Path analysis of phenotypic factors associated with grain protein in dryland winter wheat

In hard red winter wheat (Triticum aestivum L.), increased understanding of relationships between grain protein concentration (GPC) and other phenotypic traits is needed for simultaneously achieving high yield and GPC through genetic improvement and management. Two field experiments with 20 genotypes each were conducted in 2018/2019 in Uvalde and Chillicothe, TX. The primary objective was to assess direct and indirect effects of phenotypic traits on GPC using path analysis. Broad-sense heritability was high for grain yield but low for GPC, indicating that breeding selection for high yield is best done directly, but selection for elevated GPC may be approached indirectly. Grains m(-2) was positively related to GPC, though highly affected by environment, whereas 1000-kernel weight was negatively related to GPC and highly heritable. Heads m(-2) had a negative direct influence on GPC, but a positive indirect effect of head number on GPC through grain number indicated head number would positively impact GPC if additional heads increased grain number. There were conflicting results between locations on the relationship between aboveground biomass at anthesis and GPC, similar to other reports. Increased time to physiological maturity positively affected GPC, with time to anthesis being the primary offsetting indirect factor, meaning a longer grain-filling period can likewise increase GPC. Crop management practices can interact with these phenotypic factors to affect GPC, which is discussed herein. These findings provide novel information on direct and indirect effects of several phenotypic traits on GPC, giving insights into routes for improvement of wheat quality through breeding and management.