Tool helps breeders select for complex multi-gene traits

Nested association mapping (NAM) populations have proven quite useful in other crop species, such as corn and barley, as a platform to bridge the divide in knowledge between the plants genetic code (or ‘genome’) and the physical characteristics (or ‘phenotype’) of complex ‘traits’. These associations not only provide insight into basic science questions, but also yield practical tools and germplasm for plant breeders. We now have a NAM population for canola.

The spring B. napus NAM population has over 2,500 lines (RILs), which were derived from crossing or recombining the genes from 50 diverse parental lines with those of a reference line.

The existing B. napus NAM project encompassed one field season of evaluation of the large RIL population in 2016 at a single location/environment; however, extensive evaluation over several years under multi-environments is necessary to fully realize the complex trait combinations of this unique germplasm resource.

Throughout the current project, analysis continued on associations between the genome and key phenotypes based on the 2016 field data. The regions of the genome housing genes associated with flowering and maturity time, seed size and seed glucosinolates (GLS) were identified and will be validated using data in subsequent field trials containing sub-sets of the RILs (2017-19). Identified molecular markers will also immediately be used for selection within the Agriculture and Agri-Food Canada canola breeding program. For example, previously known genes controlling seed GLS plus new minor genomic locations that were identified will be used to quickly recapture this trait in populations with non-canola quality genes.

In this project, we also conducted two field trials in 2017 to further asses a sub-set of the RILs and the parental lines in unique environments. From the 2016 RIL trial, about 450 lines were identified as having ideal agronomic characteristics, thus were retested in 2017. From this trial, 93 (or only about four per cent of the entire NAM RIL population) showed an ideal combination of agronomics (days to flowering and maturity), seed quality profile (acceptable oil percentage, low GLS and low erucic) and yield greater than the reference line. This demonstrates the essential need for subsequent crossing between RILs to capture new traits in germplasm that can be used in commercial canola cultivar development.

Field testing of the NAM parental lines in 2015 across several field sites in Saskatchewan and at Beaverlodge in Alberta demonstrated the uniqueness of the extreme environment at northern latitude in the Peace River Region. Thus, we retested the parents in 2017 and compared flowering patterns confirming the utility of field trials in this region for further investigating response to different day-lengths in B. napus. This characteristic is not well understood yet is underlying the optimization of canola varieties for emerging canola growing regions at high latitudes.

To date, NAM parental lines, RILs and tester NAM-hybrids have being grown and assessed for agronomic traits and yield in more than 50 trials across Canada since 2013. This data, harvested seed and an associated database of phenotypic images will be a tremendous resource for the canola industry going forward for the study of physiological traits and yield stability as well as the study of new traits.

Furthermore, funding of this work has enabled collaborations studying new seed quality traits (protein fraction profiles), abiotic stress tolerance, existence of microbiome differences between lines and digital plant phenotypes.

Next steps in continuing to utilize this resource is increasing seed for repeated field trials of the NAM RILs in future growing seasons and development of a NAM centralized database that will enable the canola research community to address producer-determined research objectives including further development of agronomics, pre-breeding tools, and new uses of canola constituents.