Pathogenetic roles of beet necrotic yellow vein virus RNA5 in the exacerbation of symptoms and yield reduction, development of scab‐like symptoms, and Rz1‐resistance breaking in sugar beet

• Published in: Plant pathology 2021-01, Vol.70 (1), p.219-232
• Main Authors: Tamada, Tetsuo, Uchino, Hirokatsu, Kusume, Toshimi, Iketani‐Saito, Minako, Chiba, Sotaro, Andika, Ida Bagus, Kondo, Hideki
• Format: Article
• Language: English
• Subjects: Accumulation; BNYVV; Cultivars; Disease resistance; Field tests; Genomes; Inoculation; Laboratories; Laboratory tests; Plant virus diseases; resistance breaking; Ribonucleic acid; RNA; RNA5; Roots; Rz1 gene; Scab; scab‐like symptom; Strains (organisms); sugar beet; Sugar beets; Veins (plant anatomy); Virulence; Viruses; Yield
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1111/ppa.13266

Beet necrotic yellow vein virus (BNYVV) generally has a four‐segmented positive‐sense RNA genome (RNAs 1–4), but some European and most Asian strains have an additional segment, RNA5. This study examined the effect of RNA5 and RNA3 on different sugar beet cultivars using a Polymyxa‐mediated inoculation system under field and laboratory conditions. In field tests, the degree of sugar yield served as an index for assessing the virulence of BNYVV strains. Japanese A‐II type isolates without RNA5 caused mostly 15%–90% sugar yield reductions, depending on the susceptibility of sugar beet cultivars, whereas the isolates with RNA5 induced more than 90% yield losses in the seven susceptible cultivars, but small yield losses in one Rz1‐resistant and Rizor cultivars. However, a laboratory‐produced isolate containing RNA5 but lacking RNA3 caused higher yield losses in Rizor than in susceptible plants, and induced scab‐like symptoms on the root surface of both susceptible and resistant plants. In laboratory tests, A‐II type isolates without RNA5 had low viral RNA accumulation levels in roots of Rizor and Rz1‐resistant plants at early stages of infection, but in the presence of RNA5, viral RNA3 accumulation levels increased remarkably. This increased RNA3 accumulation was not observed in roots of the WB42 accession with the Rz2 gene. In contrast, the presence of RNA3 did not affect RNA5 accumulation levels. Collectively, this study demonstrated that RNA5 is involved in the development of scab‐like symptoms and the enhancement of RNA3 accumulation, and suggests these characteristics of RNA5 are associated with Rz1‐resistance breaking. BNYVV RNA3 and RNA5 are involved in the development of different types of symptoms and the presence of RNA5 increases symptom severity in susceptible sugar beet cultivars and is associated with Rz1‐resistance breaking.