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With 3 figures and 3 tables Previous studies have demonstrated that genotypes of PpACS1 and PpACS2 genes are associated with certain levels of ethylene production in Japanese pears ( Pyrus pyrifolia Nakai). This study was undertaken to examine further the relationships of PpACS1 and PpACS2 genotypes and internal ethylene concentration (IEC) with fruit firmness/softening in both European ( P. communis L.) and Japanese pears ( P. pyrifolia Nakai). Our data showed that P.  communis L. lacked genotypes ‘AB’/‘Ab’ and ‘aB’, for high and medium IEC respectively, irrespective of high levels of IEC found in the European pear cultivars/selections. PpACS1 and PpACS2 genotypes were related to IEC at 20 days after harvest (DAH) in P. pyrifolia Nakai but IEC did not have any significant relationship with fruit firmness at 50DAH in either P. communis L. or P. pyrifolia Nakai . Harvest firmness was a better predictor of postharvest firmness than IEC across both species and genotypes, explaining 46% of the variation in fruit firmness at 50DAH. We recommend breeding for higher harvest firmness within low ethylene cultivars in order to extend the shelf life/storage potential of Japanese pears. [ABSTRACT FROM AUTHOR]