Ascospore dimorphism-associated mating types of Sclerotinia trifoliorum equally capable of inducing mycelial infection on chickpea plants

Abstract

In many heterothallic fungal pathogens, mating types are found to be associated with variation in virulence and some other ecological traits. Sclerotinia trifoliorum is unique from other Sclerotinia species in that it is heterothallic with two mating types. The mating type gene has pleotropic effect on ascospore size; large ascospore isolates are phenotypically homothallic (L-type), and small ascospore isolates are heterothallic (S-type). The possible association of variation in virulence with the two mating types and hence the ascospore size in S. trifoliorum is investigated using isolates collected from naturally infected chickpea plants and isolates generated from controlled crosses. Chi-square tests showed that 57 field isolates collected from crown lesions (infection initiated by mycelium) had a 1:1 distribution of L-type (29 isolates) and Stype (28 isolates), whereas 14 isolates from stem lesions (infection initiated by ascospores) had a distribution of 10 L-type isolates and 4 S-type isolates not significantly different from 1:1. Greenhouse tests using mycelial plugs as inoculum of field and laboratory-derived isolates did not show significant difference between the two mating types in causing stem rot of chickpea. The sample size of ascosporeinitiated infection was small, and the controlled pathogenicity assays in the greenhouse only tested mycelial infection. Thus, whether the two types of ascospores have equal capability of infecting chickpea remains to be further investigated. Strong evidence of both field and greenhouse data showed that mycelia of both mating types of S. trifoliorum were equally capable of infecting chickpea.

Genetic Diversity and Mating Type Distribution of Tuber melanosporum and Their Significance to Truffle Cultivation in Artificially Planted Truffiéres in Australia

“…The only scenario where competition would be likely is if MAT1-1-1 is associated with a functional trait (linked to a gene under selection), rendering MAT1-1-1 strains with a higher fitness. Mating type genes in heterothallic fungi, in addition to their primary functions in sexual compatibility, rarely are associated with ecological and life history traits (18). However, none of these associations were ever shown to impact mating type distribution, i.e., they do not provide a competitive advantage.…”

Characterization of Kazachstania slooffiae, a Proposed Commensal in the Porcine Gut

“…As with other types of spores, ascopores are utilized for survival and dispersion [ 40 ], and other Kazachstania species have been found to form ascopores [ 41 ]. Ascopores formed by other fungal species have demonstrated their contribution to virulence, especially in causing diseases of plants [ 42 , 43 , 44 ], but they have also been found to assist in survival through the gastrointestinal tract of Drosophila [ 45 ]. Other microbes rely on sporulation to survive gut conditions [ 46 ]; therefore, ascopore formation cannot be ruled out as an important factor for K. slooffiae .…”

Genotypic variation and population structure of Sclerotinia trifoliorum infecting chickpea in California

“…Unlike S. sclerotiorum , sclerotia of S. trifoliorum can germinate carpogenically without preconditioning of cooling (Njambere et al ., ). Mycelia of both the small‐ and large‐sized ascospores are equally capable of initiating infection on chickpea (Njambere et al ., ). In nature, sclerotia of S. trifoliorum form apothecia almost exclusively in the autumn, consistent with the fact that they can germinate carpogenically without preconditioning of cooling, whereas apothecia of S. sclerotiorum are formed mainly in the spring (Williams & Western, ; Yli‐Mattila et al ., ).…”

“…Knowledge of genetic and pathogenic variation in chickpea will be helpful in selecting representative isolates for controlled screening and to devise strategies for managing Sclerotinia stem and crown rot on chickpea. Previous studies have looked at pathogenic variation associated with ascospore size‐associated mating types (Njambere et al ., ). Here, genetic diversity and population structure of S. trifoliorum infecting chickpea is reported.…”