Improving the boron uptake of boron-deficient navel orange plants under low boron conditions by inarching boron-efficient rootstock

• Under low B conditions, inarching B-efficient Carrizo citrange onto B-deficient navel orange improves the plant’s B uptake.
• Under low B conditions, inarching treatment decreased the B concentration in original rootstock roots.
• Compared to B adequate supply, inarching rootstock contributed more B to the scion under low B conditions.
• Inarch grafting might serve as a more efficient method to achieve a split-root system in trees.

Inarching is often used to correct nutrient deficiency, but the characteristic of boron (B) uptake in inarched citrus remains unknown. One-year-old ‘Newhall’ navel orange plants on trifoliate orange were inarched with Carrizo citrange seedlings. After a 15-month B deficiency, the plants were resupplied with low B for 35 days to investigate the B uptake and the contribution of inarching rootstock to B absorption in different parts by using 10B labeling and split-root methods. When resupplying low B to B-deficient plants, the B concentration and proportion of newly absorbed B in new leaves, new twigs, and old leaves were higher in inarched than non-inarched plants. By contrast, the B concentration in original rootstock roots of inarched plants was lower than that of non-inarched plants. Regardless of B treatment, the fresh weight in original rootstock roots was significantly lower in inarched than non-inarched plants. Interestingly, the enriched 10B abundance was detected in the original rootstock from split-root treatments in which only the inarching rootstock was supplied with labeled 10B, implying that newly acquired B can be retranslocated from scion to rootstock. The newly-absorbed-B contribution of inarching rootstock was higher for the scion but lower for both rootstocks under low B conditions when compared with B-adequate conditions. These results suggest that, under low B conditions, inarching B-efficient Carrizo citrange onto B-deficient navel orange improves the plant's B uptake, increases the B concentration in young scion parts, and thus enhances the tolerance of the whole plant to B deficiency.