The development and plant characteristics of interspecific hybrids between white and caucasian clover

Abstract

A series of Trifolium ambiguum x T. repens hybrid populations has been developed at the hexaploid (four T. repens and two T. ambiguum genomes) and pentaploid (four T. repens and one T. ambiguum genome) level. When tested for effectiveness of symbiotic nitrogen fixation, the 6x and 5x hybrids nodulated with either T. repens or T. ambiguum strains of rhizobia but only formed an effective N- fixing symbiosis with a mix of T. repens rhizobia strains. When grown in the field, the 6x and 5x hybrid plants had a similar morphology to white clover in that the hybrids grew surface stolons (fewer numbers than white clover) and no underground rhizomes. The advantage of the 6x hybrid was deeper roots and a greater proportion of root, a characteristic considered important for greater drought tolerance and persistence than for white clover. The 6x hybrid indicated 55% of the seed production potential of white clover, but there was large variation between plants in all reproductive traits. The 5x hybrid showed poor levels of seed set. The growth pattern of the 6x hybrids in the field indicated lower herbage yield in the first year but improved performance compared with white clover into the second year. At this early stage, the hybrid breeding populations consist of unselected and novel hybrid combinations. Variations in growth and reproductive characteristics exist between hybrid plants, thus providing scope for improvement through selection and breeding. Key words: caucasian clover, interspecific hybrid, morphology, nitrogen fixation, seed production, white clover