Genetics of the incompatibility system in the cruciferEruca sativaL

Abstract

Genetically controlled incompatibility systems in the homomorphic angiosperms fall into two categories: (i) gametophytic and (ii) sporophytic (Lewis 1954; Crowe 1964; Williams 1964). The two systems differ basically in the control of the incompatibility reaction of the pollen, whether it is determined by the genotype of the pollen-grain (hence gametophytic), or it is imposed by parental genotype (hence sporophytic) and consequently all the pollen from a given plant show the same reaction irrespective of their genotype. Furthermore, some characteristics seem to be intimately or rather fundamentally linked with the two systems (Brewbaker 1957, 1959; Pandey 1960; Lundqvist, Osterbye, Larsen & Linde-Laursen 1973), particularly cytology of pollen at dehiscence, site of inhibition of incompatible pollen and the allelic interactions in the style (table 1). Such characteristics help in the inference of the system; although Pandey (1960) has pointed out three exceptions to these broad correlations, the uniformity of the system within families with homomorphic incompatibility still holds. In the family Cruciferae, Bateman (1954, 1955) not only invoked a 1-locus sporophytic system for the SI Iberis amara but also made a reinterpretation of the earlier data in the three crucifers accommodating them in the Iberis scheme. Later workers have confirmed the uniformity of the sporophytic system in the family Cruciferae (Sampson 1957a, b, 1964; Thompson 1957; Haruta 1962). However, the only report contradictory to Bateman’s generalization of the Crucifer system is that of Narsingdas (see Singh 1958) in Eruca sativa (an oleiferous crop) wherein he explained his results on the gametophytic system (cf. Kakizaki 1930). This prompted a reinvestigation of E. sativa in order to determine the nature and genetics of the system involved. To our surprise, the intrafamilial pollinations of F₁ families revealed very abnormal data (Barjinder 1968) and the confirmation of the genetic interpretation invoked necessitated detailed analyses of F₂ families (Indra 1970), which, in turn, made it imperative to pursue the case to F₃ families involving larger numbers of plants in each family. This communication is intended to present the data, particularly of F₂ and F₃ families worked out by Miss Indra Dhir and Miss Renuka Malik respectively, and to interpret the same regarding the nature of the incompatibility system. The hypothesis has been tested in two F₄ families derived from selfings of individuals from two F₃ families. A new model proposed by D. Lewis, based on more than two loci with sporophytic control has been adopted, and at least two loci are analogous to the S and Z loci in grasses (Lundqvist 1956). The details of the genetics of the proposed model are presented in the following paper by Lewis (1976).