Screening field pea for adaptation to water and heat stress: Associations between yield, crop growth rate and seed abortion

We compared 29 pea (Pisum sativum L.) accessions including advanced breeding lines and commercial varieties in environments spanning a 3-fold range in yield. Environmental variation in yield was primarily accounted for by modelled water availability and maximum temperature in a window from 400 degrees Cd before to 200 Cd after flowering. Our aims were to investigate (i) the trade-off between yield under stress and yield under favourable conditions, and (ii) the associations between yield and two traits: growth rate in a critical developmental window, and pod wall ratio (pod wall weight/whole pod weight). Trade-offs between yield in favourable and stressful conditions were not apparent but differences among accessions in their response to favourable environments were larger than differences in yield under stress. High plasticity of yield is therefore a desirable attribute for our combination of accessions and environments. Crop growth rate, calculated from calibrated NDVI (normalised vegetative difference index), accounted for 50% of the variation in seed number and for 44% of the variation in yield; both relationships fitted a ligand-binding function. The non-linearity of the relationship between seed number per m(2) and crop growth rate suggests a decoupling between growth and reproduction that may constrain yield potential. Accessions with smaller seed set more seeds per unit crop growth rate. In a sample of 4550 pods (approx. 157 pods per accession), variation in pod wall ratio was dominated by the variation in seed weight per pod, rather than pod wall weight. Seed abortion accounted for 47% of the variation in seed weight per pod and 37% of the variation in pod wall ratio. Yield was negatively correlated with pod wall ratio, which ranged from 11 to 26% across accessions. We estimated a genotype-dependent increase in yield of 73 kg ha(-1) per 1% reduction in pod wall ratio. In combination with selection for both yield in favourable environments and yield plasticity, maintenance of crop growth rate and low pod wall ratio could contribute to adaptation to heat and water stress. (C) 2013 Elsevier B.V. All rights reserved.