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Introduction
As climate change accelerates, the frequency and severity of extreme weather events, such as heatwaves and droughts, are on the rise (Rashid et al., 2018; Egli et al., 2005). These challenges significantly impact oilseed rape (OSR; Brassica napus L.), a globally important oil crop, as it faces increased exposure to adverse weather conditions and abiotic stress (Rashid et al., 2018). However, little is known about abiotic stress effects on OSR growth and yield formation as well as the seeds’ subsequent germination ability. Hence, this study aims to explore the impact of heat and drought stress on OSR during different phenological stages.
Material and Methods
We conducted a pot experiment in controlled greenhouse chambers growing single OSR plants cv. Ability in 2L pots filled with local topsoil. We applied four experimental factors to test their single and combined effects, 1.) four levels of heat stress, 24°C, 30°C, 34°C, and 38°C applied for 14 hours with a four-hour adjustment period and 16°C night temperature for all treatments, 2.) two levels of drought stress, i.e., without drought stress (plant available water (PAW) > 60% plant available water capacity (PAWC)) and with drought stress (PAW < 20% PAWC), 3.) two levels of treatment timing, i.e., flowering stage (BBCH 61) and seed filling stage (BBCH 75), and 4.) two levels of treatment duration, 6 days and 12 days. We evaluated the effects separately on the main branch, first and second side branches, and remaining branches.
For the germination test, we placed the harvested seeds of each treatment × branch-level combination on wetted filter paper in 10 cm2 petri dishes in a climate chamber at 22°C. We ran the experiment in three replications, counting germinated seeds 12, 14, 16, 18, 20, 22, and 36 hours after wetting. Using the germination-metrics package in R studio, we computed various germination indices, including the time until 50% and 100% of seeds germinated, median germination time, mean germination rate, and germination speed. We used mixed linear models for further statistical analysis using the lme package in R.
Results and Discussion
The experiments showed significant effects on grain yield, with heat and drought stress, coupled with longer duration, resulting in decreased yields (Fig.1). Stress during flowering had a greater impact on yield compared to the seed filling stage. Interestingly, severe heat stress during flowering, which obstructed fertilization and seed set on the main branch, was fully compensated by additional siliques and seeds on the lower branches, while severe drought stress during flowering could not be compensated. Analysis of seed size and fatty acid composition provided insights into combined heat and drought stress effects. Regarding germination indices, heat, and drought stress together had a pronounced impact compared to individual stressors. Stress during flowering reduced germination percentage and time, especially with both stressors present. Drought stress lowered germination across all branches, while combined stress reduced it in the first two branches only. We explain this by the compensation of destroyed main branch flowers via additional new flowers and seeds on the lower branches after stress ceased. These findings highlight the compensation capacity of OSR against severe heat but not drought stress during flowering supporting the design of more resilient OSR cultivation systems under climate change.
References
Burris, L.G.a.J.S., Effect of heat stress during seed development and maturation on wheat (Triticum durum) seed quality.ll. Mitochondrial respiration and nucleotide pools during early germination. Canadian Journal of Plant Science, 1995. 75(4): p. 831-839
Egli, D.B., et al., Air Temperature During Seed Filling and Soybean Seed Germination and Vigor. Crop Science, 2005. 45(4): p. 1329-1335
Gillen, A.M., et al., Effects of Maturity and Phomopsis longicolla on Germination and Vigor of Soybean Seed of Near-Isogenic Lines. Crop Science, 2012. 52(6): p. 2757-2766
Rashid, M., et al., Heat stress during seed development affects forage brassica (Brassica napus L.) seed quality. Journal of Agronomy and Crop Science, 2018. 204(2): p. 147-154
Toledo, M.Z., et al., Physiological quality and enzymatic activity of crambe seeds after the accelerated aging test. Acta Scientiarum. Agronomy, 2011. 33(4)
| Keywords | Heat stress; Drought; oilseed rape |
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