Synchrotron assessment of boron sensitivity and storage in Brassica napus and B. rapa

Application of low levels of boron (B) to soil can suppress clubroot symptoms slightly on brassica crops, but phytotoxicity increases rapidly as rates of added B increase. Tolerance to added B has been reported previously in Brassica rapa and more recently in B. napus. We investigated B uptake, speciation, and storage in sensitive and tolerant lines as part of a wider examination of the potential for use of B-tolerance in B. napus to reduce clubroot severity. The current study demonstrated that B speciation and translocation in B. napus differed between B-tolerant and B-sensitive lines. A higher proportion of B was incorporated into nitrogen-containing compounds in root tissues of the putative tolerant lines relative to sensitive lines grown under normal condition (control). In treatments that received added B, trigonally coordinated B-O compounds were dominant in all plant tissues with the presence of tetragonally coordinated B-O compounds. B-tolerant lines accumulated less B in shoots relative to B-sensitive lines when exposed to excess B, which would help plants avoid B phytotoxicity. This study supports previous suggestions that application of B onto a B-tolerant cultivar could potentially be included as one strategy in an integrated crop strategy to reduce clubroot severity.