The use of incompatibility for the production of F1 hybrids in forage grasses

Abstract

SUMMARYA possible method for the production of F, hybrid seed of forage grasses in commercial quantities is described. The method depends on the two-locus incompatibility system postulated by Lundqvist (1961). Inbred lines are made, each deriving from a single genotype, having a high degree of within-line incompatibility so that when two, or more, such lines are interplanted the seed produced will be largely of hybrid origin. The consequences of multi-locus incompatibility mechanisms are examined and a general method for calculating the expected composition, in terms of incompatibility groups, of an inbred line in any generation and for any number of incompatibility loci is given. L INTRODUCTION FOSTER (1971 b) has studied the theoretical expectation of F1 hybridity resulting from bulk interpopulation hybridisation in herbage grasses and, in two other papers (Foster, 1971 a, c), he has reported on the performance of such hybrids under spaced plant and sward conditions. He found that F1 hybrids were not on average superior to the parental varieties but that certain F1's yielded up to 31 per cent more than their higher yielding parent under spaced plant conditions and up to 17 per cent more in swards. Wright (1972) has pointed out that with diploid inheritance, the mean performance of both semi-hybrid varieties of the type proposed by Foster and conventional synthetics is expected to be the same. Burton (1956) has discussed the value of F, hybrids in forage grasses and possible techniques for producing F1 seed in commercial quantities; he concluded that the extra seed cost might well be justified by the increased yields of forage. McWilliam (1962) has shown the value of F1 hybrids between species of Phalaris. It is tempting to consider the possibility of producing F1 hybrids of forage grasses more nearly along the lines used in maize, sorghum and some other crops. Usually, the production of F1 hybrids depends either on a rapid technique of mass emasculation or the use of male-sterility although sporophytic incompatibility has been used in brassicas (Thompson, 1957) and of course F, hybrids between pairs of self-incompatible genotypes are readily made and were used by both Burton (bc. cit.) and McWilliam (bc. cit.). The structure of the flowers of most forage grasses does not permit emasculation on the scale required and the effort involved in developing male-sterile lines, if such could be found, would be unlikely to be worth while. The two-locus selfincompatibility mechanism, proposed by Lundqvist (1961) for Festuca pratensis and stated by Weimark (1968) to operate in some other grasses including Lolium perenne, may provide a basis for the development of varieties consisting largely of F1 hybrid genotypes and may also permit conventional combining ability tests to be made on inbred lines.

Self-incompatibility in ryegrass

“…It would be of considerable theoretical interest if the ryegrasses turned out to have a different system from that of the other self-incompatible grasses. Furthermore, because perennial ryegrass is a crop of major economic importance, it is desirable for practical reasons that the genetical basis of its self-incompatibility should be properly understood before any attempt is made by breeders to exploit the mechanism in their improvement programmes (England, 1974).…”

Genotypic frequencies at equilibrium for a multilocus gametophytic incompatibility system

“…For comparison, the values of Charlesworth are also given for n1 =fl2 = n. Though the deviations are small, they are not due to rounding errors, as is shown in the discussion. The case of fli = =2 is a special case, when double heterozygotes cannot produce progeny (see England, 1974).…”

“…The case of n = 2 at all loci must be excluded, since in this case no seed is set on genotypes heterozygous at all loci. England (1974) gave a general solution for this situation. First the case of three loci is considered.…”

Identification of S‐locus linked PCR fragments in rye (Secale cereale L.) by denaturing gradient gel electrophoresis

“…It has been proposed also to use the bifactorial SI system for the production of hybrid seed in forage grasses (England, 1974) and rye (Wricke, 1984). However, the identification of SI genotypes, which is a prerequisite for the proposed method, is a laborious and time-consuming procedure and is only feasible once the plants begin to flower.…”