齋藤 隆德

We have previously reported that the application of- used as isoprothiolane (IPT), a fungicide against rice blast- 20 to 30 days before harvest improved peel color in satsuma mandarin fruit (Citrus unshiu Marcow). However, the mechanism by which IPT improves peel coloration is not yet fully understood. This study examined the effects of IPT on plant hormones such as gibberellic acid (GA) and abscisic acid (ABA), and carotenoid accumulation. Whole trees were treated with IPT at 25 days before harvest. Concentrations of gibberellic acid-1 (GA1) and GA4 in the flavedo of IPT-treated trees were significantly decreased at 5 days after treatment (DAT) compared to the untreated control. The expressions of CitGA20ox1 in IPT-treated flavedo were lower than those in the untreated controls at 5 and 25 DAT. The CitGA3ox expressions in IPT-treated flavedo were lower than those in the untreated control at 5 DAT. ABA concentrations in IPT-treated flavedo were significantly higher than those in the untreated control at 25 DAT. The concentrations of β-cryptoxanthin in IPT-treated flavedo were higher than those in the untreated control at 25 DAT. The chlorophyll concentrations of IPT-treated flavedo were lower than those in the untreated control at 5 and 20 DAT. These results suggest that IPT advances β-cryptoxanthin accumulation through the regulation of endogenous GA1 and GA4 based on the inhibition of CitGA20ox1 and CitGA3ox expressions. It is possible that IPT can be utilized to improve coloration in other citrus fruit. *These two authors contributed equally to this work.