Submitted to: Tree Genetics & Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2007
Publication Date: 2/9/2008
Citation: Zhu, Y., Barritt, B. 2008. Md-ACS1 and Md-ACO1 genotyping of apple (Malus x domestica Borkh.) breeding parents and suitability for marker-assisted selection. Tree Genetics & Genomics. 4:555-562. Interpretive Summary: The basis for marker-assisted breeding resides on the fact that unique traits of a plant are controlled by specific genotypes. The prerequisite for the application of marker-assisted breeding is to establish the association between genotypes and phenotypes in specific segregation population. This manuscript reports our study on the relationship between two previously reported ethylene biosynthesis gene markers and apple fruit firmness and storability. The results revealed that there is a close relationship between ethylene biosynthesis genotype and fruit firmness and storability among apple cultivars. Our study supports the practical use of these markers for marker-assisted selection for firm apple fruit. Also determined are the ethylene biosynthesis genotypes for Md-ACS1 and Md-ACO1 for a comprehensive set of breeding parents, including 60 apple cultivars and 35 advanced breeding selections, which is essential for informative selection of breeding parent combination for breeding low ethylene production cultivars.
Technical Abstract: Fruit ethylene production genotypes for Md-ACS1 and Md-ACO1 were determined for 60 apple cultivars and 35 advanced breeding selections. Two alleles for each gene are commonly found in cultivated apple. Earlier studies showed that genotypes homozygous for the ACS1-2 allele produce less ethylene and have firmer fruit than ACS1-1/2 and ACS1-1/1 genotypes. ACO1 plays a minor role compared to ACS1, with homozygous ACO1-1 having lower ethylene production. In this study, ACS1-2 and ACO1-1 homozygotes had firmer fruit at harvest and after 60 days of 0-1oC cold storage compared to other genotypes. This genotype, ACS1-2/2 and ACO1-1/1, was observed for the following 8 of 95 cultivars/selections: ‘Delblush’, ‘Fuji’, ‘Pacific Beauty’, ‘Sabina’ and 4 breeding selections. Cultivars/selections that were homozygous ACS1-2 but not ACO1-1 were: ‘Ambrosia’, ‘Aurora Golden Gala’, ‘CrimsonCrisp’, ‘Gala’, ‘GoldRush’, ‘Huaguan’, ‘Pacific Rose’, ‘Pacific Queen’, ‘Pinova’, ‘Sansa’, ‘Sonja’, ‘Sundance’, ‘Zestar’ and 17 breeding selections. Cultivars with the heterozygous ACS1-1/2 genotype were ‘Arlet’, ‘Braeburn’, ‘Cameo’, ‘Delicious’, ‘Delorgue’, ‘Empire’, ‘Enterprise’, ‘Ginger Gold’, ‘Golden Delicious’, ‘Granny Smith’, ‘Honeycrisp’, ‘Orin’, ‘Pink Lady’, ‘Silken’, ‘Suncrisp’, ‘Sundowner’, ‘Sunrise’ and 11 breeding selections. No cultivars were detected homozygous for both ACS1-1 and ACO1-1, or for both ACS1-2 and ACO1-2. This study is the first large scale allelic genotyping of both ethylene synthesis genes for a comprehensive set of apple breeding parents used in an ongoing breeding project. The data reported here are important for informative selection of parent combinations and marker-assisted selection of progeny for breeding low ethylene-producing apple cultivars for better storability and improved consumer acceptance.