I remember Sept. 27, 1997, the day I had the opportunity to participate in the selection of the first primocane-fruiting blackberry selections at the University of Arkansas. It was a day of joy; a major innovation in fruiting type of this increasingly important berry crop, but accompanied with some major challenges to make this innovation useful for growers. Looking back now 20 years, this has been an exciting experience to bring this technology to commercial production.
A primocane-fruiting selection in late July in Arkansas. (Photo credit: John Clark)
Background on Blackberries
What is primocane fruiting? First, let’s discuss the blackberry plant. Like its close relative the raspberry, blackberry is a perennial plant which has biennial canes. The first-year canes are called primocanes, and these canes, after a dormant or rest period, bloom and fruit the following year. These second-year canes are known as floricanes. After fruiting, they canes die and are removed.
But, at the same time fruiting is going on, new primocanes are growing. Almost all existing blackberry varieties are known as floricane fruiting. A major innovation in red raspberries was the advent of primocane fruiting, which began to become important in the 1980s and into the 1990s. Now, about all fresh-market red raspberries are from primocane-fruiting varieties.
Plus-Side of Primocane
What are some benefits of primocane fruiting? The foremost is shift in the fruiting time from early to mid-summer, to late summer, and fall. Anytime one can extend the production and marketing season of a crop, the crop becomes more important from grower to consumer.
Late August early harvest season of primocane-fruiting blackberries in coastal California. (Photo credit: John Clark)
And, since blackberries are a very perishable crop, and can only be stored usually for 7 days, extending the fruiting season is critical.
Another benefit is the potential for two crops from the same plant: the floricane crop in the early to mid-summer, and the later primocane crop from the current-season’s canes. Further, if only the primocane crop is produced, the canes can simply be cut to the ground each year thus greatly reducing pruning costs.
Heat Hurts Fruiting
During testing of the 1997-selected plants, along with breeding for improved primocane-fruiting progeny, it was clear that the heat of summer was very detrimental to primocane flower bud development, fruit and berry set, along with fruit size and quality. In general, temperatures over 90ºF were damaging. This greatly limited progress in breeding in Arkansas.
However, in testing of these same early selections and with later-developed selections, it was found that moderate summer temperatures such as found in Oregon’s Willamette Valley and coastal California contributed to much better fruit yield and quality. A memorable day for me was Oct. 14, 2001, when blackberry breeding colleague Dr. Chad Finn (USDA-ARS, Corvallis, OR) showed me the Arkansas selections APF-8 and 12 under trial in Aurora, OR.
The plants had huge amounts of large berries, plus many flowers and flower buds. I could not believe the difference between the hot environment of Arkansas and the more moderate Oregon test site. I had spent many years teaching plant breeding students about genotype by environment interaction. But on this day, I truly saw this expressed. My excitement was difficult to contain!
Primocane of Prime-Ark 45 showing flower bud formation on the tip of the cane, late June in Arkansas. The berry was harvested from a floricane on the same plant. (Photo credit: John Clark)
First Releases
These two selections were released as the world’s first primocane-fruiting blackberries, ‘Prime-Jan’ and ‘Prime Jim.’ I recommended these for home garden and local market production use, as their fruit quality and storage potential were much less than existing floricane-fruiting varieties. Plus, they were thorny.
Moving forward, in 2009 the first commercial-quality variety was released, ‘Prime-Ark 45.’ It has been the most successful blackberry of this type developed, with more than 2.5 million plants sold between 2010 and 2016. The planting of ‘Prime-Ark 45,’ largely in coastal California, and has contributed to a substantial amount of fruit to the domestic market in a period when very limited blackberries available.
Subsequent developments include ‘Prime-Ark Freedom,’ the first thornless cultivar, was targeted for the garden and local production market, and ‘Prime-Ark Traveler’ for the commercial shipping market. There are additional proprietary varieties in production also in the United States now also, derived from the original University of Arkansas genetics.
Prime-Ark 45 with heavy fall crop in October in coastal California. (Photo credit: John Clark)
There is yet a long path to travel to make primocane-fruiting blackberries of equal importance to this type of plant in fresh-market red raspberries. But, the technology is improving, researchers and growers are developing innovative production techniques to increase production and quality, the outlook is bright for making this type of blackberry a major part of our domestic blackberry supply.
Looking back 20 years and seeing this innovation develop has been quite the experience. Now it is particularly exciting to see growers and consumers benefit. Let the good times roll!