Influence of extramatrical hyphae on mycorrhizal dependency of wheat genotypes

Three wheat cultivars were grown in a three-compartment pot culture system with or without the arbuscular mycorrhizal (AM) fungus Glomus versiforme in a soil with low phosphorus availability. The objective was to compare the mycorrhizal dependencies of the three genotypes and to explore the possible mechanism underlying the relationship between hyphal development and mycorrhizal dependency, and the associated partitioning of carbohydrate between shoots and roots. Mycorrhizal dependency was very low (105-114%) and varied significantly among the wheat genotypes. Root-to-shoot ratio was 0.38-0.42, with extramatrical hyphal length densities ranging from 0.19 to 0.62 m g(-1), and hyphal phosphorus (P) uptake was 0.74-1.40 X 10(-13) Mol m(-1) s(-1), representing a range of hyphal contributions to plant P uptake of about 30 to 38%. The results suggest that mycorrhizal dependency was determined by hyphal development as affected by carbohydrate partitioning between shoots and roots, most likely under genetic control.