Root type is not an important driver of mycorrhizal colonisation in Brachypodium distachyon

Breeding for favourable root traits in food and energy crops should be considered in the context of interactions with soil biota, notably those that can increase the nutrient use efficiency of crops. Arbuscular mycorrhizal (AM) fungi can provide services to plants but a better understanding of the interactions between root traits and AM fungi is required to maximise these benefits. One source of intraspecific variation in root architecture is the allocation of resources to different root types. We hypothesized that different root types would have different traits and be colonised differently by AM fungi, either in the amount of colonisation or identity of colonisers. We studied communities colonising the seminal, coleoptile nodal and leaf nodal roots of seven Brachypodium distachyon accessions grown in three crop or pasture soils. Leaf nodal roots had low specific root length compared to coleoptile nodal and seminal roots, yet all three root types harboured similar AM fungal communities and levels of colonisation. Most of the variation in the AM fungal communities was explained by soil; significant proportions were explained by plant accession and root type but these effects were weak. Differential allocation of resources between root types is not a trait that could be selected to maximise beneficial interactions with AM fungi and we found no link between a root phenotypic trait (specific root length) and AM fungal colonisation. Accessions did vary in extent of colonisation by arbuscules, meaning B. distachyon may be a useful model to study mechanisms underlying the symbiotic interface and mycorrhizal growth response of cereals.