Distribution and Mobility of Foliar-Applied Boron (10B) in Citrange Rootstock Under Different Boron Conditions

Although foliar-applied boron (B) could rapidly and effectively relieve B deficiency of plants, the distribution and mobility of foliar-applied B in citrange, an important rootstock of citrus, are poorly understood. This study aimed to investigate the transportation and variation of B allocation in different parts of citrange under different B conditions by spraying B-10 on the lower mature leaves of citrange rootstock for 8 weeks. The results indicated that foliar B on lower mature leaves led to higher B-10 abundance and B-10 concentration in different parts of plants. Compared with the low-B plants, B-10 abundance in stems, lower, and upper mature leaves of medium-B plants increased 23.95, 7.22, and 8.33% respectively. Moreover, under low- and medium-B conditions, abundance and percentage of B-10 were higher in roots than that in other tissues after foliar application B-10. Meanwhile, abundance and percentage of foliar-B-10 in stems and old leaves under B-insufficient condition were much lower than that of B-sufficient condition. Furthermore, the B-10 allocation rate was the highest in roots under the two different B conditions. There were higher B-10 allocation rates in new leaves and lower mature leaves, and lower B-10 allocation rates in stems and upper mature leaves in medium-B plants comparing with that in low-B plants. All these results suggest that foliar-applied B-10 on lower mature leaves could be translocated to every part of citrange rootstock, with the majority distributed in roots, and the mobility of foliar B from lower mature leaves to other parts was different between low- and medium-B treatments, leading to a significant variation in translocation rate for each part of citrange.