Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2001
Publication Date: N/A
Interpretive Summary: Solanum ochranthum is a wild relative of the cultivated tomato, and a potential source of new genes for disease and pest resistance. Since S. ochranthum and tomato cannot be crossed via conventional means to transfer these genes, hybrids between tomato and S. ochranthum were previously created by fusing cells of the respective species. Attempts to cross these hybrids to tomato in order to advance cultivar development, have been unsuccessful. Chromosome counts, cell division events and pollen viability in these hybrids were evaluated to help account for these observations and identify hybrids with moderate fertility. Hybrids with double the expected chromosome number were found, as expected, in addition to hybrids with triple the expected chromosome number. Analysis of cell division in developing pollen revealed events which result in chromosome breakage, rearrangement and loss, thus accounting for reduced fertility. Very low to moderate levels of pollen viability were found in these hybrids. Through this research we have identified unique hybrids with moderate fertility to facilitate gene transfer between these species. This research benefits researchers developing improved tomato cultivars for farm production.
Technical Abstract: Solanum ochranthum is a non-tuber bearing, cross-incompatible wild relative of the cultivated tomato, and a potential source of new genes for disease and pest resistance. Attempts to backcross somatic hybrids between S. ochranthum and tomato have been unsuccessful. Ploidy determinations, meiotic events and pollen viability in these somatic hybrids were evaluated to help account for these observations and identify hybrids with moderate fertility. Chromosome counts of dividing root tip cells delineated tetraploid (2n=4x=48) and hexaploid (2n=6x=72) genotypes and aneuploidy in these hybrids. Meiotic analysis of developing microspores confirmed the presence of laggard chromosomes at metaphase and anaphase in hexaploid and tetraploid hybrids. Bridges were observed in hexaploids at anaphase I and II and chromosomal ring configurations were observed at diakinesis. Multivalents and univalents were evident in nearly all cells examined. Aberrant microsporocytes with five to six developing microspores were noted in hexaploids. Low to moderate levels of pollen fertility (0% - 52.3%) were found in tetraploid hybrids, while little or no viable pollen (0% - 4%) was observed in hexaploids.