Interspecific Incompatibility in Solanum Species

Abstract

Pandey, K.K. (Crop Res. Div., D.S. & I.R., Lincoln, Christchurch, New Zealand.) Interspecific incompatibility in Solanum species. Amer. Jour. Bot. 49(8): 874–882. Illus. 1962.—A diallel cross involving 11 self-incompatible and 3 self-compatible species of Solanum was made to study the genetic basis of interspecific incompatibility. Interspecific incompatibility was not limited to crosses in which a self-compatible species was used as the male parent onto a self-incompatible species (unilateral incompatibility). A number of crosses between self-incompatible species were incompatible. In one cross, Q vernei X verrucosum, a self-compatible species was successful as a pollen parent with a self-incompatible species. Unlike other hybrids between self-compatible and self-incompatible species, which are self-incompatible, these F1 hybrids were self-fertile, and cross-fertile among themselves and with both parents. The self-fertile S. polyadenium was cross-incompatible as a female as well as a male parent with all other species. It is suggested that the unilateral incompatibility is a property of the allele SC which originated as a consequence of one kind of breakdown of the SI gene; the SC allele produces “bare” pollen growth substances which are inactivated in an incompatible style. It is proposed that the failure of the principle of unilateral interspecific incompatibility in solanaceous species may be due to the action of alleles at the second incompatibility locus revealed in certain Mexican species. It is assumed that the South American species are selected intraspecifically only for the action of S alleles but that in certain interspecific crosses and rarely in intraspecific crosses the alleles at the second locus may be expressed, thus interfering with the usual action of S alleles. The F1 hybrids Q verrucosum (self-fertile) X simplicifolium (self-sterile) were self-incompatible at the tetraploid as well as the diploid level, and their cross-compatibility behavior was consistent with the expected activity of the SC and SI alleles of the 2 parents respectively.