Cytogenetic studies of South American diploid Solanums, section tuberarium

Abstract

Meiosis is regular in a majority of the microsporocytes in a number of clones of six South American diploid species and their hybrids. Meiotic abnormalities such as the presence of univalents, quadrivalents, chromatin bridges and fragments, laggards, formation of restitution nuclei, micronuclei and other irregularities are extant in a small percentage of microsporocytes. The presence of occasional quadrivalents in certain clones of some species and hybrids suggests the existence of some structural differences between certain chromosomes. This probability is further supported by the occurrence of a bridge and fragment resulting from inversion heterozygosity and delayed separation of certain bivalents. The presence of univalents may be caused by segmental or genetic differences between homologous chromosomes as well as to other factors and cannot be entirely explained as being due to precocious separation of rod bivalents. However, the fact that the maximum possible number of bivalents are realized in a large number of the pollen mother cells suggests that such structural differences cannot be very extensive. An unusual type of nucleolus formation occurs. The frequency of various types of secondary groupings is variable.