Search

Plants interacting with mutualistic fungi (MF) or antagonistic fungi (AF) can form associations with bacteria. We assessed whether the performance gain conferred by mutualistic bacteria to fungal‐associated plants is affected by the interaction between symbiont traits, type of bacterial‐protective traits against AF and abiotic/biotic stresses. Results showed that (A) performance gain conferred by bacteria to MF‐associated plants was greater when symbionts promoted distinct rather than similar plant functions, (B) bacterial‐based alleviation of the AF's negative effect on plants was independent of the type of protective trait, (C) bacteria promoted a greater performance of symbiotic plants in presence of biotic, but not abiotic, stress compared to stress‐free situations. The plant performance gain was not affected by any fungal‐bacterial trait combination but optimised when bacteria conferred resistance traits in biotic stress situations. The effects of bacteria on fungal‐associated plants were controlled by the interaction between the symbionts' functional traits and the relationship between bacterial traits and abiotic/biotic stresses. [ABSTRACT FROM AUTHOR]

Few studies have evaluated the effects of bacteria that form associations with fungi on plant-microbial symbioses. We investigated the effects of a novel symbiotic bacterium (E226) of Epichloë , a well-researched mutualistic fungal endophyte of grasses, on perennial ryegrass (Lolium perenne) also associated with Epichloë. We hypothesised that E226 would promote plant growth but would not interfere with the in-planta growth of Epichloë and its production of antiherbivore alkaloids. E226, identified as Micrococcus luteus, formed an ectosymbiotic relationship with Epichloë when cultured on artificial media (i.e., bacterial cells were located on the hyphal surface) and possessed plant-growth promoting traits identified through whole genome analysis. Seeds of L. perenne , already colonised by an Epichloë strain, were inoculated with E226. The bacterium established within the seedlings, and the abundance of M. luteus populations initially increased with plant age. In agreement with our hypotheses, plant inoculation with E226 enhanced the production of leaves and did not affect the growth of Epichloë or the concentration of Epichloë -derived alkaloids. The putative abilities of E226 to solubilise phosphate and produce vitamins and metabolic cofactors may explain the observed plant growth promotion. • Micrococcus luteus strain E226 was an ectosymbiont of Epichloë endophytes. • E226 promoted the growth of plants. • E226 did not compromise the Epichloë growth and alkaloid production. • E226 promoted the plant growth likely via enhancing the host nutrition. [ABSTRACT FROM AUTHOR]