Microbial associations can protect cultivated sunflowers (Helianthus annuus L.) from being infected by the ascomycete fungal pathogen Sclerotinia sclerotiorum (Lib.) deBary, potentially saving millions of dollars in losses annually. Here we isolated bacteria from sunflower rhizosphere soil, performed full length 16S rRNA gene sequencing for identification, and then measured inhibition of S. sclerotiorum in co-cultures. Isolated bacterial strains that inhibited S. sclerotiorum (n = 13) matched six environmental operational taxonomic units (OTUs) sequenced from rhizosphere soils of resistant sunflower genotypes. Four of these six OTUs were detected in sunflower rhizosphere soils from 15 different sites across the Great Plains region of the U.S., indicating a broad distribution and potential for use as biocontrol agents. However, the relative abundance of inhibitor OTUs across 95 sunflower genotypes was not negatively correlated with S. sclerotiorum incidence in the Carrington, ND, field evaluation site. All inhibitors we isolated are known to possess antifungal properties and have been tested as potential biocontrol agents in previous studies. Our work shows that soils associated with resistant sunflower plants naturally contain inhibitory bacterial strains. This opens up the potential for using augmentation of locally occurring bacteria as a strategy for biocontrol, potentially by coating seeds or spraying aboveground parts with slurries of one or more of these taxa.
Vimercati et al. (Thu,) studied this question.