comparable assemblages. Higher soil fungal diversity was associated with greater postharvest storability of carrots. Weather during the growing season also affected the observed fungal biodiversity, which was higher at sites with lower temperatures and less rain prior to harvest.