Variations and correlations within and between morphology, pathogenicity, and pectolytic enzyme activity in Sclerotinia from Saskatchewan

Abstract

One hundred and fourteen isolates of Sclerotinia from 23 different hosts in many parts of Saskatchewan were grouped, according to their morphology, on minimal medium. Two types of seedling pathogenicity tests on six host species were conducted on at least one isolate from each morphological group and one from each host species. A total of 38 isolates was tested. Assays for pectolytic enzyme activities of the same 38 isolates were done using a defined medium, and Swede turnip and carrot tissue as substrates. Polygalacturonase, pectin transeliminase, and pectin methylesterase were all tested. The results showed that an endopolygalacturonase was probably the most prevalent enzyme. Some isolates also produced exopolygalacturonase and pectin methylesterase, but pectin transeliminase was never detected. There was no correlation between pathogenicity of the isolates and their enzyme activities in vitro or in vivo, suggesting that pectolytic enzymes are not responsible alone for pathogenicity. Agglomerative classification was used to demonstrate relationships between the isolates. However, the isolates did not fall into discrete groups based on morphological, pathological, physiological, or even combined characteristics. Neither were there clear host or geographic associations. This continuous variation rather than a segregated population is consistent with Purdy's "broader concept of the species S. sclerotiorum."

Pathogenicity of morphologically different isolates of Sclerotinia sclerotiorum with Brassica napus and B. juncea genotypes

“…However, similar differences among S. sclerotiorum isolates have been reported by other workers even where a larger number of isolates were investigated (e.g., Riddle et al 1991;Ekins et al 2007;Morrall et al 1972). While variations in pathogenicity have been reported among isolates, the differences did not justify grouping of S. sclerotiorum isolates on the basis of their pathogenicity.…”

“…While variations in pathogenicity have been reported among isolates, the differences did not justify grouping of S. sclerotiorum isolates on the basis of their pathogenicity. This is further supported by the observations of Melzer and Boland (1996) working on lettuce and Morrall et al (1972) on 23 different hosts, who defined a 'continuum' (in contrast to distinct categories) in the pathogenicity of this pathogen. Even where significant differences in pathogenicity among isolates of this pathogen occur, their responses were found to be overlapping (e.g., Riddle et al 1991;Ekins et al 2007).…”

“…There are very few published reports of significant genotype × S. sclerotiorum interactions of the type we observed in our study, probably because in most of previous studies either more isolates were included but with only a very small number of genotypes or viceversa (e.g., Riddle et al 1991;Ekins et al 2007;Morrall et al 1972;Auclair et al 2004;Pratt and Rowe 1995). It is interesting that no significant interaction was observed between Glycine max and S. sclerotiorum isolates (Auclair et al 2004) in Canada where five host cultivars and four pathogen isolates were involved or with five isolates and seven alfalfa cultivars (Pratt and Rowe 1995) in the USA.…”

Mycelial compatibility groups in Buenos Aires field populations of Sclerotinia sclerotiorum (Sclerotiniaceae)

“…Errampalli and Kohn (1995) did not find any correlation between pectic zymograms and 15 MCGs and Kull et al (2001) and Ekins (1999) observed that MCGs did not vary in aggressiveness. Even isolates that had been single-ascospore cultures from the same sclerotium were quite different with respect to their morphological, physiological and pathological characteristics (Morrall et al 1972). Furthermore, considerable variation in cultural morphology and aggressiveness was observed among protoplast-regenerated isolates of S. sclerotiorum, as compared with the isolates from different sources (Boland and Smith 1991).…”

Case Study: Sclerotinia sclerotiorum: Genetic Diversity and Disease Control

“…Also, at least part of the resistance to S. sclerotiorum infection among lines of the scarlet runner bean (Phaseolus coccineus) could be attributed to differences in oxalate sensitivity (Chipps et al, 2005). Nonetheless, variation in these factors does not appear to be the primary determinant of pathogenicity as correlations have not always been apparent (Morrall et al, 1972). As an example, in S. trifoliorum, a degenerative non-virulent isolate of the pathogen produces more proto-pectinases than a normal string, but only the normal isolate secretes a toxin and is considered virulent (Held, 1955).…”