The effects of elevated temperature stress on grain-filling in wheat (Triticum aestivum L.)

Abstract

Temperatures outside certain thresholds during specific growth phases of plants can cause stress and inefficiencies for productivity, including elevated temperatures or heat stress. To identify thermotolerance of 32 diverse wheat genotypes, multiple-environment (MET) and multiple-trait MET analyses identified genotype x environment interactions for yield and determined the key traits and environmental conditions associated, including maturity biomass, harvested index, grain-filling duration, and vegetative minimum temperature (r = 0.64, 0.48, 0.27, 0.44 respectively). Grain-filling was investigated further in a subset of genotypes (14) and found tolerant genotypes increased grainfilling rate and/or grain number and main stem biomass remobilisation to compensate for the reduced grain-filling duration under heat-stress. Stem biomass accumulation and remobilisation efficiency in the form of water-soluble carbohydrates was investigated in a further subset of 7 genotypes. WSC dynamics were measured throughout grain-filling and calculated for glucose, fructose, sucrose, and fructans, which confirmed that tolerant genotypes maintained pre- and post-anthesis WSC accumulation, as well as remobilisation efficiency over time and along the stem under stress. Controlled environment facilities were then used to assess the effect of priming (seven-leaf stage; 35/28°C for 48h) and the impact and recovery of subsequent heat stress (4- or 7-days at 38/5°C) on grain-filling and fructan synthesis on 6 genotypes. This study highlighted heat stress affects grainfilling and yield negatively and improvement is required given predicted future climatic conditions; however, thermotolerance can be achieved through compensation responses and adaptability associated with increased carbon assimilation and increased carbon remobilisation, which alleviates source limitations and dependency on more heat-liable photoassimilates during grain-filling under stress conditions.