Vail: To germinate or not to germinate? Towards understanding the role dormancy plays in canola seed and seedling vigour and stand establishment
Date: May 2018
Term: 3 years
Status: Completed
Researcher(s): Sally Vail, Agriculture and Agri-food Canada, Saskatoon SK, Rob Gulden, University of Manitoba and Steve Shirtliffe, University of Saskatchewan
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
Researchers in Saskatchewan conducted a project to resolve the connection between primary and secondary dormancy, premature germination (sometimes found in the pods of maturing canola), overall seed biology, and seed and seedling vigour related traits across a diverse panel of Brassica napus (canola) lines. The results showed a very wide range in secondary dormancy potential (SDP) across a spring B. napus diversity collection with several high SDP lines being much greater than those identified in the earlier studies. However, the study found no association between SDP and any of the other germination or seed vigour parameters, demonstrating the need for screening for SDP in commercial seedlots. Overall the results from this project will guide plant breeding approaches to ultimately reduce the secondary or inducible dormancy potential of canola.
Seedling emergence of Brassica napus canola in western Canada is low relative to the amount of seed typically planted, with about half emerging, and the other half remaining in the seed bank or dying prior to emergence. Volunteer canola ranks as the 4th most occurring weed on the Canadian prairies and can be a problem in subsequent rotational herbicide tolerant canola crops. It is believed secondary dormancy is the physiological mechanism leading to the extended presence of seed in the seed bank. However, the role seed dormancy plays in establishment of canola stands on the Canadian prairies is not well understood other than an understanding that variation for secondary seed dormancy in Canadian canola cultivars exists, with many cultivars being classified as possessing high secondary dormancy potential. Furthermore, knowledge of overall seed biology and how it relates to germination, vigour of seed and seedlings, and dormancy potential in B. napus are relatively poorly understood.
Researchers with Agriculture and Agri-Food Canada in the Saskatoon Research and Development Centre (SRDC), the University of Saskatchewan and the University of Manitoba conducted a three-year project to resolve the connection between primary and secondary dormancy, premature or precocious germination (found in the pods of mature canola), overall seed biology, and seed and seedling vigour related traits across a diverse panel of B. napus lines. Researchers also investigated the effect of the growth environment for production of seed and the effect of processing on secondary dormancy potential of canola seed. The project included four main objectives.
The first two objectives of the project focused on testing the variation in commercial B. napus lines for secondary dormancy potential (SDP), and testing for associations between dormancy and other seed and stand-establishment related traits. A set of diverse B. napus lines were grown in multiple field environments, then characterized for premature germination, primary dormancy and SDP of mature seed as well as seed and seedling vigour potential. In addition to genotypes, different treatments included seedlots derived from contrasting environments and storage treatments. The SDP values for all seedlots were compared to total germination, rates of germination, primary dormancy, seed vigour measurements (controlled deterioration test and pre-chill germination test), seed size and precocious germination.
Results from this project show a very wide range in SDP across a spring B. napus diversity collection with several high SDP lines being much greater than those identified in the earlier studies. Additionally, the effect of seed production sites was evident, especially for a subset of diverse lines, which exhibited contrasting SDP between sites. The lines with the consistently high SDP phenotypes are much larger and more consistent than lines previously reported. From the study, new check lines of B. napus have been identified to use for secondary dormancy screening.
The study also found no association between SDP and any of these other germination or seed vigour parameters, demonstrating the need for screening for SDP in commercial seedlots. The results also showed that in some commercial seedlots, a significant portion of the seed has potential to be induced into secondary dormancy. Researchers are working with hybrid seed producers and commercial seed testing facilities to re-examine seeding rate and blending recommendations based on the study results. These results also lay the groundwork to study the genetics controlling SDP.
Another component of the study evaluated the effect of storage and conditioning on high and low SDP lines. A subset of 6 lines with contrasting SDP was selected and seed was produced again in 2017. These seedlots were subjected to 12 different temperature regimes representing seed treatment and storage conditions (room, cold vs. frozen temperatures, variable times). The study used a thermal gradient plate at AAFC-SRDC to simulate segments of temperature regimes encountered during the post-harvest processing of hybrid canola seed to see if these factors are contributing to secondary dormancy induction. The results confirmed that SDP decreases over time and with exposure to non-freezing temperatures, reducing SDP of commercial seedlots.
Results of this project also found SDP variation between varieties and maternal production environments. With high SDP varieties, seed production environment contributes to significant increases of SDP for a given seedlot. These results will be of value for the canola seed production industry in prioritizing selection for decreased SDP in commercial varieties. Researchers are now working with major hybrid canola seed companies to assess commercial seedlots of hybrids produced in different environments and the effect of environmental conditions seedlots are exposed to on secondary dormancy potential.
In the fall of 2017 researchers also began profiling the major seed components to see if content of oil, protein or fiber influence secondary dormancy potential. Preliminary results show that protein and seed fiber content appear to be moderately associated with dormancy potential and associations with additional seed quality traits continue to be assessed.
Overall the results from this project will guide plant breeding approaches to ultimately reduce the secondary or inducible dormancy potential of canola. These results lay the groundwork to study the genetics of SDP that would result in the identification of molecular-markers that would have commercialization potential for canola seed companies.