Farmers face their annual dilemma. They select crop cultivars for their farms from sales data provided by the vendor and from performance reports of provincial crop trials.
But do trial results from conventionally managed field sites apply to organic farmers? Generally, the answer is no. What is an organic farmer supposed to do?
Despite a small number of organic soy-bean growers, around 150 in Ontario, there is a growing market for this product and organic soybeans command a higher price compared to their conventional counterpart. Breeding soybeans for organic systems is an opportunity to close the yield gap between organic and conventional soybean production. For example, fields under organic production can have lower P and K soil budgets than conventional fields, and organic managers also use more labour through mechanical weed control. Selecting robust breeding lines that are better adapted to organic field management will increase product competitiveness in a growing market. Pioneering work is contributing to a greater understanding of soybean breeding for organic production systems.
“Soybeans can be a challenging crop to grow in an organic system, since tools such as herbicides and soluble fertilizers are prohibited,” notes Dr. Istvan Rajcan, professor and soybean breeder at the university of Guelph. “Our goal with this project is to provide organic producers with cultivar options that are better suited to their production system.”
Most cultivars used in organic production systems were originally selected within conventional farming systems and selected for attributes that respond to conventional practices. However, a principle of plant breeding is that varieties should be evaluated under conditions that they are expected to encounter on the farm, such as those found on organic farms. Factors such as site fertility and organic weed management techniques provide unique conditions for certain breeding lines to excel over others, which go unnoticed at a conventional test site.
A soybean cultivar is traditionally assessed for important traits such as susceptibility to lodging, seed yield, seed protein and oil content. However, additional traits are important for organic growers that address soil fertility differences and competitiveness with weeds. These traits of interest include plant canopy development, root morphology, and nodule mass. Rapid canopy development can shade out weeds that compete with the crop. In the coming seasons, Dr. Rajcan’s team will be using drone technology to measure plant canopy.
The efficiency of the plant’s ability to take up nutrients should also be considered. The analysis of the N, P, and K contents in leaf samples will estimate the plant’s nutrient use efficiency. Nutrient uptake and assimilation are studied by way of root samples, which explore plants’ root volume, root surface and root nodule dry mass.
Dr. Rajcan directs this novel organic soybean breeding project along with retired professor Dr. Ralph Martin and PhD student Xin Lu. Their work builds upon previous research led by Dr. Rajcan and a former MSc student, Torin Boyle. Mr. Boyle’s research demonstrated that certain soybean cultivars performed better when grown in an organic production system compared to a conventional system.
Mr. Boyle established a link between cultivar yield performance and root architecture in organic systems: certain cultivars produce root systems that can better access limited nutrients. Therefore, the evaluation of breeding populations in organic production systems can lead to robust soybean cultivars that can be better suited to organic systems.
Dr. Rajcan is conducting two experiments at six sites in Ontario: three under organic and three under conventional management. One experiment consists of an evaluation of 50 soybean cultivars under both management systems. The other experiment consists of two f6 generation breeding populations, which will be evaluated for superior performing lines at organic sites.
In addition to the project’s Ontario trials, two organic field sites are under the supervision of Dr. Martin Entz, a professor at the University of Manitoba, where 39 cultivars were grown in 2019. It can take seven to ten generations, after making the initial cross, to get a soybean line to the later stages of a breeding program and ready for commercial release.
The organic and conventional test sites require different crop management practices throughout the test period. At the conventional field sites, herbicides are employed, whereas inter-row cultivation is performed early in the season until V5, the growth stage at which the soy- bean has five unrolled trifoliate leaves. It is then followed by hand weeding at the organic field sites.
The study will also analyze the DNA from the breeding populations to identify quantitative trait loci (QTLs), which are regions of the soybean genome associated soybean yield in the two production systems. With this information, genetic markers can be developed in the future to guide the selection of parental lines used when breeding for organic production systems.
(OSC3) Originally published in Organic Science Canada magazine, Issue #2, Spring 2020
