Relationship Between Polygalacturonase Activity and Cultural Characteristics of Verticillium Isolates Pathogenic in Cotton. M. V. Wiese, Technician, Department of Plant Pathology, University of California, Davis 95616, Senior author’s current address: Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823.; J. E. DeVay(2), and A. V. Ravenscroft(3). (2)(3)Professor, and Technician, respectively, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 60:641-646. Accepted for publication 3 November 1969. DOI: 10.1094/Phyto-60-641.
Analyses were made of the pectic enzymes produced in vitro by isolates of Verticillium that differed in virulence in cotton, Gossypium hirsutum cultivars ‘Acala 4-42’ and ‘Deltapine Smoothleaf’. A single predominant pectic enzyme, endopolygalacturonase (PG), was detected in dialyzed culture liquids of a severe and two intermediate isolates of V. albo-atrum and a mild isolate of V. nigrescens grown in standing culture on pectin-glucose-potato broth. Regardless of virulence, culture age, pH, composition of the medium, or method of enzyme preparation, lyases, pectinmethylesterase, and other pectic hydrolases were present only in trace quantity or not detected. Among the four isolates, PG activity was inversely correlated with virulence, and when tests were expanded to include 25 additional isolates of V. albo-atrum, the relative activity of PG per µg protein averaged 3.09, 1.40, and 0.99 in eight mild, 13 intermediate, and eight severe isolates, respectively.
Mild isolates were principally mycelial, whereas severe isolates developed black microsclerotial colonies on potato-dextrose agar. In liquid culture, none of the 29 isolates produced microsclerotia. Mycelial variants obtained from a severe microsclerotial isolate showed a six-to-tenfold increase in PG activity, and a concomitant, but not proportional, decrease in virulence. The mycelial variants, like their severe microsclerotial parent, still caused the defoliation of infected plants, though the defoliation rate was significantly reduced.
Peroxidase and polyphenol oxidase were not detected in culture liquids of sclerotial or mycelial isolates. Polyphenol oxidase and, especially, peroxidase were present in cotton stem tissues and vascular fluids, but were unaffected by disease development or symptom severity. Preparations from healthy and Verticillium -infected plants exhibited only traces of PG activity.