Self-incompatibility (SI) in plants had long been assumed to be ancestral to the angiosperms, but is now known to have evolved repeatedly from a pre-existing multigene family. The objective of this work is to determine the time of origin of SI within the Solanaceae. Amino acid sequences of both S and non-S alleles of several species in the Solanaceae will be determined and phylogenetic trees based on sequence divergence of both S and non-S RNases will be constructed to obtain an estimate of their relative rates of evolution. This project should result in an estimation of the age of the SI system within the Solanaceae, sequences for non S-RNases that also can be used by other researchers, and an indication of the nature of selection acting on the non-S RNases. The Solanaceae include a number of commerically important plant species, including tomatoes, potatoes, and tobacco. An understanding of the diversity of SI systems has important implications for crop breeding.
