Inheritance of apomictic seed production in Kentucky bluegrass (Poa pratensis L.)

Apomixis, as it exists in Kentucky bluegrass (Poa pra-tensis L.), is a nearly ideal way of maintaining superior hybrids and complex traits. It combines the genetic advantages of vegetative propagation (maintenance of the genotype) with the agronomic advantages of sexual reproduction (use of the seed). Lack of knowledge on its inheritance at present hinders attempts to manipulate and transfer the apomic-tic trait beyond natural sexual barriers. We analyzed the occurrence of meiotic (haploid) and aposporic (diploid) parthenogenesis in P. praten-sisgenotypes with contrasting degrees of apomixis using embryo rescue and in vitroculture techniques. The in vitrorescue of autonomous embryos obtained after auxin-induced parthenocarpy permitted us to investigate and establish the embryological derivation of progeny plants of certain parthenogenetic origin. All recovered plants were characterized both for chromosome number and DNA fingerprint to ascertain their genetic origin. Our experiments indicated that parthenogenetic capacity is preferentially expressed by aposporic egg cells and so the genetic determinants for apomixis seem to be closely linked and inherited together. We also documented parthenogenetic development of meiotic egg cells. In a highly sexual genotype that when auxin tested showed considerable parthenogenetic capacity, the egg cells appeared to exert this potential irrespective of their cytological origin. Thus, events of segregation of apospory from parthenogenesis are rare, but possible. Although the question remains open, apomixis seems to be the result of a few tightly clustered genes rather than the combination of two processes, apospory and parthenogenesis, determined by independent genetic factors.