State of emergence and control measures for benzimidazole-resistant Pestalotiopsis eriobotrifolia and Pestalotiopsis neglecta, the causal fungi of loquat gray leaf spot
2002
Komine, M. (Nagasaki-ken. Fruit Tree Experiment Station, Omura (Japan)) | Souda, E. | Nakamura, Y.
A study on benzimidazole-resistant strains of Pestalotiopsis eriobotrifolia and Pestalotiopsis neglecta, the causal fungi of loquat gray leaf spot was conducted based on field surveys in order to identify the state of emergence,mechanism of resistance,and control measure. 1 . Assuming that fungi whose hyphae can grow at a benomyl concentration of 100 ppm are considered as benomyl-resistant fungi,it was confirmed that benomyl-resistant fungi emerged in about half of all the fields of loquat in the Mogi District in Nagasaki City,and that such fungal strains amounted to about 40 %. 2 . The majority of the bebomyl-resistant fungal strains presented high resistance,and their hyphae could grow at a benomyl concentration of even 1000 ppm. 3 . It was found that the benomyl-resistant fungal strains had undergone amino acid substitution due to the occurrence of point mutation of genes in the microtubule protein (beta tubulin) that is the site of action of benzimidazole chemicals. 4 . Benomyl-resistant fungal strains comprised both diethofencarb-resistant strains and diethofencarb-sensitive strains. 5 . Both the iminoctadine albesilate chloride water-dispersible powder and the fluazinam water-dispersible powder at low concentrations suppressed the growth of hyphae of the benomyl-resistant fungal strains cultured in a PDA medium. 6 . In the fields where benomyl-resistant fungi are predominant, the iminoctadine albesilate chloride water-dispersible powder had a higher effect of fungal control than the thiophanate-methyl water-dispersible powder.
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