Effect of Sheet Mulching on Auraptene and Polymethoxyflavone Contents in the Peel of Mid-late Maturing Citrus ‘Kawachibankan’ Fruit

Effects of sheet mulching on auraptene (AUR) and polymethoxyflavone (PMF) contents in the peel of mid-late maturing citrus ‘Kawachibankan’ (Citrus kawachiensis hort. ex. Y. Tanaka) fruit were investigated. Six vigorous nine-year-old trees were used, and three of them were mulched with a permeable plastic sheet on the ground from September to January. The results showed that no significant difference was observed in fruit development between mulch and control. Mulching cultivation caused higher rind color a* and b* values than in the control. Soluble solid content in the juice of mulched fruit markedly increased after treatment, which retained higher levels even in May. The juice citric acid content in treated fruit was also higher than in untreated fruit until the end of March, although no significant difference was observed thereafter. Peel AUR in mulched fruit showed a significantly higher content in December and April compared with the control. Peel AUR in whole fruit had the highest content in April. The juice AUR content in mulched fruit was also higher than in the control in April and June. No difference in the PMF content in peel was found between the treatment and control. Mulching cultivation caused rapid increases in total sugar, glucose, and fructose contents in the peel in October. These results indicate that peel AUR in whole fruit had the highest content in April and May, whereas mulching cultivation is effective to increase the amount of AUR in the peel and juice, suggesting that these were caused by drought stress and cold temperature.