Determination of optimum temperature for long-term storage and analysis of ripening-related genes in 'Rainbow Red' kiwifruit
Kiwifruit is considered a climacteric fruit since exogenous ethylene induces ripening-associated changes. However, we previously reported that low temperature modulated ripening in kiwifruit since ripening occurred faster during storage at 5°C compared to 20°C, in the absence of any detectable ethylene. It is therefore not clear which temperature is suitable for long-term storage of kiwifruit. The purpose of this study was to determine the optimum temperature for long-term storage, and analysis of ripening-related genes in 'Rainbow Red' kiwifruit. Kiwifruit were harvested at commercial maturity, and stored at either 0, 2, 5 or 22°C in ethylene-free chambers. During storage, incidence of fruit deterioration and changes in fruit firmness, soluble solids concentration (SSC) and titratable acidity (TA) were monitored at 4-week intervals. Real-time PCR was also conducted to analyze the changes in expression of selected ripening-related genes. Incidence of fruit fast senescence and deterioration was high at 22°C, so kiwifruit could only be stored for a maximum of 8 weeks. Nevertheless, healthy fruit at 22°C remained firm and maintained high TA for 8 weeks. The incidence of ethylene-producing fruit, and consequent fast senescence, was greatly reduced at 5°C, while it was completely suppressed at 0 and 2°C. Fruit at 5°C decreased in firmness and TA faster, attaining eating-ripe quality within 8 weeks. At 2°C, fruit decreased in firmness and TA gradually, achieving eating-ripe quality after 12 weeks. Conversely, fruit at 0°C maintained higher firmness and TA, and did not attain eating-ripe quality even after 12 weeks. SSC increased at all storage temperatures, although the lowest levels were observed in fruit at 0°C. Real-Time PCR analysis revealed that cell-wall-modifying genes (AcPG, AcPL2, AcEXP1 and AcXET2) and carbohydrate-metabolism-associated genes (Acβ-AMY1 and Acβ-AMY2) were markedly induced in fruit at 5°C. Overall, these results indicate that 0°C is the suitable temperature for long-term storage of kiwifruit, while 2°C is suitable for medium-term storage. For short-term storage, 5°C can be recommended.
Mitalo, O.W., Tokiwa, S., Kasahara, Y., Tosa, Y., Kondo, Y., Asiche, W.O., Kataoka, I., Suezawa, K., Ushijima, K., Nakano, R. and Kubo, Y. (2018). Determination of optimum temperature for long-term storage and analysis of ripening-related genes in 'Rainbow Red' kiwifruit. Acta Hortic. 1218, 517-524
low-temperature-modulated ripening, eating quality, cell-wall-modifying genes, carbohydrate-metabolism-associated genes