Identifying Winter Tolerant Thornless Trailing Blackberry Selections and Cultivars
Thirty-four 2001 planted USDA blackberry selections and standards and forty-seven 2002 planted USDA blackberry selections were trained up in August 2002 to maximize exposure to winter temperatures, and were evaluated for bud break spring 2003. Other traits, such as vigor, fruiting season, yield and machine harvestability, were scored over the course of the 2003 season. An additional 33 USDA selections and standards were planted this spring 2003, trained-up this past August, and will be evaluated along with the initial 81 selections over the next several years.
While the winter of 2002 – 2003 started with record cold temperatures at the end of October and early November, after that period we had another mild winter. Lows got down to the low 20’s or high teens on a couple of occasions and while these events were sometimes accompanied by high winds (20-35 mph) there was still no significant cold injury to the buds or canes noted in any of the germplasm. In 2002, we had cold injury resulting from low temperatures and high winds during the delayed dormant period in March. This year there wasn’t any obvious delayed dormancy injury, but cool weather during flowering may have negatively effected pollination and their fruit set. Several of the selections had rough looking or crumbly berries, despite testing negative for RBDV. Therefore, cold tolerance can be divided into several different components: degree of injury due to extremely cold temperatures during dormancy (winter), negative effects of cold temperatures during bud break (delayed dormancy) and negative effects of cold temperatures during flowering. In 2003, many of the selections showed rough berries from poor fruit set, probably from cold and wet pollination weather (Figure 1).
Machine harvestability and machine harvest yield was thoroughly examined and results are shown in Table 1. We used an over-the-row Littau harvester with Christi heads. Some new selections, including ORUS 1324-1 and NZ 9373-1 had yields reaching over 10 tons / acre, almost twice that of the standard ‘Marion’. Most selections were rated as acceptable for machine harvestability, but some were poor and had problems including a fairly high pedicel count (poor release), too many red berries (especially at the tip), and hard to remove berries (left on bush after several attempts). When working with such small plots, it was hard to completely determine how well a particular selection machined. Machine adjustments, such as ground speed, amount of head weight, beater speed, and frequency of harvest, can vary, sometimes significantly from selection to selection. Using these small 5 plant plots can determine the leading candidates for machine harvestability efficiency, but to get improved results, the selections need to be planted in bigger blocks.
