Development of a ploidy series from a single interspecific Trifolium repens L. . nigrescens Viv. F1 hybrid

The objective of the current research was to generate a ploidy series of backcross progenies froma single triploid (2n=3x=24) Trifolium repens×T. nigrescens F^sub 1^ hybrid (3x H-6909-5). The 3x H-6909-5 plant was highly sterile and produced no seeds from approximately 3000 reciprocal backcrosses to both parental species. Chromosome doubling by an in vitro colchicine method resulted in a marked increase in fertility. Pollen stainability was increased from 9.9% in 3x H-6909-5 to an average of 89.2% (range 87.7-90.9%) in the three chromosome-doubled 6x H-6909-5 plants. Subsequent backcrosses of 6x H-6909-5 and interbreeding of backcross derivatives resulted in an array of fertile hybrids at 4x, 5x and 7x levels and some aneuploids. The occurrence of 7x BC^sub 1^F^sub 1^ progeny from the T. repens×6x H-6909-5 (4x×6x) cross is the first unequivocal evidence of functional female 2n gametes in white clover. Meiotic pairing in F^sub 1^ and BC^sub 1^F^sub 1^ progeny indicated the presence of allosyndetic pairing, suggesting that genetic exchange between the two species is possible.[PUBLICATION ABSTRACT]