The Basic Features of Self-Incompatibility
All early workers (see for instance Herbert, Scott, Munro, stated in Darwin, 1880) and many authors in this century (Sutton, 1918; East and Mangelsdorf, 1925; East, 1929; Riley, 1935; Sears, 1937) have defined as self-sterility the incapacity of fertile p
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1.1 A Choice of Terms All early workers (see for instance Herbert, Scott, Munro, stated in Darwin, 1880) and many authors in this century (Sutton, 1918; East and Mangelsdorf, 1925; East, 1929; Riley, 1935; Sears, 1937) have defined as self-sterility the incapacity of fertile plants to reproduce upon selfing. As was pointed out by Stout (1917) and admitted by East (1940), the terminology is improper and self-incompatibility is obviously the best name for describing a situation which, as will be seen throughout this book, involves a participation from both the pollen and the pistil and is, as such, basically different from male or female sterility where the phenotypic expressivity of the sterility genes is independent, before fertilization, of the genotypic constitution in the mating partner. The DeJinition oj Self-Incompatibility. All definitions of self-incompatibility implicitly or explicitly underline the function of the phenomenon as an outbreeding mechanism but the literature is unclear as to whether or not the use of the term must be restricted to pre-fertilization processes or extended for describing all events which prevent fertile hermaphrodites from setting seeds upon selfing. Whereas, for instance, Brewbaker (1958) and Arasu (1968) defined self-incompatibility as "the inability oj a plant producing Junctional gametes to set seeds when self-pollinated," other authors referred to: 1. "the hindrance to Jertilization" (Lewis, 1949 a), 2. "the impossibility oj the pollen to Jertilize the egg" (East and Park, 1917), 3. "the Jailure, Jollowing mating or pollination, oj a male gamete and a Jemale gamete to achieve Jertilization where each oj them is capable oj uniting with other gametes oj the breeding aJter similar mating or pollination" (Mather, 1943). Consulted on the matter, Lundqvist (see discussion of Lundqvist, 1964) clearly stated that the term "incompatibility" should not include zygote lethality. With the one exception of Borago oJJicinalis, for which Crowe (1971) has demonstrated a post-fertilization system of self-rejection, it seems that all known systems of self-incompatibility are indeed pre-zygotic and that Lundqvist was right in requesting that no confusion be made between self-incompatibility and the diversity of accidents occurring upon inbreeding during seed formation. Recessive embryonic lethality may, in some ways, be compared to self-compatibility and effectively depends, for expression, upon a contribution from both the male and female partners, but the phenomenon, with few exceptions, such as the previously mentioned case of B. oJJicinalis, does not seem to contribute extensively to the establishment and permanence of allogamy in natural populations. Its D. de Nettancourt, Incompatibility in Angiosperms © Springer-Verlag Berlin Heidelberg 1977
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The Basic Features of Self-Incompatibility
function, especially in those cases where only a small number of unlinked recessive lethals are operating, appears far more flexible and essentially concerned, at the cost of a very considerable mobil
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