No abstract

Unfamiliar necrotic symptoms on or within potato tubers of cultivars Nishiyutaka and Dejima were observed in Nagasaki prefecture, Japan, in 1992. Symptoms were typically on the surface of the tuber, which either protruded at first and then became sunken, or showed necrotic spots, with necrosis within the tubers. Symptoms sometimes appeared at harvesting but more often appeared after storage for several months. Investigations revealed that the causal agents of the disease were isolates of Potato virus Y necrotic strain (PVYNTN) and the disease was potato tuber necrotic ringspot disease (PTNRD), previously reported in Europe and Lebanon. Five potato cultivars were inoculated with an isolate from necrotic tubers. The highest percentage of progeny tubers showing PTNRD was found in cv. Nishiyutaka (23.3%). In contrast, cvs. Shima-bara, Mayqueen, and Danshaku showed a low percentage of PTNRD. Additional potato tubers with PTNRD were also observed after storage of the tubers. To investigate the relatedness between isolates of PVYNTN and of necrotic strain PVYN, previously isolated in Japan, Nishiyu-taka was inoculated with an isolate of PVYN, which also induced PTNRD. Nucleotide sequences of coat protein (CP) genes of six PVYNTN isolates were determined. The CPs were 267 amino acids in length, with a substitution of one or no amino acid among each of the six isolates. The phylogenetic relationship based on nucleotide sequences of CP genes showed that these six PVYNTN isolates clustered together with PVYN isolates. This is the first report of PTNRD caused by PVYNTN isolates in Asia.

The genetic structure of Potato virus Y (PVY) populations in Japan was analysed using 20 isolates; five were retrieved from the public DNA sequence databases, and an additional 15 complete genomic sequences were determined using field samples collected in Japan. Recombination and phylogenetic analyses of a total of 149 isolates from Japan and other countries showed that PVY has three major lineages (C, N and O); at least one, two and six sublineages in C, N and O lineages, respectively. One recombination pattern was newly found among Japanese PVY NTN strain isolates, which was most closely related to the PVY NTN strain isolates previously found in Europe and North America. On the other hand, PVY O was a complex of several divergent lineages, and there were at least three non-recombinant subpopulations in Japan. Studies on nucleotide diversities of populations and phylogenetic relationships of the isolates in the PVY sequences showed that Japanese PVY populations were in part distinct from the European and North American populations.

No abstract

A phytotoxin isolated from Calonectria ilicicola, the causal agent of soybean red crown rot, was identified as PF1070A, a cyclic peptide consisting of four amino acids. This compound is known as an antitumour antibiotic and to induce synthesis of metallothionein in mouse Ltk -cells. We tested PF1070A against three soybean cultivars that differ in susceptibility to C. ilicicola; however, there was no significant difference among their responses to the toxin. We determined the amount of PF1070A produced by 17 isolates of C. ilicicola, and found that there was a strong positive correlation between virulence and PF1070A production. Together, these results suggest that the phytotoxin PF1070A has a role in the virulence of C. ilicicola.Résumé: Une phytotoxine isolée chez Calonectria ilicicola, agent causal de la pourriture du collet chez le soja, a été identifiée en tant que PF1070A, un peptide cyclique constitué de quatre acides aminés. Ce composé est connu comme antibiotique antitumoral et il induit la synthèse de la métallothionéine dans les cellules Ltk -chez la souris. Nous avons testé PF1070A sur trois cultivars de soja de sensibilité différente à C. ilicicola. Toutefois, il n'y a pas eu de différence significative entre les réactions à la toxine. Nous avons déterminé la quantité de PF1070A produite par 17 isolats de C. ilicicola et nous avons trouvé qu'il y avait une forte corrélation positive entre la virulence et la production de PF1070A. L'ensemble de ces résultats suggère que la phytotoxine PF1070A joue un rôle dans la virulence de C. ilicicola.