USE OF ZOOSPORES OF POLYMYXA-BETAE IN SCREENING BEET SEEDLINGS FOR RESISTANCE TO BEET NECROTIC YELLOW VEIN VIRUS

A system to culture viruliferous Polymyxa betae and to produce zoospor es is described. The zoospores were used for inoculation of beet seedl ings, grown in nutrient solution, in tests for resistance to beet necr otic yellow vein virus (BNYVV). On most occasions in a time course exp eriment, and with various zoospore cultures, the partially resistant c ultivar Rima and the accession Holly-1-4 had virus concentrations simi lar to the susceptible cultivar Regina, but the virus concentration in Beta vulgaris ssp. maritima accession WB42 was significantly lower (P < 0.05). 'Regina' could be distinguished from various resistant acces sions by a significantly higher virus concentration (P < 0.05) shortly after inoculation, or after transplanting the seedlings from the nutr ient solution into sand. Results of screening for resistance to BNYVV, using zoospores for inoculation, did not correspond with results of a test in which infested soil was used. Tests in which seedlings are gr own in nutrient solution and inoculated with zoospores are suitable fo r the detection of accessions with a high level of resistance to BNYVV . To obtain virus infection in all plants, the optimal density of the zoospore suspension should first be determined and plants should be as sayed shortly after inoculation.