Facilitating efficient Rosaceae tree fruit breeding by modeling seedling selection
Sushan Ru: PhD candidate, Department of Horticulture
The Rosaceae family includes most of the temperate tree fruit crops of economic value, such as
apple, apricot, peach, nectarine, pear, and sweet cherry. A common strategy of rosaceous tree
fruit breeding is to create desirable genetic combinations by skillfully designing and making
biparental crosses and selecting among resulting progenies for individuals predicted to have the
required genetic components of superior performance to become potential cultivars. The process
of identifying ideal seedlings for the purpose of developing new cultivars is called seedling
selection. In traditional seedling selection, genetic potential is determined predominantly by
phenotypic evaluation. With the availability of DNA tests for some agronomically important
traits, breeders have the opportunity to include DNA information in their seedling selection
operations – known as marker-assisted seedling selection (MASS). A major challenge in
conducting MASS for rosaceous tree fruit is a lack of knowledge about relative efficiency of
various MASS strategies compared to phenotypic selection alone.
To overcome this challenge, this study aims to establish a framework for optimizing seedling
selection efficiency by modeling the overall efficiency of alternative strategies available to
breeders. Three aspects of seedling selection efficiency were investigated: genetic gain, cost, and
time. Genetic gain is defined here as the increase in the mean genotypic value of selected
individuals compared to all individuals before selection. The first objective was to establish a
framework for optimizing genetic gain by modeling alternative seedling selection strategies. The
second objective was to enable flexible and accurate cost estimation for seedling selection by
development of a decision-support tool. The third objective was to successfully demonstrate
choosing efficient seedling selection strategies by modeling overall selection efficiency in an
apple seedling population.
A framework was proposed for optimizing genetic gain and overall efficiency of seedling
selection for single traits where DNA tests providing genotypic information are available. Based
on this framework, methods were also proposed to identify efficient schemes for selecting
multiple traits by considering importance of trait levels and correlations among traits. Results
from this study provide rosaceous tree fruit breeders, for the first time, guidance in designing
efficient MASS schemes. This study will facilitate increased efficiency in seedling selection for
rosaceous tree fruit crops as well as other clonally propagated crops with similar breeding
schemes.