Improving the Adaptation of Wheat (Triticum aestivum) to Heat Stress Conditions

Abstract

Heat stress is a significant abiotic stress limiting crop production in many regions globally, including in the Mediterranean-type environments of southern Australia. Various approaches have been used to understand the negative impacts of heat stress conditions on plant function and crop productivity, with several loci identified with proposed benefits for adaptation to heat stress conditions. However, there has been little uptake of targeted selection for heat stress traits or loci by breeding programs. This study used a combination of controlled environment evaluation targeting heat stress conditions during grain filling (three consecutive days of 36°C with a wind speed of 40 km h-1 starting 10 days post anthesis), and evaluation over multiple representative field environments. Field environments were targeted to achieve a range of heat stress conditions during the sensitive anthesis and grain filling developmental stages and were conducted within the South Australian cereal producing region, with temperature co-variates used to quantify the level of stress in each environment. A series of experiments evaluated relevant Australian varieties and advanced breeding lines to evaluate the level of adaptation to heat stress conditions currently available in adapted germplasm. This allowed the impacts of heat stress on grain yield, and the role of heat stress during anthesis and grain filling on variety performance to be evaluated. In a second component of the study, seven doubled haploid mapping populations were evaluated to identify QTL for adaptation to heat stress conditions. The QTL analysis was conducted to identify performance (QTL with stable performance regardless of heat stress treatment, or across a range of stress conditions in the field), and to identify responsiveness (QTL with a favourable response to heat stress treatments in a controlled environment, or a favourable response to increasingly stressful conditions experienced in the field), with numerous QTL identified in both controlled environment and field conditions. The QTL identified provides opportunities for breeders to target improved adaptation to heat stress conditions through two mechanisms: performance QTL for stable and elite adaptation across all environments, and responsiveness for specific adaptation allowing selection of a favourable response to stressed conditions. This study proposes that assessing adaptation to heat stress conditions as the combination of performance and responsiveness is an improved definition and framework to assess tolerance to heat stress conditions, and is of greater relevance to breeders’ selection objectives.