Identifying the Genes Associated With Day-Neutrality in Strawberry Using a QTL Approach


NRI Award # 2005-35300-15468
PI: Jim Hancock, CoPIs: Kim Lewers, Steve van Nocker and Dechun Wang
Department of Horticulture
Michigan State University, East Lansing, MI 48824
E-mail: hancock@msu.edu
Telephone: 517-355-5191


Accomplishments:

Our first objective was to develop a molecular map and identify QTL associated with repeat flowering in a population of ‘Honeoye’ × ‘Tribute’ after phenotyping them in multiple environments. Our intent was to begin mapping with the AFLP markers that we had already developed, but to incorporate SSRs as fast as we could identify them. We first 387 single dose restriction fragments (SDRFs) on a consensus map of 1310.7 cM with 42 linkage groups. Individuals from the mapping population were observed for their flowering habit throughout the growing season in Michigan (MI), Minnesota (MN), Maryland (MD), Oregon (OR) and California (CA). Eight QTL were found that were either location specific or shared among locations. None of these QTL explained more than 36 % of the phenotypic variation, indicating that the inheritance of repeat flowering is likely a polygenic trait. At all three eastern sites, one QTL was identified on Linkage group (LG) 17 that was a strong regulator of day-neutrality; additional QTL were identified in MI on LG 17 and in MN on LGs 7, 20 and 28. In the western states, only one significant QTL was identified on LG 7 which accounted for 22 % of the phenotypic variation in CA. This same peak was uncovered with a P value less than 0.2 in MI.

In our emerging SSR data, we have identified a marker genetically linked to repeat fruiting in the cross of ‘Tribute’ × ‘Honeoye’. The repeat fruiting trait was mapped as a qualitative trait: parents and progeny flowering after June 6 in Beltsville, Maryland were scored as repeat fruiting. The trait fit a 1:1 segregation ratio. The SSR marker and the trait were linked by 11 cM at a LOD score of 9.96, approximately a one-in-a-billion chance that this linkage does not reflect physical proximity between the SSR locus and the trait locus. When the Maryland data are treated qualitatively, the trait also is linked by 8 cM to the AFLP marker previously identified as the major QTL marker for the trait when evaluated in Maryland as well as Michigan, Minnesota, and New York (LOD 4.49 due to small number of individuals scored for both the AFLP and the trait). The two molecular markers flank the trait with the current data set. Additional marker data will be added to strengthen the validity of these findings. Conversion of the AFLP marker to a SCAR marker is underway, as is the addition of SSR data to the mapping data set.

Our second objective was to develop a molecular map and identify QTL associated with dayneutrality in another large segregating population with the same SD parent (‘Honeoye’), but a different DN F. virginiana parent (RH 30). We have now generated a family of 167 individuals of this cross and phenotyped them for their photoperiod sensitivity in the field. Over 80 % of the hybrids appeared to be day-neutral in the greenhouse , compared to 50 % of the ‘Tribute’ x ‘Honeoye’ population. DNA has been extracted from this new hybrid population and we will begin mapping it this winter. We will also replicate the progeny individuals via runners and set them in the field next spring to further test their photoperiodic responses.

Broad Impacts:

The QTL on LG 17 that was prominent in all three eastern states, but absent in CA and OR, may be involved in regulating heat tolerance.

Deliverables:

  • Publications
  • C.K. Weebadde, D. Wang, C.E. Finn, K.S. Lewers, J.J. Luby, J. Bushakra, T.M. Sjulin and J.F. Hancock. 2007.Using a linkage mapping approach to identify QTL for day-neutrality in the octoploid strawberry (Fragaria ×ananassa Duch ex Rozier). In Press – Plant Breeding
  • Jim Hancock, Cholani Weebadde and Sedat Serçe. 2007. Challenges faced by day-neutral strawberry breeders in the continental climates of the eastern USA and Canada. In press - - HortScience
  • Presentations
  • C. K. Weebadde and J. F. Hancock. 2005. QTL associated with day-neutrality in strawberry. HortScience 40:1121
  • Community resources generated (sequences, populations, plant materials, etc)
  • Two populations segregating for day-neutrality are available for distribution, ‘Tribute’ × ‘Honeoye’ and ‘Honeoye’ × RH 30 (F. virginiana)
  • Training:
  • Cholani Weebadde (PhD. student) developed the AFLP linkage map for ‘Tribute’ × ‘Honeoye’. Sue Hammer (technician), Emma Bradford (PhD. Student) and Elena Sierra-Ponce (undergraduate assistant) are developing the RH 30 x Tribute map.
  • Kate Rappaport (technician) assembled and processed PCR reactions and extracted sizing data from the ABI 3730 Genetic Analyzer.
  • Ernalyn Peralta (biological science aid) assembled and processed PCR reactions and extracted sizing data from the ABI 3730 Genetic Analyzer. Ms. Peralta will be resigning in early December to pursue a career in her chosen field, biological engineering.
  • Sheena Mathew (biological science aid), currently attending U. C. Davis as a sophomore, assembled and processed PCR reactions.
Collaborations:

The grant itself initiated a strong collaboration between the co-PIs Kim Lewers and Jim Hancock. We have begun to interact with Tom Davis (Univ. New Hampshire) and Kevin Folta (Univ. Florida) to determine if the linkage maps developed in F. vesca are transferable to the octoploids.