High night‐time temperature during flowering and pod filling affects flower opening, yield and seed fatty acid composition in canola

Abstract

Winter canola (Brassica napus L.) is highly sensitive to increasing temperatures during the reproductive and pod‐filling stages. Although the impact of high day‐time temperature stress on yield and quality has been documented in canola, similar information under high night‐time temperature (HNT) stress is not available. Using six hybrids and four open‐pollinated cultivars, we observed a marked shift in peak flowering towards earlier, cooler hours of the morning under HNT. Averaged across two independent experiments, the photochemical efficiency of photosystem II was significantly decreased (3%), with a significant increase in thylakoid membrane damage (13%) in the leaves of susceptible cultivars under HNT stress. Similarly, the susceptible cultivars also recorded significant reduction in biomass (34%), pod number (22%), pod weight (37%) and total seed weight (40%) per plant while the same set of agronomic traits were not affected among the tolerant cultivars. Quantitative impact of heat stress was confirmed with increased sensitivity to HNT exposure from gametogenesis until maturity resulting in a significantly higher yield loss compared to stress exposure from post‐flowering till maturity. HNT significantly decreased oil concentration, but increased protein concentration and saturated fatty acid levels in seeds of the susceptible cultivars. However, HNT had no impact on the unsaturated fatty acids in both hybrids and the open‐pollinated cultivars. Breeding targets based on fatty acid composition for enhancing canola seed quality may not be easily amenable due to the inconsistency documented with the compositional changes under heat stress. In summary, our findings conclude that canola hybrids are better suited to regions experiencing heat stress, compared to open‐pollinated cultivars, indicating the possibility of a complete shift to hybrid canola cultivation under predicted hotter climates in the future.

Transient daily heat stress during the early reproductive phase disrupts pod and seed development in Brassica napus L.

“…Night temperatures are also critical to the impact of heat stress treatments. High night temperatures during reproductive growth reduced grain yield in canola (Pokharel et al, 2020), and similar observations were made in rice (Bheemanahalli et al, 2017;Coast et al, 2015), quinoa (Lesjak & Calderini, 2017), wheat, and barley (García et al, 2015). Seed set, grain number, and grain yield in winter wheat declined when both daytime (35°C) and night-time (24°C) temperatures were high (Narayanan et al, 2015).…”

“…This suggests that lower night-time temperatures may partially compensate for moderate levels but not for high levels of transient daily heat stress. Pokharel et al (2020) found that high night-time temperature (20°C) significantly reduced pod numbers (22%) and total seed yield (40%) in canola compared to cool night-time temperature (15°C) when the daily maximum was 23°C. Dreccer et al (2018) also found that higher minimum temperature after flowering was associated with lower canola seed yield across four major production zones in the 2009-2013 national variety trials in Australia.…”

“…Pokharel et al. (2020) found that high night‐time temperature (20°C) significantly reduced pod numbers (22%) and total seed yield (40%) in canola compared to cool night‐time temperature (15°C) when the daily maximum was 23°C. Dreccer et al.…”

The stage sensitivity of short‐term heat stress to lodging‐resistant traits and yield determination in canola (Brassica napus L.)

“…Heat stress also negatively affects photosynthetic capacity, respiration, water balance, biomass accumulation and even oil quality‐related attributes (Kaushal et al., 2016; Mayer et al., 2014). The resultant yield and quality decreases due to heat stress ultimately reduce the economic returns and the global supply of canola oilseed (Koscielny, Gardner, et al., 2018; Pokharel et al., 2020; Wu et al., 2018).…”

“…Canola plants also experience heat stress at different phenological stages, such as the early inflorescence emergence stage where flower bud development is affected, or the late grain filling stage where the pod filling process is restricted (Gan et al., 2004; Pokharel et al., 2020; Prasad et al., 2017; Singh et al., 2013). Early exposure to heat stress before flowering may have little effect on pollen viability and final pod fertility in canola, but may reduce photosynthesis and biomass accumulation, enhance plant respiration and carbohydrate loss during the plant life cycle and lead to the alteration of plant morphology and even yield loss (Siebers et al., 2017; Suraweera et al., 2020; Wu & Ma, 2018).…”