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The 1-aminocyclopropane-1-carboxylic acid synthase (ACS) gene is a member of the ACS gene family that is involved in apple ( Malus x domestica Borkh.) fruit ripening. Presence of an allele ( Md-ACS1-2) of this gene is associated with low internal ethylene concentration in some apple cultivars. In this study, inheritance of Md-ACS1 was determined for 50 apple cultivars/advanced selections and 101 F(1) seedlings from five populations. Following this, the softening pattern of apples stored at 20 degrees C for up to 40 days was examined using 35 fruiting cultivars/selections of defined Md-ACS1 status. Md-ACS1 is inherited in a Mendelian fashion and was found to be linked to fruit softening. Maturity season of genotypes also significantly affected fruit softening. Late-season genotypes in the Md- ACS1-2/2 class had the slowest rate of softening, while early-season Md- ACS1-1/1 genotypes had the most rapid softening rate. The implications of these results are discussed in relation to parental selection and breeding for storage ability in apple.

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Although Valsa canker caused by Valsa ceratosperma (Tode ex Fr.) Maire is one of the most destructive diseases in apple (Malus · domestica Borkh.) especially in eastern Asia, information available to help with breeding against Valsa canker in apples is limited. In this work, 53 accessions of diverse Malus species and their interspecific hybrids were tested for resistance to V. ceratosperma, using an excised shoot assay. Dormant shoots and succulent growing shoots from each accession were inoculated with a virulent isolate AVC-12 of V. ceratosperma, and the length of necrosis was measured at 10 days post-inoculation for the dormant shoots and at 7 days post-inoculation for the growing shoots. The lesion length relative to the susceptible control ÔFuji' in dormant shoots (RL D ) and to that in growing shoots (RL G ) were simple but useful parameters to differentiate between resistant and susceptible accessions. Fourteen accessions from M. baccata, M. florentina, M. halliana, M. micromalus, M. pratii, M. sieboldii, M. yunnanensis, M. · floribunda and M. · platycarpa gave low RL D and RL G values of less than 0.6 and were evaluated as resistant regardless of the difference in the stage of growth. The highest level of resistance was found in M. sieboldii. This high level of resistance in M. sieboldii was effective against different isolates of V. ceratosperma.