Aneuploid hybrids from 5x x 4x crosses in potato: chromosome number, fertility, morphology and yield

The objective of this study was to characterize six S. commersonU - S. tuberosum progenies deriving from 5x - 4x crosses to provide evidence that they can be used in potato breeding. Hybrids analyzed (coded PTH) had a chromosome number between the 4x and the 5x level. In particular, progeny means for chromosome number ranged from 50• to 54• with most (70%) genotypes exhibiting a low aneuploid level of 48 to 53 chromosomes. Despite being aneuploid, the hybrids did not generally show phenotypic aberrations or vigor reduction common to aneuploids of other species. Most genotypes resembled S. tuberosum in growth habit, whereas corolla type, eye depth, and stolon length varied between and within progenies. Aneuploid hybrids produced tubers under long-day conditions. However, tuber yields were not as high as expected, probably due to lack of adaptation of the S. commersonii genome to long-day conditions. Although aneuploidy has often been associated with reduced male and female fertility, many 5x - 4x hybrids were fertile in crosses with S. tuberosum. The average berry set and number of seeds/berry were 33% and 34.7, respectively, following PTH x S. tuberosum crosses, and 40% and 51.7, respectively, for S. tuberosum x PTH crosses. The useful variation for fertility and tuber traits found in this material is being used for further breeding efforts.