Interspecies hybrids and polyploidy

Abstract

Polyploidy has featured strongly in plant evolution as a means of conserving favoured hybrid combinations during sexual reproduction. Combining different genomes is likely to extend adaptation rather than increase yield per se . Subsequent stabilization by polyploidy depends on the degree of differentiation of the genomes and on the breeding system, but success is mediated by low chromosome numbers while reduced fertilities may be offset where the crop is harvested primarily for vegetative parts and/or is perennial. In old established grain crops like the cereals, raw synthetic polyploids are not likely to offer immediate advantages but may be subsequently improved by arduous selection in an extended gene pool (e.g. triticale). The relatively undeveloped herbage grasses offer unique opportunities. Flexibility in grass swards is presently sought through unstable mixtures of races and species. It is the breeders’ aim to combine genetically the complementary features of these in stable varieties. Agronomically useful hybrids between diploid Lolium species have been stabilized at the tetraploid level through tetrasomic inheritance reinforced by a degree of preferential pairing. This preferential pairing may be genetically enhanced, thus raising the possibility of producing a new agriculturally useful amphiploid ryegrass species. Prospects for developing useful amphiploid hybrids between less closely related Lolium / Festuca species is considered and related to more limited objectives of transferring desirable genes or gene complexes.