Inheritance of resistance to beet necrotic yellow vein virus in Beta vulgaris conferred by a second gene for resistance

Rhizomania is a serious disease of sugar beet, caused by beet necrotic yell ow vein virus (BNYVV). The disease can only be controlled by the use of res istant cultivars. The accession Holly contains a single dominant gene for r esistance, called Rz. The identification of a locus for resistance that dif fers from Rz would provide possibilities to produce cultivars with multiple resistance to BNYVV, Inheritance of resistance to BNYVV was studied by scr eening progenies of crosses between resistant plants of the accessions Beta vulgaris subsp. maritima WB42 and B. vulgaris subsp. vulgaris Holly-1-4 or R104. Observed and expected segregation ratios were compared to elucidate whether the resistance genes in the three accessions are alleles or situate d on different loci. STS markers, linked to the genes for resistance, were used to study the segregation in more detail. The results demonstrated that the genes for resistance to BNYVV in Holly-1-4 and WB42 are closely linked . The gene for resistance in R104 is at the same locus as in Holly-1-4, and also closely linked to the gene in WB42. As the Holly resistance gene has been named Rz, the name Rz2 is proposed to refer to the resistance gene in WB42. Consequently, the gene Rz should be referred to as Rz1.