Submitted to: National Berry Fruit Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/11/1999
Publication Date: N/A
Interpretive Summary: Rosette is a blackberry disease that seriously limits blackberry production in the Southeastern United States. A breeding program was started at Poplarville, Miss. to develop rosette resistant varieties capable of supporting a pick-your-own blackberry industry. 'Humble', a variety selected from the wild in Texas, was used as the source of rosette resistance. Through crossing and selection, two resistant plants with acceptable blackberry traits were identified. One selection was thornless. These plants have been crossed with other selections to improve yield and quality of fruit from rosette resistant plants. Progress in the breeding program is slowed by the inability to inoculate plants to test for disease resistance. All selections must be made in the field with natural rosette infection.
Technical Abstract: Rosette or double blossom is a serious disease of most erect blackberries and probably the most limiting factor in blackberry production in the southern United States. The cultivar Humble has been reported variously as immune or tolerant to rosette. A breeding program was initiated at Poplarville, Miss. with the objective of breeding thornless cultivars with rosette resistance derived from 'Humble'. A productive rosette resistant plant (MSUS29) was identified from the cross 'Humble' X 'Brazos'. MSUS29 was backcrossed to standard cultivars and thornless cultivars. An elite thornless selection (MSUS119) was identified from crosses with the thornless cultivar Navaho. The most recent crosses were made between selections with 'Humble' as the source of rosette resistance and either 'Arapaho' or MSUS119 as the source of thornlessness. It is a challenge to select rosette resistant plants because we have not been able to develop a reliable screening procedure and all seedlings are screened in the field using natural infection. To determine the tendency of 'Humble', 'Brazos', and 'Rosborough' to transmit rosette resistance, we studied its heritability in blackberry. Only 'Humble' transmitted enough resistance to be usable as a parent. We evaluated the effect of rosette on ripening date, yield, and berry weight. Berries ripened about the same time and weighed about the same when grown at either a rosette-free or disease- present location. However, yield was reduced on some clones and not others where rosette was present.