Biorational potential, pectinase activity, and correlations to virulence among isolates of Chondrostereum purpureum
Date
1997
Authors
Rathlef, Sean
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Abstract
The basidiomycete Chondrostereum purpureum is a white-rot fungus which is pathogenic to many deciduous species including poplar, maple, and alder. A phytotoxin activity assay was developed to assist in developing C. purpureum as a weed biocontrol agent. Analysis of small mass toxins produced by C. purpureum was carried out utilizing several techniques. An important consideration in the development of a mycoherbicide is the elucidation of phytotoxic factors involved in the pathogenic process. Many plant pathogenic fungi are known to secrete lipid soluble toxins which break down cell membrane stability causing host cell necrosis and helping the pathogen to establishing disease. Though no dominant phytotoxic chemical (or chemical group) was readily detected within culture filtrates of the fungus, small mass toxins were confirmed to be produced. Through the use of an excised leaf disk assay and an electrolyte leakage assay, foliage active phytotoxins were detected in ethyl acetate extracts of C. purpureum-conditioned media. There was an apparent decrease in overall activity when phenolic fractions were purified. The amount of small mass toxins detected in various isolates of C. purpureum did not appear to vary.
Chondrostereum purpureum also produced a pectin degrading enzyme known as ndopolygalacturonase. Endopolygalacturonase has been shown to be a key enzyme in the degradation of plant cell walls, and is the causal agent of silver leaf disease. Pectinases produced by the fungus, like endopolygalacturonase, were shown to play a major role in the phytotoxicity of C. purpureum. Using leaf disk, electrolyte leakage, and viscosity assays, pectinase production by several isolates of the fungus was measured, and the pectinase levels were found to be correlated to virulence of these isolates towards red alder saplings. There was a strong correlation between pectinase activity of various isolates of C. purpureum and the initial slopes of the mortality rates by these same isolates (P-value = 0.0306 by ANOV A). Of twelve selected isolates of C. purpureum, the ones that produced higher levels of pectinases in liquid culture were also more virulent in greenhouse pathogencity tests.