Crossability relationships among wild potato species with different ploidies and Endosperm Balance Numbers (EBN)

Abstract

Three wild potato species with different ploidies and Endosperm Balance Numbers (EBN) were crossed in a complete diallel design and the development of the embryo and endosperm as well as the type of seeds produced were analyzed. The compatible crosses – intraspecific intra-EBN and interspecific intra-EBN – produced more than 89% plump seeds, whereas in the incompatible crosses – intraspecific inter-EBN and interspecific inter-EBN – more than 85% of the seeds were not as well developed or were shrunken. The histological analysis revealed that inviable seeds had less developed or collapsed endosperms and thicker endotheliums than viable ones. A gradation of crossabilities was observed among species. The self-compatible species Solanum acaule had good performance as a female but not as a male parent. Among the self-incompatible species, Solanum gourlayi was the best male parent but had a poor performance as a female, whereas Solanum commersonii had an intermediate behavior. Differences in crossabilities among genotypes within species were also observed. These results can not be solely explained by the EBN hypothesis. It is, therefore, suggested that the EBN may be part of a more complex system of interspecific barriers acting at the pre- and post-zygotic levels.