Evidence for Genetic Similarity of Vegetative Compatibility Groupings in Sclerotinia homoeocarpa

Abstract

Vegetative compatibility groups (VCGs) are determined for many fungi to test for the ability of fungal isolates to undergo heterokaryon formation. In several fungal plant pathogens, isolates belonging to a VCG have been shown to share significantly higher genetic similarity than those of different VCGs. In this study we sought to examine the relationship between VCG and genetic similarity of an important cool season turfgrass pathogen, Sclerotinia homoeocarpa. Twenty-two S. homoeocarpa isolates from the Midwest and Eastern US, which were previously characterized in several studies, were all evaluated for VCG using an improved nit mutant assay. These isolates were also genotyped using 19 microsatellites developed from partial genome sequence of S. homoeocarpa. Additionally, partial sequences of mitochondrial genes cytochrome oxidase II and mitochondrial small subunit (mtSSU) rRNA, and the atp6-rns intergenic spacer, were generated for isolates from each nit mutant VCG to determine if mitochondrial haplotypes differed among VCGs. Of the 22 isolates screened, 15 were amenable to the nit mutant VCG assay and were grouped into six VCGs. The 19 microsatellites gave 57 alleles for this set. Unweighted pair group methods with arithmetic mean (UPGMA) tree of binary microsatellite data were used to produce a dendrogram of the isolate genotypes based on microsatellite alleles, which showed high genetic similarity of nit mutant VCGs. Analysis of molecular variance of microsatellite data demonstrates that the current nit mutant VCGs explain the microsatellite genotypic variation among isolates better than the previous nit mutant VCGs or the conventionally determined VCGs. Mitochondrial sequences were identical among all isolates, suggesting that this marker type may not be informative for US populations of S. homoeocarpa.

Distribution of active ingredients of a commercial aflatoxin biocontrol product in naturally occurring fungal communities across Kenya

“…Simple sequence repeats (SSR) are effective at differentiating genotypes of A. flavus (Grubisha and Cotty, 2015; Picot et al ., 2018; Senghor et al ., 2020). Fungal VCGs frequently contain multiple closely related SSR haplotypes (Berbegal et al ., 2010; Chang et al ., 2014). SSR markers are valuable tools for genotyping A. flavus from agricultural (Tran‐Dinh et al ., 2009; Grubisha and Cotty, 2010, 2015; Sweany et al ., 2011; Ortega‐Beltran et al ., 2020) and clinical settings (Hadrich et al ., 2010; Dehghan et al ., 2014).…”

Something in the agar does not compute: on the discriminatory power of mycelial compatibility in Sclerotinia sclerotiorum

“…Mycelial compatibility in S. sclerotiorum is considered by some to be synonymous with vegetative compatibility (Kohn et al 1990;Schafer and Kohn 2006), yet evidence to the contrary exists in S. sclerotiorum (Ford et al 1995), S. homoeocarpa (Jo et al 2008;Chang et al 2014), Verticillium dalhiae (Papaioannou and Typas 2014), and Neurospora crassa (Micali and Smith 2003). The crux in these cases is that barrage formation may only serve as indirect evidence for vegetative incompatibility.…”

“…One explanation for the lack of congruence between MCG and VCG is that MCG represent subsets of VCG, such that one MCG may represent more than one VCG. While there is evidence that MCG are nested within VCG in S. homoeocarpa (Chang et al 2014), the relationship between mycelial compatibility and vegetative compatibility in S. sclerotiorum is more complex, as shown in Table 4 of Ford et al (1995), where one MCG was represented by two VCG and, in turn, both of these VCG represented two MCG. Microscopically, however, it was shown that the hyphae remained in a stable, heterokaryotic state, as evidenced by 4,6-diamidino-2-phenylindole (DAPI) staining and stable transfers of colonies.…”

Something in the agar does not compute: On the discriminatory power of mycelial compatibility in Sclerotinia sclerotiorum

“…Mycelial compatibility in S. sclerotiorum is considered by some to be synonymous with vegetative compatibility (Kohn et al 1990;Schafer and Kohn 2006), yet evidence to the contrary exists in S. sclerotiorum (Ford et al 1995), S. homoeocarpa (Jo et al 2008;Chang et al 2014), Verticillium dalhiae (Papaioannou and Typas 2014), and Neurospora crassa (Micali and Smith 2003). The crux in these cases is that barrage formation may only serve as indirect evidence for vegetative incompatibility.…”

“…One explanation for the lack of congruence between MCG and VCG is that MCG represent subsets of VCG, such that one MCG may represent more than one VCG. While there is evidence that MCG are nested within VCG in S. homoeocarpa (Chang et al 2014), the relationship between mycelial compatibility and vegetative compatibility in S. sclerotiorum is more complex, as shown in Table 4 of Ford et al (1995)…”