BREEDING FOR RESISTANCE TO RHIZOMANIA IN SUGAR-BEET (BETA-VULGARIS L)

In breeding for resistance to rhizomania, breeding material was routin ely examined for resistance to the rhizomania virus over several years . This study was performed in order to investigate the value of virolo gical examination of sugarbeet breeding material in breeding for resis tance to the rhizomania virus. Tests were conducted with varieties sus ceptible or partially resistant to rhizomania, as well as with several new and more-resistant hybrids. A test on young plants showed that al l genotypes contained beet necrotic yellow-vein virus (BNYVV), but tha t the virus content differed widely. Plants of two commercially used p artially resistant varieties had, on average, only half the virus cont ent of susceptible varieties in their roots, and plants of eight new h ybrids still in the process of registration contained less than one th ird of that amount. There was a significant negative correlation betwe en the quantity of BNYVV in young plant roots and final yield under di sease conditions in the field. Opportunities for further improvement i n the level of the resistance to BNYVV in sugarbeet by means of conven tional breeding programmes are discussed.