Building bridges to success - Accessing Brassica diploid variation for canola improvement
Date: February 15, 2024
Term: 3 years
Status: Complete
Researcher(s): Steve Robinson, Jean-Sebastien Parent, Alex Diederichsen, Hossein Borhan, AAFC
SaskCanola Investment: $55,000
Total Project Cost: $165,000
Funding Partners: ACPC, MCGA
Grower Benefits
The diploid Bridging Lines developed can be directly crossed with wild relatives possessing valuable disease resistance alleles and subsequently introduced into B. napus by tetraploid resynthesis. The allelic diversity introduced this way can be directly accessed and evaluated by canola breeding programs. While the gene editing strategy still needs to be evaluated, the Bridging Lines immediately add new capacity for future canola improvement strategies.
Project Summary
New opportunities protecting canola yield from biotic and abiotic stress can be developed by harnessing genetic diversity found in crop wild relatives. However, significant barriers prevent breeders from accessing this variation, impeding crop improvement goals. Using a combination of conventional genetic and gene-editing technology, this project has established bridging lines by transferring key domestication traits from canola into its diploid relatives. These new genetic resources establish a platform to easily access variation from crop wild relatives protecting against persistent pathogens.
Access to genetic diversity is key to the success of crop breeding programs and canola is limited in this regard due to its natural history being formed from an interspecific hybridization event between its diploid parents B. rapa (A genome) and B. oleracea (C genome). While other breeding strategies exist, crop wild relatives possess greater levels of diversity, acting as a rich reservoir of alleles offering solutions to breeding objectives if they can be deployed effectively. Unfortunately, significant barriers are present to impede the transfer of useful alleles from crop relatives into B. napus.
This project aimed to develop material, specifically designed for accessing new alleles in crop wild relatives using targeted gene-editing to remove hybridization barriers and conventional crosses. These new genetic resources can be used to access valuable alleles necessary to deliver enhanced disease and pest resistance into canola breeding programs.
Using successive rounds of backcrossing aided with marker-assisted selection, alleles promoting self-compatibility and fertility, were transferred from B. napus into both B. rapa and B. oleracea. These were combined with alleles promoting a spring growth habit, early flowering and seedling vigour identified in diploid individuals. The resulting lines possess the necessary alleles for resynthesizing B. napus that are fertile, self-compatible and adapted to the prairie environment. In parallel, new material was developed using targeted gene-editing (CRISPR) to alleviate hybridization barriers found in diploid species. This innovation can also promote the development of synthetic B. napus.
The use of wild relatives for crop improvement holds great potential but is obstructed by significant hybridization barriers common to interspecific crosses. Gene editing in target alleles controlling hybridization barriers was performed to remove these obstacles. Additionally, the problems associated with chromosome imbalance resulting from triploidy and aneuploidy in successive rounds of backcrossing were overcome through painstaking use of embryo rescue, tissue culture and marker-assisted selection to identify optimal genotypes.
Accessing the genetic diversity of wild diploid parent species is crucial for the continued improvement of canola cultivars and the long-term success of the industry in general. In particular, it would give access to a number of disease resistance genes that could protect yields and reduce growers’ reliance on pesticides. Getting access to this genetic diversity has however been prevented by the reproduction barriers that exist between canola and its parents. This project has taken a two-pronged approach to address this problem; one approach has used conventional crossing, and the other has used a novel gene editing strategy in B. oleracea. The gene editing technique has been successfully applied to create mutant plants, but these lines still need to be tested for reproductive barriers. Importantly, the project has delivered Bridging Lines that can immediately be used to tap into the genetic diversity found in diploid populations for canola improvement.