Japanese Journal of Phytopathology

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Inoculation tests using Mycopappus alni isolates, the frosty mildew fungus of Crataegus chlorosarca (Rosaceae), were performed for leaves of 21 tree species in 15 genera of Betulaceae, Rosaceae, Fagaceae, Juglandaceae and Hamamelidaceae. The M. alni isolate caused obvious lesions with propagules on leaves of 14 species in Betulaceae, Rosaceae, Juglandaceae and Hamamelidaceae, suggesting its pathogenicity to those species. In Fagaceae, the isolate caused lesions on leaves of Fagus crenata and Castanea crenata, suggesting its pathogenicity to both species. However, the virulence of the isolate to those species is thought to be weak because formation of the lesions and propagules was less frequent than species in other families. The isolate caused no lesion on leaves of Quercus spp., suggesting no pathogenicity to Quercus species. Microscopic observations revealed that the fungus invades C. chlorosarca leaves through stomata.

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To create a new biological control technique for a necrotic spot disease on melons caused by Melon necrotic spot virus (MNSV), we screened bacteria collected from the soil of melon-cultivated fields for antagonism against the viral fungus vector, Olpidium bornovanus. The protective efficiency against O. bornovanus infection of melon roots and degree of suppression of MNSV accumulation in plants was evaluated. Strain BS-242 the best antagonist throughout these screenings, was identified as a new species of Bacillus sp., based on several biological properties and identity of its 16S rDNA sequence.

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We developed a new method to detect Acidovorax avenae subsp. citrulli in watermelon seeds, by modifying the membrane filter immunostaining method, which was developed to detect Burkholderia glumae in rice seeds. The detection threshold of this new method for A. avenae subsp. citrulli was several cfu per 100 ml phosphate buffer using 1000 commercial watermelon seeds. Living cells of A. avenae subsp. citrulli could be obtained by stamping the membrane on selective medium plate before immunostaining.

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Dieback of young shoot tips of olive (Olea europaea) have been observed frequently in recent years in orchards on Shodoshima Island, Kagawa Prefecture. The symptoms often develop on the entire branch and cause branch dieback. The major microbes isolated from the symptoms were Colletotrichum species, and C. acutaum Simmonds ex Simonds was frequently isolated. Inoculation with C. acutatum reproduced the same symptoms on olive shoots, and the fungus was reisolated from the symptoms, indicating that the causal agent is C. acutaum.

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