Effects of 'Konejime' (Citrus neo-aurantium HORT) rootstocks on tree vigor, fruit yield and quality of 'Shiranui' [Citrus hybrid]

'Shiranui'('Kiyomi' tangor x ponkan) trees grafted on trifoliate orange rootstocks exhibit decline in tree vigor when they begin fruit bearing. The fruit size becomes smaller and the reduction in juice acidity is delayed in such trees. In this work, therefore, the effects of 'Konejime' (Citrus neo-aurantium HORT) rootstocks on tree vigor, fruit yield and quality of 'Shiranui' were examined. Furthermore, the effects of 'Konejime' root grafting to trees on trifoliate orange rootstocks were also evaluated. l) The trees grafted on 'Konejime' rootstocks showed the greatest tree vigor in terms of trunk circumference and tree crown volume. In the rhizospheres, they had greater mass of fine roots with stronger and more elastic properties than trees on trifoliate orange rootstocks. 2) The trees on 'Konejime' rootstocks had the greatest cumulative yield during 7 years of experiments amounting to 2.1-fold greater yield than trees on trifoliate orange. More than 50% of fruit were over 2L-grade fruit and there were many high-necked fruit. 3) Brix content was greater in fruit from trees on trifoliate orange rootstocks than those from trees on 'Konejime' rootstocks. Even fruit from trees on 'Konejime' rootstocks exhibited 13.7 in Brix on average. Acidity in the fruit was lower by 0.37 from trees on 'Konejime' rootstocks than trifoliate orange rootstocks. 4) Grafting 'Konejime' roots to trees on trifoliate orange rootstocks increased the tree vigor in which trunk circumference and tree crown volume were 2-fold compared with trees on trifoliate orange rootstocks. The root-grafted trees had slightly greater fruit yield and greater percentage of over 3L-grade fruit than trees on trifoliate orange rootstocks. However, Brix content in the fruit juice was higher in trees on trifoliate orange rootstocks but little differences in acidity between the root-grafted and control trees were observed.