Many small brownish lesions develop over entire leaf 20-50 days after sowing. Two defense-related genes, PBZ1 and PR1, activated in leaves; high expression of PBZ1 correlated with lesion formation. Levels of momilactone A, a major phytoalexin of rice, increased approximately 100- to 400-fold relative to wild type levels. Suspension-culture cells of cdr1 produced higher levels of H2O2 than those of wild type when treated with calyculin A, an inhibitor of protein phosphatase 1. Thus, biochemical lesions of cdr1 may exist in early signaling steps that lead to activation of NADPH oxidase, and type-1 protein phostphatase may be operative in protein dephosphorylation involved in NADPH oxidase activation.