No abstract

Antibiotics are used extensively to control animal, plant, and human pathogens. They are sprayed on apple and pear orchards to control the bacterium Erwinia amylovora , the causative agent of fire blight. This phytopathogen is developing antibiotic resistance and alternatives either have less efficacy, are phytotoxic, or more management intensive. The objective of our study was to develop an effective biological control agent colonizing the host plant and competing with Erwinia amylovora. It must not be phytotoxic, have a wide spectrum of activity, and be unlikely to induce resistance in the pathogen. To this end, several bacterial isolates from various environmental samples were screened to identify suitable candidates that are antagonistic to E. amylovora . We sampled bacteria from the flowers, leaves, and soil from apple and pear orchards from the springtime bloom period until the summer. The most effective bacteria, including isolates of Pseudomonas poae , Paenibacillus polymyxa , Bacillus amyloliquefaciens and Pantoea agglomerans , were tested in vitro and in vivo and formulated into products containing both the live strains and their metabolites that were stable for at least 9 months. Trees treated with the product based on P. agglomerans NY60 had significantly less fire blight than the untreated control and were statistically not different from streptomycin-treated control trees. With P. agglomerans NY60, fire blight never extended beyond the central vein of the inoculated leaf. The fire blight median disease severity score, 10 days after inoculation, was up to 70% less severe on trees treated with P. agglomerans NY60 as compared to untreated controls.

This paper reports brief systematization of the current knowledge of the biology of mycoviruses, viral morphology, and genetics in particular as well as characteristics of the virus transmission and infection symptoms in fungal cells. The mechanisms involved in antiviral defense in the members of different classes of fungi are discussed. Insights into the role of hypovirulent mycoviruses in the biotechnological control of phytopathogenic fungi are provided.