CROSSING RELATIONSHIPS AMONG DIPLOID SPECIES OF THE SOLANUM NIGRUM COMPLEX IN NORTH AMERICA

Abstract

Crosses were made in all combinations of the six diploid species of the Solarium nigrum complex that occur in North America. Some interspecific pollinations failed to yield viable seed; successful crosses gave rise to moderately to highly sterile F1 hybrids. Results of interspecific crosses suggested phylogenetic relationships that were not completely in accord with those suggested by morphology. Interspecific crosses also gave varied results. All interpopulational crosses within S. interius and S. sarachoides produced fully fertile hybrids. In contrast, hybrids within S. americanum and S. douglasii varied from fully fertile to almost completely sterile. Populations of S. pseudogracile could be divided into two groups which are geographically separated but not morphologically differentiated. Fully fertile hybrids resulted from crosses within a group, whereas crosses between groups gave hybrids with reduced fertility. Four crossing groups were observed within 5. nodiflorum; three of the parental groups are sympatric and are morphologically differentiated. Although hybrid sterility in interspecific crosses is sometimes used to support delimitation of species, the presence of sterility in intraspecific crosses suggests that such an interpretation is unwarranted for the S. nigrum complex. Hybrid sterility, therefore, is not considered to have special taxonomic significance in this complex.