Effect of seed zinc content on early growth of barley (Hordeum vulgare L.) under low and adequate soil zinc supply

Worldwide, barley is often grown on zinc (Zn) deficient soils. Screening for varieties tolerant of low soil Zn (Zn-efficient varieties) generally involves assessing growth or yield of plants grown at different levels of Zn supply. Seed nutrient reserves can influence the growth of the plant; however, there have been no reports on the effect of seed Zn content on the growth of barley. In 2 experiments, we studied the effect of seed Zn content on early growth of barley in 2 genotypes, Amagi Nijo and Tantangara. In Expt 1, the amounts of Zn in the seed ranged from 0.4 to 0.7 mu g/seed, whereas in Expt 2, seed Zn ranged from 0.7 to 5.0 mu g/seed. The plants were grown in a Zn-deficient siliceous sand with Zn added at 0, 0.04, 0.2, 0.8, and 3.2 mg Zn/kg soil in Expt 1 and at 0, 0.04, and 0.8 mg Zn/kg soil in Expt 2, and harvested at tillering. Growth and expression of visual symptoms were measured. Plants grown from seed with low Zn content developed symptoms of Zn deficiency by the 2-leaf stage in soil with no soil-applied Zn. Symptoms were reduced markedly as seed Zn content increased. Shoot and root growth increased as the amount of Zn in seed increased, but the effect was most evident when soil Zn supply was limiting plant growth (less than or equal to 0.04 mg Zn/kg soil). For instance, when no Zn was added to the soil, shoot dry weight of plants grown from high-Zn seed was 108% greater than that of plants grown from low-Zn seed, whereas at 0.04 and 0.8 mg Zn/kg soil, the increases were only 52% and 18%, respectively. Soil Zn application significantly increased tissue Zn concentrations. However, the effect of seed Zn content on tissue Zn concentrations was significant only at very high levels of seed Zn. The results presented showed that seed Zn improves vegetative growth in barley, especially when Zn supply is deficient for plant growth. Seed Zn content also affected the determination of Zn efficiency of genotypes, and comparisons of dry matter production of seedlings grown from seed with a wide range in Zn content may alter their rankings for Zn efficiency as determined in this pot assay. The results indicate that seed of similar Zn content needs to be used when comparing genotypes for determination of Zn efficiency.