Physiological drought resistance and accumulation of leaf phenolics in white clover interspecific hybrids

Abstract

© 2015 Elsevier B.V. This study investigated drought responses in first (BC₁) and second (BC₂) backcross generation hybrids of Trifolium repens L. × T. uniflorum L., and compared these to high-yielding T. repens L. (white clover) cultivars. Plant attributes included accumulation of leaf phenolics as well as other biochemical and physiological water stress responses. Measurements were made across broad clover types as well as on a subset of related material. Under drought, net photosynthesis decreased by 44-48% and transpiration rates decreased by 60% in the BC₂ family and in the white clover parent, but were unaltered in the BC₁ family. Drought-induced decreases in leaf water potential were more pronounced in the BC₁ family (-47%) than the BC₂ (-31%) and parental (-28%) material. Quercetin glycoside accumulation generally increased 2-3 fold under drought. Compared with the BC₂ family and with parent plants, the BC₁ family had 2.5-4x higher constitutive kaempferol glycoside levels, and 1.5-2.5x higher kaempferol glycoside accumulation under drought. Constitutive kaempferol glycoside accumulation was related to reduced senescence and to less pronounced decreases in shoot DW under drought stress. Hydroxycinnamic acid accumulation increased by 56-73% under water stress, particularly for the BC₁ generation. These results identify physiological and biochemical traits that help explain drought resistance of T. repens × T. uniflorum hybrids. The findings suggest merit for the selection of BC₁ families with increased accumulation of protective phenolic compounds in breeding programmes for improved drought resistance.