EFFECT OF THE ROOTSTOCK ON THE COMPOSITION OF CITRUS TREES AND FRUIT

Abstract

In previous studies (3), it was shown that the amount of boron that accumulates in citrus leaves is influenced by the rootstock variety. The relative order or type of boron accumulation in the leaves of seedling trees of different varieties is the same as that impressed or imposed upon the leaves of the scion variety by these seedling varieties when used as rootstocks. This rootstock influence was found to affect many of the other inorganic constituents of Valencia orange leaves and rootlets (4). Recently it was pointed out (5) that the rootstock variety may affect the content of total phosphorus in citrus flowers. The effect of rootstocks on fruit quality, for the most part, has dealt with the organic constituents of the fruit. As a result of a seven-year investigation on the effects of the rootstock on the composition of oranges and grapefruit (9), considerable data are now available regarding the total soluble solids, total and reducing sugars, pH, titratable acidity, dry matter, ash, and inorganic constituents of the peel, pulp, and juice of these fruits. Scarcely any data are available regarding the effect of the rootstock on the accumulation of inorganic constituents in the vegetative portions of lemon trees or in lemon fruit, and further data of this kind for orange and grapefruit trees and fruit are very desirable. It is reported (2) that rootstocks affect the prevalence of lemon tree decline as well as the yields of fruit. In certain areas in the United States and abroad, the use of sweet orange scions on sour orange as the rootstock may be accompanied by a rapid tree decline (10, 12). The present paper deals largely with differences in the inorganic composition of the peel of citrus fruits and of the leaves and rootlets of trees in which the scions (buds) of any one variety were obtained from a single parent tree and in which the seedlings used as rootstocks were carefully selected (11). The soil and other environmental factors were quite similar for each row of trees and frequent use was made of plot replications in order to make more accurate comparisons. The results presented in this paper add emphasis to the care required in the collection of citrus tree samples in order not to have the frequently unknown factor of rootstock variety nullify the results of careful chemical analysis. Thus in cases in which the fertilizer requirements or status of a soil are sought by means of compositional variations in various portions of citrus trees or fruit, it becomes most necessary to know that the observed chemical differences are not due instead to the nature of the rootstock varieties involved.