Heterosis and Hybrid Seed Production in Barley

The potential use of gametophytic factors in the production of F1 hybrid varieties

“…Gametophytic factors (or pollen `killer' genes, gametocidal genes, gamete eliminators, gamete aborters) have now been described in several economically important plant species including maize (Mangelsdorf & Jones, 1926 ;Burnham, 1941 ;Schwartz, 1950), tobacco (Cameron & Moav, 1957), wheat (Loegering & Sears, 1963), tomato (Rick, 1966 ;Alexander, 1973), lima beans (Allard, 1963) and barley (Ramage, 1983) . Such factors usually represent dominant alleles (designated Ga) at a single Mendelian locus which have a marked selective advantage in gametes over their, usually recessive, allelic counterparts (designated ga) .…”

“…In support of this argument recent studies in barley indicate that the frequency of induction of Ga mutants is high and suitable mutants have readily been obtained in that species (Lehmann et al ., 1979 ;Foster & Fothergill, 1982 ;Ramage, 1983) . In addition, we emphasise that cytoplasmic male sterility (cms) mutants were, until their potential value in the use of hybrid varieties was recognised, also rarely reported in plants and regarded as genetic oddities of little practical interest .…”

“…Given that both Ga and ms mutant alleles are relatively uncommon in most species, it seems reasonable to argue that they will rarely be found occupying closely adjacent positions on the same chromosome . Recent experience in barley indicates that it has been relatively easy to obtain Ga mutant alleles closely linked to male sterility loci (Ramage, 1983) so that populations with more than 95% male sterile plants are readily obtained (Foster & Fothergill, 1982 ;Lehmann, 1982) . However, barley is a diploid species and male sterile plants are found at a relatively high frequency in mutagen-treated populations (compared to the polyploid species wheat and oats for example) and there has been for many years an intensive programme to collect, map and 79 catalogue chromosomal male sterility genes in barley (e .g .…”

“…These include the use of chemicals (gametoficants) to restore fertility in chromosomal male steriles (Kasembe, 1967 ;Hockett et al ., 1978), the use of `marker' genes linked to the male sterility locus to facilitate the chemical or physical rogueing of male fertiles from the female parents of hybrids (e .g . Wiebe, 1960 ;Falk et al ., 1982), the use of seedling lethal genes which are linked to the male sterility locus to develop self-rogueing female lines (Forster, 1979), the balanced tertiary trisomic system in barley (Ramage, 1965(Ramage, , 1983) and the XYZ system in wheat (Driscoll, 1972(Driscoll, , 1981 . However, none of these systems have yet found widespread commercial application because of practical difficulties in their development or use .…”

“…In recent years, considerable effort has gone into the development of a hybrid production system in barley based on the use of microgametophytic factors or male gamete eliminators (Forster, 1976) closely linked to a chromosomal male sterility locus (Forster & Fothergill, 1982 ;Lehmann, 1982 ;Ramage, 1983) . The purpose of this paper is to emphasize (i) that the use of gametophytic factors in F, hybrid production is potentially applicable to a wide range of crop species and (ii) that gametophytic factors which act on both micro-and macrogametophytes are likely to have considerable practical advantages over those that operate only in microgametophytes .…”