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This article in JEQ

  1. Vol. 1 No. 3, p. 244-249
    Received: Dec 13, 1971

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Southern Leaf Blight of Corn—Present Status and Future Prospects1

  1. A. L. Hooker2



Two races, T and O, of Helminthosporium maydis Nisikado & Miyake cause southern blight of corn (Zea mays L.). The new race T spread widely in the USA in 1970 and to a lesser extent in 1971. It produces a pathotoxin specific to cms-T cytoplasm of corn plants and infects the leaf, leaf sheath, husk, and ear parts. Race O, normally confined to the warmer parts of the USA, does not produce a specific pathotoxin and infects leaves primarily. Other races may exist or appear in the future.

Resistance to race O is based on nuclear genes, and in most sources is quantitative in expression and polygenic in inheritance; one source with recessive gene inheritance expresses chlorotic lesions with reduced fungus sporulation. Resistance to race T is both cytoplasmic and nuclear. Normal cytoplasms and many cytoplasms for male-sterility such as the cms-C and cms-S types are highly resistant in the field. Resistance in cms-T cytoplasm is partial and probably due to the same nuclear genes that give resistance to race O.

A diversity of cytoplasms within hybrids and the selection of high levels of nuclear-gene resistance in a stalk rot resistant background are suggested as breeding and seed production objectives.

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