Effects of pre-harvest application of ethephon or abscisic acid on ‘Kohi’ kiwifruit (Actinidia chinensis) ripening on the vine
Introduction
Kiwifruit is classified as a climacteric fruit because it ripens in response to exogenous ethylene, and its ripening is characterized by a period of autocatalytic ethylene production (Park and Kim, 1995). The ripening of kiwifruit appears to be different from that of other typical climacteric fruit because fruit produces little ethylene while on the vine (Patterson et al., 2003). However, kiwifruit ripens with ethylene treatment after harvesting (Sfakiotakis et al., 1997, Mworia et al., 2010). There are two commercially important species of kiwifruit: Actinidia deliciosa and Actinidia chinensis. A. deliciosa, including cultivars such as ‘Hayward’, is widely known for its large fruit size, green flesh, and long storage life (Thompson et al., 2000). A. chinensis, including such cultivars as ‘Hort 16A’, ‘Sanuki Gold’, and ‘Kohi’, has yellow flesh, high soluble solids and low organic acid concentrations, but a short storage life (Xu et al., 1998, Xu et al., 2000). In general, A. chinensis produces more ethylene than A. deliciosa (Asiche et al., 2016). These results may hint that the fruit of A. chinensis could ripen more easily than that of A. deliciosa and also, the fruit has a shorter storage and shelf life than that of A. deliciosa. Ethylene is a kind of plant hormone that is involved in fruit ripening in many plants (Guo and Ecker, 2004). Ethephon has been applied to both A. deliciosa and A. chinensis commercially to accelerate ripening after harvest (Park et al., 2006, Mworia et al., 2010, Zhang et al., 2012, Pranamornkith et al., 2012). If kiwifruit can be ripened on the vine, the fruit may be more marketable.
ABA concentrations are very low in unripe climacteric fruit such as tomato (Solanum lycopersicum) (Zhang et al., 2009a), peach (Pruns persica) (Zhang et al., 2009b), and avocado (Persea americana) (Chernys and Zeevaar, 2000) but increase during fruit ripening. Therefore, ABA may also play an important role in regulating fruit ripening. The previous research suggested that ABA stimulated the processes of fruit ripening and promoted ethylene biosynthesis in climacteric fruits such as banana (Musa sapientum L.) (Jiang et al., 2000) and apple (Malus domestica) (Kongsuwan et al., 2012). However, the interaction between ABA and ethylene biosynthesis in ‘Kohi’ kiwifruit on the vine is unclear. Nordihydroguaiaretic acid (NDGA) is an ideal inhibitor of NCED enzyme and blocks ABA biosynthesis (Zhang et al., 2009a). NDGA was treated to clarify the roles of ABA in kiwifruit ripening. In this study, the possibility of the fruit ripening on the vine and the effects of ethylene or ABA on the ripening of ‘Kohi’ kiwifruit on the vine were investigated.
Section snippets
Plant material
Three-year-old ‘Kohi’ kiwifruit (A. chinensis) vines top-grafted on ‘Hayward’ kiwifruit (A. deliciosa) vines at a Chiba University field, located at 35°N, Lat. 140°E, and elevation 37 m, were used in the experiment. Four hundred fruits were randomly divided into four groups at 155 DAFB (mature stage). The mature stage of kiwifruit has 95% black seeds and the color change of outer pericarp commences (Richardson et al., 2011). In the first group, the fruits were dipped into a 250 μL/L ethephon
Fruit firmness and concentrations of soluble solids and malic acid
Fruit firmness in ethephon-treated fruit decreased significantly at 3 DAT, and the fruit became edible at 9 DAT on the vine (Fig. 1). The soluble solids concentration (SSC) in ethephon-treated fruit increased significantly at 3 DAT, and the malic acid concentration decreased at 6 DAT. The SSC was higher in ABA-treated fruit than in the untreated control at 12 DAT. The fruit drop rate in the ethephon-treated fruit was 4% when the fruit reached edible condition at 9 DAT and was significantly
Discussion
Kiwifruit contains little endogenous ethylene at harvest but is highly sensitive to exogenous ethylene after harvest (Schroder and Atkinson, 2006). Ethylene application promoted fruit softening in kiwifruit after harvest (Ritenour et al., 1999). In addition, the results of our study indicated that ethephon treatment can increase SSC in ‘Kohi’ kiwifruit on the vine. Together, these results suggest that the ethylene signal can enhance both the conversion from starch to sugars and the reduction of
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