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

Abstract

Sclerotinia trifoliorum, an important pathogen of cool season legumes, displays both homothallism and heterothallism in its life cycle, unique among members of the genus Sclerotinia. Very little is known about its genetic diversity and population structure. A sample of 129 isolates of S. trifoliorum from diseased chickpea in California was investigated for genetic diversity, population differentiation and reproductive mode. Genetic diversity was estimated using mycelial compatibility (MCG) phenotypes, rDNA intron variation, and allelic diversity at seven microsatellite loci. Genetic analysis revealed high levels of genotypic diversity demonstrated by high genotypic richness (0Á88). Similarly, high levels of gene diversity (mean expected heterozygosity H E = 0Á68) were observed at the microsatellite loci. Geographic populations of S. trifoliorum were highly admixed as evident from low F ST values (0-0Á11), suggesting high contemporary or historical gene flow. Hierarchical analysis of molecular variance showed that more than 92% of the genetic variation occurred among isolates within populations. Bayesian clustering analysis identified four cryptic genetic populations that were not correlated to geographic location, and index of multilocus association was non-significant in each of the four genetic populations. However, the presence of identical haplotypes within and among populations indicates clonal reproduction. The high levels of haplotype diversity and population heterogeneity, a lack of correspondence between MCG and microsatellite haplotype, and low levels of population differentiation suggest that populations of S. trifoliorum in chickpea have been undergoing extensive outcrossing and migration events probably shaped by human-mediated dissemination, the underlying diverse cropping systems, and chickpea disease management practices.

Population Structure of Sclerotinia subarctica and Sclerotinia sclerotiorum in England, Scotland and Norway

“…(Attanayake et al, 2013, 2014; Njambere et al, 2014). The markers used in this study map to different chromosomes of the S. sclerotiorum reference genome (Amselem et al, 2011) with the exception of 7-2 and 114-4 which both map to chromosome 4 and 13-2 and 110-4 which both map to chromosome 6.…”

“…In contrast to S. sclerotiorum and S. minor, S. trifoliorum is bipolar heterothallic (Uhm and Fujii, 1983) and has a more limited host range, being found mainly on cool-season forage and vegetable legumes (Willetts et al, 1980). A recent population study of S. trifoliorum on chickpea in California identified high levels of diversity based on MCGs and microsatellites (Njambere et al, 2014). Compared to the other Sclerotinia spp., S. subarctica was only identified relatively recently on the wild hosts yellow marsh marigold ( Caltha palustris ), dandelion ( Taraxacum sp.…”

Independently founded populations of Sclerotinia sclerotiorum from a tropical and a temperate region have similar genetic structure

“…Water and DNA of two isolates of S . trifoliorum (06CWM-G22, L-type and 06CWM-G27, S-type) previously characterized by Njambere et al [ 26 ] were used as negative controls. PCR reactions were performed in a final volume of 20 μl with 2 μl of DNA, 0.5 μl of each primer at 10 mM, 0.5 μl of dNTPs at 10 mM, 2 μl of the 10x Standard Taq Reaction Buffer that includes 1.5 mM MgCl 2 , 10mM Tris-HCl and 50 mM KCl (New England Biolabs Inc., Ipswich, MA, USA) and 0.1 μl of Taq DNA polymerase (New England Biolabs, Inc.).…”

The evolutionary and molecular features of the broad‐host‐range plant pathogen Sclerotinia sclerotiorum

“…For example, S. trifoliorum hosts include diverse Fabaceae species such as fenugreek ( Trigonella foenum‐graecum ) in Tunisia (Gargouri et al, 2017) and clover ( Trifolium spp.) and chickpea ( Cicer arietinum ) in the USA (Baturo‐Ciesniewska et al, 2017; Njambere et al, 2014); hosts of S. minor include the Asteraceae species lettuce ( Lactuca sativa ) in the USA (Subbarao, 1998) and safflower ( Carthamus tinctorius ) in Turkey (Erper et al, 2020), and the Fabaceae species peanut ( Arachis hypogaea ) in the USA (Crutcher et al, 2018). The most poorly characterized species of the three, S. nivalis , also has a broad host range as it can infect plants in at least 10 different families (Wang et al, 2021).…”