Fruit Ripening Process in Red Kiwifruit Cultivar ‘Rainbow Red’ (Actinidia chinensis) on Vines

We present a detailed study of differences in the fruit ripening stage on the vines and ethylene treatment in the red kiwifruit cultivar ‘Rainbow Red’ ( Actinidia chinensis ). We evaluated the fruit quality (core and flesh firmness, soluble solid content (SSC), and titratable acid (TA)); ethylene metabolism; and gene expression of ACS1 , ACO3 , EIL4 , ERF14 , and PGB at each stage. Fruits on the vines somewhat softened gradually. SSC increased, and core and flesh firmness as well as TA decreased gradually. However, rapid ethylene production was not observed, and gene expression of ACS1 , ACO3 , EIL4 , ERF14 , and PGB was at the basal level at each stage. While the fruit quality following ethylene conditioning, core and flesh firmness, and TA rapidly decreased, SSC and ethylene production rapidly increased. It was confirmed that gene expression of ACS1 , ACO3 , EIL4 , ERF14 , and PGB rapidly increased. These results suggested that the ripening of ‘Rainbow Red’ on the vines is not associated with ethylene.