BORON CONTENT OF CITRUS TREES GROWN ON VARIOUS ROOTSTOCKS

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Abstract
The investigation deals with the rootstock var. as it affects the accumulation of B in the fruit, leaves and bark of citrus trees growing in exptl. plots under comparable soil, cultural, and climatic conditions. The source of the rootstock within a given rootstock var. may be reflected in some cases by differences in the B accumulation in the leaves of the scion. The leaves of like scions vary in their B content according to the rootstock var. Conversely, the B content of leaves of the scion may be of some assistance in the detn. of the rootstock var. The variations in available B at different soil depths, the transpiration rates, and the distribution of the roots in the soil may all be factors involved but primarily it is the nature of the cells of the rootstock that accounts for the behavior in the scion accumulations. The significance of analytical data for B in healthy plants is enhanced by taking into consideration the rootstock var. and its source. The mobility of B in citrus is far greater than is commonly understood. The little that is known concerning B in citrus flowers is discussed as is also the method of growth of the flowers. The growth in citrus flowers (a dicot) is similar to that in the fruits of the date palm (a monocot). The B content of citrus flowers was reduced when the B supply was made inadequate. The water-insoluble B content was uniform in the dry matter of citrus flowers. In the dry matter of lemon and grape-fruit flowers, the water-soluble B was low as compared with that in orange flowers. The B content of the peel of Valencia oranges from trees on sweet and sour rootstocks was slightly less than when other rootstocks were used. Gradients occur in the peel of Valencia orange and Eureka lemon fruits. Differences in the B content of the outer and inner portions of the peel in orange and lemon fruits were greatest when the rootstock was sour orange: The water-insoluble B content of the dry matter of Valencia orange leaves of trees on various rootstocks is remarkably uniform. Large differences occur in the water-soluble and in the total B content and these differences are definitely related to the rootstock var. This relationship is also shown for the leaves of lemon, grapefruit, and navel orange scions when grown on various rootstocks. The leaves of seedling trees of different vars. show roughly the same order of B accumulation as do the leaves of other vars. used as scions on these same seedling roots. The effect of the rootstock on B in scion leaves is slightly greater for sweet than for sour orange rootatocks and the effects are greater for lemon and grapefruit than for the leaves of navel or Valencia orange scions. The trunk bark does not give so clear a picture of the B situation within the tree as do the leaves. This probably is the result of the intermediate position of these trunk parts and their functions.