Sclerotinia sclerotiorum populations: clonal or recombining?

Abstract

Sclerotinia sclerotiorum, a homothallic plant pathogen, undergoes sexual reproduction via haploid selfing (equivalent to clonal reproduction), and produces long-lasting surviving vegetative structures called sclerotia, enhancing clonal persistence and spread. Thus it is not surprising to detect clones of the species. Whether outcrossing can occur in the homothallic S. sclerotiorum remains unanswered. Early studies showed that S. sclerotiorum has a clonal population structure, consistent with its life history traits. However, recent studies using polymorphic and co-dominant molecular markers showed frequent genetic recombination, suggesting outcrossing. This review focuses on recent developments in population genetics studies related to detecting recombination, random association of alleles and dynamic mating type (MAT) alleles in Sclerotinia. Despite frequent reports of random association of alleles, the mechanisms for outcrossing in a homothallic species remain elusive. Recent intriguing findings are: the MAT genes in Sclerotinia are subject to inversion or deletion in every meiotic generation, the MAT gene deletion is related to ascospore dimorphism and mating type switching in S. trifoliorum, and ascospore dimorphism was also observed in S. sclerotiorum. Determining the nature of the dimorphic ascospores and their prevalence in relation to environmental cues could significantly advance our understanding how S. sclerotiorum populations behave in nature.

Carbon source dependent-anaerobic soil disinfestation (ASD) mitigates the sclerotial germination of Sclerotinia sclerotiorum

“…Cabbage and leek cull piles as C sources in ASD against sclerotia germination of S. sclerotiorum was tested for the first time. These findings are very important since the pathogen biology, population genetic structure and host range of S. sclerotiorum is well understood (Anderson and Kohn 1995;Attanayake et al, 2018;Boland and Hall, 1994), but still it poses a serious threat to worldwide agriculture. Therefore, National Strategic Plan for the Sclerotinia Initiative 2017-2021 has clearly identified thematic research areas and necessity in continuing working towards a common management plan.…”

Genetic Diversity and Recombination in the Plant Pathogen Sclerotinia sclerotiorum Detected in Sri Lanka

“…This infers that the individuals of a population of S. sclerotiorum do not recombine with individuals of other populations, but recombination could occur among individuals within genetic clusters or sub populations. Therefore, it is clear that cryptic population structure reduces the power of detecting the recombination [41]. In heterothallic fungi, mating loci carry one of two MAT idiomorphs; MAT 1-1 and MAT 1-2 as well as other related genes such as MAT 1-1-1, MAT 1-1-2, MAT 1-2-1.…”

“…In the present study, 50% of the isolates were inversion plus. Though the mechanism of mating type loci inversion in the outcrossing process is still unclear, higher inversion rates might induce error in mating type idiomorphs possibly of preventing self-fertility and promoting outcrossing [41].…”

Phenotypic and genotypic characterization of single isolate-derived monoascospore strains of Sclerotinia sclerotiorum from common bean

“…populations (Milgroom 1996;Attanayake et al 2019). However, molecular studies using microsatellite markers evidenced crosses among different isolates and high variability (Atallah et al 2004;Sexton and Howlett 2004;Mert-Türk et al 2007;Gomes et al 2011;Sirjusingh and Kohn 2001).…”

“…Microsatellite markers (e.g. SSR) have been used in population studies for the evaluation of outcrossing potential in S. sclerotiorum and their relation with mycelial compatibility groups (MCGs) (Atallah et al 2004;Attanayake et al 2019;Pannullo et al 2019), a kind of marker that have been thoroughly discussed in a recent review (Kamvar and Everhart 2019). Sympatric isolates originated from different hosts have shown significant phenotypic variability (Mert-Türk et al 2007;Attanayake et al 2013).…”