Genotype × environment analysis of flavonoid accumulation and morphology in white clover under contrasting field conditions

White clover (Trifolium repens) is a beneficial legume in temperate pastures as a provider of high quality feed to stock and nitrogen to grassland. However, its growth is often strongly impaired by summer drought. The aim of this study was to investigate the association of flavonoids and biomass production in environments contrasting in moisture availability, and to identify trait ideotypes to be used in breeding plants for stress environments. In two separate field experiments, cloned individuals from a mapping population consisting of full sib progeny of a bi-parental cross were exposed to two contrasting field environments: water-limited (WL) and water sufficient (WS). Most measured morphological, physiological traits and flavonol glycoside accumulation were affected by the contrasting WL and WS environments. WL decreased carbon isotope discrimination by 5.5%. Under WL the levels of quercetin glycosides (Q) and of the quercetin:kaempferol glycoside ratio (QKR) increased by 62% and by 36%, respectively, relative to the WS environment. The WL environment reduced shoot dry matter (SDM) by 68%, with the most productive genotypes showing the greatest proportional reduction. Stolon numbers per plant decreased by 48% under WL, but stolon density (stolon number m−2 canopy area) increased by 48%. In principal component analysis, drought-induced changes in plant morphology were closely aligned to changes in Q, but not kaempferol glycosides. The increased induction of Q accumulation in response to water deficit stress was related to retaining higher levels of SDM production. This study also enabled the identification of individual plant trait combinations useful for white clover breeding programs focussed on developing improved cultivars for dryland environments.

► Growth of white clover is impaired by summer drought.
► Water deficit in the field reduces carbon isotope discrimination.
► Quercetin glycosides are preferentially synthesised over kaempferol glycosides.
► Accumulation of quercetin glycosides is related to retaining biomass.
► Stolon density is inversely related to stolon numbers under water deficit.