Boron concentration vs. Content as criterion for estimating boron tolerance in wheat

The objective of this study was to investigate the relationships among boron (B) concentration, boron content, and tolerance to excess boron in 40 wheat (Triticum aestivum L.) genotypes. Boron tolerance was estimated at seedling stage by filter paper technique, imposing three boron treatments (50, 100 and 150 mg L-1 boric acid, H3BO3) and comparing the response of root length and dry weight to the control (0.93 mg L-1 H3BO3). Although substantial variation in boron tolerance, concentration, and content has been found among the studied wheat genotypes, regression analysis showed no relationship between neither root length reduction and boron concentration, nor dry weight reduction and boron concentration. On the other hand, a positive linear relationship was found between boron content and both root length and dry weight response to high external boron; tolerant wheat genotypes were characterized by higher boron content than the sensitive ones. The results may be explained by significant decline of root length and dry weight in sensitive genotypes, which caused reduced uptake of all nutrients, including boron. Vice versa, root length and dry weight of tolerant genotypes were affected by boron treatments to the smaller extent, allowing the uptake of higher amounts of boron and resulting in comparatively high boron content