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

Abstract

Sclerotinia species are important fungal pathogens of a wide range of crops and wild host plants. While the biology and population structure of Sclerotinia sclerotiorum has been well-studied, little information is available for the related species S. subarctica. In this study, Sclerotinia isolates were collected from different crop plants and the wild host Ranuculus ficaria (meadow buttercup) in England, Scotland, and Norway to determine the incidence of Sclerotinia subarctica and examine the population structure of this pathogen for the first time. Incidence was very low in England, comprising only 4.3% of isolates while moderate and high incidence of S. subarctica was identified in Scotland and Norway, comprising 18.3 and 48.0% of isolates respectively. Characterization with eight microsatellite markers identified 75 haplotypes within a total of 157 isolates over the three countries with a few haplotypes in Scotland and Norway sampled at a higher frequency than the rest across multiple locations and host plants. In total, eight microsatellite haplotypes were shared between Scotland and Norway while none were shared with England. Bayesian and principal component analyses revealed common ancestry and clustering of Scottish and Norwegian S. subarctica isolates while English isolates were assigned to a separate population cluster and exhibited low diversity indicative of isolation. Population structure was also examined for S. sclerotiorum isolates from England, Scotland, Norway, and Australia using microsatellite data, including some from a previous study in England. In total, 484 haplotypes were identified within 800 S. sclerotiorum isolates with just 15 shared between England and Scotland and none shared between any other countries. Bayesian and principal component analyses revealed a common ancestry and clustering of the English and Scottish isolates while Norwegian and Australian isolates were assigned to separate clusters. Furthermore, sequencing part of the intergenic spacer (IGS) region of the rRNA gene resulted in 26 IGS haplotypes within 870 S. sclerotiorum isolates, nine of which had not been previously identified and two of which were also widely distributed across different countries. S. subarctica therefore has a multiclonal population structure similar to S. sclerotiorum, but has a different ancestry and distribution across England, Scotland, and Norway.

Resistance to Sclerotinia sclerotiorum in wild Brassica species and the importance of Sclerotinia subarctica as a Brassica pathogen

“…The four S. sclerotiorum isolates used in this study were obtained from infected lettuce (L6, L44), pea (P7) and buttercup ( Ranunculus acris , DG4) from different locations in England. These isolates also represented different genotypes, as identified previously using microsatellite markers (Clarkson et al ., ; Table ). The pathogenicity of these isolates had been tested previously against three Brassica species, with L6 and P7 identified as aggressive, L44 as intermediate and DG4 as weak in terms of their virulence (Taylor et al ., ).…”

Inoculum potential of Sclerotinia sclerotiorum sclerotia depends on isolate and host plant

“…A single isolate of S. subarctica (isolate HE1 from wild buttercup) was also included for comparison; this related pathogen often produces larger sclerotia than S. sclerotiorum isolates (Clarkson et al ., ). Isolates represented different microsatellite haplotypes assigned through a previous study investigating the population structure of S. sclerotiorum and S. subarctica in the UK (Clarkson et al ., ; Table ). In addition, the relative aggressiveness of the same 18 isolates had also been evaluated previously on three brassica hosts (Taylor et al ., ).…”

Narrow windrow burning canola (Brassica napus L.) residue for Sclerotinia sclerotiorum (Lib.) de Bary sclerotia destruction

“…The locality and host of the original S. sclerotiorum isolates were: Geraldton (canola, 2014), Eneabba [lupin ( Lupinus angustifolius L.), 2013], Mount Barker (canola, 2014) and South Stirling (canola, 2014) in the grain belt of Western Australia. Based on intergenic spacer sequencing (IGS), these S. sclerotiorum isolates were comprised of haplotypes IGS3, IGS5 and IGS7 . Upon canola senescence, mature sclerotia were collected from canola stalks and sieved (CMT Equipment, Tweed Heads, NSW, Australia) into three size fractions (<3, 3–4 and >4 mm) (Fig.…”