Effect of plant tissue culture parameters on the ploidy level of Physalis grisea, Solanum lycopersicum, and Solanum prinophyllum regenerants

Plants regenerated from seedling explants (hypocotyls and cotyledons) of the Solanaceae family members Physalis grisea (groundcherry), Solanum lycopersicum (tomato), and Solanum prinophyllum (forest nightshade) were used to determine the in vitro culture parameters that contribute to the incidence in polyploidization of tissue culture-derived plants (regenerants) from these species. We examined the possible effects of zeatin concentration in the plant regeneration medium, explant source, and species. Plants were grown to maturity under greenhouse conditions, pollen was collected and germinated. Flow cytometry analysis verified the utility of the pollen germination method for determining differences in ploidy, which was based on the number of pollen tubes produced with one tube representing diploid and two indicating polyploid. As for zeatin concentration, we assessed the effect of our standard method of initiation on medium containing 2 mg/l followed by 1 mg/l 2 weeks after culture initiation in comparison with 0.25, 0.5, and 1 mg/l throughout the culture lifetime. There were no major correlations for zeatin concentration on ploidy status across the species except for plants regenerated from S. lycopersicum hypocotyl explants where the percentage of polyploid regenerants increased with increasing concentrations. As for species and explant effects, P. grisea plants regenerated from hypocotyl explants had the highest percentage of polyploid plants at 81% compared to 43% and 35% for S. lycopersicum and S. prinophyllum, respectively. From cotyledons, 8% of S. lycopersicum and 20% of S. prinophyllum were polyploid. A comparison with P. grisea could not be made because cotyledon explants do not regenerate on zeatin-containing medium. The results indicated the incidence of polyploidization cannot be generalized for zeatin concentration, however, an influence of explant type and species was observed. Effects of increased ploidy on plant morphology were primarily larger flower and seed size; however, no significant differences were observed in plant or fruit size.