Modern apple breeding is associated with a significant change in the allelic ratio of the ethylene production gene Md-ACS1.

摘要

Increasing consumer demand for firm apple fruit has raised interest among scientists and breeders to identify heritable traits that affect fruit texture. One such candidate gene is the bi-allelic Md-ACS1 locus, that shows a strong association between genotype and internal ethylene content in ripening fruit. However, associations between genotype and fruit firmness, or between genotype and fruit softening during storage, have been somewhat unclear. In order to determine the potential importance of allelic variation at this locus, we used PCR methods to investigate Md-ACS1 alleles in 137 apple cultivars. In addition, we also compiled data from previously published studies, to achieve an eventual dataset with 270 cultivars. Allele 1, associated with higher ethylene concentrations in ripening apples, was much more common in older cultivars (relative frequency=0.88 in cultivars introduced before 1800; 0.84 in cultivars introduced between 1800-1899; and 0.70 in cultivars introduced in 1900-1959). Conversely, allele 2 associated with lower ethylene concentrations, was more common in modern cultivars (relative frequency=0.57 in cultivars introduced since 1960). The frequencies of the three Md-ACS1 genotypes (1/1,1/2,2/2), as well as the relative allele frequencies (1 vs. 2), varied significantly depending on the date of introduction of the investigated cultivars (i.e., 1800-1899 vs. 1900-1959; and 1900-1959 vs. >=1960). The significant shift in allelic ratios at the Md-ACS1 locus observed during the 20th century was probably associated with the substantial impact that a small number of heterozygous cultivars have had on modern apple breeding. Allelic variation at the Md-ACS1 locus may thus be one of the most influential factors in modern apple breeding.