Calderini, D. F. | Search bioRxiv

bioRxiv2024

Resilience of rapeseed to heat stress during grain filling in a high yielding environment

Global climate change is driving the temperature increase, which negatively impacts on crop production. Most heat stress studies in rapeseed have been conducted under controlled conditions, limiting their results to true field crops. This study aimed to assess the sensitivity of rapeseed to temperature increase during two phases of the grain filling period in southern Chile, a high-yield potential environment. To our knowledge, this is the first field study evaluating the effects of heat stress at different phases of grain filling in rapeseed. Three field experiments were conducted with two adapted spring rapeseed hybrids, Lumen and Solar CL, under three temperature treatments: a control at ambient temperature, a 5{degrees}C increase from the beginning of flowering to 15 days after flowering (DAF), and the same increase from 15 to 30 DAF. Crop and climate variables, including air temperature and solar radiation were recorded along the experiments. Slight effects on grain yield due to heat stress were found, however, the hybrids exhibited different sensitivities, with Lumen being less affected than Solar CL. Grian yield of the last hybrid showed positive association with photothermal quotient and negatively with temperature, while Lumen did not show relationship. The most significant impact on grain yield occurred during the first half of grain filling (0-15 DAF), resulting in a reduction of 26.8% of grain number in Solar CL, compared to a 6.0% reduction in Lumen across experiments. Grain weight remained little affected by thermal stress, indicating its conservative behaviour and tolerance in southern Chile conditions. Grain oil concentration was scarcely sensitive, while grain protein concentration increased under heat stress. The low impact on the crop outcomes of our studies may be attributed to the lower background temperature of southern Chile, suggesting that this environment may confer greater rapeseed heat tolerance during grain filling than in other agroecosystems.

physiology↗

bioRxiv2024

The trade-off between grain weight and grain number in wheat is explained by the overlapping of the key phases determining these major yield components

Enhancing grain yield is a primary goal in the cultivation of major staple crops, including wheat. Recent research has focused on identifying the physiological and molecular factors that influence grain weight, a critical determinant of crop yield. However, a bottleneck has arisen due to the trade-off between grain weight and grain number, whose underlying causes remain elusive. In a novel approach, a wheat expansin gene, TaExpA6, known for its expression in root tissues, was engineered to express in the grains of the spring wheat cultivar Fielder. This modification led to increases in both grain weight and yield without adversely affecting grain number. Conversely, a triple mutant line targeting the gene TaGW2, a known negative regulator of grain weight, resulted in increased grain weight but decreased grain number, potentially offsetting yield gains. This study aimed to evaluate four wheat genotypes: (i) a transgenic line expressing TaExpA6, (ii) its wild-type counterpart (Fielder), (iii) a TaGW2 triple mutant line, and (iv) its wild-type. Conducted in southern Chile, the study employed a Complete Randomized Block Design with four replications, under well-managed field conditions including fertilization, irrigation, and pest control. The primary metrics assessed were grain yield, grain number, and average grain weight per spike, along with detailed measurements of grain weight and dimensions across the spike, and ovary weight at pollination (Waddingtons scale 10). The expression levels of TaExpA6 and TaGW2 were also monitored post-anthesis. Results indicated that both the TaExpA6 line and the triple mutant line achieved significantly higher average grain weights compared to their respective wild types. Notably, the TaExpA6 line did not exhibit a reduction in grain number, thereby enhancing grain yield per spike. In contrast, the triple mutant line showed a reduced grain number per spike, with no significant change in overall yield. Analysis of ovary size, grain weight dynamics, and gene expression patterns suggests that the trade-off between grain weight and number could be attributed to the overlapping of the critical periods for the determination of these traits.

plant biology↗