Blackberries - the essential details
Derek Jennings, the well known soft fruit breeder, explains some of the botanical intricacies of the blackberry.
The botanical group that gives us blackberries is complicated and has several sections. In particular, the blackberries of Western America belong to a section called Ursini and are so distinct that we should not compare them with blackberries of the more common Moriferi section. They occur only along the west coast from British Columbia to California and are isolated from the eastern types by the prairies and rockies. They are prized for their flavour and are one of the main types used by the important processing industry in these parts. By contrast, the blackberries of the Moriferi are distributed widely in both eastern and southern America and in Europe. They are also diverse, and there are big differences between the varieties found in these contrasting parts. Thus, all the European types have a trailing habit, many of eastern American ones are more hardy and are erect or semi-erect and those from southern America have a low chilling requirement and are more adapted to a warm climate. Such a major division implies a difference in evolution and so it is not surprising that there are large differences in many aspects of their form and function.
In the wild, the Ursini blackberries have separate male (stamens only) and female (pistillate) forms, and early breeders had to seek natural hybrids with other sections to obtain forms with bisexual flowers able to set fruit in monoculture. Breeders must also take account of the big differences in chromosome number, the Usini having high numbers, commonly 42 but sometimes 56 or 84, whereas the Moriferi have fewer, mostly 28 or 14. Such differences limit the possibilities for gene exchange between the two sections and is one of the reasons why they have remained distinct. It is also a reason why hybrids between the sections are often infertile.
As well as the Usini’s trailing growth habit (European but not eastern American species of the Moriferi are also trailing), they are earlier ripening and show a characteristic aromatic flavour, which has contributed so much to the flavour of their hybrids with the raspberry, notably the Loganberry and Tayberry. They also have a softer texture, which is why they are less suitable for supermarket sales in spite of their superior flavour, and why they are more popular with amateur gardeners.
Historically, the most common Ursini blackberry grown in America, particularly for processing, is the Marion, but many more are now available, including Silvan, Kotata, Waldo, Olallie and my variety Helen. The variety known as Mr Aughinbaugh's blackberry (a pistillate selection from the wild ) and Aurora, respectively the parents chosen to breed the Loganberry in 1881 and the Tayberry in 1979 each have 56 chromosomes instead of the more common 42 ,and were chosen because they combine well and give fertile progeny with raspberries which have 28 chromosomes instead of the usual 14.
Derek Jennings
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