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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.