Impact of drought and heat during flowering on canola yield
Term: 4 years ending Feb 2023
Status: Complete
Researcher(s): Raju Soolanayakanahally, Sally Vail, Stephen Robinson, Isobel Parkin, Raed Elferjani, AAFC; Chithra Karunakaran, Canadian Light Source; Eiji Nambara, University of Toronto
SaskCanola Investment: $178,703
Total Project Cost: $511,488
Funding Partners: ADF
Grower Benefits
Heat had a significant effect on yield by preventing seed set and had a more negative effect than drought on seed oil composition. This leads to enhanced levels of saturated fatty oils and desaturation efficiency, which is a measure of oil frying ability.
In some ways, wax deposition on canola leaf surfaces protects against drought damage.
As part of the cysteine (an amino acid) pathway, sulphur contributes to stress resilience in canola, which is further linked to abscisic acid (ABA), which leads to stomatal closure. Due to the redirected sulphur, oil content is adversely affected.
Based on ABA profiling in this project, researchers were able to identify canola Nested Association Mapping (NAM) population founder lines (FLs) that produce less ABA and are able to cope with drought stress.
Carbon and oxygen stable isotopes (proxies for water use efficiency and transpiration efficiency, respectively) could be used as physiological markers for selecting high yielding canola lines since they integrate growing season signals.
Project Summary
Droughts in 2001, 2008 and 2021 adversely affected crop production in Saskatchewan. Canola’s resilience to heat and drought depends on when these stresses occur within the crop lifecycle. Plants may recover after stress during the vegetative stage, but stress during flowering and/or pod development usually has a negative effect on yield. This study had several objectives, the first was to evaluate spring canola Nested Association Mapping population founder lines for drought, heat and combined stresses in the greenhouse and later evaluate abiotic stress tolerance under field conditions. Researchers also wanted to complete a comprehensive analysis of plant metabolites exhibiting enhanced stress-responsive roles leading to the discovery of biomarkers and select stress-tolerant canola varieties based on the ABA level. Lastly, researchers explored new rapid and non-destructive biomolecular imaging techniques to predict stress tolerance using mid-IR spectroscopy at the Canadian Light Source.
Fifty founder lines of the spring canola NAM population and a common parent (reference line) were used in this study. Traits that were measured and characterized during the duration of the experiment included 14 morphological, 13 physiological, four flowering phenology and three yield-related traits (Table 1).
Table 1. Traits that were measured throughout the study.
While the greenhouse experiments were conducted, concurrent studies in the field collected seed yield and TSW at five locations (Saskatoon, Outlook, Melfort, Scott, SK and Beaverlodge, AB). These experiments showed high variation in yield traits, especially pod weight, among the lines. The most variable traits were stomatal conductance and transpiration rate, while the variation in other physiological traits was moderate or low. Pod length, root diameter and phenology traits (DTB, DTF and DTM) had a noticeable variation and high heritability estimate as well. Between all traits, the proportion of variance explained by the genotype was higher than that explained by population, which suggests that the selection of founder lines should be based on each genotype’s performance apart and not on sampling lines among populations. Traits that were measured in the field showed a positive correlation with those measured in the greenhouse, especially for shoot and root morphology and flowering phenology and to a lesser extent for TSW. This was supported by a positive correlation between yields from the greenhouse versus the five field locations. Metabolite profiling was less of a discriminator between lines although four lines showed a noticeable high content of proline and one line had a high content of arginine. The screening of the diversity panel suggests there is potential for genetic gain and should give valuable information for the selection of founder lines.
In the second part of the project, researchers studied the plant growth environment and added stress treatments of different temperatures (23-29°C daytime temperatures) and water amounts (30% and 90% soil water holding capacity) for N99-508, a cultivar used in AAFC’s breeding program. Gas exchange measurements were performed and isotope values for Δ13C and δ15N were calculated in leaf tissue. Growth in terms of normalized difference vegetation index (NDVI) was measured as well as plant height at physiological maturity prior to the siliques being harvested. Following harvest, fatty acid and protein and oil content of seeds was analyzed. This experiment showed a divergence between the effects of drought, heat, and heat & drought on canola seed yield and oil quality. Drought affected the carbon assimilation rate mainly through the limitation of CO2 diffusion through the stomata and seed yield components. The effects of heat were seen in the alteration of the reproductive organs and process, leading to a reduction in the number of siliques and yield. Heat had a larger effect over drought on seed composition, which resulted in higher levels of saturated fatty oils. Higher levels of saturated fat under warmer climates could affect taste, freshness, and shelf life of canola oil. While adverse effects can be mitigated with irrigation and/or using genotypes with greater WUE, heat requires the breeding of heat tolerant canola.
In the third part of the study, two spring canola cultivars that were previously screened for drought tolerance were selected from a diversity panel. Czyzowska, a drought-resistant cultivar from Poland and BN-1, a drought-sensitive cultivar from India were used. Again, growth environment was observed with fluctuations in day/night temperatures and photoperiod, watering conditions and relative humidity to mimic drought conditions. Also measured was photosynthetic activity, night gas exchanges, leaf waxes, cysteine and sucrose, and growth and yield. This part of the study showed a noticeable response of leaf cysteine and sulphur to drought exposure in both cultivars, which agrees with previous studies demonstrating the involvement of sulphur and its derivatives in mitigating the effect of abiotic stressors on plants. The correlations between cysteine, ABA and stomatal conductance suggest a role of cysteine and sulphur in modulating the stomata movement under water deficit conditions. Also, the accumulation of significant levels of aspartic acid plays a crucial role during intermittent periods of drought. This mechanism is beneficial as it helps prevent leaf death and preserves nitrogen and carbon resources. The canola plant greatly benefits from the ability of its leaves to survive brief drought episodes. When favorable moisture conditions return, instead of waiting for new leaves to grow, the plant can promptly resume its photosynthetic activity. The study also demonstrated the responsiveness of load and composition of epicuticular waxes to drought in Brassica napus and the importance of water losses through stomata during dark periods and early mornings.
Full Report PDF: Impact of drought and heat during flowering on canola yield