Insight into the Physiological Traits Underlying the Genotypic Differences in Response of Durum Wheat (Triticum durum Desf.) to Boron Availability

Boron (B) is a critical element for plant growth. Its role in plant physiology is still being debated. B deficiency, toxicity, and optimality for crop growth and yield are challenging. The specific needs of wheat for B and how tolerant genotypes act are still lacking. Analyze the physiological behavior of three durum wheat (Triticum durum Desf.) genotypes (khiar, maali, and razek) regarding B availability in the rhizosphere and highlight useful traits of tolerance. The experiment was conducted in a potted greenhouse under natural light. Plants were irrigated with a nutrient solution with different B concentrations (0-200 mu M). Plant growth, photosynthesis and gas exchange, SPAD index, B distribution and interrelationships were deeply analyzed. Durum wheat genotypes expressed their maximum growth and normal metabolic functioning at 80 mu M of B in the rhizosphere. B deficiency as well as toxicity significantly reduced plant growth, net photosynthesis, and SPAD index. These metabolic reactions are strictly dependent (positively or negatively) on the shoot B concentration. The genotype khiar was revealed to be tolerant to B deficiency by developing better B use efficiency for plant growth (BUE-DW), important tolerance index (TI) and effective mechanisms of B management to support the metabolic need for this nutrient under deficient conditions and by sequestering B in roots under toxicity. Although they have the same optimal concentration (80 mu M), durum wheat genotypes respond differently to B availability. The identified physiological traits, BUE-DW and TI, determine the genotypic differences in response to B deficiency or toxicity.