DISTURBED MENDELIAN SEGREGATIONS AT ISOZYME MARKER LOCI IN EARLY BACKCROSSES OF LOLIUM-MULTIFLORUM X FESTUCA-PRATENSIS HYBRIDS TO L-MULTIFLORUM

The segregation of interspecific recombinant Festuca pratensis (Fp) al leles, introgressed into the germplasm of Lolium multiflorum (Lm), at four loci (PGI/2, AcP/2, GOT/3 and BAP) is described. Heterozygous (Lm /Fp) plants were backcrossed to L. multiflorum (2n = 2x = 14) and subs equent BC2 Lm/Fp sibling genotypes intercrossed. In crosses between BC 1 heterozygous plants (Lm/Fp) used as males and L. multiflorum, there was a reduced transmission of the F. pratensis (Donor Parent) derived alleles in the populations with PGI/2 and AcP/2 marker loci compared t o the reciprocal cross but the reduction was not significantly differe nt in those with GOT/3 and BAP markers. Two PGI/2 marked BC2 half-sib families in particular exhibited a more extreme deficiency of Fp/Fp pr ogeny plants than anticipated from the BC2 segregations indicating pos sible linkage to zygotic lethals. Deficiencies of F. pratensis alleles were, in most cases, less marked in BC2 half-sib families indicating that a further round of recombination had reduced the size of the intr ogressed chromosome segment or that deleterious linkages had been brok en. A tendency towards heterozygote advantage was found in one BAP mar ked half-sib family. The significance for forage grass breeding of red uced transmission rates of Donor Parent alleles in early back-cross ge nerations especially through the male gametes is discussed.