Pathogenic Characteristics of Berkeleyomyces basicola Causing Black Root Rot of Carrot

The pathogenic soilborne and postharvest fungus Berkeleyomyces basicola, a newly reported pathogen in Serbia, caused significant disease symptoms on carrot roots and seedlings in inoculation assays. In October 2023, machine-washed and cold-stored carrot roots showed symptoms of black rot of patches and abundant sporulation. The influence of the postharvest treatment of machine washing was confirmed by additional sampling at the production site. The collected roots were machine or manually washed and stored under similar conditions as during shelf life (cold storage followed by incubation at room temperature). The machine-washed roots had a much higher disease incidence than the manually washed roots (75 and 15%, respectively). From all samples, only uniform Berkeleyomyces-like, dark gray colonies were obtained. Morphology and multilocus phylogeny (based on ITS, LSU, and MCM7) confirmed the presence of B. basicola. Koch's postulates were confirmed after artificial inoculations of carrot roots using spraying or injecting spore suspension or inserting colony fragments, and symptoms developed on both wounded and nonwounded roots 7 days after inoculation. Pathogenicity tests on wounded and nonwounded carrot seedlings by spraying or watering with spore suspension or placing colony fragments next to the root neck showed that B. basicola can infect and sporulate only wounded carrot seedlings. The ability of B. basicola to infect carrot seedlings had not been tested previously, and our results suggest that carrot could be infected earlier than postharvest, as previously believed. In 2024, a follow-up survey of fresh market, symptomatic carrot roots confirmed the continuous presence of B. basicola in Serbia.