Project Number: 1275-21000-180-03
Project Type: Reimbursable

Start Date: Jul 01, 2005
End Date: Jun 30, 2009

Objective:
1) Develop a molecular map and identify QTL associated with day-neutrality in an expanded population of "Honeoye" × "Tribute" after phenotyping them in multiple environments. 2) Develop a molecular map and identify QTL associated with day-neutrality in another large segregating population of at least 250 individuals with the same SD parent ("Honeoye"), but a different DN F. virginiana parent (RH 30) (Hancock et al, 2002; Serce and Hancock, 2004). 3) Develop RFLP markers from cloned flowering-time genes of Arabidopsis and characterize the hybridization signals in "Honeoye", `Tribute¿ and RH 30, along with 10 genotypes of each of the two families. 4) Attempt to anchor our two new octoploid linkage maps with existing maps of F. ×ananassa and diploid F. vesca.

Approach:
The profitability of strawberries was greatly enhanced in California, when Bringhurst and Voth (1984) transferred genes for day-neutrality (DN) from a native clone of Fragaria virginiana ssp. glauca from the Wasatch Mountains of Utah to the commercial strawberry F. ×ananassa. Instead of being limited to spring harvests, the producers could now harvest strawberries in all seasons but winter. Unfortunately, cultivars with the Wasatch source of DN have not been so successfully deployed in the rest of the US. Only two DN cultivars, Tribute and Tristar, have been released in the last 20 years outside of California and their commercial use has been limited due to poor reproductive performance. Under hot, summer temperatures, these cultivars produce only a few flower buds and the fruit are small and soft. Further complicating DN cultivar development, is the fact that the genetics of day-neutrality is unclear. Day-neutrality was originally shown to be regulated by a single dominant gene in the Cal-Davis breeding population, but its inheritance has been shown to be much more complex in other studies. This is an important issue, as the backcrossing strategies currently being utilized are only effective if DN is regulated by one or a very limited number of genes. In addition, DN displays incomplete penetrance, with the same segregating populations often expressing differing percentages of day-neutral progeny at different locations. To develop commercially important DN cultivars that perform well under high summer temperatures, we will need to identify new genes regulating DN. To do this, we propose to use a QTL approach employing AFLP and SSR markers. We will search for genetic linkages within a traditional breeding population containing genes derived from the Wasatch source, and another population where the DN trait came from a different native clone of F. virginiana ssp virginiana that is day-neutral and does well under high summer temperatures. Improved day neutral cultivars will impact the large commercial strawberry farms in California, as well as countless small farmers all across the U.S.