Disturbed Mendelian segregations at isozyme marker loci in early backcrosses of Lolium multiflorum × Festuca pratensis hybrids to L. multiflorum

The segregation of interspecific recombinant Festuca pratensis (Fp) alleles, introgressed into the germolasm 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=2×=14) and subsequent BC2 Lm/Fp sibling genotypes intercrossed.
In crosses between BC1 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 to the reciprocal cross but the reduction was not significantly different 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 progeny plants than anticipated from the BC2 segregations indicating possible 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 introgressed chromosome segment or that deleterious linkages had been broken. A tendency towards heterozygote advantage was found in one BAP marked halfsib family.
The significance for forage grass breeding of reduced transmission rates of Donor Parent alleles in early back-cross generations especially through the male gametes is discussed.