Dr. Amy Iezzoni, Michigan State University
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, and efficiently combine fruit size and disease resistance into commercial cultivar candidates.
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!
Genetic insight about chromosome 2 enables breeders to design crosses that yield a large proportion of seedlings with large fruit, minimizing the number of seedlings having small fruit. Genetic understanding of the cherry fruit size locus on chromosome 2 is especially important when tart cherry, Prunus maackii, is used to introduce leaf spot (Blumeriella jaapii) resistance to domesticated varieties. Although P. maackii cherries carry disease resistance, they unfortunately have small fruit (~ 1-2 grams) (Fig.1).
Figure 1. Prunus maackii, (left) has extremely small fruit, yet is resistant to cherry leaf spot. The domesticated tart cherry cultivar ‘Montmorency’ (P. cerasus; right) has adequate fruit size and is susceptible.
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.