Cytogenetic studies in Solanum verrucosum variety spectabilis

Abstract

Solanum verrucosum var. spectabilis Correll has the somatic chromosome number 72, whereas other varieties of S. verrucosum are diploids (2n=24). It also differs from the diploid varieties in growth habit, corolla shape and color and berry shape. Meiosis is regular in the microsporocytes of spectabilis and the plants are self-fertile. Crosses between spectabilis and the diploid varieties of S. verrucosum fail but reciprocal crosses with S. demissum (2n=72), which belongs to the same taxonomic series as S. verrucosum, are successful. Hybrids from such crosses have a mean number of 17 and 25 univalents per cell at metaphase I of meiosis and they are pollen and ovule sterile. This behavior suggests that at least one set of 12 chromosomes of spectabilis and demissum differ from each other. The result is contrary to the generally held view that there is no chromosome differentiation among the species of the section Tuberarium. It is concluded that var. spectabilis is a distinct species and it is named Solanum spectabilis (Correll) Swaminathan and Hougas.