補植苗の葉いもち病勢進展過程からみた全般発生開始期の予測

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Rice leaf blast, caused by Pyricularia grisea, usually starts in a region with a general leaf blast epidemic. Most(if not all)inoculum sources are believed to come from infected seedlings which are left in mats in the fields and used to fill vacant space in rows after mechanical transplanting. We determined the conditions that promote leaf blast within a seedling mat and the threshold level of disease severity in the mat that leads to general epidemics in a region. When the mat contained a few seedlings infected with the blast fungus, waves of newly infected seedlings appeared at several-day intervals across a mat. Each wave was caused when favorable conditions for infection occurred ; this was determined by the length of the leaf wetness period and the temperature during the period. The leaf wetness period for infection began when it rained and continued until total cumulative solar radiation had reached 5.9MJ/m^2. The criterion to judge whether or not an infection occurred during a leaf wetness period was based on the ratio of the actual percentage of fungal penetration for a given leaf wetness period and the potential percentage of fungal penetration over a long enough time at a given temperature. When this ratio exceeded 0.1, the conditions were favorable for infection. Diseased mats can play a role as a potential inoculum source for general epidemics of leaf blast, when the disease severity within the mat is greater than a certain threshold, which in this study was when 90cm^2 of the leaves in a mat were dead.
2001-08-25

著者

原澤良栄
新潟県農業総合研究所作物研究センター

補植苗の葉いもち病勢進展過程からみた全般発生開始期の予測

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