The WtmsDW Locus on Wheat Chromosome 2B Controls Major Natural Variation for Floret Sterility Responses to Heat Stress at Booting Stage.

Million F Erena,Nicholas C Collins,Livinus C Emebiri,Julian D Taylor,Iman Lohraseb,Isabel Munoz-Santa

doi:10.3389/fpls.2021.635397

Abstract

Heat stress at booting stage causes significant losses to floret fertility (grain set) and hence yield in wheat (Triticum aestivum L.); however, there is a lack of well-characterized sources of tolerance to this type of stress. Here, we describe the genetic analysis of booting stage heat tolerance in a cross between the Australian cultivars Drysdale (intolerant) and Waagan (tolerant), leading to the definition of a major-effect tolerance locus on the short arm of chromosome 2B, Wheat thermosensitive male sterile Drysdale/Waagan (WtmsDW). WtmsDW offsets between 44 and 65% of the losses in grain set due to heat, suggesting that it offers significant value for marker-assisted tolerance breeding. In lines lacking the WtmsDW tolerance allele, peaks in sensitivity were defined with reference to auricle distance, for various floret positions along the spike. Other (relatively minor) floret fertility response effects, including at the Rht-D1 dwarfing locus, were considered likely escape artifacts, due to their association with height and flowering time effects that might interfere with correct staging of stems for heat treatment. Heat stress increased grain set at distal floret positions in spikelets located at the top of the spike and increased the size of spikelets at the base of the spike, but these effects were offset by greater reductions in grain set at other floret positions. Potentially orthologous loci on chromosomes 1A and 1B were identified for heat response of flowering time. The potential significance of these findings for tolerance breeding and further tolerance screening is discussed.

Highlights

Heat stress reduces yields of wheat in most global production environments, and the situation is worsening with climate change (Asseng et al, 2015).Elevated temperatures accelerate development, senescence, and water use, reducing the opportunity to accumulate biomass and yield (Asseng et al, 2011; Hunt et al, 2018)
After identifying a strong floret fertility heat tolerance locus on chromosome 2B (WtmsDW), KASPTM assays were utilized to map this region in more detail and develop Wheat thermosensitive male sterile Drysdale/Waagan (WtmsDW) nearisogenic lines
In the doubled haploid (DH) quantitative trait loci (QTL) experiment, all traits measured after heat treatment responded to heat in the DH lines, except for number of spikelets per spike (Figure 1)

Summary

Introduction

Heat stress reduces yields of wheat in most global production environments, and the situation is worsening with climate change (Asseng et al, 2015).Elevated temperatures accelerate development, senescence, and water use, reducing the opportunity to accumulate biomass and yield (Asseng et al, 2011; Hunt et al, 2018). Heat stress reduces yields of wheat in most global production environments, and the situation is worsening with climate change (Asseng et al, 2015). Wheat has two periods of sensitivity to the floret sterility effects: during booting (flag leaf sheath extending, 1–2 weeks before anthesis), and 2–3 days before anthesis (Saini and Aspinall, 1982; Tashiro and Wardlaw, 1990a; Craufurd et al, 2013; Prasad and Djanaguiraman, 2014; Barber et al, 2017). Heat stress during early grain filling reduces the weight of individual grains (Tashiro and Wardlaw, 1990b; Stone and Nicolas, 1995). Grain filling heat stress can affect grain physical and biochemical traits determining processing characteristics and end-use quality (Stone and Nicolas, 1998; Wrigley, 2007)

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