Genotypic variation in tolerance to boron toxicity in 70 durum wheat genotypes

By using 70 durum wheat (Triticum durum) genotypes, a greenhouse experiment has been carried out to study genotypic variation in tolerance to boron (B) toxicity in soil. Plants were grown in a soil containing 12 mg extractable B kg-1 soil and treated additionally with (+B: 25 mg kg-1 soil) and without B (-B: 0 mg B kg-1 soil). Following 30 days of growth, only shoots have been harvested and analyzed for dry matter production and shoot concentrations of B. There was a large genotypic variation in tolerance to B toxicity based on the severity of leaf symptoms and decreases in dry matter production caused by B toxicity. Among the genotypes tested, the growth of the genotypes Sabil-1, Stn ÒSÓ, Aconhi-89 and Wadelmez-2 was not affected; even, there was a tendency for an increase in growth by B treatment. By contrast, the dry matter production of all other genotypes was markedly decreased by the applied B, particularly in the genotypes Lagost-3, Dicle-74, Brachoua/134xS-61 and Gerbrach. In case of the genotypes Brachoua/134xS-61 and Gerbrach, B application reduced dry weight of the plants by 2-fold. Interestingly, there was no relationship between shoot B concentrations and relative decreases in shoot dry weight by B toxicity. The most B-sensitive genotypes had generally much lower amount of B in shoot than the genotypes showing higher tolerance to B toxicity. This result indicates that the B-exclusion mechanism is not involved in differential expression of B tolerance within 70 durum wheat genotypes. It seems very likely that the internal mechanisms (e.g., adsorption to cell walls and compartementation of B in vacuoles) could be a more plausible explanation for B tolerance in the durum wheats tested in the present study.