Endophytic Inoculation and Growth of Metarhizium brunneum in Wheat, and Lack of Effect on Bird Cherry-Oat Aphid, Rhopalosiphum padi

Endophytic fungi can develop apparently symbiotic relationships with their plant hosts, sometimes providing protection to plants against phytophagous insects. We evaluated a) the artificial endophytic colonization of wheat plants with the entomopathogenic fungus Metarhizium brunneum, and b) effect of this endophyte upon establishment of bird cherry-oat aphid, Rhopalosiphum padi on fungus-colonized plants. The Metarhizium strain used is pathogenic (as conidia) to this aphid. Wheat seeds were inoculated with Metarhizium. Plants obtained were artificially infested with R. padi in the greenhouse. After two months, fungus-inoculated and non-inoculated plants were cut and transferred to selective culture media and aphid numbers were obtained. Colonization of plants by endophytic Metarhizium was confirmed in fungal treatments: two-months old inoculated wheat had averages of 3.51 Metarhizium colonies inside leaves and 7.07 in roots, vs. 0.005 and 0.04 colonies in untreated leaves and roots, respectively: p<0.01). However, the endophyte had no or slight effect on aphid populations (<20% difference in aphid numbers). The relationships between plants, entomopathogenic endophytes and insects should be further investigated.