Cherry Self-Fertility

Plant Breeding and Genomics September 13, 2013 Print Friendly and PDF

Author:

Dr. Amy Iezzoni, Michigan State University

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, RosBREED describes them as “Jewels in the Genome” (Iezzoni, 2010).

Introduction

The S-locus is selected as one of RosBREED’s “Jewels in the Genome," because knowledge of S-locus variants is leading to more efficient breeding of self-fertile varieties of cherry, almond, apricot and plum.

Self-Fertility

Self-fertility is the ability to set fruit following self-pollination. Self-fertility contributes to higher more consistent yields in many Prunus species, because pollen from self-incompatible almond, sweet cherry, tart cherry, plum, and apricot cultivars is unable to grow the length of its own pistil. In self-fertile selections, pollen borne in a flower is able to successfully grow down the style, resulting in self-fertilization and fruit set. Self-fertile varieties have the advantage of not requiring orchard space for “pollinator” varieties. Additionally, self-fertile varieties characteristically have higher yields than self-incompatible varieties, as compatible (“self”) pollen is always available at the perfect time.

Genetic Control of Self-Fertility

For many Prunus species; such as almond, sweet cherry, tart cherry, apricot, and plum; we know the two major genes that control self-fertility! These two genes reside at the S-locus on stone fruit chromosome 6. One gene is expressed in the style and encodes a cytotoxic ribonuclease, called the S-RNase. The second gene, expressed in the pollen, encodes an F-box protein, named SFB,that interacts with the S-RNase in an allele specific manner. Most of the self-fertile alleles described to date in these Prunus species disrupt either the S-RNase function in the style or the SFB function in the pollen, leading to self-fertility (Fig.1).

pollen growth arrested in one example and successfully growing in another example

Figure 1: Incompatible versus compatible pollination: If the S-allele in the pollen matches the S-allele in the style, pollen growth is arrested in the style. When all pollen is incompatible, fertilization does not occur and the fruit does not develop. However, when the S-allele in the pollen has a mutation that causes it to be self-fertile (Sf), pollen grows the length of the style, fertilization is successful, and fruit development follows. Photo credit: Michigan State University.

Variation and Detection

Knowledge of genetic changes in S-RNase and SFB that lead to self-fertility has resulted in the development of simple diagnostic tests to screen progeny for self-fertility early in a breeding program. For example, the S-allele in the self-fertile sweet cherry varieties, ‘Lapins’ and ‘Sweetheart’, is called S4' (Boškovic et al. 2000). This allele has a four base pair deletion in the S4 SFB gene that results in the production of a shortened non-functional SFB protein. Pollen containing non-functional SFB protein is self-fertile and compatible on styles of all other cherry varieties. The DNA diagnostic test for self-fertility simply involves differentiating between S4 and S4', which can be accomplished by resolving the four base pair difference. Identification of self-fertile variants enables breeders to select parental combinations that maximize their chances of obtaining self-fertile offspring.

Reference Cited

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.

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USDA / NIFA

This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.