| Summary: | Two species, Solanum commersonii Dun. and S. acaule Bitt., have been investigated. ii The two subspecies of S. commersonii, commersonii and malmeanum (Bitt.) Hawkes et Hjerting, have diploid and triploid forms. There are reciprocal differences between subspecies in diploid-diploid crosses, and between levels of ploidy in diploid-tetraploid crosses. Diploidtetraploid crosses produce mostly triploids and in this S. commersonii differs from other species. The selfincompatibility of the diploids breaks down in the tetraploids. In subsp. commersonii 'conventional' triploids are considered to be autopolyploids, and 'anomalous' triploids to be intersubspecific hybrids. Triploid cytotypes of subsp. malmeanum are probably autopolyploids. Diploid hybrids between the subspecies are also likely to be formed. Hybridization between S. commersonii and S. chacoense Bitt. is probably rare. S. acaule has three tetraploid and one hexaploid subspecies which are all probably segmental allopolyploids. The tetraploid subsp. aemulans (Bitt. et Wittm.) Hawkes et Hjerting is considered to be most closely related to other species; an alternative hypothesis is proposed for its origin. Attempts to obtain dihaploids of the tetraploid subspecies using diploid and autotetraploid pollinators, and from polyembryonic hybrid seeds have been unsuccessful. Previously unrecorded crosses of S. acaule with other species are reported. Embryological studies have been carried out in S. acaule, and embryo culture techniques developed. Polyembryony has been found in several taxa, and its occurrence in the tuber-bearing Solanums is reviewed.
|
|---|
