Quantification of the confounding effect of seed manganese content in screening for manganese efficiency in durum wheat (Triticum turgidum L. var. durum)

Whether due to the genotype or the environment of the mother plant, the nutrient content of seeds vary over a wide range; the amount of the nutrient contributes greatly to seedling vigor, especially on deficient soils and may result in major differences in grain yield. This effect has important implications for breeding programs. This paper examines the impact of seed manganese (Mn) on screening of durum wheats for tolerance to Mn-deficient soils. Seed stocks with a range of Mn contents (0.4-2.4 micrograms seed-1) were produced, and the effect on expression of Mn efficiency measured as either relative yield or shoot Mn content for two durum wheat (Triticum turgidum L. var durum) genotypes differing in Mn efficiency. Both genotypes responded to seed Mn contents in terms of enhanced root and shoot growth; there was no genotype by seed Mn interaction, so Mn provided in seed was utilized additively by both Mn-efficient and Mn-inefficient genotypes. Manganese efficiency, measured as relative yield, was a function of seed Mn content and varied from 40 to 70% in Hazar and 58 to 90% in Stojocri 2, in the same assay using seed of variable Mn content. From the response curves of yield vs. soil Mn added, the Mn required for 90% relative yield was determined for each level of seed Mn content. Seed Mn was regressed against the soil added Mn needed to obtain 90% of maximal growth at each level of seed Mn content (a total of 8 levels) for each of two genotypes. There was an inverse linear relationship between the amount of soil Mn and seed Mn needed for each genotype. Using Mn-efficient genotype with high seed Mn content, the soil Mn needed to obtain 90% growth was nil, while inefficient genotypes with low Mn content required 75 mg Mn kg-1 soil to produce the same relative yield. This relationship can be used to adjust the levels of soil applied Mn to be used in a pot bioassay when seeds have a certain Mn content, so as to maintain the screening at an optimal overall level of Mn stress.