ABSTRACT
The relationship between the nucleotide sequences of CYP51, its expression level and its sensitivity to ipconazole of Fusarium fujikuroi isolates were investigated. Single nucleotide polymorphisms (SNPs) were observed in the CYP51 of isolates with different sensitivities to ipconazole, but no amino acid substitution was detected in the putative amino acid sequence of the CYP51 protein. On the other hand, the expression of CYP51 was enhanced by the presence of ipconazole, and it tended to be higher in isolates with lower sensitivities and no gibberellin productivity. In the presumed promoter region, the upstream nucleotide sequence of CYP51, several common SNPs and insertions of nucleotides were detected in the lower sensitivity isolates. These results suggest that F. fujikuroi isolates consist of 2 different groups in sensitivity and gibberellin productivity, and no amino acid substitution in CYP51 protein may contribute to the stably high efficacy of ipconazole against rice Bakanae disease for more than 25 years.
ABSTRACT
Fusarium fujikuroi is a pathogenic fungus that infects rice. It produces several important mycotoxins, such as fumonisins. Fumonisin production has been detected in strains of maize, strawberry, and wheat, whereas it has not been detected in strains from rice seedlings infested with bakanae disease in Japan. We investigated the genetic relationships, pathogenicity, and resistance to a fungicide, thiophanate-methyl (TM), in 51 fumonisin-producing strains and 44 nonproducing strains. Phylogenetic analyses based on amplified fragment length polymorphism (AFLP) markers and two specific genes (a combined sequence of translation elongation factor 1α [TEF1α] and RNA polymerase II second-largest subunit [RPB2]) indicated differential clustering between the fumonisin-producing and -nonproducing strains. One of the AFLP markers, EATMCAY107, was specifically present in the fumonisin-producing strains. A specific single nucleotide polymorphism (SNP) between the fumonisin-producing and nonproducing strains was also detected in RPB2, in addition to an SNP previously found in TEF1α. Gibberellin production was higher in the nonproducing than in the producing strains according to an in vitro assay, and the nonproducing strains had the strongest pathogenicity with regard to rice seedlings. TM resistance was closely correlated with the cluster of fumonisin-nonproducing strains. The results indicate that intraspecific evolution in Japanese F. fujikuroi is associated with fumonisin production and pathogenicity. Two subgroups of Japanese F. fujikuroi, designated G group and F group, were distinguished based on phylogenetic differences and the high production of gibberellin and fumonisin, respectively.IMPORTANCEFusarium fujikuroi is a pathogenic fungus that causes rice bakanae disease. Historically, this pathogen has been known as Fusarium moniliforme, along with many other species based on a broad species concept. Gibberellin, which is currently known as a plant hormone, is a virulence factor of F. fujikuroi Fumonisin is a carcinogenic mycotoxin posing a serious threat to food and feed safety. Although it has been confirmed that F. fujikuroi produces gibberellin and fumonisin, production varies among strains, and individual production has been obscured by the traditional appellation of F. moniliforme, difficulties in species identification, and variation in the assays used to determine the production of these secondary metabolites. In this study, we discovered two phylogenetic subgroups associated with fumonisin and gibberellin production in Japanese F. fujikuroi.
