Abstract
1. The effects of manganese deficiency on Unshiu orange trees were studied, in relation to: (a)growth of non-fruiting spring shoots ; (b)number of flowers and new spring shoots sprouted from one-year-old non-fruiting spring shoots ; and (c)quality of fruits.
2. Both fifty non-fruiting spring shoots bearing healthy leaves (25ppm Mn in oven dried leaves) and manganese deficient leaves (15ppm Mn in oven dried leaves) were selected on Oct. 25, 1956, from eight 16-year-old Tsujimura Unshiu on trifoliate orange rootstock in the orchard of Kanagawa Citrus Experiment Station. On April 3, 1957, the growth was measured both with one-year-old shoots of normal leaves and those of manganese deficient chlorotic leaves. The number of new shoots sprouted from the above one-year-old shoots and the number of flowers born on the new shoots were also counted with them on May 12, 1957.
There were no significant differences in the growth (diameter, length and weight) between the shoots of normal leaves and those of manganese deficient chlorotic leaves. When the old spring shoots bearing manganese deficient chlorotic leaves were compared with those bearing healthy leaves, the former tended to be superior to the latter in the total number of flowers and number of flowers without shoot, and inferior in the total number of new shoots and number of new shoots without flower.
3. In September of 1957, sixteen 17-year-old Owari Unshiu on trifoliate orange rootstock showing moderate chlorosis in the orchard of Tokyo University, Kanagawa Pref., were selected for additional observations. The next year, 1958, they were divided into 4 groups, which were applied with manganese fertilizer in the soil or by foliar spray of manganese solution. Manganese soil application alone gave no correction of chlorosis on new leaves, but foliar applications of manganese solution corrected completely the chlorosis on new leaves. Each forty non-fruiting spring shoots were labeled in the above 4 groups on Oct. 30. In April of 1959, the numbers of new shoots and flowers sprouted from one-year-old shoots were counted.
Manganese applications did not affect the total number of new shoots and number of flowers with shoot, but reduced the total number of flowers and number of flowers without shoot.
It may be suggested that the low manganese content in the leaves on non-fruiting spring shoot caused an increase of total number of flowers in the next spring, and that the change of total number of flowers was influenced mainly by the number of flowers without shoot, some of which might be dormant on the old shoot bearing normal leaves.
4. The level of manganese nutrition in Unshiu orange trees did not cause generally any changes in the fruit quality, though moderate deficiency of manganese tended to be associated with hard fruit and high refractive index of fruit juice in some cases.
