Determining the Genetic Architecture of Reproductive Stage Drought Tolerance in Wheat Using a Correlated Trait and Correlated Marker Effect Model

Abstract

Water stress during reproductive growth is a major yield constraint for wheat ( Triticum aestivum L). We previously established a controlled environment drought tolerance phenotyping method targeting the young microspore stage of pollen development. This method eliminates stress avoidance based on flowering time. We substituted soil drought treatments by a reproducible osmotic stress treatment using hydroponics and NaCl as osmolyte. Salt exclusion in hexaploid wheat avoids salt toxicity, causing osmotic stress. A Cranbrook x Halberd doubled haploid (DH) population was phenotyped by scoring spike grain numbers of unstressed (SGNCon) and osmotically stressed (SGNTrt) plants. Grain number data were analyzed using a linear mixed model (LMM) that included genetic correlations between the SGNCon and SGNTrt traits. Viewing this as a genetic regression of SGNTrt on SGNCon allowed derivation of a stress tolerance trait (SGNTol). Importantly, and by definition of the trait, the genetic effects for SGNTol are statistically independent of those for SGNCon. Thus they represent non-pleiotropic effects associated with the stress treatment that are independent of the control treatment. QTL mapping was conducted using a whole genome approach in which the LMM included all traits and all markers simultaneously. The marker effects within chromosomes were assumed to follow a spatial correlation model. This resulted in smooth marker profiles that could be used to identify positions of putative QTL. The most influential QTL were located on chromosome 5A for SGNTol (126cM; contributed by Halberd), 5A for SGNCon (141cM; Cranbrook) and 2A for SGNTrt (116cM; Cranbrook). Sensitive and tolerant population tail lines all showed matching soil drought tolerance phenotypes, confirming that osmotic stress is a valid surrogate screening method.

A Physio-Morphological Trait-Based Approach for Breeding Drought Tolerant Wheat

“…This means that the measurement of yield attributing physio-morphological traits independent of grain yield improves the efficiency of selection by reducing the reliance on final grain yield. This approach may increase the possibility of making more successful crosses in a breeding program by exploiting the potential for additive gene action (Reynolds et al, 2009a;Ataei et al, 2017;Dolferus et al, 2019), as already noted above. In addition, it is always an advantage if the physiological trait considered for selection under a harsh environment has heritability higher than yield itself, which confers a greater chance for success for the development of a stress tolerant variety.…”

Drought Affected Wheat Production in Bangladesh and Breeding Strategies for Drought Tolerance

“…Conventional hybridization is the most widely used breeding procedure in wheat, where genetic variability is created through combination and recombination of desirable genes in the background of diverse adapted genotypes followed by a selection of desirable plants in subsequent generations to develop improved varieties for the target environment [4]. Generally grain yield is the primary basis for selection for drought tolerance but indirect selection based on related yield-contributing and physiological traits can be more effective for developing drought tolerant varieties [89,[93][94][95]. In this connection, several wheat lines collected from various national and international sources especially CIMMYT (International Maize and Wheat Improvement Center) are evaluated for their performance in diverse growing environments of Bangladesh [4].…”

Reproductive Stage Drought Tolerance in Wheat: Importance of Stomatal Conductance and Plant Growth Regulators

“…The wheat cultivars used in this study, drought-tolerant Halberd and drought-sensitive Cranbrook, were previously described [49]. Screening of a Cranbrook x Halberd doubled haploid (DH) population for QTL mapping previously identified the DH lines CH67 and CH115 as the most tolerant and sensitive lines respectively of the mapping population [52,53]. The two Australian commercial lines, Westonia and Excalibur, were shown to be drought-tolerant using our standard drought-tolerance assay (Dolferus et al, unpublished data).…”