LochNess blackberry

Derek Jennings, for many years the soft fruit breeder at the Scottish Crop Research Institute,  surveys the development of the modern thorn-free blackberry.

For those of us who are already in the midst of a blackberry harvest it is difficult to envisage the major changes that have occurred in a very short time. It is not so long ago that our cultivated blackberries were all thorny, were completely prostrate in growth and did not ripen until mid-September in the UK. Nowadays, we have redesigned them so that the earliest ripen in June and their growth is both erect and thorn-free. These major changes have occurred through the cooperation and generosity of workers in several countries who have freely exchanged their germplasm in a way which is rarely possible in these days of commercial exclusivity.
 
Cultivated forms,of course, are usually obtained by selecting from among locally abundant wild forms, which are then further improved by plant breeding. They therefore tend to share characters with the wild forms where they were bred. Hence, growers in eastern America are used to blackberries with erect canes, because their wild forms are nearly all erect, but they still sought earlier ripening forms and thornlessness.
 
The first major advance came when workers at the John Innes Institute in the UK discovered a thorn-free blackberry in their hedgerow. They improved it by breeding and in 1938 produced the variety Merton Thornless. Breeders in Maryland, USA were among the first to make crosses with the variety, but they found that the progenies were very ill-adapted to eastern America. The original thorn-free plant was not hardy because it came from the species Rubus rusticanus which occurs along the Atlantic coast from southern England to Spain, where severe winter frosts occur only rarely. Hence the American breeders found that their progenies were not only prostrate, unlike most of the varieties that they were used to, but suffered severely from frost damage in their climate. Fortunately, they persevered over several generations, and in 1966 produced the varieties Smoothstem and Thornfree, which were the first thorn-free varieties of any importance.The breeding work was continued in Illinois by Jack Hull and Chester Zych, who in 1981 and 1985 produced the varieties Hull Thornless and Chester Thornless, which have since attained some importance.
 
A free exchange of germplasm was maintained throughout this work and we at the Scottish Crop Research Institute in Dundee were able to use American germplasm from an early stage. Scotland has such a short growing season that earlier cropping became a high priority in our selection work. Our first success was LochNess, which we launched in 1988. Largely due to its earlier bud-burst in spring it typically crops from early August to late September, and, thanks to its American parents it is also erect and thorn-free. It became apparent that a variety’s` cropping season was determined not only by its time of bud-burst but also by the time required from flowering to fruit-ripening. Variation in the latter is considerable, but had not been used in selection before. It ranged from about 46 days in the variety Ashton Cross, 56 days in LochNess to 69 days in the American variety Thornfree. Thus, further breeding involving a derivative of Ashton Cross gave us the variety LochTay, which in the UK ripens in July in the open, while growing it in tunnels gives us fruit in June. Like LochNess, it has erect, thornfree canes.
 
More recently, the variety which is making an impact is Tupi from Brazil. Its very large, flavoursome fruits are much in evidence in the supermarkets in all seasons and the variety seems likely to become the one most responsible for promoting blackberries to one of our major fruits. It produces very large crops in Mexico and elsewhere, where growers have learnt how to manage their plants to produce two or three crops a year and the climate allows for cropping in all seasons. All these varieties belong to the blackberry species of Europe and Eastern America. The blackberries of western America are very different in many ways and so are the many hybrid Rubus fruits that are now available. Discussion on the improvements in these must be a subject for another date.

Derek Jennings