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  • Author or Editor: Larry Douglass x
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As part of a program to improve highbush blueberry (Vaccinium corymbosum L.) cultivars via tissue culture and genetic engineering, studies were conducted to determine optimum conditions for organogenesis from leaf explants of the previously recalcitrant cv. Bluecrop. The effects of a pretreatment, growth regulators, and age of explant source on shoot organogenesis were investigated. A maximum of 98% explants regenerated shoots with a mean of 11 shoots per leaf explant after 62 days when explants of 2-week-old shoot cultures were incubated on the following regime: pretreatment medium #1 containing 5 μm TDZ and 2.6 μm NAA for 4 days, pretreatment medium #2 containing 7 μm zeatin riboside and 2.6 μm NAA for 3 days, regeneration medium containing 1 μm TDZ for 6 weeks, and last on medium without growth regulators for 10 days. No shoot regeneration occurred if explants were incubated without exposure to pretreatment prior to incubation on regeneration medium. There were no significant differences in percentage of regeneration or the number of shoots regenerating per explant from leaf explants derived from either 1-, 2-, or 3-week-old shoot cultures. Shoot production per explant on regeneration medium containing 1 μm TDZ was about three times that on 0.5 μm TDZ or 20 μm zeatin riboside, and nine times that on 5 μm TDZ. Chemical names used: 1-phenyl-3-(1,2,3-thiadiazol-5-yl)urea (thidiazuron, TDZ); 9-(β-D-ribofuranosyl)-6-(4-hydroxy-3-methyl-but-2-enylamino)purine (zeatin riboside).

Free access

Abstract

Following the termination of rest, 16-, 20-, or 24-hr photoperiods hastened flower development of 7 cultivars of hydrangeas [Hydrangea macrophylla (Thunb.) Ser.] compared to those at 8- or 12-hr photoperiods. The interruption of a 16-hr dark period with 4- or 8-hr incandescent illumination was as effective as continuous light. Stem elongation and cyme expansion increased with length of photoperiod, while the interruption of the dark period had an intermediate effect upon these parameters. Plants undergoing continuous development without defoliation or a rest treatment responded similarly to rested and defoliated plants in rate and extent of growth and initiated flowers more uniformly at an 8-hr photoperiod than at longer photoperiods.

Open Access

Abstract

Thornless blackberry plants were trained on 2 trellis types to determine the effect of primocane-floricane separation on plant productivity. Plants grown on a divided canopy had less shaded primocanes and more productive floricanes than those grown on a single canopy. Light interception was correlated positively to an increase in number of fruit per raceme and soluble solid/acid ratio. Dormant pruning had no effect on light interception or yield.

Open Access