Quantitative studies on resistance to Polymyxa betae and beet necrotic yellow vein virus in beet = Kwantitatief onderzoek naar resistentie tegen Polymyxa betae en het bieterhizomanievirus in de biet

Beet necrotic yellow vein virus (BNYVV) causes rhizomania in sugar beet. The virus is transmitted by the soil-borne fungus Polymyxa betae . Rhizomania in sugar beet can cause serious losses in sugar yield. Breeding for resistance is the most promising way to control the disease. Several aspects of quantitative screening for resistance to rhizomania were investigated. A greenhouse test was established to screen and select beet seedlings for resistance to BNYVV. Plants were grown in a mixture of sand and infested soil. Virus concentrations were determined by enzyme- linked immunosorbent assay (ELISA). Data of various fields were analysed using multiplicative models for cultivar by location interaction. Interactions for yield and quality parameters were described in terms of virus concentrations in beet plants grown in the greenhouse and in the field. After screening various beet material of the sections Beta , Corollinae and Procumbentes, it was concluded that resistance to P. betae could have some effect on the infection with BNYVV, but low numbers or even absence of resting spores did not always result in low virus concentrations. When viruliferous zoospores of P. betae were used to inoculate plants, resistant accessions often had virus concentrations similar to those of the susceptible control. Resistant and susceptible accessions could only be distinguished shortly after inoculation with zoospores or after transplanting the inoculated plants into sand. it is recommended to combine resistant accessions, which differ genetically and in their mechanism of resistance, in order to obtain sugar beet cultivars with a high level of resistance to rhizomania.