ベトナムの主要な2つの稲作地帯,Red River Delta(北部)およびMekong River Delta(南部)から採集したイネいもち病菌計78菌系を用いて,両地域における本病菌の個体群構造を比較検討した。レトロトランスポゾンMAGGYをプローブとしたDNAフィンガープリンティングの結果,北部の菌株は4つのリネージ(VL1-VL4)に分かれたが,南部の菌株はこれらとは異なる単一リネージ(VL5)に分類された。このことから,北部の個体群の方が遺伝的多様性に富むことが示唆された。さらに,判別品種を用いた病原性検定の結果,両集団におけるレース構成は大きく異なり,共通のレースは見いだされなかった。以上のことから,遺伝的にも病原性においても両個体群の構造は大きく異なることが示唆された。
We investigated the distribution of Kouyawarabi plants (Onoclea sensibilis L.) infested with Pseudomonas plantarii in Yamagata prefecture and confirmed survival activity of the overwintered bacterium in the plants. Of 239 samples collected from 19 locations in the prefecture, 77 leaf samples were infested with the bacterium. The leaf samples collected from Mogami-machi were highly infested with P. plantarii. High infestation rate of bacterial seedling blight of rice was also observed in Mogami-machi area. The plants were artificially inoculated with the organism and exposed outdoors in summer. In the following spring, the bacteria were re-isolated from the leaves, stems and rhizomes of the plants. The pathogenic bacteria were successfully re-isolated from the overwintered whole plants at the level of 1.2×104-3.4×106cfu/g. Because the organism appears to survive in Kouyawarabi plants under natural conditions in Yamagata prefecture, the plants are considered to be an important infection source of the disease.
In November 1997, prairie gentian plants with necrotic yellow symptom were found in Iwate Prefecture, Japan. A spherical virus with a diameter of ca. 80nm was isolated. The virus infected 22 plant species of 11 families after mechanical inoculation. By serological tests, the virus was closely related to tomato spotted wilt virus (TSWV). In RT-PCR with TSWV specific primers, a fragment of about 550bp was amplified. The fragment had a high degree of sequence homology to TSWV-RNA. Based on these results, the virus isolated from prairie gentian was identified as TSWV. This is the first report of TSWV on prairie gentian in Japan.
Detection of Japanese yam mosaic potyvirus (JYMV) in Chinese yam (Dioscorea opposita Thunb. cv. ichoimo) by the immunocapture polymerase chain reaction (IC-PCR) and differentiation of virulent and attenuated isolates using restriction fragment length polymorphism (RFLP) of IC-PCR products using Tsp 509 I were investigated. JYMV was detected by IC-PCR from diseased leaves, bulbils, tubers or diseased leaves frozen at -40°C for 6 months with a sensitivity of 108, 105, 106 and 107-fold dilutions, respectively. The sensitivity of IC-PCR for the detection of JYMV from diseased leaves was about 8000-fold over ELISA and 10, 000-fold over RT-PCR. PCR-RFLP revealed different banding patterns for the virulent and attenuated isolates of JYMV. This will be useful for distinguishing virulent and attenuated isolates from Chinese yam (cv. ichoimo).
A vascular wilt disease of sunflower (Helianthus annuus L.) caused by Verticillium sp. was found in Hokkaido Prefecture, Japan, in 1996 and 1997. The diseased plants showed symptoms of wilting, leaf chlorosis, defoliation, stunting and vascular discoloration of the stem. Based on size of conidia, morphological characteristics of microsclerotia and extracellular polyphenol oxidase activity, the Verticillium wilt pathogen of sunflower belongs to Verticillium dahliae Klebahn.