The phytopathogenic fungi Magnaporthe grisea and Alternaria alternata produce melanin via the polyketide biosynthesis, and both fungi form melanized colonies. However, the site of melanin deposition and the role of melanin in pathogenicity differ between these two fungi. M. grisea accumulates melanin in appressoria, and their melanization is essential for host penetration. On the other hand, A. alternata produces colorless appressoria, and melanin is not relevant to host penetration. We examined whether the melanin biosynthesis genes of A. alternata could complement the melanin-deficient mutations of M. grisea. Melanin-deficient, nonpathogenic mutants of M. grisea, albino (Alb-), rosy (Rsy-), and buff (Buf-), were successfully transformed with a cosmid clone pMRB1 that carries melanin biosynthesis genes ALM, BRM1, and BRM2 of A. alternata. This transformation restored the melanin synthesis of the Alb- and Buf- mutants, but not that of the Rsy- mutant. The melanin-restored transformants regained mycelial melanization, appressorium melanization, and pathogenicity to rice. Further, transformation of Alb- and Buf- mutants with subcloned ALM and BRM2 genes, respectively, also produced melanin-restored transformants. These results indicate that the Alternaria genes ALM and BRM2 can restore pathogenicity to the mutants Alb- and Buf-, respectively, due to their function during appressorium development in M. grisea.

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. IMPORTANCE Fusarium 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.

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A new virus disease occurred in tomato in Shizuoka and Aichi prefectures. The virus from Shizuoka was transmitted by Bemisia tabaci of B biotype, but not by sap. Its narrow host range was restricted to five species from two families. Geminate particles were observed in partially purified virus preparation from infected leaves of Datura stramonium. Specific DNA bands were detected from infected plants by polymerase chain reaction using two sets of primers designed for DNA A component of geminiviruses. The viruses from Shizuoka and Aichi had extremely high degrees of nucleotide sequence similarities (98%) with a mild isolate of tomato yellow leaf curl virus from Israel (TYLCV-Is-M). Their genomic organization of DNA A was the same as that of TYLCV. The amino acid sequence similarity between six ORFs of TYLCV-Is-M and the equivalent ORFs of the virus isolates from Shizuoka and Aichi was over 95%. From these results, the two virus isolates were identified as TYLCV and were closely related to TYLCV-Is-M from Israel. This report is the first on the occurrence of TYLCV in tomato in Japan.

We determined the complete nucleotide sequence of a potyvirus purified from a Japanese yam plant. The genomic RNA of this virus is 9,757 nucleotides (nts) in length, excluding the 3'-terminal poly(A) tail. It contains a single open reading frame (ORF) encoding a polyprotein of 3130 amino acids (aa) with a calculated Mr of 356,793. The genomic organization of this potyvirus is similar to that of other members of the genus Potyvirus and nine potential cleavage sites for the viral proteinase were found by comparison of its sequence with those available for other potyviruses. The nucleotide sequence and genome characteristics show that this isolate is a new potyvirus species. Its polyprotein differs substantially from Yam mosaic virus (YMV) (50% amino acid sequence identity) and fourteen other potyvirus species examined (44-59% identity). Although this potyvirus has been classified as YMV, our results suggest that the potyvirus infectious to the Japanese yam plant in Japan is distinct from YMV. Therefore, we propose that the Japanese yam potyvirus should be designated as Japanese yam mosaic virus (JYMV).