Outcome variation in maize interaction with arbuscular mycorrhizal fungi is correlated with extent of extra-radical mycelium

In light of the rising cost, and often limited availability, of agricultural fertilizers, arbuscular mycorrhizas are attracting ever greater interest for their potential to promote more efficient use of the world9s mineral resources. And yet, this potential remains largely unrealized, in part because of a lack of understanding of the factors determining the outcome of the symbiosis in any given context. In this work, we evaluated a panel of maize inbred lines, selected to maximize genetic diversity, under low phosphate availability, with or without inoculation with arbuscular mycorrhizal fungi. Concomitant with measurement of plant growth, we characterized fungal morphology, element profiles and accumulation of transcripts encoding the PHT1 family of phosphorus transporters. We identified the lines Oh43 and Mo18W to show similar performance when not inoculated, but outlying high and low performance, respectively, when inoculated with arbuscular mycorrhizal fungi. We observed a correlation between the high responsiveness of Oh43 and the extent of the extra-radical fungal mycelium, consistent with the interpretation that the phosphorus contribution from the mycorrhizal uptake pathway is determined largely by the abundance of hyphae in the soil.