Pythium helicoides is an important pathogen causing root rot of several crops, especially miniature rose and kalanchoe in ebb-and-flow irrigation systems that recycle nutrient solutions. In this study, we developed a PCR detection method with species-specific primers to determine sites inhabited by P. helicoides. The primers were designed based on the sequences of the internal transcribed spacer region of rDNA. The specificity of the primers was examined using 34 species and two groups of Pythium including P. helicoides, and three species in a closely related genus. The amplification with the primers detected only P. helicoides, confirming the specificity of the primers. The PCR amplified as little as 100 fg of genomic DNA of P. helicoides. When the PCR was used with naturally infested soil, the detection limit ranged from 14 to 35 cfu/g of dry soil. When this detection method was used to investigate location of P. helicoides in commercial production of miniature rose and kalanchoe, the pathogen was detected both inside and outside the greenhouses but not in the potting soil mixture, suggesting a different source other than potting soil for pathogen contamination. There are several sources of P. helicoides to contaminat clean plant, soil and the recycling nutrient solution during culture.
Application of AGREVO EX, a plant energizer made of yeast extract (YE), promotes root growth and suppresses plant diseases. Because no antimicrobial activity was found in the YE itself, YE induction of the plant's self-defense system has been suggested. To study the mechanism of enhanced disease resistance, the effect of YE on the expression of defense-related genes was analyzed in detached tobacco leaves. YE induced the expression of basic PR-1, -2, and -6 genes but not the acidic PR-1 gene. The YE solution itself produced ethylene, and ethylene emission from tobacco leaf discs was enhanced by the YE treatment. Also YE induced accumulation of PR-1, -2, and -3 proteins, and its suppression by treatment with silver thiosulfate (STS), which inhibits the perception of ethylene, suggesting the involvement of ethylene in YE-induced PR protein accumulation. The YE treatment did not induce resistance to Tobacco mosaic virus (TMV), but likely induced resistance to Ralstonia solanacearum and Rhizoctonia solani in tobacco plants, suggesting that YE may enhance resistance against necrotrophic pathogens.
Ornithogalum mosaic virus (OrMV) occurred in Akita Prefecture. An OrMV isolate obtained from a diseased O. thyrsoides could infect not only O. thyrsoides and O. dubium but also five dicot plants (Nicotiana clevelandii, Gomphrena globosa, Chenopodium amaranticolor, C. quinoa and Tetragonia tetragonoides). Another isolate from a diseased O. dubium, by contrast, was transmissible via sap inoculation to the two Ornithogalum plants but not to any dicot plants tested. The two isolates caused mosaic symptoms on the two Ornithogalum plants. This is the first report on the occurrence of OrMV in Japan.
Isolates of a Fusarium graminearum species complex causing Fusarium head blight on wheat and barley were collected from the western part of Japan in 2002, and their mycotoxin productivity on a rice medium for deoxynivalenol (DON), nivalenol (NIV), T-2 toxin and zearalenone (ZEA) was examined using liquid chromatography/mass spectrometry. Fifty-eight percent of the isolates produced more NIV than DON; none of the isolates produced T-2 toxin and 96% produced ZEA. Among nine selected NIV-producing isolates, eight were significantly more virulent than isolate H-3 of a highly virulent DON chemotype, and all the NIV-producing isolates produced NIV in wheat grains obtained from a field inoculation test.
An outbreak of a new fungal disease of poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) was recorded in Hyogo Prefecture (2003) in Japan and caused dark, gray necrosis on stem and wilt. The pathogen reproduced the original symptoms after inoculation of whole plant of poinsettia. Then it was identified as Phytophthora nicotianae van Breda de Haan (1896). The name Phytophthora blight of poinsettia, in Japanese “Eki-byo” is proposed for the disease.
A new disease of wax gourd (Benincasa cerifera Savi) characterized by scab of fruit was observed in Okayama Prefecture, Japan in July 2003. Fungal isolates frequently obtained from diseased fruits of the plants were identified as Rhizoctonia solani AG-4 HG-I based on hyphal anastomosis and cultural morphology. In inoculation tests, these isolates were pathogenic on fruits of wax gourd and caused the same symptoms, and were re-isolated from the lesions of the diseased fruits. This is the first report of a fruit disease of wax gourd caused by R. solani. Therefore, the name brown scab of wax gourd is proposed for the new disease.