Abstract
Lettuce black root rot disease caused by Berkeleyomyces rouxiae occurred in Japan recently. B. rouxiae had been reported in Japan as a causal agent of various plant species before the occurrence of lettuce black root rot. However, virulence of Japanese isolates from non-lettuce plants on lettuce was slight. These isolates never acquired high virulence even after repetitive inoculation and reisolation on lettuce plants. Moreover, phylogenetic analysis using microsatellite sequences revealed that isolates of lettuce black root rot pathogen are distinct not only from Japanese non-lettuce isolates, but also from American isolates that are pathogenic on lettuce. Therefore, the infection source of lettuce black root rot occurring in Japan remains unknown. Highly sensitive lettuce cultivars have been cultivated in Japan for several decades. We infer that some change in the pathogens induced the occurrence of lettuce black root rot in Japan. Salinas-type lettuce cultivars with high sensitivity have been increasing since approximately 2000. This increase might be involved with the disease occurrence. Additional research must be conducted to elucidate the occurrence of lettuce black root rot in Japan.
https://ror.org/01hjzeq58 
