Sunghee Guak

Chill unit models for predicting dormancy completion of floral buds in apple and sweet cherry

Temperature-controlled experiments were conducted to determine the relative contribution of temperatures to dormancy completion of floral buds in ‘Gala’ apple (Malus domestica Borkh.) and ‘Sweetheart’ sweet cherry (Prunus avium L.). Shoots were collected right before chill inception, and exposed continuously to seven different temperatures in the range of −2°C and 16.8°C for 1320 hours. Chilling requirements were determined on sequential field samples from plots of days to bud break against sampling date. Temperature-response curves, which were best fit in a four parameter logistic nonlinear regression, indicated that optimum chilling temperatures were between −2°C and 5.5°C for ‘Gala’ and between −2°C and 7°C for ‘Sweetheart’, with no chilling effect above 13°C in both species. The derived chill unit models predicted that chill unit accumulations required for dormancy completion averaged 921 for ‘Gala’ and 740 for ‘Sweetheart’ over the three year period. The year-to-year variation in ‘Gala’ apple was smaller with our ‘Gala’ model than with the ‘Utah’ model (14% vs 23.5% coefficients of variation), while similar to each other in ‘Sweetheart’ sweet cherry.

Effects of Rooting Agents and Shading Treatments on Rooting and Growth of Highbush Blueberry Hardwood Cuttings

Rooting agents and shading treatments were tested in two different experiments to determine their effects on the establishment success of hardwood cuttings of three highbush blueberry varieties ‘Bluecrop’, ‘Duke’ and ‘Sunrise’. For the experiment with rooting agents, one-cm long bases of the cuttings were dipped into solutions of IBA or NAA for 5 s, both at 0, 500 and 1000 mg · L ?1 in 50% ethanol, and were also treated with Rootone® powder. Determined 90 days after cutting, the percent rooting and root weight were increased by NAA at 500 mg · L ?1 in ‘Bluecrop’ and ‘Sunrise’, while in ‘Duke’ IBA at 500 mg · L ?1 was effective. These auxin treatments were found to work better than a commercial product Rootone®. The rooting agent-induced increases in root development resulted in better shoot growth of the cuttings in all three varieties, as determined after 90 days of further growth in individual containers. In the experiment with shading treatments, different levels of the shading treatment (30 to 90%) were imposed over the cutting bed under no mist. In all three varieties, 30% shading increased the percent rooting and root and shoot growth, compared to no shading control. However, shading levels higher than 50% shading were found to be inhibitory for hardwood cuttings of highbush blueberries, especially under the environmental conditions with no mist system.