VIEW ARTICLE

Comparative Specificity of the Toxins of Helminthosporium carbonum and Helminthosporium victoriae. Mong- shang Kuo, Graduate Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823, Senior Author is now Associate Professor, Department of Plant Pathology, Taiwan Provincial Chung-Hsing University, Taichung, Taiwan; O. C. Yoder(2), and R. P. Scheffer(3). (2)(3)Graduate Assistant and Professor, respectively, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Phytopathology 60:365-368. Accepted for publication 25 September 1969. DOI: 10.1094/Phyto-60-365.

A toxin preparation from Helminthosporium carbonum (HC) caused 50% inhibition of seedling root growth of a H. carbonum-susceptible corn hybrid at 1.0 µg/ml, but caused only 13% inhibition of a near-isogenic resistant hybrid at 25.0 µg/ml. This preparation stimulated root elongation of susceptible corn at 0.125 and resistant corn at 3.125 µg/ml. Inbred corn lines that are low, intermediate, or high in resistance to H. carbonum had the same relative rank in sensitivity to HC-toxin. Of several plant species tested (barley, corn, cucumber, oats, radish, sorghum, tomato, and wheat), susceptible corn was the most sensitive to HC-toxin, while resistant corn was among the most tolerant. The sensitivity of several nonhost plants fell between these extremes. In contrast, a preparation of H. victoriae (HV) toxin completely inhibited root growth of susceptible oats at 0.009 µg/ml, but caused only partial inhibition of resistant oats and other plants (tomato, corn, wheat, sorghum, and barley) at 3,600 µg/ml. Thus, resistant oats and other nonhost plants will tolerate > 400,000 times higher concentrations of HV-toxin than will susceptible oats. HV-toxin inhibited growth of nonhost plants about the same as did methionine.