XVI International Botanical Congess
An allele of the apple ripening-specific ACS gene (Md-ACS1-1) has a 5 $B%f (J-flanking region possessing an inserted retroposon-like sequence. Apple species can be classified into three groups that are heterozygous or homozygous for the ACS1-1 and ACS1-2 alleles. We measured the internal ethylene concentration (IEC) in climacteric fruit of 35 apple cultivars with respect to genotype. Eleven ACS1-2 -homozygous cultivars exhibited much lower IECs than cultivars homozygous and heterozygous for ACS1-1. Furthermore, F1 ACS1-2 homozygous progenies derived from a crossing between heterozygous cultivars fruited with a very low IEC. We concluded that the low ethylene production in the fruit of some cultivars is caused by reduced transcription activity of ACS1, which is the main gene responsible for system 2 ethylene production.