The efficiency of boron utilisation in canola

Boron (B) deficiency is a common abiotic stress in many countries and is known to reduce canola yields. Growing B-efficient canola cultivars on deficient soils can reduce the impact of this deficiency, but to date little is known of the mechanisms associated with the efficiency trait. This work investigated the factors underlying the observed genotypic variation in the ability of different cultivars of canola (Brassica napus L.) to grow under low B supply. Previous studies have identified the cultivars Huashuang-2 and Dunkeld as B-efficient and the cultivar Barossa as B-inefficient. It was found that in Huashuang-2, efficiency was not related to uptake of B to the shoots, possibly indicating efficiency in B utilisation. A correlation was established between B efficiency and the ratio of the B concentration in the younger relative to the older leaves. Comparison ofthe distribution of B in young and old leaves under deficient and adequate B conditions showed that when B was limited, the concentration of B in the older leaves decreased with plant age, whereas when sufficient B was supplied, the concentration in these leaves continued to increase with age. The loss of B from mature leaves under deficient conditions suggested retranslocation to other tissues. Experiments in which boric acid enriched with ¹⁰B was applied to mature leaves showed that in only one ofthe efficient cultivars, Huashuang-2, was B retranslocated to younger leaves. In the other two cultivars, the sink for the ¹⁰B exported from the older leaves was not identified. It was concluded that there exist multiple mechanisms for B efficiency in canola.