DEVELOPMENT OF A PLOIDY SERIES FROM A SINGLE INTERSPECIFIC TRIFOLIUM-REPENS L X TRIFOLIUM-NIGRESCENS VIV F1-HYBRID

The objective of the current research was to generate a ploidy series of backcross progenies from a single triploid (2n=3x=24) Trifolium rep ens x T. nigrescens F-1 hybrid (3x H-6909-5). The 3x H-6909-5 plant wa s highly sterile and produced no seeds from approximately 3000 recipro cal backcrosses to both parental species. Chromosome doubling by an in vitro colchicine method resulted in a marked increase in fertility. P ollen stainability was increased from 9.9% in 3x H-6909-5 to an averag e of 89.2% (range 87.7-90.9%) in the three chromosome-doubled 6x H-690 9-5 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 BC1F1 proge ny from the T. repens x 6x H-6909-5 (4x x 6x) cross is the first unequ ivocal evidence of functional female 2n gametes in white clover. Meiot ic pairing in F-1 and BC1F1 progeny indicated the presence of allosynd etic pairing, suggesting that genetic exchange between the two species is possible.