Node 1032 RosBREED's Jewels in the Genome: Sweet Cherry Fruit Size Author: Dr. Amy Iezzoni An individual’s genome is the full complement of genetic information inherited from its parents. Within this vast repertoire of genetic information, individual genes are being discovered that control critical production and fruit quality traits. As valuable rosaceous gene discoveries are made and put into breeding applications, we describe them as “Jewels in the Genome.” Fruit size is a critical fruit quality trait; in which a difference of only 2 mm diameter for fresh market sweet cherries can make the financial difference between profit and loss. Although other fruit quality parameters are also important, adequate fruit size is absolutely essential. A genetic region that controls cherry fruit size has been identified near the middle of sweet cherry’s 2nd chromosome (Zhang et al. 2010). More than seven DNA types were identified for this genetic region, and those types associate with large, medium, and small fruit. Unfortunately, large-fruited trees tend to be soft-fruited and firm-fruited trees tend to be small-fruited. Data from Washington State University’s sweet cherry breeding program reveal that one DNA type is associated with large and firm fruit that were also sweet and delicious! This valuable genetic insight enables, breeders to design crosses that yield a large proportion of seedlings with large fruit, while minimizing the number of seedlings that will have soft fruit. Additionally, offspring carrying the undesirable DNA types can be weeded out as young seedlings so that breeders avoid wasting resources producing and growing trees that will eventually bear small fruit. Figure 1. Prunus macckii, tart cherry (left) has extremely small fruit, yet is resistant to cherry leaf spot. The domesticated Montmorency (right) has adequate fruit size and is susceptible. Genetic understanding of the cherry fruit size locus on chromosome 2 is especially important when tart cherry is used to introduce leaf spot (Blumeriella jaapii) resistance to domesticated varieties. Although tart cherries carry disease resistance, they unfortunately have small fruit (~ 1-2 grams) (Fig.1). The cherry fruit size locus on chromosome 2 is selected as one of RosBREED's “Jewels in the Genome, because breeders can now use DNA diagnostics to identify unfavorable fruit size genetics in young seedlings; efficiently combining disease resistance and large fruit size into commercial cultivar candidates. References Cited Zhang, G., Sebolt, A.M., Sooriyapathirana, S.S., Wang, D., Bink, M.C.A.M,, Olmstead, J.W., Iezzoni, A.F. 2010. Fruit size QTL analysis in an F1 population derived from a cross between a domesticated sweet cherry cultivar and a wild forest sweet cherry. Theoretical and Applied Geneticss 6:25-36. Funding Statement Development of this page was supported in part by the USDA's National Institute of Food and Agriculture (NIFA). Project title: RosBREED: Enabling marker-assisted breeding in Rosaceae is provided by the Specialty Crops Research Initiative Competitive Grant 2009-51181-05808. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s)and do not necessarily reflect the view of the United States Department of Agriculture.