Nuclear and cytoplasmic genome components of Solanum tuberosum + S. chacoense somatic hybrids and three SSR alleles related to bacterial wilt resistance.

The somatic hybrids were derived previously from protoplast fusion between Solanum tuberosum and S. chacoense to gain the bacterial wilt resistance from the wild species. The genome components analysis in the present research was to clarify the nuclear and cytoplasmic composition of the hybrids, to explore the molecular markers associated with the resistance, and provide information for better use of these hybrids in potato breeding. One hundred and eight nuclear SSR markers and five cytoplasmic specific primers polymorphic between the fusion parents were used to detect the genome components of 44 somatic hybrids. The bacterial wilt resistance was assessed thrice by inoculating the in vitro plants with a bacterial suspension of race 1. The disease index, relative disease index, and resistance level were assigned to each hybrid, which were further analyzed in relation to the molecular markers for elucidating the potential genetic base of the resistance. All of the 317 parental unique nuclear SSR alleles appeared in the somatic hybrids with some variations in the number of bands detected. Nearly 80 % of the hybrids randomly showed the chloroplast pattern of one parent, and most of the hybrids exhibited a fused mitochondrial DNA pattern. One hundred and nine specific SSR alleles of S. chacoense were analyzed for their relationship with the disease index of the hybrids, and three alleles were identified to be significantly associated with the resistance. Selection for the resistant SSR alleles of S. chacoense may increase the possibility of producing resistant pedigrees.

Meiotic behavior of pollen mother cells in relation to ploidy level of somatic hybrids between Solanum tuberosum and S. chacoense.

Potato somatic hybrids obtained by protoplast fusion between Solanum tuberosum (4x) and Solanum chacoense (2x) were investigated for genome stability and meiotic behavior associated with the pollen viability in order to elucidate the mechanism influencing the fertility of the somatic hybrids. The ploidy level detections conducted in 2004 and 2007 demonstrated that 68 out of 108 somatic hybrids had their ploidy level changed to be uniform and euploidy after successive in vitro subcultures, which mainly occurred in octaploids, aneuploids, and mixoploids, while 74% hexaploids were still stable in their genome dosage in 2007. Different types of abnormal meiotic behavior were observed during the development of pollen mother cells (PMCs) including the formation of univalents, multivalents, laggard chromosomes, and chromosomal bridges, as well as triads and polyads. A higher proportion of abnormal meiosis seemed to be accompanied with a genome dosage higher than the hexaploids expected in this study. A significant positive correlation between defective PMCs and the number of small pollen grains and negative correlation between number of small pollen grains and pollen viability strongly suggested that abnormal meiosis could be a causal factor influencing the fertility of the somatic hybrids. The hexaploids with stable genome dosage and a certain level of fertility will have great potential in a potato breeding program.