Wheat yellow mosaic virus (WYMV) is a soilborne virus transmitted by Polymyxa graminis. Experimental data suggested the occurrence of WYMV strains in Japan. Based on their susceptibility to Japanese isolates WYMV-M and WYMV-T, three wheat cultivars Nanbukomugi, Fukuhokomugi and Hokkai 240 were selected as differential cultivars. Nanbukomugi is susceptible to both WYMV-M and WYMV-T. Fukuhokomugi is susceptible to WYMV-T and resistant to WYMV-M. Hokkai 240 is resistant to both isolates. WYMV isolated from wheat fields in Japan and from virus-infested fields of the wheat breeding programs were grouped into three pathotypes based on their infectivity on the differential cultivars. Type I, represented by WYMV-T and mainly isolated from west and central part of Japan, infects Fukuhokomugi and Nanbukomugi, type II, represented by WYMV-M and mainly isolated in northern Japan, infects only Nanbukomugi; and type III, isolated in Fukuoka Prefecture, infects all three differential cultivars. The differential cultivar set is available for breeding programs of WYMV-resistant wheat cultivars in Japan.
We investigated the vertical distribution of Pot2 genotypes of Pyricularia grisea by means of rep-PCR fingerprinting and pathogenic races of rice blast fungus within a diseased rice hill in a paddy field in two geographically separated areas in the Shonai district of Yamagata Prefecture, Japan. Four rice hills with rice cv. Haenuki, 2 rice hills from each paddy field were examined. Three monoconidial isolates of the rice blast fungus were obtained from each lesion on leaf blades 7 and 10, the flag leaf, panicle neck, and rice husks and then analyzed. There were multiple Pot2 genotypes of this fungus on all rice hills tested. Four and two kinds of genotypes were identified from the two respective rice hills in one area, and four and seven genotypes the two respective hills in the other area of paddy field. Generally, the Pot2 genotypes of the isolates from panicle tissue tended to be more diverse than those from the lesions on lower leaf tissues. With respect to race, all the isolates from each lesion on three of four rice hills were identified as one pathogenic race, 007.0. However, the isolates from another rice hill comprised two races, 007.0 and 037.1.
From diseased leaves of Lisianthus plants [Eustoma grandiflorum (Raf.) Shinn.] with necrotic stunt symptoms Nagano and Shizuoka prefectures in Japan, we isolated two viruses with a diameter of ca. 30 nm and tentatively named them Nag-4 and Shiz-1, respectively. Both viruses reproduced necrotic spots on healthy lisianthus plants after mechanical inoculation. Based on virion morphology, double-stranded RNA analysis, molecular mass of the coat protein (CP) and serological tests, the viruses were closely related to species in the genus Tombusvirus. In a comparison of the amino acid sequence of the CP genes, Shiz-1 had high identity with that of Tomato bushy stunt virus-nipplefruit strain (TBSV-Nf), whereas Nag-4 shared less than 87% identity with sequences reported for tombusviruses, suggesting that the virus might be a new species in the genus Tombusvirus. This is the first report of tombusvirus disease on lisianthus in the world.
A new bacterial disease was observed on leaves of broccoli (Brassica oleracea L. var. italica Plen.) in a field in Gunma Prefecture, Japan in 2001. The causal agent was identified as Xanthomonas campestris pv. campestris (Pammel 1895) Dowson 1939. Healthy seedlings were inoculated with the isolated bacterium, symptoms of the disease were reproduced, and the bacterium was reisolated from the margin of lesions on the leaves. We propose the name black rot of broccoli for the disease.