83 NASS / NASGA PROCEEDINGS. 2007. Genetic Mapping with Octoploid Strawberry K.S. Lewers 1* , T.-L. Ashman 2 , J.F. Hancock 3 , and D. Main 4 1 U.S. Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Fruit Laboratory, Bldg. 010A, BARC-West, 10300 Baltimore Ave., Beltsville, MD 20705 2 Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260 3 Department of Horticulture, Michigan State University, East Lansing, MI 48824 4 Department of Horticulture and Landscape Architecture, Washington State University, Pullman, WA 99164 ADDITIONAL INDEX WORDS. Fragaria, SSR, gender, sterile, day-neutral ABSTRACT. In 2004, the USDA–CSREES call for proposals for the National Research Initiative Program 52.1, Plant Genetics, focused on crops within the plant family Rosaceae. Two of the funded projects focus on molecular marker mapping of flowering traits of Fragaria L. (strawberry): sex determination in F. virginiana Mill. and day-neutrality in Fragaria ×ananassa Duchesne ex Rozier, the cultivated strawberry. Both traits affect fruit yield qualitatively and quan- titatively and are important to the strawberry industry. The testcross data from the gender-mapping project indicate that the single locus, three-allele model for gender control may be too simple. The day-neutrality mapping population segregated for repeat flowering at three of the five locations, but all progeny were classified as repeat flowering at the other two locations, suggesting that the primary factor, in this population, contributing towards repeated flower- ing through the season, may not be day-neutrality. Approximately 300 simple sequence repeat (SSR) markers were identified specifically for these projects, and over 200 primer pairs have been used in parental screens. Around 90% amplify a product in the parental DNA, and about 73% of those detect polymorphisms between mapping parents. Up to eight products were amplified in polymerase chain reactions (PCR) with most of the SSR primer pairs, but multiple products from the same primer pairs did not cosegregate and could not be mapped as a codominant marker as they were when used to map in diploid F. vesca L., a diploid progenitor species of F. virginiana and F. ×ananassa. Rather, individual amplification products could be mapped as dominant markers and products amplified by any single primer pair often were genetically linked. So far, none of the SSRs have been linked to the phenotypes of sex-determination or day-neutrality; this includes SCAR2, a sequence characterized amplified region (SCAR) marker linked to the seasonal flowering locus in F. vesca. However, two SSRs previously linked in F. vesca, also are linked in F. virginiana. ABBREVIATIONS. amplified fragment length polymorphism (AFLP), polymerase chain reaction (PCR), deoxyribonucleic acid (DNA), sequence characterized amplified region (SCAR), single-dose restriction fragment (SDRF), Agricultural Research Service Fruit Lab (ARSFL), expressed sequence tag (EST) The strawberry has been the focus of increased molecular genetic studies in the past decade. Strawberry genes have been partially or completely sequenced and deposited in GenBank (Folta et al., 2005). Molecular markers have been developed (Ashley et al., 2003; Bassil et al., 2006; James et al., 2003; Lewers et al., 2005), associated with phenotypic traits (Cekic et al., 2001; Deng and Davis, 2001; Haymes et al., 1997; Lerceteau-Köhler et al., 2004), and used to characterize germplasm (Davis et al., 2006). The first molecular-marker maps have been generated for diploid strawberry (Davis and Yu, 1997; Sargent et al., 2004) and for octoploid strawberry (Lerceteau-Köhler et al., 2003). In addition, at least one strawberry breeding program, Driscoll Strawberry Supplementary funding for these projects was contributed by the USDA-CSREES NRI. The authors wish to thank Sam Garrett for propagating the plants for testing; Denise Cole, Carine Collin, Jaleah Robinson, and Lynn Wright for conducting test crosses, planting, or scoring progeny; John Enns for establishing and maintaining the strawberry field and harvesting fruit; Kate Rappaport, Ernalyn Peralta, and Karen Williams for extracting the marker data; Cholani Weebadde for data from a previous supporting project; Margaret Staton for bioinformatics support; and John Hartung, plus the anonymous reviewers for their constructive comments. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommenda- tion or endorsement by the U.S. Department of Agriculture. *Corresponding author. Email: lewersk@ba.ars.usda.gov Associates, has used molecular markers to select desired seedlings (T.M. Sjulin, personal communication). It could be argued that all the materials and information are available to associate more strawberry phenotypes with molecular markers and make those markers available to breeders, and all that is needed now is the additional effort to do so. Two such efforts were funded in 2004 when the USDA- CSREES National Research Initiative Plant Genetics Program focused on crops within the Rosaceae plant family. Both proposals focus on molecular marker mapping of flowering traits of straw- berry: sex-determination and day-neutrality. Both traits affect fruit yield qualitatively and quantitatively and are important to the strawberry industry. In the sex-determination project, the accepted hypothesis is that sex-determination or gender is controlled at one locus with three alleles (F> > h>m) with F for female, for female, h for hermaphrodite, and m for male (Ahmadi and Bringhurst, 1989). Developing markers surrounding this locus would allow strawberry breeders to intro- gress desirable genes from wild germplasm more efficiently. In the day-neutrality project, multiple loci are expected to affect day-neutrality, because multiple genes are thought to contribute to varying degree, depending on the population: one locus in some populations and environments (Ahmadi et al., 1990; Bringhurst and Voth, 1978) and more than one locus in other studies (Hancock, 1999; Shaw, 2003) Developing markers