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Physiology and Biochemistry

Heat- and Aging-Induced Tolerance of Sorghum and Oat Tissues to Host-Selective Toxins. Charlotte R. Bronson, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824; Robert P. Scheffer, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824. Phytopathology 67:1232-1238. Accepted for publication 24 March 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1232.

Intact sorghum seedlings were held at high temperatures (37/30 C, day/night) and the roots were exposed to host-selective toxin from Periconia circinata. After 4 days, the plants had no visible symptoms, whereas toxin-treated plants at 22 C were dead. Assays based on net electrolyte losses from tissues showed that intact plants given brief thermal treatments were highly resistant to toxin, and that full sensitivity was regained within 3 days. Excised sorghum leaves pretreated in water at 35, 40, and 45 C for 15, 4.5, and 0.8 min had 50% as much toxin-induced loss of electrolytes as did controls exposed to water at 22 C. Prior thermal treatments also prevented toxin-induced increases in tissue respiration. Inoculated plants failed to develop symptoms at 37/30 C. Within 3 hr after excision, sorghum leaves at 22 C had 50% as much toxin-induced leakage of electrolytes as did freshly-cut leaves, and by 24 hr excised leaves leaked very little in response to toxin. Toxin sensitivity of excised sorghum leaves was maintained by treatment with kinetin (10^–4M). Excision and aging did not reduce sensitivity of oat leaves to toxin from Helminthosporium victoriae, although sensitivity was lost after thermal treatments; longer exposure times or higher temperatures were needed to reduce toxin-induced losses in oats than in sorghum. The data are useful for design of toxin assays and may contribute to an understanding of the seasonal development of Periconia blight.