VIEW ARTICLE

Comparative Effects of Host-Specific Toxins and Helminthosporium Infections on Respiration and Carboxylation by Host Tissue. Mong- shang Kuo, Graduate Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823, Senior author is current address: Professor, Department of Plant Pathology, Taiwan Provincial Chung-Hsing University, Taichung, Taiwan; R. P. Scheffer, Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Phytopathology 60:1391-1394. Accepted for publication 13 April 1970. DOI: 10.1094/Phyto-60-1391.

Oxygen uptake and CO₂ fixation in the dark were used as parameters to compare the response of corn to Helminthosporium carbonum (HC) and to its host-specific toxin. Further comparisons were made with the effects of H. victoriae (HV) toxin on susceptible oats. Helminthosporium carbonum infection and HC-toxin caused small increases in respiration of corn leaves. H. carbonum and its toxin, as well as HV-toxin, increased the capacity of susceptible tissues to fix CO₂ in the dark. Cell-free preparations from HC-toxin-treated corn leaves fixed more CO₂ with ribose-5-P as the substrate than did the control from nontreated tissues. No increase in CO₂ fixation was evident when HC-toxin was added to extracts from nontreated corn tissues. The data, plus previously published genetic studies, show that HC-toxin is as significant in pathogenesis and host-specificity of H. carbonum as is HV-toxin to H. victoriae.