To address the lack of weed management options in mustards and to try to find solutions in both Carinata and Juncea canola by screening of a large mutagenized population for tolerance to different herbicides under both greenhouse and laboratory conditions.
Canada is the world’s largest exporter of condiment mustard, i.e. yellow mustard (Sinapis alba) and Brown and Oriental mustard (Brassica juncea), with a market value of $120-140M. Carinata (B. carinata) as a new and dedicated industrial feedstock crop for the emerging bio economy has great potential to add to this existing base. One major challenge for the production of both crops is very limited herbicide options for managing broadleaf weeds. In front of this background, the objective of this study was to create herbicide-tolerant lines of carinata and Oriental mustard through seed mutagenesis.
At AAFC-SRDC, methods to mutate whole seeds of B. carinata and B. juncea and to screen mutated and non-mutated germplasm for tolerance to Group 2 and Group 4 herbicides were developed. Mutated B. carinata and B. juncea seed was created through chemical mutagenesis using ethyl methanesulfonate (EMS) and through gamma radiation, followed by high throughput screening in both greenhouse and field for the identification of herbicide tolerant plants and introgression of the herbicide tolerance trait into elite breeding lines. B.carinata line UF-S2 (and selections thereof) with tolerance to the Group 4 herbicide dicamba were identified and the tolerance of this material confirmed in repeated screening experiments under controlled conditions and in the field. However, both the advanced selections of UF-S2 and F1 progeny from crosses with elite carinata breeding lines have shown a low level of segregation for the level of herbicide tolerance in greenhouse experiments at AAFC-SRDC. In order to address the issue of trait segregation and reach homozygosity of the herbicide tolerance trait, a modified single-seed descent approach and the development of doubled haploid (DH) lines were initiated; however, due to recent concerns over dicamba drift issues in the United States, which could also affect the use of dicamba by producers in Canada, these latter project activities have been put on hold until further clarification on the regulatory status of dicamba going forward. Agrisoma Biosciences, whose main commercial interest for dicamba-tolerant carinata lies in countries such as Uruguay, has been pursuing the development and screening of DH lines stemming from crosses of UF-S2 and UF-S3 advanced selections and elite carinata breeding lines. Dicamba tolerance of 26 promising DHs will be validated in Uruguay in 2019. Efforts to create Group 2 herbicide tolerant B. carinata germplasm are still ongoing.
The development of Group 4 herbicide tolerance in Oriental mustard through mutagenesis has been more challenging. Although some plants have exhibited low to moderate levels of tolerance, commercially acceptable levels of tolerance have not been identified. The recent deployment of a modified mutagenesis protocol involving a longer exposure time to the mutagen EMS has resulted in the identification of one Oriental mustard line with increased levels of tolerance to imazamox (Solo). Confirmation of tolerance in the field is planned for 2019.