Epidemiology of rhizomania disease of sugar beet.

摘要: Rhizomania disease of sugar beet is caused by necrotic yellow vein virus (BNYVV). The transmitted the soil-borne fungus Polymyxa betae. can cause severe losses in yield, depending on level infestation soil, environmental conditions during growing season and susceptibility cultivar. Several aspects epidemiology were studied. A quantitative bioassay was developed to assess inoculum potentials vector soil. allowed estimate most probable numbers (MPN) infective units P.betae with or without from incidence infected bait plants a dilution series infested recovery bioassay, effect duration detection BNYVV soil treatments infectivity viruliferous resting spores assessed. MPN method enabled establishment nonlinear relationship between potential before sowing yield parameters at harvest an artificially field. In same field, dynamics pathogen populations two successive crops absence presence drip irrigation rapid increase found and, highest initial (inoculum applied 50 g m -2 ), reduced 10% first 66% second year. Horizontal dispersal spread movement zoospores root growth host limited small distances. Displacement tillage practices resulted over larger Newly formed roots BNYVV-resistant less than those susceptible plants. high BNYVV-resistance will be needed reduce build-up which contribute durability resistance.