Polyploidy of Cells in Sweet Cherry Fruit, Poster Board #388

Cell flow cytometry was used to investigate cell activity of sweet cherry (Prunus avium L.) cultivars during fruit development.  The nuclei of ‘Chelan’, ‘Bing’ and ‘Sweetheart’ sweet cherry fruit became highly polyploid during early, rapid fruit growth, compared to small-fruited wild cherry (Prunus sp.) and choke cherry (Prunus virginiana). Polyploidy was observed only in fruit; flowers at full-bloom and leaf tissues were largely 2-C (> 90%). For all cultivars, there was a rapid increase of the 4-C, 8-C and 16-C levels of DNA content during the "stage-I" growth phase. DNA content stabilized during "stage-II" (pit hardening) to approximately 30%, 45%, 20% and 5% of the 2-C, 4-C, 8-C, and 16-C levels, respectively, and remained largely unchanged throughout "stage-III" development.  Polyploid differences among cultivars were not observed.  Development of polyploidy demonstrated that cell divisions cease soon after full bloom. Bagged fruit (unpollinated and unfertilized) showed a much smaller increase in polyploidy.  ‘Sweetheart’ spur cropload level (high and low) did not affect ploidy number of cells.  A survey of small to large sweet cherry fruit (diverse genotypes) is underway to determine if a correlation exists between fruit size and polyploidy.  Results from these studies could be useful in breeding programs focused on improving fruit size, and for early detection of fruit set.