Tolerance of 65 durum wheat genotypes of zinc deficiency in a calcareous soil

Sixty-five durum wheat (Triticum turgidum ssp. durum) genotypes were grown in a zinc (Zn)-deficient calcareous soil in a greenhouse for 32 days with (+Zn = 5 mg Zn kg(-1) soil) and without (-Zn) Zn supply to study genotypic variation in tolerance to Zn deficiency. Genotypes were ranked for their tolerance to Zn deficiency based on the relative shoot growth (Zn efficiency ratio) defined as the ratio of shoot dry weight under Zn deficiency to the shoot dry weight under adequate Zn supply. Zinc deficiency resulted in marked decreases in shoot dry matter production of the genotypes following 32 days of growth. Shoot dry weight of most genotypes was similar under adequate Zn supply, but differed greatly under Zn deficiency. Consequently, the Zn efficiency ratio showed a large variability and ranged between 20% to 51%. Generally, the genotypes showing lower tolerance to Zn deficiency had lower absolute shoot dry weight under Zn deficiency than the genotypes having greater tolerance to Zn deficiency. Differences in tolerance to Zn deficiency were related very significantly to the total amount (content) of Zn per shoot of the genotypes, but poorly to the concentration of Zn in shoot. As the shoot Zn concentration did not vary much between the genotypes under Zn deficiency, the higher amount of Zn per shoot of the Zn-efficient genotypes was a reflection of their greater shoot dry weight. Seed Zn concentration of the genotypes was quite similar and ranged from 18 to 25 mg kg(-1) DW for almost all genotypes. Therefore, the genotypic variation in tolerance to Zn deficiency was most likely inherent and not related to the seed Zn content. The results of the present study show existence of a large variation in tolerance to Zn deficiency in durum wheat, and suggest that the absolute shoot growth like the relative shoot growth (Zn efficiency ratio) can be used as a reliable plant parameter for screening the durum wheat genotypes for their tolerance to Zn deficiency, provided that genotypes have a similar growth rate under adequate Zn supply.