Strawberry Genetics

By evolutionary biologist Richard Buggs

The cultivated strawberry (Fragaria x ananassa) is a hybrid between two American strawberry species, F. chiloensis and F. virginiana. It first arose <http://www.nal.usda.gov/pgdic/Strawberry/book/bokfour.htm> in Europe in the early 1700s, after travelers to the New World brought back American strawberry plants with larger fruits than European strawberries.  

The French spy who brought F. chiloensis to Europe made the mistake of bringing only female plants. In the absence of F. chiloensis males, botanists fertilized the females with F. virginiana pollen, and so the hybridization occurred. The hybrid soon became very popular, because its fruits were large, sweet and flavorful. 

The strawberry genus, Fragaria, contains 23 species. Different strawberry species have varying numbers of chromosomes.  They all have seven basic types of chromosomes in common, but some species are diploid, having two sets of the seven chromosomes (14 chromosomes total), others are tetraploid (28 chromosomes), hexaploid, or octoploid.

The cultivated strawberry, Fragaria x ananassa and its two parental species are all octoploid. At some point in history, these octoploids must have derived from diploid species, but identifying exactly which of the 13 diploid strawberry species they arose from is very difficult. Scientists continue investigate this in Kevin Folta’s lab <http://www.arabidopsisthaliana.com/> at the University of Florida and Thomas Davies’ lab<http://strawberrygenes.unh.edu > at the University of New Hampshire. 

The fact that cultivated strawberry has eight sets of seven chromosomes makes its genetics very complex. Scientists are therefore working on wild diploid strawberries which are easier to analyze, and then seek to apply knowledge across to the cultivated strawberry. In 2004, scientists in the UK produced the first genetic map of the diploid strawberry genome <http://www.innovations-report.com/html/reports/life_sciences/report-37487.html>. In 2008, US scientists published <http://www.nature.com/hdy/journal/v101/n6/abs/hdy2008100a.html> a genetic map of the octoploid strawberry F. virginiana.

Geneticists now have sequences for about 10000 strawberry genes <http://www.bioinfo.wsu.edu/gdr/projects/fragaria/unigeneV3/>. Ten to 15 percent of these genes appear to be unique to the genus <http://www.strawberrygenomics.com/> (such genes are sometimes known as orphans as they have no traceable evolutionary history). The function of these genes is under investigation in Kevin Folta’s lab <http://www.strawberrygenomics.com/> at the University of Florida.

Strawberries have been grown for many centuries and improved by selection and hybridization. New knowledge from molecular genetics and genomics should allow scientists to continue that process in the years ahead.