Meiosis in hybrids between Lycopersicon esculentum and Solanum pennellii

Abstract

Meiotic chromosome cytology was compared between Solanum pennellii, Lycopersicon esculentum, and the F₁ hybrid. Pachytene chromosomes are very similar in gross morphology, but several of the S. pennellii chromosomes were found to have somewhat longer chromatic regions with discrete chromomeres, and darkly staining chromomeres in the achromatic regions. Little evidence could be found for the existence of rearrangements between chromosomes of the two species. With respect to chromomere pattern, on the other hand, a number of differences were seen. Meiosis in the hybrid is strictly regular. Only size inequalities occur in certain bivalents. Considering the evidence from chromosome pairing, hybridization compatibility, hybrid fertility, and plant morphology, it is concluded that the phylogenetic relationship is much closer between S. pennellii and L. esculentum than it is between either one and S. lycopersicoides. Attention is called to the present unsatisfactory placement of S. pennellii and to the need for revising the taxonomy to place it and L. esculentum in the same genus, possibly in the same subgeneric category.