Environmental stress hampers pea productivity. To understand the genetic basis of heat resistance, a genome-wide association study (GWAS) was conducted on six stress responsive traits of physiological and agronomic importance in pea, with an objective to identify the genetic loci associated with these traits. One hundred and thirty-five genetically diverse pea accessions from major pea growing areas of the world were phenotyped in field trials across five environments, under generally ambient (control) and heat stress conditions. Statistical analysis of phenotype indicated significant effects of genotype (G), environment (E), and G × E interaction for all traits. A total of 16,877 known high-quality SNPs were used for association analysis to determine marker-trait associations (MTA). We identified 32 MTAs that were consistent in at least three environments for association with the traits of stress resistance: six for chlorophyll concentration measured by a soil plant analysis development meter; two each for photochemical reflectance index and canopy temperature; seven for reproductive stem length; six for internode length; and nine for pod number. Forty-eight candidate genes were identified within 15 kb distance of these markers. The identified markers and candidate genes have potential for marker-assisted selection towards the development of heat resistant pea cultivars.

Heat and drought, individually or in combination, limit pea productivity. Fortunately, substantial genetic diversity exists in pea germplasm for traits related to abiotic stress resistance. Understanding the genetic basis of resistance could accelerate the development of stress-adaptive cultivars. We conducted a genome-wide association study (GWAS) in pea on six stress-adaptive traits with the aim to detect the genetic regions controlling these traits. One hundred and thirty-five genetically diverse pea accessions were phenotyped in field studies across three or five environments under stress and control conditions. To determine marker trait associations (MTAs), a total of 16,877 valuable single nucleotide polymorphisms (SNPs) were used in association analysis. Association mapping detected 15 MTAs that were significantly (p ≤ 0.0005) associated with the six stress-adaptive traits averaged across all environments and consistent in multiple individual environments. The identified MTAs were four for lamina wax, three for petiole wax, three for stem thickness, two for the flowering duration, one for the normalized difference vegetation index (NDVI), and two for the normalized pigment and chlorophyll index (NPCI). Sixteen candidate genes were identified within a 15 kb distance from either side of the markers. The detected MTAs and candidate genes have prospective use towards selecting stress-hardy pea cultivars in marker-assisted selection.

Growth and yield of pea crops are severely affected by various fungal diseases, including root rot, Ascochyta blight, powdery mildew, and rust, in different parts of the world. Conventional breeding methods have led to enhancement of host plant resistance against these diseases in adapted cultivars, which is the primary option to minimize the yield losses. To support the breeding programs for marker-assisted selection, several successful attempts have been made to detect the genetic loci associated with disease resistance, based on SSR and SNP markers. In recent years, advances in next-generation sequencing platforms, and resulting improvements in high-throughput and economical genotyping methods, have been used to make rapid progress in identification of these loci. The first reference genome sequence of pea was published in 2019 and provides insights on the distribution and architecture of gene families associated with disease resistance. Furthermore, the genome sequence is a resource for anchoring genetic linkage maps, markers identified in multiple studies, identification of candidate genes, and functional genomics studies. The available pea genomic resources and the potential application of genomic technologies for development of disease-resistant cultivars with improved agronomic profile will be discussed, along with the current status of the arising improved pea germplasm.

This research aimed to identify quantitative trait loci (QTLs) associated with seed protein concentration in a recombinant inbred line (RIL) population of pea and aimed to validate the identified QTLs using chromosome segment-introgressed lines developed by recurrent backcrossing. PR-25, an RIL population consisting of 108 F7 bulked lines derived from a cross between CDC Amarillo (yellow cotyledon) and CDC Limerick (green cotyledon), was used in this research. The RIL population was genotyped using an Axiom 90K SNP array. A total of 10,553 polymorphic markers were used for linkage map construction, after filtering for segregation distortion and missing values. The linkage map represents 901 unique loci on 11 linkage groups which covered a map distance of 855.3 Centimorgans. Protein concentration was assessed using near-infrared (NIR) spectroscopy of seeds harvested from field trials in seven station-years in Saskatchewan, Canada, during the 2019–2021 field seasons. Three QTLs located on chromosomes 2, 3 and 5 were identified to be associated with seed protein concentration. These QTLs explained 22%, 11% and 17% of the variation for protein concentration, respectively. The identified QTLs were validated by introgression lines, developed by marker-assisted selection of backcross lines for introgression of corresponding chromosome segments (~1/4 chromosome) harboring the QTL regions. Introgression line PR-28-7, not carrying any protein-related QTLs identified in this study, was 4.7% lower in protein concentration than CDC Amarillo, the lower protein parent of PR-25 which carried one identified protein-related QTL. The SNP markers located at the peak of the three identified QTLs will be converted into breeder-friendly KASP assays, which will be used for the selection of high-protein lines from segregating populations.

