Progress and Challenges in Primocane-Fruiting Blackberry Breeding and Cultural Management

The University of Arkansas blackberry breeding program began to focus on primocane-fruiting (PF) breeding in the mid 1990s, and has expanded this effort since then. Cultivars released since then include 'Prime-Jan'(R) ('APF-8'), 'Prime-Jim'(R) ('APF-12') in 2004 and 'APF-45' in 2009. Immediate challenges in breeding were seen, the most significant was heat damage to primocane flowers and fruits in Arkansas, along with development of commercially acceptable fruit size, quality, and plant productivity. One of the most striking observations made in the early 2000s was that the selections 'APF-8' and 'APF-12' performed much better in the more moderate climate of the Willamette Valley of Oregon. They had larger, more plentiful fruits, and overall plant performance was superior in Oregon to that in Arkansas. Fruiting began later compared to Arkansas, with mature fruits present from early September to late October. This striking environmental effect indicated that advances in PF breeding could benefit from multi-location testing and breeding. Expanded locations for PF genotype trials have further supported this observation. Near the time of release of 'Prime-Jim'(R) and Prime-Jan'(R), it was evident that innovative cultural management of these genotypes would be required to provide for commercially acceptable yields. The initial studies conducted by Oregon State University indicated that tipping of primocanes was required to manage cane height and increase yields. Subsequent work evaluated tipping heights, mowing of canes to adjust the fruiting season, and high tunnel production and resulted in substantial yield increases and extension of the fruiting season. The combination of research in breeding, testing in diverse climates and locations, and development of cultural management systems has resulted in the beginning of commercial PF blackberry production in the USA. Further research and expanded commercial acreage will likely enhance precision timing of extended-season and off-season production.