Pathological and Physiological Identification of Race C ofBipolaris maydisin China

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Abstract
Five of 116 isolates of Bipolaris maydis collected from diseased corn (Zea mays) leaves in 12 provinces in China induced significantly larger lesions on leaves of inbred lines of corn with cms-C than on leaves of the same lines with CMS-T, cms-S, or normal (N) cytoplasm. The greater virulence to plants with cms-C was observed both in seedlings in the greenhouse and in adult plants inoculated in the field. The isolates with virulence specific to cms-C Z. mays are designated race C, a new race of B. maydis. Crude preparations race C toxin were obtained by chloroform extraction from filtrates of 2-wk-old cultures of race C in Czapek''s solution. Treatment of leaf sections with C-toxin at 1,000 .mu.g/ml greatly increased the rate and total amount of electrolyte leakage from leaves of cms-C but not cms-T, cms-S, or N cytoplasm.C toixin was also significantly enhanced activity of phenylalanine ammonia-lyase in treated tissue of cms-C but not cms-T, whereas T toxin from race T enhanced activity in material of cms-T but not cms-C. Viscosity of cytoplasm indicated by time of centrifugation required for displacemnet of chloroplasts in subepidermal cells of Z. mays coleoptiles was reduced in plants of cms-C by C-toxin and in plants of cms-T by T-toxin, but not vice versa. Thus, the evidence from several physiological and pathogenicity tests supports the designation of race C as a new race of B. maydis, which produces a toxin specifically active against Zea mays lines with cms-C.