Crossing relationships and chromosome numbers of Solanum section Solanum in Uganda
8 November 2014
Olet, Eunice; Lye, Kare A.; Stedje, BritaA total of 800 crosses were made, involving 246 combinations. Less than half of these combinations were successful, producing F1 offspring. All accessions studied are self-compatible and most accessions crossed readily with accessions of their own species. Most crossings between species failed, or when seeds were obtained the F1 did not germinate, or when they germinated the F1s either did not have stainable pollen implying that a crossing barrier exists; or they had stainable pollen, but chromosome numbers indicating reproduction by apomixis. The crossing experiments support the taxonomic categories assigned to the Solanum accessions using classical, numerical and partly molecular evidences. The material studied represents six Ugandan species. S. americanum is a diploid (2n=2x=24), S. florulentum, S. memphiticum, S. tarderemotm, S. villosum ssp. villosum and S. villosum ssp. miniatum are tetraploids (2n=4x=48), while S. scabrum subsp. scabrum and S. scabrum subsp. laevis, are hexaploid (2n=6x=72). In addition to confirming the ploidy levels of the Ugandan accessions, the previously unknown ploidy levels of S. florulentum, S. memphiticum and S. tarderemotum are now established. S. sarrachoides consists of non-Ugandan material and is diploid. Knowledge of the crossing behaviour and ploidy levels in Solanum will facilitate breeding for character improvement in the species that are used as food and/or medicine.