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Published in Crop Sci 15:385-389 (1975)
© 1975 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Effect of Helminthosporium maydis, Race T, Pathotoxin on Growth and Ribonuclease Levels of Corn Roots1

C. M. Wilson and G. A. Apel2

The growth of corn (Zea mays L.) roots with Texas male-sterile cytoplasm is inhibited by. a pathotoxin produced by race T of Helminthosporium maydis Nisik. and Miyake. Application of toxin solutions to the primary root tip for only 20 rain was enough to inhibit root growth. This inhibition formed the basis for a rapid semi-quantitative toxin assay requiring only small volumes of toxin solution. Also, the geotropic response of roots was affected by the toxin.

Changes in ribonuclease (RNase) activity of toxintreated roots were studied to determine whether or not the known corn RNase could be specifically implicated in the processes leading to inhibition of growth. The RNase activity of inhibited root tips was greatly increased over that of untreated controls, but only when growth was drastically reduced. The increase in RNase was concluded to be a secondary reaction occurring after the toxin had damaged the growing regions of the root. Tests for the specific nucleases in corn roots did not detect appreciable differences in the relative amounts of the different enzymes; all increased together. RNase increased in the terminal 15 mm of the tip; the increase could be detected within 6 hours after a brief treatment of the tip with pathotoxin.

Key Words: Zea mays L. • Southern corn leaf blight • Toxin assay

1 Cooperative investigations of the ARS, USDA, and the Dep. of Agron, U. of Ill., Urbana. Portions of this paper were submitted by the junior author in partial fulfillment of the requirements for the M.S. degree.

2 Research chemist, ARS, USDA, and former graduate research assistant, respectively, Dept. of Agron., U. of Ill., Urbana, IL 61801.

Received for publication May 11, 1974.




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