Genotypic differences in boron accumulation in barley: Relative susceptibilities to boron deficiency and toxicity

Abstract

Boron accumulation in genotypes of barley displaying a large range of susceptibility to B toxicity was studied in solution culture experiments. The relationship between susceptibility to B toxicity and to B deficiency was also examined.

Plants were cultured for 5–6 weeks at B concentrations ranging from deficient to toxic and then examined for dry matter production and B contents of roots and shoots. The effect on grain production of B supply from soil was also studied.

At low and excessive B supply, respectively, symptoms of B deficiency and toxicity developed and growth was depressed. The extent to which individual genotypes were affected varied greatly and the responses closely reflected differences in B content.

At high B supply, genotypes with most tolerance to excess B accumulated less B in both roots and shoots than did genotypes susceptible to B toxicity. B concentrations in roots were always much lower than in shoots. No genotype displayed an ability to tolerate shoot B concentrations greater than 150–200 mg kg^-1 dry matter without growth being depressed. It was concluded that tolerance to excess B in barley was governed by the ability of genotypes to restrict B uptake.

At low B supply, genotypes tolerant to excess B had relatively low tissue B concentrations compared to other genotypes, and were susceptible to B deficiency. Conversely, genotypes that had relatively high tissue B concentrations, and were susceptible to B toxicity, were the least susceptible to B deficiency.

Barley genotypes displayed marked differences in rates of B uptake (B accumulation), and these differences were independent of B supply. The order of genotypes when ranked for B concentrations in either roots or shoots was identical at all levels of supply. Similar patterns emerged with respect to grain production.

These results have two important implications. Firstly, they suggest that genotypes can be assessed simultaneously for relative susceptibility to both B deficiency and toxicity without imposing severe nutrient stress, because relative B concentrations of roots and shoots directly reflect these susceptibilities. Secondly, they point to a major complication for breeding programs aimed at incorporating either increased B efficiency or tolerance into commercial varieties.