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Of the 1,200 single spore isolates of Alternaria mali causing apple leaf spot and fruit decay, the mycelial colonies showed 76, 96 and 15% growth at 100,000 ㎍/㎖ of captafol, chlorothalonil and folpet, respectively, and five and three percent growth at 10,000 ㎍/㎖ of iprodione and polyoxin. These isolates showed cross-tolerance of mycelial growth, spore formation, or spore germination to the above five fungicides plus captan, garbenda, and thiophanate methyl. Captafol, mancozeb, polydong, and propineb did not show any cross-tolerance of spore germination since no spore was germinated at 100 ㎍/㎖ which was much lower than the concentration used by apple growers. Benomyl, fenarimol, oxidong, and triademefon showed medium degree of cross-tolerance of the fungal growth, spoculation, and spore germination.
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