Submitted to: Proceedings of the North American Bramble Growers Association Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: December 7, 2005
Publication Date: January 6, 2006
Citation: Lewers, K.S. 2006. Molecular markers for blackberry. Proceedings of the North American Bramble Growers Association Annual Meeting. p. 145-147.
Interpretive Summary: Breeding of blackberries, raspberries, and strawberries is slow in part because, without advanced technology, seedlings derived from breeders’ crosses must be grown to maturity for evaluation of many horticultural traits such as fruit quality. This of course takes years to accomplish, and requires large investment in land, greenhouses, staff and equipment. The breeding process would be greatly accelerated, and would be much more efficient, if a breeder could test a small seedling and know with confidence what traits that seedling will have if grown to maturity. A DNA based method, called “marker assisted selection” is available to accomplish this, but requires DNA “markers” that can be used to identify the seedlings the breeder should “select”. This makes the selection step easy; developing the markers is not as easy. We are developing a comprehensive set of such markers for use in brambles and strawberries by screening 18,000 genes from blackberry for the presence of such markers. This is being done through a contract with Clemson University. So far we have identified 1,200 potential markers. In initial tests, it appears that the large majority of these will be useful for breeding purposes. Our results will greatly accelerate the breeding of blackberries, raspberries, and strawberries for desirable horticultural traits, including production of more than one crop per year. Our results are of immediate interest to bramble and strawberry breeders and in the near future to the berry producers and consumers worldwide.
Traditional blackberry breeding relies on years of evaluation to allow a breeder to select potential cultivars. It takes longer to identify plants with certain traits that require either plant maturity or specific environments to express. For blackberry, examples would be fall-fruiting or orange rust resistance. As a result, the process of developing new bramble cultivars can take longer than breeders, nurseries, and growers would prefer. In the future, breeders will have available genetic assay tools called simple sequence repeat molecular markers (SSRs) that will allow them to select indirectly for certain traits that otherwise can take years to become evident. Previous NABGA-funded research concluded that only a small number of raspberry and strawberry SSRs are sufficient for use with blackberry and that SSRs derived from blackberry are needed. We contracted with Clemson University to develop SSRs from ‘Merton Thornless’, the source of thornlessness for nearly all US thornless blackberry cultivars. Over 18,000 expressed genes were archived. The sequences for 3,000 of those were obtained and searched for candidates from which to design SSRs. Over 1,200 potential SSRs were identified, and primers were designed to test with blackberry, raspberry, and strawberry. Of the 23 SSRs tested so far, 18 (78%) will be useful with a blackberry mapping population we are working on in collaboration with Dr. John Clark at the University of Arkansas. In addition, 11 SSRs (48%) will be useful with a raspberry mapping population we are working on with Dr. Courtney Weber of Cornell University, New York, and three SSRs (13%) will be useful with our strawberry mapping populations.