Microsatellite markers used for genome-wide association mapping of partial resistance to Sclerotinia sclerotiorum in a world collection of Brassica napus

Abstract

The fungal pathogen Sclerotinia sclerotiorum causes stem rot of oilseed rape (Brassica napus) worldwide. In preparation for genome-wide association mapping (GWAM) of sclerotinia resistance in B. napus, 152 accessions from diverse geographical regions were screened with a single Canadian isolate, #321. Plants were inoculated by attaching mycelium plugs to the main stem at full flower. Lesion lengths measured 7, 14 and 21 days after inoculation were used to calculate the area under the disease progress curve (AUDPC). Depth of penetration was noted and used to calculate percent soft and collapsed lesions (% s + c). The two disease traits were highly correlated (r = 0.93). Partially resistant accessions (AUDPC <7 and % s + c <2) were identified primarily from South Korea and Japan with a few from Pakistan, China and Europe. Genotyping of accessions with 84 simple sequence repeat markers provided 690 polymorphic loci for GWAM. The general linear model in TASSEL best fitted the data when adjusted for population structure (STRUCTURE), GLM + Q. After correction for positive false discovery rate, 34 loci were significantly associated with both disease traits of which 21 alleles contributed to resistance, while the remaining enhanced susceptibility. The phenotypic variation explained by the loci ranged from 6 to 25 %. Five loci mapped to published quantitative trait loci conferring sclerotinia resistance in Chinese lines.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-016-0496-5) contains supplementary material, which is available to authorized users.

Partial stem resistance in Brassica napus to highly aggressive and genetically diverse Sclerotinia sclerotiorum isolates from Australia

“…However, a growing list of publications show that partial, quantitative resistance exists in B. napus germplasm and many of its close relatives (Mei et al, 2011;Uloth et al, 2013Uloth et al, , 2015Taylor et al, 2015;Rana et al, 2017). In some cases, resistance has been identified by inoculation of the main stem of adult plants (Buchwaldt et al, 2005;Gyawali et al, 2016). The resulting lesions on partially resistant genotypes are relative small with a dark brown to black border between healthy and infected tissue, and more importantly, the majority of the stem lesions remain firm (Buchwaldt et al, 2005;Gyawali et al, 2016).…”

“…In some cases, resistance has been identified by inoculation of the main stem of adult plants (Buchwaldt et al, 2005;Gyawali et al, 2016). The resulting lesions on partially resistant genotypes are relative small with a dark brown to black border between healthy and infected tissue, and more importantly, the majority of the stem lesions remain firm (Buchwaldt et al, 2005;Gyawali et al, 2016). In contrast, susceptible lines develop typical whitish or tan coloured lesions that extend longitudinally as well as into the stem, resulting in soft and collapsed stems, which in the field can result in lodging of infected plants.…”

“…The objectives of the present study were to: (i) identify genetically diverse and highly aggressive Australian isolates of S. sclerotiorum and (ii), to use these isolates to screen B. napus accessions previously identified as partially resistant to a Canadian isolate, #321 (Gyawali et al, 2016). Here we confirm that the four B. napus accessions, PAK93, PAK54, DC21 and K22, are partially resistant to highly aggressive isolates that represent the genetic diversity of the pathogen population in Western Australia.…”

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

“…Identifying sources of resistance in Brassica is challenging as there can be considerable variability in plant screening assays, depending on conditions, plant growth stage and S. sclerotiorum isolate (Garg et al, 2010b;Uloth et al, 2013;Ding et al, 2015;Taylor et al, 2015). Despite these problems, some sources of partial resistance have been identified and mapped in B. napus (Zhao et al, 2006;Li et al, 2009;Yin et al, 2010;Taylor et al, 2015;Gyawali et al, 2016;Wu et al, 2016). However, a higher level of resistance to SSR has been identified in more diverse cruciferous plants, including wild species (Navabi et al, 2010;Mei et al, 2011;Uloth et al, 2013).…”

An update on the arsenal: mining resistance genes for disease management of Brassica crops in the genomic era

“…In total, 39 candidates were proposed. Gyawali et al 88 performed a GWAS using microsatellite markers in a global collection of 152 accessions and found that 34 loci were significantly associated. To date, many loci opposing SR have been characterized but none have been functionally characterized.…”