White clover (Trifolium repens L.) is a widely used and highly valued temperate legume; however, its productivity and survival are restricted under dryland and drought conditions. This study investigated whether drought resistance of white clover could be improved by interspecific hybridisation with Trifolium uniflorum L. After almost 4 months without irrigation in a rain-shelter facility, shoot dry weight (DW) decreased significantly less in first-generation backcross (BC1) hybrids (–47%) than second-generation backcross (BC2) hybrids (–68%) and white clover (–69%). Stolon morphological parameters such as internode length and leaf lamina area also decreased less under water stress in the BC1 hybrids than in BC2 and white clover. There was also lower senescence in BC1 under water stress than in the other clover types. Genotypes with smaller changes in leaf lamina area, internode length, senescence and lateral spread had smaller changes in shoot DW, and there were significant correlations between constitutive levels of some characteristics and the effect of water stress on shoot DW. Under water stress, the growth form of the BC1 hybrids was compact, dense and prostrate, whereas white clover was more spreading and open. Increased allocation of dry matter to roots under drought, and greater root diameter, may also have influenced the ability of BC1 hybrids to maintain water uptake and key physiological processes. Overall, the data confirm that the drought resistance of white clover can be improved through hybridisation with T. uniflorum.
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Vol. 65 • No. 9