DISTRIBUTION AND INCIDENCE OF YELLOWING VIRUSES IN SUGAR-BEET CROPS IN SPAIN FROM 1990 TO 1993

Surveys of the principal yellowing viruses of sugar beet, beet yellows virus (BYV) and beet mild yellowing virus (BMYV) in Spain were carrie d out from 1990-1993. Beet yellowing viruses were detected in all prov inces, although the mean percentages of plants infected with BYV and B MYV were practically zero in the southern zone. Within the northern zo ne high variations from one province to another could be observed. The mean percentages of plants infected with BYV were higher in the Ebro Valley than in the Duero Valley. Areas infected with BYV were very res tricted, while BMYV could be found to a variable extent all over Spain , although the infection levels were lower. The incidence and distribu tion of these viruses in the Spanish sugar beet crop makes the study a nd application of control measures for beet yellowing viruses necessar y.