Fusarium oxysporum f. sp. crypti, a novel forma specialis causing Fusarium wilt of mitsuba, Cryptotaenia japonica.

Abstract

Fusarium oxysporum isolates causing Fusarium wilt in mitsuba (Cryptotaenia japonica Hassk.; also referred to as Japanese honeywort, Japanese honewort, or Japanese parsley) have traditionally been classified as f. sp. apii. However, some reports have indicated that the host-pathogenic F. oxysporum isolates derived from mitsuba are nonpathogenic to celery, the principal host of f. sp. apii. In this study, we aimed to elucidate the differences among isolates from mitsuba, coriander, and celery in terms of host range, phylogenetic relationships, genomic synteny, and effector profiles. Inoculation assays revealed a clear distinction in host range between the mitsuba, coriander, and celery isolates. Phylogenetic analyses based on the rDNA intergenic spacer and translation elongation factor sequences indicated a distant relationship between mitsuba isolates and those from coriander and celery. Whole-genome analysis based on high-quality de novo-assembled genomes, including telomere-to-telomere-level assemblies of isolates from mitsuba, coriander, and celery, showed that the mitsuba isolates possess conserved accessory chromosomal regions absent in celery and coriander isolates. Moreover, effector profiling identified a specific pattern of effector repertoires shared by the mitsuba isolates. These findings suggest that the host-pathogenic F. oxysporum isolates derived from mitsuba represent a forma specialis distinct from f. sp. apii. Thus, we propose designating the F. oxysporum isolates from mitsuba that cause Fusarium wilt as Fusarium oxysporum f. sp. crypti forma specialis nova.