The Inheritance of Self-Incompatibility in Hybrids of Lycopersicon Esculentum Mill. x L. Chilense Dun.

OTH self-fertile and self-incompatible species are found in the genus BLycopersicon (LAMM 1950). The self-incompatibility in L. peruuianum was shown to be of the Nicotiana or multiple-allelic gametophytic type by MCGUIRE and RICK (1954). Less extensive evidence suggested similar genetic control in L. hirsutum, L. glandulosum, and L. chilense (L. peruvianum f . dentatum) . I n addition, the inheritance of self-incompatibility in F, hybrids of L. esculentum x L. peruuianum was investigated. All the plants of both generations were selfincompatible. The F, hybrids from a given cross were of two intraincompatible, intercompatible types determined by the incompatibility (S) allele inherited from L. peruvianum. The pollination relationships of the F, indicated a recombination of S alleles, as expected, and also a sporophytically determined restriction of crosses of the F, to unrelated pistillate L. peruuianum plants. This barrier was interpreted as the action of one or two genes from L. esculentum. LEWIS and CROWE (1958) have summarized the results of many attempted hybridizations of self-fertile with self-incompatible species. Usually such crosses are successful only when the self-fertile species is used as female. This phenomenon was termed unilateral hybridization by HARRISON and DARBY (1955). The exceptional self-fertile species which can successfully fertilize self-incompatible types are suggested by LEWIS and CROWE (1958) to be intermediates in the evolution of self-fertility from self-incompatibility. In only one case has the inheritance of self-incompatibility been studied in such crosses beyond the F, generation. In hybrids of Petunia axillaris x P. uiolacea, MATHER (1943) found a dominance of self-incompatibility but a weakening of the reaction in the backcross hybrids. He attributed this to the dilution through backcrossing to the self-fertile parent of the polygenes affecting self-incompatibility. In the present study the genetic differences between Lycopersicon esculentum and L. chilense with respect to self-incompatibility and related morphological characteristics were investigated in F,, F,, and backcross generations.