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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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Two apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] homologous fragments of FLO/LFY and SQUA/AP1 (AFL and MdAP1, respectively) were analyzed to determine the relationship between floral bud formation and floral gene expression in `Jonathan' apple. The AFL gene was expressed in reproductive and vegetative organs. By contrast, the MdAP1 gene, identified as MdMADS5, which is classified into the AP1 group, was expressed specifically in sepals concurrent with sepal formation. Based on these results, AFL may be involved in floral induction to a greater degree than MdAP1 since AFL transcription increased ≈2 months earlier than MdAP1. Characterization of AFL and MdAP1 should advance the understanding of the processes of floral initiation and flower development in woody plants, especially in fruit trees like apple.

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.

Cross-genus application of SSR markers developed in pear and apple was examined for quince (Cydonia oblonga) in order to conduct a genetic characterization. It was revealed that 77 out of 118 SSR markers producing 1 or more reproducible amplified bands could be used in quince, including 20 SSRs from pear and 57 SSRs from apple. Twenty quince varieties, including 15 accessions, 3 clones of 'Smyrna' and 2 clones of 'Kaori', were analyzed by using 39 polymorphic SSRs. A total of 122 polymorphic amplified fragments were obtained by using 39 SSR markers, which could divide 20 varieties into 12 genotypes. Cultivars vegetatively propagated and maintained in different areas showed identical SSR genotypes. Parentage of 'Kaori' was confirmed because all the putative alleles of 'Kaori' were transmitted from its parents 'Smyrna' and 'Zairaishu' without any discrepancy at tested SSR markers. A phenogram based on genetic similarity was constructed, showing major groups corresponding to the purposes of fruit production and rootstocks. Nine cultivars including almost all the varieties used as rootstocks showed only 0 to 4 differences in SSR fragments, suggesting that these cultivars were genetically very close. The SSR markers could be utilized as a reliable tool for the identification of quince varieties.

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