Resistance Evaluation of 96 Sugar Beet Varieties to Rhizomania, Root-Knot Nematode, and Root Rot Using Molecular Markers and Field Phenotyping

Sugar beet (Beta vulgaris L.) is a major sugar-producing crop worldwide, yet rhizomania, root-knot nematode, and root rot diseases severely constrain its yield and quality. Screening resistant germplasm is critical for disease-resistant breeding and sustainable sugar beet production. In this study, we evaluated the disease resistance of 96 introduced sugar beet cultivars via molecular marker assays and field disease nursery trials. The results showed that 76 cultivars (79.2%) carried the strong resistance genotype for rhizomania, and 20 cultivars (20.8%) carried the weak resistance genotype. For root-knot nematode, 87 cultivars (90.6%) were heterozygous resistant, while 9 cultivars (9.4%) were homozygous susceptible; no homozygous resistant genotype was detected in this study. Field evaluation of root rot showed that disease incidence ranged from 15.45% to 100%. Only one cultivar (KWS7772) was rated as resistant (R), accounting for 1.0%, and two cultivars were moderately resistant (MR), accounting for 2.1%. Among all tested cultivars, KWS7748 showed combined resistance to rhizomania, root-knot nematode, and root rot. These findings provide candidate resistant germplasm resources and baseline resistance data under the tested conditions for sugar beet disease resistance breeding; further multi-environment and multi-year validation is needed, particularly for root rot resistance, before these varieties can be recommended for commercial deployment.