Molecular identification, relative prevalence, and host range of Berkeleyomyces species associated with the lettuce and other leaf vegetables in Brazil

One of the most important soil-borne diseases of lettuce is the black root rot caused by two Berkeleyomyces species (B. basicola and B. rouxiae). However, no information is yet available about the prevalence of Berkeleyomyces species affecting lettuce and other leafy crops as well as the host ranges of these pathogens in Neotropical areas. Herein, we characterized via molecular approaches and inoculation bioassays a collection of 47 Berkeleyomyces isolates associated with these vegetables. Phylogenetic analyses were carried out based on sequence information of the large subunit of rDNA (LSU), and the DNA replication licensing factor mini-chromosome maintenance complex (MCM7). The MCM7 region was informative, allowing a consistent discrimination of both Berkeleyomyces species. The species-specific primers for B. basicola and for B. rouxiae demonstrated strong consistency with phylogenetic analysis, effectively distinguishing the two fungal species. Our results reveal a broad distribution of both pathogens across five Brazilian regions, with similar prevalence. We identified 24 isolates of B. basicola and 23 of B. rouxiae, including 18 and 21 isolates from lettuce, respectively. Molecular evidence further indicates that both fungi naturally infect endive, while B. rouxiae infects chicory and radicchio in Brazil. Isolates of both Berkeleyomyces species were pathogenic to 12 cultivars of five out of ten leaf vegetables. The present work is the first molecular evidence of lettuce and endive as natural hosts of both species and chicory and radicchio as natural hosts of B. rouxiae. Moreover, cultivars of Swiss chard and coriander were identified as novel experimental hosts of both species. All the cultivars of spinach, Brassica juncea, arugula, parsley, and watercress were not infected with the isolates of both species and they could be alternatives for crop rotation systems.