Nitrogen fixation in hybrids of white clover (Trifolium repens L.) and Caucasian clover (Trifolium ambiguum M. Bieb)

Hybrids between white clover (Trifolium repens L.) and Caucasian clover (or Kura clover, Trifolium ambiguum M. Bieb) are a potential route for the imp rovement of drought tolerance and persistence in white clover. However, to be agronomically viable they must show no significant reduction in their po tential for nitrogen fixation relative to white clover. A comparative study of growth rate and nitrogen fixation was carried out in flowing solution c ulture without a supply of mineral nitrogen to the plants. The two parental species and two generations of backcross hybrids, with white clover as the recurrent parent, were assessed. The growth rate and N content of T. ambig uum were significantly lower than those of the other lines. However, dry ma tter production, nodule biomass per plant and rates of fixation were simila r in second-generation backcross plants and white clover. The results sugge st that the agronomic potential of this novel germplasm is not compromised by limitations with respect to nitrogen fixation.