Genotypic variation in white clover growth and branching in response to temperature and nitrogen

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Abstract
Polycross progenies of 7 New Zealand white clover plants and their F1 progeny after hybridisation with a Spanish population were grown at a range of temperatures. Symbiotic ‘N-sufficiency’ was measured as the ratio of stolon growth with symbiotic-N: stolon growth with non-limiting mineral-N. N-sufficiency for stolon growth was close to 1.0 at the highest day/night temperature (27.5°C/18.0°C), but was markedly less at lower temperatures (down to 12.5°C/6.0°C). Over all temperatures, hybridisation with Spanish plants conferred greater N-sufficiency in stolon growth than did interpollination with New Zealand material, although the plants showed wide genotypic variation in this characteristic. Increased stolon branching was shown by clover plants grown at low temperature, and plants dependent on symbiotic-N. As the temperature increased, the difference between the N treatments became less marked. Genotypic differences in branching in relation to N source were also identified. Genotypic variation in N-sufficiency, and stolon branching response to different N sources is discussed in relation to the breeding of white clover cultivars for use in high-N soils.