Building bridges to success – accessing Brassica diploid variation for canola improvement

Project Summary

Background

Genetic diversity is the key resource to ensure the future success of plant breeding. The natural history of Brassica napus (rapeseed) is responsible for its low level of genetic variation as it was formed from a recent hybridization event between B. rapa (turnip) and B. oleracea (cabbage). The extent of its diversity has been further reduced from selection pressure to develop canola quality characteristics and other beneficial agronomic traits. The natural history of B. rapa and B. oleracea is much older than B. napus, providing more time for natural selection to enrich these species with valuable alleles leading to disease resistance and adaptations to abiotic stresses as they evolved to occupy an extensive range of ecological niches.

This means B. rapa, B. oleracea and other wild relatives of Brassica act as a genetic reservoir of alleles that are of value to canola breeders. Accessing new variation present in related species has always been problematic for breeders of polyploidy crops and the resulting material is difficult to evaluate and often poorly suited for introduction into on-going breeding programs. This project makes use of new diploid variation generated at the Saskatoon Research and Development Centre (SRDC), where the introduction of domestication alleles has developed diploid bridging species that can be used to introduce new variation into canola.

Purpose

The security and future success of the canola crop is dependent on adapting varieties to meet both present and future production challenges. Timely solutions addressing these challenges need to be made to ensure the continued delivery of the high yields that support the Canadian agricultural economy. Acute challenges can manifest with an urgent need to rapidly introduce new disease resistance alleles. Conversely, chronic challenges require constant germplasm improvement to better adapt the canola crop to the prairie environment. Moreover, these adaptive goals are shifting due to the effects of the changing climate and the information derived from climate modeling highlights both the severity and urgency of the challenge.

The most effective way to meet these challenges is to identify and deploy the available variation from plant populations that have already developed solutions through their evolutionary history. However, efficient access to alleles in crop relatives is often challenging in polyploidy crop species where the major reserve of valuable alleles often exists in diploid relatives, where reproductive incompatibility is a major impediment. This project will utilize recent scientific advancements in order to develop specific germplasm accessible through the creation of bridging lines. These will enable access to valuable alleles ultimately delivering a new technology that will be available to canola breeders.

The development of domesticated diploid bridging species represents a new technology for the canola industry. Their combination with targeted diploid germplasm using a conventional crossing and marker-assisted selection approach will increase the efficiency with which alleles can be introduced into B. napus and their potential evaluated.

Objectives

This research is focused on the development of new diploid bridging germplasm that is generated by successive backcrossing and marker-assisted selection, followed by the generation of new fertile synthetic B. napus using these diploids as parents. Additional experiments will be conducted to reduce the strength of the genetic block that significantly impede interspecific crossing efficiency for more direct access to diploid genetic diversity. The specific objectives of the study are:

1. Domesticate identified A- genome and C-genome variation including C-genome variation with new blackleg resistance by introducing identified B. napus alleles.
2. Generate synthetic B. napus germplasm using the domesticated A and C diploid germplasm.
3. Confirm the successful introgression of blackleg resistance into B. napus using disease assays.
4. Use genome engineering to reduce the impact of key pathways that maintain the genetic block preventing interspecific hybridization.