TRANSFER OF CLOVER CYST-NEMATODE RESISTANCE FROM TRIFOLIUM-NIGRESCENSVIV TO TRIFOLIUM-REPENS L BY INTERSPECIFIC HYBRIDIZATION

Resistance to clover cyst nematode (Heterodera trifolii) has been succ essfully transferred from Trifolium nigrescens to T. repens by intersp ecific hybridisation. A sterile triploid hybrid (H-6909-5, 2n = 3x = 2 4) was initially produced with the aid of embryo culture. The hybrid w as chromosome-doubled from axillary meristems by an in vitro colchicin e method. Three chromosome-doubled plants were obtained, and these sho wed a marked increase in pollen stainability from 10% in 3x H-6909-5 t o an average of 89% (range 88-91%) in 6x H-6909-5. T. nigrescens was a source of clover cyst nematode resistance. A mean of 23 (range 0-150) cysts per plant was recorded for T. nigrescens in comparison to a mea n of 150 (range 50-240) cysts per plant for T. repens. The 3x and 6x i nterspecific hybrids were shown to be as resistant as the most resista nt. T. nigrescens genotype and were significantly lower in cyst number per gram of root dry weight than the susceptible T. nigrescens and T. repens genotypes.