Mode of Action of Pefurazoate against “Bakanae” Disease Caused by Fusarium moniliforme

Abstract

Pefurazoate was highly effective against major rice seed-borne diseases including “Bakanae” disease (Fusarium moniliforme), Helminthosporium leaf spot (Cochliobolus miyabeanus) and blast (Pyricularia oryzae) as a seed disinfectant. The mode of action of the compound against “Bakanae” disease was investigated with reference to relationship between deposit of the compound on and in whole seeds (unhulled rice) and translocation into grains. This fungicide was systemically active and translocated from surface of seed to its interior very rapidly, and the amount of compound translocated into grains was greatly exceeded the concentration range of MIC values against F. moniliforme. On the other hand, whole seeds and hulled rice grains were placed on PDA medium, and pathogenic fungus was isolated. From the whole seeds, the pathogenic fungus was not isolated at all, but from hulled rice grains it could be isolated with frequencies about 10%. When the paper disks containing hyphae of F. moniliforme were treated with this fungicide, the result was similar to that obtained with infected seeds. From these facts, the antifungal action of pefurazoate was considered to be fungistatic as in the case of benomyl. However, mycelia treated with pefurazoate were remarkably suppressed their growth in compared with benomyl when the paper disks were washed after soaking in the fungicides solution. The stable effect of pefurazoate was considered due to a large amount of active ingredient deposited on and in the seeds, which will act as a barrier against further developing of pathogenic fungus surviving in the grains.