Oat phenotypes for drought adaptation and yield potential

We measured yield and its components, phenology, leaf greenness, and concentration of water soluble carbohydrates and concentration of nitrogen in shoots of 29 oat varieties to determine (i) the phenotypic plasticity of these traits as a means to capture genotype-by-environment interactions, (ii) the role of these traits and their plasticity in adaptation to drought, and (iii) putative trade-offs between drought adaptation and yield potential. Varieties spaned grain, hay and grazing types, and ranged from 1301 to 1927 °Cd from sowing to anthesis. Yield was measured in nine environments while other traits were measured in 4-7 out of the 9 environments. Averaged across varieties, yield varied from 0.3 to 4.2 t ha−1. The main environmental drivers of yield were water supply:demand from 500 °Cd before to 500 °Cd after anthesis, and minimum temperature in the same period. Phenotypic plasticity of yield, quantified as variance ratio, ranged from 0.60 to 1.22 for grain types and from 0.28 to 1.06 for their grazing and hay counterparts; high yield plasticity was associated with an asymmetric response to growing conditions: yield increased 3.3 ± 0.28 t ha−1 per unit increase in plasticity under favourable conditions, and 0.6 ± 0.16 t ha−1 per unit increase in plasticity under stress. For our combination of varieties and environments, genotypes were better discriminated in favourable environments, where selection for high plasticity would improve both yield potential and drought adaptation. After accounting for plasticity, yield residuals revealed consistent phenological thresholds (943 °Cd for GS31, 1470 °Cd for GS60) for adaptation to both favourable and stressful conditions. Yield correlated with leaf greenness (SPAD), particularly during grain fill. As expected from theory, yield was closely related to grains per m2 and weakly related to grain weight. Grains per m2 were negatively related to concentration of water soluble carbohydrates in shoots, which were in turn negatively correlated with shoot nitrogen concentration. Under favourable conditions, some varieties maintained a high concentration (>20%) of water soluble carbohydrates at harvest. Selection against this trait could improve yield potential, but residual labile carbohydrates can also be exploited in dual grain-feed varieties, and can provide flexibility for hay growers when logistics preclude cutting at the common water ripe (GS71) target.