High temperature effects on wheat yield, grain quality, and pollen lipids

Abstract

Wheat (Triticum aestivum L.) contributes ~20% of global dietary calories and 21% of daily protein intake, underpinning global food security. However, high-temperature (HT) stress increasingly threatens wheat yield and quality by accelerating development, impairing reproduction, and altering grain composition. This thesis investigates HT effects on wheat grain traits and reproductive resilience using both field and controlled-environment experiments across genotypes differing in heat tolerance.

Field trials were conducted in 2019 and 2020 at Narrabri (NSW), Horsham (VIC), and Merredin (WA), employing early and late sowing to vary HT exposure during grain filling. Cultivars included Berkut and Flanker (heat-tolerant), Sokoll and Suntop (moderately tolerant), and Cobra (sensitive). Analyses encompassed yield, thousand kernel weight (TKW), protein fractions, starch, fibre, RVA profiles, mineral content, and phytate levels. Statistical analyses included ANOVA and Tukey’s HSD.

HT generally reduced yield and TKW, while crude protein increased, especially in sensitive cultivars, though glutenin-to-gliadin ratios declined. Starch content and pasting properties deteriorated under HT, with some cultivars (e.g., Cobra, Sokoll) exhibiting significant reductions in peak and breakdown viscosities. Crude fibre increased in some cases, likely due to accelerated lignification. HT also influenced mineral uptake and phytate concentration, shaped by cultivar and soil type, with Berkut retaining higher mineral levels.

A controlled-environment experiment assessed pollen lipid composition in four cultivars under three temperature regimes (22/15°C, 35/22°C, and 40/22°C). HT reduced both saturated and unsaturated fatty acids, particularly in Cobra, correlating with poor pollen viability. In contrast, Flanker and Suntop maintained lipid homeostasis, indicating superior thermotolerance.