Potential ecological effects of Piriformospora indica, a possible biocontrol agent, in UK agricultural systems

Piriformospora indica (Sebacinaceae), a root endophytic fungus, was originally isolated from an arid sub-tropical soil. P. indica forms mutualistic symbioses with a broad range of host plants, increases biomass production, resistance and tolerance to fungal pathogens and abiotic stresses. These characteristics make it a very attractive component of more sustainable agriculture. So, it is desirable to understand its wider ecosystem effects. We determined how long P. indica could survive in the soil and how it interacts with other soil microorganisms and some important arable weeds. Survival of P. indica in the soil, under winter and summer conditions in the UK was tested by isolating DNA and RNA of P. indica from pots of soil which had been left open to winter-summer weather conditions without host plants, followed by PCR and reverse transcription-PCR (RT-PCR) with P. indica-specific primers. P. indica effects on other soil and root microorganisms were tested by PCR-denaturing gradient gel electrophoresis analysis of DNA extracted from soil and roots from pots in which P. indica-infected wheat had been grown. The effect of P. indica on growth of black-grass (Alopecuris myosuroides), wild-oat (Avena fatua) and cleavers (Galium aparine) was tested alone and in competition with wheat. In soil P. indica-mRNA and DNA could still be detected after eight months, but not after 15 months. Soils from P. indica-inoculated pots had distinct fungal and bacterial species communities which were more diverse than non-inoculated controls. P. indica infected A. myosuroides and A. fatua but was not detected in G. aparine. The average above-ground competitiveness of the weeds with wheat was decreased. If applied to field crops in the UK, P. indica would be persistent for up to 15 months and likely to alter competitive relations within vegetation. Increased soil microbial diversity during the first eight weeks after inoculation, although usually desirable, could alter soil composition or functioning.