The ascomycete, Sclerotinia sclerotiorum , has a broad host range and causes yield loss in dicotyledonous crops world wide. Genomic diversity and aggressiveness were determined in a population of 127 isolates from individual canola ( Brassica napus ) fields in western Canada. Genotyping with 39 simple sequence repeat (SSR) markers revealed each isolate was an unique haplotype. Analysis of molecular variation showed 97% was due to isolate and 3% to geographical location. Testing of mycelium compatibility identified clones of mutually compatible isolates, and stings of pairwise compatible isolates not seen before. Importantly, mutually compatible isolates had similar SSR haplotype, in contrast to high diversity among incompatible isolates. Isolates from the Province of Manitoba had higher allelic richness and higher mycelium compatibility (61%) than Alberta (35%) and Saskatchewan (39%). All compatible Manitoba isolates were interconnected in clones and strings, which can be explained by wetter growing seasons and more susceptible crops species both favouring more mycelium interaction and life cycles. Analysis of linkage disequilibrium rejected random recombination, consistent with a self-fertile fungus and restricted outcrossing due to mycelium incompatibility, and only one meiosis per lifecycle. More probable sources of genomic diversity is slippage during DNA replication and point mutation affecting single nucleotides, not withstanding the high mutation rate of SSRs compared to genes. It seems accumulation of these polymorphisms lead to increasing mycelium incompatibility in a population over time. A phylogenetic tree grouped isolates into 17 sub-populations. Aggressiveness was tested by inoculating one isolate from each sub-population onto B. napus lines with quantitative resistance. Results were significant for isolate, line, and isolate by line interaction. These isolates represent the genomic and pathogenic diversity in western Canada, and are suitable for resistance screening in canola breeding programs. Since the S. sclerotiorum life cycle is universal, conclusions on sources of genomic diversity extrapolates to populations in other geographical areas and host crops. Author summary: Sclerotinia sclerotiorum populations from various plant species and geographical areas have been studied extensively using mycelium compatibility tests and genotyping with a shared set of 6-13 SSR markers published in 2001. Most conclude the pathogen is clonally propagated with some degree of outcrossing. In the present study, a population of S. sclerotiorum isolates from 1.5 million km ² area in western Canada were tested for mycelium compatibility, and genotyped with 9 published and 30 newly developed SSR markers targeting all chromosomes in the dikaryot genome (8+8). A new way of visualizing mycelium compatibility results revealed clones of mutual compatible isolates, as well as long and short strings of pairwise compatible isolates. Importantly, clonal isolates had similar SSR haplotype, while incompatible isolates were highly dissimilar; a relationship difficult to discern previously. Analysis of population structure found a lack of linkage disequilibrium ruling out random recombination. Outcrossing, a result of alignment of non-sister chromosomes during meiosis, is unlikely in S. sclerotiorum , since mycelium incompatibility prevents karyogamy, and compatibility only occur between isolates with similar genomic composition. Instead, genomic diversity comprise transfer of nuclei through hyphal anastomosis, allelic modifications during cell division and point mutation. Genomic polymorphisms accumulate over time likely result in gradual divergence of individuals, which seems to resemble the ‘ring-species’ concept. We are currently studying whether nuclei in microconidia might also contribute to diversity. A phylogenetic analysis grouped isolates into 17 sub-populations. One isolate from each sub-population showed different level of aggressiveness when inoculated onto B. napus lines previously determined to have quantitative resistance to a single isolate. Seed of these lines and S. sclerotiorum isolates have been transferred to plant breeders, and can be requested from the corresponding author for breeding purposes. Quantitative resistance is likely to hold up over time, since the rate of genomic change is relatively slow in S. sclerotiorum .