Synchrotron assessment of boron sensitivity and storage in <i>Brassica napus</i> and <i>B. rapa</i>

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.