NRI Award #2005-35300-15536
PI: Tia-Lynn Ashman, Co-PI: Kimberly Lewers
Department of Biological Sciences
University of Pittsburgh
Pittsburgh, PA 15260
E-mail: tia1@pitt.edu
Telephone: 412-624-0984
Website: http://www.pitt.edu/~biohome/


Accomplishments:

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Objective 1: Identify and characterize gender-related genes in octoploid wild Fragaria via QTL mapping.
Using a qualitative assessment of sex, we have found that sex in the strawberry population we are studying is determined by two linked loci. One locus controls male sterility; the dominant allele confers male sterility (lack of pollen production/vestigial anthers) and the recessive allele confers pollen-producing anthers. The second locus controls fruit set (i.e. female fertility/sterility). The allele conferring female sterility is recessive. The two loci conferring male and female sterility are linked together. The presence of neuter progeny (those that neither set fruit nor produce pollen) from this cross, is critical confirmatory evidence of the presence of two loci. On the same linkage group, we have identified an SSR molecular marker, ARSFL_7, very closely linked to both traits. We are completing the quantitative assessment of gender. Thus far we have quantitatively characterized female fertility (fruit set, ovule number) and male fertility (flower number, anther sterility, anther number) for 1200 progeny of the mapping population. We are in the process of quantifying pollen per anther and pollen viability for the pollen producing progeny of this cross. We are continuing to develop markers to complete the genetic map of F. virginiana in order to proceed with QTL mapping. In particular, we are focusing on markers linked to ARSFL_7 in a map generated from a diploid strawberry population in case there is any association between marker order in diploid strawberry and octoploid strawberry.

Objective 2: Determine the level of similarity between peach (or Prunus) and Fragaria genomes.
We tested several hundred markers derived from sequences received from Dr. Dorrie Main in common with strawberry and other Rosaceae species, including peach. The majority of these, when they amplified products in strawberry, did not detect polymorphisms between parents of our mapping populations. Broader Impacts We have not only found two loci that determine sex in strawberry, but also have identified a SSR molecular marker that is very closely linked to the dominant male sterile allele. These results will not only lead to increased understanding of strawberry sex determination and transfer of the desired sex to potential cultivars in backcrosses, but also has potential to contribute to enhancing marketable yield and fruit size via marker assisted selection. In particular, our QTL results will inform on whether our SSR marker for female sterility will also be useful to select for ‘king’ berries (those developed only at the primary & secondary positions). The fact that these two are linked leads to the hypothesis that this may be a “sex chromosome” – it will be of interest to determine whether other quantitatively expressed traits related to fertility are located on this linkage group. Our results also show mixed evidence for the usefulness of diploid markers in the octoploid strawberry. Although there is linkage between Fvi6b and ARSFL_7 in a diploid map of developed by Sargent (personal communication), they were not linked in our mapping population. Two other markers, however, did show similar groupings between the two ploidy maps. Therefore, linkages discovered in diploid strawberry may not translate into all octoploid populations. Instead, the utility of diploid maps for informing studies on the octoploid, cultivated strawberry may vary.

Deliverables:

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• Publications
• Lewers, K.S., T-L. Ashman, J.F. Hancock, D. Main. Genetic mapping with octoploid strawberry.
• In Barclay Poling and Fumi Takeda (eds). North American Strawberry Symposium 2007. ASHS Press

• Presentations
• Ashman, T-L. The ecological Context for gender evolution: studies in wild strawberry.
• Department of Ecology, University of Lund, Lund, Sweden (Jan 25)
• Department of Ecology and Natural Resource Management, The Norwegian University of Life Sciences, Ås, Norway (April 17)
• Department of Biological Sciences, University of New Orleans, NOLA (April 30) Wenn-Gren Foundation Symposium on Mating System Evolution, Fiskebackskil, Sweden, (May 30-June 2)
• Department of Ecology and Evolutionary Biology, Tulane University, NOLA (June 11)

• Meeting Abstracts
• Spigler, R. S., K. S. Lewers, D. Main. & T-L. Ashman. 2007. Genetic mapping of sex determination in octoploid strawberry. PAG XVI San Diego CA
• Community resources generated (sequences, populations, plant materials, etc)
• Germplasm characterized for both gender, and SSR markers, including neuters.

• Training:
• Undergraduates:
• Sheena Mathew. Summer 2007.;
• Danielle Feather. Fall 2006 through present.;
• Emily Pfeufer. Summer 2007.;
• Kimm Freeman. Summer 2007.;
• Steven Wong. Summer 2007.;
• Pradhuman Parihar. Summer 2007.;
• Jason Eddie. Summer 2007.
• All involved in PCR Reactions;
• Emily Korns 2006-2007.;
• Sophia Good 2006-2007.
• Camile McNalley 2006-2007. Plant care and scoring of plant phenotypes.

• Postdoctoral Associates:
• Dr. Carine Collin. 2007 Plant care and student organization;
• Dr. Rachel Spigler. 2007 QTL mapping, data analysis, phenotyping and manuscript preparation.

• Technicians:
• Kate Rappaport. 2006-07. Planted and extracted DNA from mapping population. Trained students in PCR, data organization, annotation and extraction.
• Karen Williams. 2006-07. Planted and extracted DNA from mapping population. Trained students in PCR, data organization, annotation and extraction.
• Eric Early. 2007.Quantitative scoring of sex related traits, data organization.