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Title:   Author  item
                                            Lewers, Kimberlyitem
                                            WEBER, COURTNEY - CORNELL UNIV
  Submitted to: HortScience
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 3/31/2005
                                    Publication  Date: 7/19/2005
                                    Citation: Lewers, K.S., Weber, C.A. 2005. The trouble with genetic mapping of raspberry. Hortscience.     ***meeting abstractInterpretive Summary: abstract- no summary required
                                Technical Abstract: Researchers developing new cultivars of red raspberry (Rubus idaeus subsp. idaeus L. and R. idaeus subsp. strigosus Michx.) and american black raspberry (R. occidentalis L.) observe progeny of breeding populations for several seasons to identify those that perform reliably at a superior level in multiple environments. Maintaining these plants consumes significant resources. If a portion of any breeding population could be eliminated based on a qualitative character, resources used for that portion could be used for other progeny or projects. The same is true if molecular markers genetically linked to a trait can be used to eliminate progeny with undesirable characteristics. Our objective is to identify such molecular markers for red raspberry and black raspberry. A black raspberry × red raspberry cross of 'Jewel' × NY322 was made to develop a map of each parent in the F1 generation. The F1 population segregates for fall fruiting, root production of adventitious shoots (suckering), tip rooting, and other important traits that would be good candidates for marker-assisted selection.  An F2 population was generated to join the maps. The molecular markers used were previously published simple sequence repeat (SSR) markers derived from red raspberry and strawberry. Of those SSR products amplified from the red raspberry parent, 40% did not segregate in the F1 generation; the PCR product was amplified from all F1 progeny. Twice this level was observed for black raspberry. In the F2 generation, 90% (red raspberry) and 70% (black raspberry) of these markers segregated in a 3:1 ratio indicating the parents were homozygous. Of the SSRs segregating in a 1:1 ratio in the F1 generation, and present in the F1 parent of the F2 population, only 20% segregated in the expected 3:1 ratio in the F2 generation. The observed segregation skewing indicates severe problems with transmission. Our findings help quantify the relative levels of homozygousity previously reported for red raspberry and black raspberry. In addition, the severe skewing observed in the F2 generation provides a molecular perspective to the fertility problems previously reported for the black raspberry × red raspberry hybrids (purple raspberry). Since black raspberry is highly homozygous, purple raspberry has transmission and fertility problems, and black raspberry breeders have reported a frustratingly low level of diversity in this subgroup, development of a black raspberry map is expected to require twice the markers as for a red raspberry map, emphasizing the need for black raspberry sequences from which to develop molecular markers.


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