Prolonged nitrogen fixation (PNF) during periodic moisture stress to enhance yield and protein accumulation in soybean

Principal Investigator: Malcom Morrison

Research Institution: Agriculture and Agri-Food Canada

Timeline: April 2022 – March 2024   

Objectives:

• Using field and growth cabinets, find a test for the presence of the prolonged nitrogen fixation (PNF) trait in Canadian adapted lines (maturity group (MG) 0, 00) from crosses with lines possessing this trait from the southern US (MG IV).
• Find a method to test for PNF under field conditions to develop new moisture stress tolerant Canadian varieties of soybean using original parent sources in growth cabinet conditions and backcrossed derived material in fields.
• Determine the economic benefit of incorporating the genes for PNF into our varieties by field testing in Ontario and Manitoba.
• Examine the effects of PNF traits on soybean protein concentration in Ontario and with collaborators in Manitoba.

Impacts:

• The selection of adapted soybean varieties with PNF under moisture stress will increase yield and profitability in dry years or years with periodic moisture stress during critical periods like seed filling. This characteristic will enhance yield of soybean in farmers’ fields.
• Varieties with PNF will have more N available for seed protein.
• There is no negative impact from incorporating the PNF trait into soybean varieties, therefore, even marginal increases in yield (50 to 500 kg/ha) will result in huge economic advantages to Ontario farmers.
• Plant breeders are quick to include new traits into their varieties so the entire soybean industry will benefit by including the PNF trait in food and feed type soybean.

Scientific Summary:

Climate change is a reality. Canadian climate models predict that soybean growing areas will be hotter, with increased precipitation irregularity (PIR) resulting in a greater likelihood of periodic moisture stress. While not as devastating as drought, periodic moisture stress occurs when there is an interval of two or more weeks without precipitation. This depletes available soil moisture and, if it occurs at flowering or seed filling, results in significant yield losses. While no crop plant can be productive without water, there are adaptive mechanisms that ensure that plants can survive periodic moisture stress well enough to recover and achieve reasonable yield. Moisture stress tolerance mechanisms that are beneficial in dry years but result in a yield penalty in normal years are not useful for farmers.

Soybean derives 50 to 80% of its nitrogen from symbiotic N₂-fixation, which is more susceptible to moisture stress than either photosynthesis or growth. In the US, soybean lines with prolonged N₂-fixation (PNF) under moisture stress have been discovered and shown to have higher yields during periodic moisture stress than the controls. These US varieties are Maturity Group IV to MG VII and are not adapted to Ontario, Quebec, or Manitoba. The soybean breeding program at ORDC is currently backcrossing the PNF trait into new MG 0 and 00 varieties.  A marker for the PNF trait has not been identified to assist in variety selection. While field testing can be used to select for appropriate maturity among progeny, specific tests need to be developed to determine if the PNF trait has been retained. This research project will build on two years of field research investigating ORDC backcross derived MG 0 and 00 germplasm potentially exhibiting the PNF trait. The research will be done in Ontario and in Manitoba. Visual and spectral imaging will be used to examine growth rate, biomass differences, and leaf N concentration in the leaves, stems, and seeds to determine the presence and function of PNF under moisture stress. Backcross progeny retaining the PNF traits will be identified for future soybean varieties capable of withstanding PIR, increasing yield and seed protein concentration.

External Funding Partners:

Manitoba Pulse and Soybean Growers