Root associated organisms modify the effectiveness of chemically induced resistance in barley

Root infection by mycorrhizal fungi and nematodes both had a negative effect on plant growth. Adverse effects of G. etunicatum suggest that parasitic effects of mycorrhizal fungi outweighed positive effects under the optimal growth conditions provided by the experiment. Bion® either did not affect or decreased the number of lesions caused by powdery mildew at low and medium levels of infection by G. etunicatum or H. avenae, but increased it at high levels of root infection. This clearly proves the important role of root-associated biota in modulating the effectiveness of IR. However, plant accumulation of the resistance related protein BCI-4 was not impaired by G. etunicatum or H. avenae. Soil biota thus appear to impact later steps of the defense pathway, rather than preventing the onset of resistance.