|Wisler, Gail - UNIV. FLORIDA|
|Liu, Hsing Yeh|
Submitted to: American Society of Sugarbeet Technologists
Publication Type: Proceedings
Publication Acceptance Date: March 25, 2003
Publication Date: N/A
Interpretive Summary: Beet necrotic yellow vein virus (BNYVV) and Beet soil-borne mosaic virus (BSBMV) are both transmitted by the soil-borne plasmodiophorid Polymyxa betae. However, only BNYVV causes the symptoms associated with the disease, rhizomania. Both viruses are found infecting sugar beet in the United States. Little is known about the effect of BSBMV on sugar beet production, or about the effect of mixed infections on beets. Soils naturally infested with cultures of aviruliferous P. betae and viruliferous P. betae carrying BNYVV and BSBMV, alone and in combination, were compared to non-infested soil for their effects on seedling emergence, plant fresh weight, and virus content as measured by ELISA. Two sugar beet varieties were used: one with resistance to rhizomania (BNYVV), and one that is susceptible. The rhizomania-resistant variety did not confer resistance to BSBMV, because BSBMV ELISA values were high in both the BNYVV resistant and susceptible varieties for soils infested with BSBMV alone. When BSBMV existed as a mixed infection with BNYVV, whether in the rhizomania resistant or susceptible variety, BSBMV ELISA values were significantly reduced. BNYVV may suppress BSBMV in mixed infections, even in rhizomania-resistant varieties in which ELISA values for BNYVV are extremely low. P. betae alone had a significant negative effect on growth of sugar beet in greenhouse pot cultures. Soils infested with P. betae, and with one or both viruses, showed significantly reduced fresh weight of seedlings.
Technical Abstract: Soils naturally infested with cultures of aviruliferous Polymyxa betae and viruliferous P. betae carrying the two sugar beet benyviruses Beet necrotic yellow vein virus (BNYVV) and Beet soil-borne mosaic virus (BSBMV), alone and in combination, were compared to non-infested soil with regard to their effects on virus content, fresh plant weight, and seedling emergence. Two sugar beet varieties were used: a diploid (Rzrz) that carries resistance to rhizomania caused by BNYVV, and a triploid rhizomania-susceptible variety (rzrzrz). These studies clearly demonstrated that the Rz resistance gene does not confer resistance to BSBMV. Additionally, P. betae alone had a significant negative effect on growth of sugarbeet, and soils infested with P. betae containing one or both viruses, tended to have reduced seedling emergence and reduced fresh weight, even when protective fungicides were used. BSBMV titers were significantly higher in single infections than in mixed infections with BNVV in both rhizomania resistant and susceptible varieties. In contrast, BNYVV titers were very high in single and in mixed infections in the Rhizomania-susceptible variety, but low in the resistant variety. Therefore, in the absence of BNYVV, BSBMV concentrations are high in infected roots, regardless of the resistance genotype. In the presence of BNYVV, however, BSBMV concentrations are low in both resistant and susceptible varieties, with absorbance readings similar to those of plants grown in non-infested soils. It appears that even at low levels, BNYVV either out competes or suppresses BSBMV, and suggests that both viruses target similar cellular processes in the sugarbeet plant.