Quantifying the Impact of Heat Stress on Pollen Germination, Seed Set, and Grain Filling in Spring Wheat

Abstract

Exposure to temperatures ≥30°C during flowering and grain filling stages can negatively affect seed set and seed weight in spring wheat (Triticum aestivum L.). The screening of a large set of germplasm under hot wheat growing environments (Indo‐Gangetic Plain in India) led to the identification of promising heat‐tolerant genotypes. The selected set of 28 diverse spring wheat genotypes were exposed to heat stress (34/16°C day/night temperatures) for 10 d during flowering and for 30 d during grain filling to quantify genetic variability in pollen germination, photosynthesis, and yield parameters under controlled‐environment conditions. Pollen grains collected immediately at anthesis (between 0530 and 0630 h) were incubated on liquid in vitro pollen germination media. Averaged across wheat genotypes, a significant reduction in pollen germination (39.9%, P < 0.001) was recorded from plants exposed to heat stress. Heat stress for 10 d during flowering induced significant reduction in seed number (15.4 and 23.0%) and seed weight (32.3 and 34.6%) on main and primary spikes, respectively, compared with the control. Heat stress during grain filling had a more pronounced impact on seed weight (16 and 22%) than seed number (2.7 and 9.3%) in main and primary spikes, respectively. Genotypes KSG025 and KSG1214 with higher seed number, seed weight, and harvest index and appreciable pollen germination under heat stress were identified as candidate donors for simultaneously enhancing flowering and post‐flowering heat tolerance in spring wheat.

Heat stress during flowering in cereals – effects and adaptation strategies

“…One of the primary effects of heat stress on the male reproductive organ is poor anther dehiscence, limiting the release of mature pollen, resulting in lower pollen load on the stigma (Jiang et al , ). Pollen is highly sensitive to heat stress but a large genetic variation for pollen viability exists that can help in reducing heat stress‐induced crop yield losses (cotton ( Gossypium hirsutum ), Kakani et al , ; pearl millet, Djanaguiraman et al , ; tomato ( Solanum lycopersicum ), Paupiere et al , ; sorghum, Sunoj et al , and wheat, Bheemanahalli et al , ). Heat stress exposure on chamber grown sorghum resulted in increased accumulation of reactive oxygen species (ROS) in pollens, leading to pollen membrane damage, collapsed and desiccated pollen, ultimately resulting in 62–90% reduction in seed set (Djanaguiraman et al , ; Fig.…”

High night temperature induced changes in grain starch metabolism alters starch, protein, and lipid accumulation in winter wheat

“…Daytime mean temperature above 30 o C or maximum temperatures ≥34 o C, particularly during the sensitive flowering and grain-filling stages, is shown to reduce wheat yields under field conditions (Bergkamp, Impa, Asebedo, Fritz, & Jagadish, 2018;Tack, Barkley, & Nalley, 2015). Similarly, wheat plants grown in controlled environment chambers with maximum day temperatures of ≥34°C at anthesis, recorded significantly lower pollen germination and seed-set compared with plants grown at 25°C (Aiqing et al, 2018;Bheemanahalli et al, 2019).…”

“…Daytime mean temperature above 30 o C or maximum temperatures ≥34 o C, particularly during the sensitive flowering and grain‐filling stages, is shown to reduce wheat yields under field conditions (Bergkamp, Impa, Asebedo, Fritz, & Jagadish, ; Tack, Barkley, & Nalley, ). Similarly, wheat plants grown in controlled environment chambers with maximum day temperatures of ≥34°C at anthesis, recorded significantly lower pollen germination and seed‐set compared with plants grown at 25°C (Aiqing et al, ; Bheemanahalli et al, ). Although increasing frequency and intensity of daytime heat spikes do pose a challenge to maintain genetic gains, a more gradual but consistent increase in night‐time temperature is emerging as a more serious threat to global crop production (Peng et al, ; Sillmann, Kharin, Zwiers, Zhang, & Bronaugh, ).…”

Deterioration of ovary plays a key role in heat stress‐induced spikelet sterility in sorghum

“…However, a substantial increase in temperature variability around the mean is a significant new dimension that most crops are not programmed to cope with. This increase in variability will lead to more intense but short episodes of heat stress, which, when coincided with a critical reproductive stage such as flowering, leads to significant reduction in yield and productivity of field crops (maize [ Zea mays L.], Siebers et al, ; rice [ Oryza sativa L.], Jagadish et al, ; sorghum [ Sorghum bicolor [L.] Moench], Sunoj et al, ; and wheat [ Triticum aestivum L.], Aiqing et al, ; Bheemanahalli et al, ). Even under current environmental conditions, heat stress coinciding with reproductive stages has resulted in significant economic losses in field crops grown in different geographical locations (rice [Ishimaru et al, ]; sorghum [Tack, Lingenfelser, & Jagadish, ]; wheat [Tack, Barkley, & Nalley, ]).…”