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- Author or Editor: David K. Wildung x
A single application of 50, 100 or 500 mg/liter gibberellic acid (GA) during 75% full bloom induced seedless fruit development in lingonberries growing in their native habitat in Alaska. Fruit set was increased by the 500 ppm GA treatment in the absence of insect pollination. Fruit set was not increased by GA in open-pollinated plants. Berry weight and diameter were unaffected by GA treatments.
‘Northblue’ blueberry (Vaccinium corymbosum L.) plants propagated by tissue culture (TC) have a branching pattern and growth rate different from plants propagated by leaf-bud cuttings. Two to 3 times more basal branches were formed on tissue culture-derived plants by the time they were 27 to 34 weeks old. These basal branches were maintained on older plants in the field, where lateral branching was also twice as high. The growth rate of the young TC-derived plants was 3 times the rate of young leaf-bud, cutting-propagated (ST) plants. However, lateral branch length of older plants in the field was similar for both groups of plants, indicating a reduction in the growth rate of TC-derived plants from 34 to 82 weeks after propagation. Pruning and chilling methods reduced basal branch length and the number of lateral branches produced in the field, while enhancing the length of lateral branches and total buds per lateral branch. Although TC-derived blueberry plants had numbers of total flower buds and total buds per lateral branch similar to ST-derived plants, they produced more flower buds per plant. The enhanced branching framework of TC-derived plants, composed of rapidly forming basal and lateral branches, may increase photosynthesis at an early age and hasten fruit production.
Three seedling populations of lingonberries from Fairbanks, Alaska, Oulu, Finland, and the Pasvik River Valley, Norway were exposed to 0, 170, 344, 513, 681, 843, 1013, and 1185 hours of continuous chilling temperatures (4 ± 1°C) to determine chilling requirements necessary to satisfy rest. Both the Finnish and Alaskan populations required at least 681 hours of chilling to obtain maximum terminal vegetative budbreak. Continuous chilling for 1185 hours was insufficient to obtain maximum budbreak in the Norwegian population. In the Finnish and Alaskan populations neither the percentage of stems exhibiting lateral budbreak nor the number of lateral branches per stem differed among chilling treatments. Plants from Norway showed significantly greater lateral budbreak in the 513- and 681-hour treatments than in all other treatments. At least 681 hours of chilling were necessary to achieve normal flowering in the Finnish population.
As part of our hardy strawberry (Fragaria ×ananassa) breeding program, winter hardiness of 15 strawberry cultivars was evaluated in the field after Winter 2005–2006 and a test Winter 2006–2007 with no snow cover at Grand Rapids, MN. After the snow-covered Winter 2005–2006, plant stand (percent leaf coverage for the designated area for each plot) increased for all cultivars in the mulched treatment and some cultivars in the unmulched treatment with slight decreases only for several cultivars in the unmulched treatment. However, after Winter 2006–2007, the plant stands of all cultivars drastically decreased in both mulched and unmulched treatments. ‘Clancy’, ‘Evangeline’, and ‘L'Amour’ were the three most sensitive cultivars among the 15 cultivars tested. ‘Kent’, ‘Mesabi™’, ‘Cavendish’, and ‘Brunswick’ were the highest yielding cultivars for both 2006 and 2007 in the mulched treatment. In the unmulched treatment, ‘Brunswick’, ‘Mesabi™ ’, ‘Cavendish’, ‘Sable’, and ‘Kent’ were the top yielding cultivars after Winter 2006–2007. During Winter 2005–2006, with 20 to 30 cm snow cover throughout the season, the 5- and 10-cm soil temperatures remained constant at ≈30 to 31.5 °F in both mulched and unmulched treatments. In contrast, during Winter 2006–2007, there were 16 and 24 days (consecutive) in February below 18 °F at 5-cm soil depths for mulched and unmulched treatments, respectively, which probably led to the severe winter damage. Although straw mulch afforded the plants some protection, snow cover is critical to the survival of strawberries in northern Minnesota and other areas with similar weather conditions.
Plants of `Northblue' blueberry, propagated in tissue culture (TC) or from softwood, single-node cuttings (ST), were evaluated in field plantings established in 1984 at Becker and Grand Rapids, in central and northern Minnesota, respectively. Plantings were observed from 1987 through 1994 to determine the persistence of such effects as increased vigor, more spreading growth habit, and higher yield observed for TC plants during the initial 3 years after planting. TC plants had significantly higher yields at Grand Rapids in 1989 and 1994. At Grand Rapids, the consistently greater plant spread (bearing area) of TC plants resulted in higher yields of TC plants over all years combined. At Becker, TC and ST plants did not differ for plant height or spread after 10 years and, in 2 of 5 years, ST plants had heavier average berry weights. At Grand Rapids, TC plants did not differ consistently in height, or subjective ratings of the amount of bloom or crop. The effects of propagation method on yield and growth habit of `Northblue' are limited to early years in warmer locations, but can be of longer-term significance in colder areas with shorter growing seasons and lower winter temperatures, where plant spread is a more important factor than plant height in determining yield.