Complex G × E Interactions and QTL Clusters Govern End-Use Quality Traits in Hexaploid Wheat
Abstract Evaluation of wheat end-use quality in terms of loaf volume (LV) requires enormous time and labor inputs. Hence, many studies have attempted to use grain, flour and dough properties to predict LV. Many quantitative trait loci (QTL) underlying these traits have also been identified to facilitate breeding. However, correlations between such predictive tests and LV as well as their QTLs could be influenced by the environment. In this chapter, we review recent literature on the correlations and G × E interaction (GEI) of the bread making quality traits grain protein content (GPC), sodium dodecyl sulphate sedimentation volume (SV), dough rheological traits (DRT) and LV. We briefly discuss our results from the evaluation of a hexaploid wheat recombinant inbred line population for GPC, SV, LV and nine DRT by mixograph analysis in six year-location environments in India, which revealed that correlations between DRT and LV were not stable across environments. In addition, GEI measured in terms of principal components using Additive main effects and multiplicative interaction model showed up to 47 % contribution to the total variation of the traits, which was reflected in the location-specificity of QTLs expressed in single as well as multiple environments. Even though 16 QTL clusters for four to seven traits were identified, only one of them involved LV. The strong influence of the environment on complex interrelationships between DRT and the other end-use quality traits suggested that during breeding for wheat end-use quality, markerbased selection of these traits would be more efficient if specific agro-climatic zones are targeted separately.
Keywords AMMI analysis • Bread • Dough rheology • Interaction • Loaf volume • QTL • Quality
Selection for End-Use Quality Traits in Hexaploid Wheat: The Challenges
Improving wheat grain quality to cater to its diverse end uses is necessary to make its cultivation profitable. The quality of the industrial products made from hexaploid wheat such as leavened loaf bread depends critically on the properties of the grain, flour, dough and its responses during baking. Selection in the early generations for the most perceptible indicator of bread making quality (BMQ) namely, loaf volume (LV) is difficult due to the requirement of substantial quantities of grain and lack of high-throughput in evaluating it. BMQ is determined by many complex traits like grain protein content (GPC), gluten strength, dough viscosity, extensibility and elasticity. Hence, to predict LV, dough rheological traits (DRT); gluten strength often determined by sodium dodecyl sulphate sedimentation volume (SV) and GPC have been evaluated. However, determining simple and reliable predictive tests for LV and identification of consistent quantitative trait loci (QTL) with substantial contribution for such traits to aid marker-assisted selection (MAS) have proved difficult. This is due to the complex inter-relationships among the traits, large number of QTLs governing them, their co-location and possible pleiotropic effects as well as genotype × environment interactions (GEI) (Mann et al. 2009; Li et al. 2013). In this Chapter, we discuss the recent literature on these aspects and present a brief summary of our work on QTL and GEI analyses of the BMQ contributing traits.
Predictive tests for LV need to have high correlations with it that are stable in diverse environmental conditions and are simple, quick, require small sample size and should be able to clearly distinguish between genotypes. The breeding material thus selected can eventually be evaluated for LV in advanced stages. Various instruments such as farinograph, alveograph and mixograph have been employed to assess dough rheological changes during processing for the quality control of the end products. Among these, the computerized mixograph instruments can measure DRT when flour-water blend is subjected to a fixed mixing time. Though mixograph characters like dough development time, peak height and width are often employed to evaluate BMQ, single or few mixograph parameters as predictors of loaf volume have not been conclusively established (Mann et al. 2009; Caffe-Treml et al. 2010). More recently, Li et al. (2013) suggested small-scale tests like swelling index of gluten and lactic acid retention capacity to predict LV; however, further studies on the stability of their correlations with LV are needed.
For both LV and its potentially predictive parameters, many QTLs have been identified; however, their consistent expression across environments is necessary for their effective use (Li et al. 2012; El-Feki et al. 2013 and references therein). We performed detailed GEI, correlation and QTL analyses of end-use quality traits in a recombinant inbred line (RIL) population of 105 individuals derived from a bread wheat cross HI977 × HD2329. HI977 (good BMQ) possesses Glu-A1 (2*), Glu-B1 (17 + 18) and Glu-D1 (5 + 10) and HD2329 has Glu-A1 (2*), Glu-B1 (7 + 9) and Glu-D1 (2 + 12) and is poor in BMQ. Phenotypic evaluations were performed in three agro-climatically diverse locations in India namely, Karnal, Kota and Pune for two consecutive years (2003–04; 2004–05) and 12 BMQ related traits, viz. GPC,
Table 33.1 Dough rheological traits measured by mixograph analysis in HI977 × HD2329 RIL population
SV, LV and nine mixograph traits that could quantitatively reflect the energy used during the mixing process, changes in dough consistency and elasticity, optimum dough development time and the rate of the gluten network breakdown during over-mixing were recorded (Table 33.1) (Elangovan et al. 2008, 2011; Prashant et al. 2015).