Abstract

Background: Boron (B) is an essential micronutrient for plants, and B deficiency reduces fruit set in sweet cherry trees. Several studies showed the advantages of foliar and soil B applications in fruit trees, but there is little information on the distribution of B in the plant, becoming an important issue when nutritional corrections are needed. Aims: The study aims to determine B mobility and distribution in sweet cherry trees, applying B-10 to the flowers and soil, at different timings and under two levels of soil B availability. Methods: Two experiments were conducted with sweet cherry trees. In the two previous seasons, the plants were managed in two soil B availability conditions (deficient and adequate). The experiments consisted of the applications of B-10 solution to the flowers and the soil at different timings and under both soil B conditions. Results: Higher B-10 absorption occurred when the B-10 was applied to the soil at full bloom than when it was applied before leaf senescence. Boron was mobilized to all the tissues, but mainly to the leaves. Nevertheless, the fruit presented no differences in B-10 excess for both application timings. Irrespective of soil B conditions, the B-10 applied to the soil at full bloom was absorbed and mobilized to different tissues, that is, roots + rootstock + trunk (39%-44%) and stems + leaves (53%-55%), showing no differences between them. A lower percentage of B was located in the fruit, with 1% and 8% at soil B-deficient and B-adequate conditions, respectively. The highest percentage of the B-10 applied to the flowers remained in the fruit (similar to 70%), and nearly 20% and 10% were mobilized to stems + leaves and roots + rootstock + trunk, respectively, independent of the soil B condition. Conclusions: Boron applied to soil at full bloom or before leaf senescence, under B-deficient soil condition, is absorbed and mobilized to all the plant tissues, enhancing the B status in sweet cherry trees particularly when it is applied at full bloom. However, B soil application before leaf senescence would improve the availability of B (reserves) to the flowers in the following season. Boron applied to the flowers, at full bloom, remains in a high proportion in the fruit, becoming an effective complementary method to meet the fruit demands of the growing season, independent of the soil B conditions.