A few species of the Solanum nigrum L. complex were selected to determine the relationship among them as revealed by crossability studies and chromosome-pairing behaviour of their hybrids. Cytomorphology of S. americanum Mill., Indian diploid S. nigrum L., S. nodiflorum Jacq., and S. douglasii Dun. was studied. Crosses between S. douglasii and other species were compatible if S. douglasii was used as the male parent. The isolation of S. americanum, Indian diploid S. nigrum, and S. nodiflorum from S. douglasii by hybrid breakdown is most likely due to differences between the parents in chromosome structure as well as gene content. Although the F1 hybrids were normal and fertile, the F2 plants showed meiotic breakdown and reduced fertility. It is suspected that S. nodiflorum, S. nigrum (2x), and S. americanum represent a single biological species, S. americanum. The distinction of S. douglasii as a separate species is justified. Key words: Solanum, diploid, hybrids.
[Show abstract][Hide abstract] ABSTRACT: Species from the Solanum nigrum complex are not as popular as potatoes and peppers but are economically important fruit or leafy vegetables in some parts of the world. The aim of this study was to look at the hybridization potential of genotypes from the Solanum nigrum complex, and two cocktail tomato cultivars, to facilitate a future breeding program. Solanum americanum Mill., S. burbankii Bitter, S. chenopodioides Lam., S. retroflexum Dun. and S. scabrum L. are some of the species found in Southern Africa. Crosses, including reciprocals, were made between these five species and two cocktail tomato cultivars. Fifty percent of the crosses made, resulted in fruit set, but only 22.5% of the produced seeds germinated to yield progeny. Cytological analyses of the chromosome numbers showed no variation from the normal euploid series. The occurrence of polyploidy between the species is probably the most efficient barrier to natural hybridization between the species.
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