Analysis of the Resistance-Breaking Ability of Different Beet necrotic yellow vein virus Isolates Loaded into a Single Polymyxa betae Population in Soil

Abstract

The genome of most Beet necrotic yellow vein virus (BNYVV) isolates is comprised of four RNAs. The ability of certain isolates to overcome Rz1-mediated resistance in sugar beet grown in the United States and Europe is associated with point mutations in the pathogenicity factor P25. When the virus is inoculated mechanically into sugar beet roots at high density, the ability depends on an alanine to valine substitution at P25 position 67. Increased aggressiveness is shown by BNYVV P type isolates, which carry an additional RNA species that encodes a second pathogenicity factor, P26. Direct comparison of aggressive isolates transmitted by the vector, Polymyxa betae, has been impossible due to varying population densities of the vector and other soilborne pathogens that interfere with BNYVV infection. Mechanical root inoculation and subsequent cultivation in soil that carried a virus-free P. betae population was used to load P. betae with three BNYVV isolates: a European A type isolate, an American A type isolate, and a P type isolate. Resistance tests demonstrated that changes in viral aggressiveness towards Rz1 cultivars were independent of the vector population. This method can be applied to the study of the synergism of BNYVV with other P. betae-transmitted viruses.

Occurrence of resistance‐breaking strains of Beet necrotic yellow vein virus in sugar beet in northwestern Europe and identification of a new variant of the viral pathogenicity factor P25

“…() showed by means of reverse genetics that this amino acid exchange alone is responsible for the induction of Rz1 resistance‐breaking (RB) ability in an European A type strain. Bornemann & Varrelmann () showed that RB strains retained their resistance‐breaking abilities even after loading of another virus‐free soilborne vector population. It was supposed that Rz1 selected for this resistance‐breaking mutation, because another resistance source, Rz2 (Scholten et al ., ), in combination with Rz1 still effectively reduces replication of mutated strains (Liu et al ., ; Pferdmenges et al ., ; Bornemann & Varrelmann, ).…”

“…Bornemann & Varrelmann () showed that RB strains retained their resistance‐breaking abilities even after loading of another virus‐free soilborne vector population. It was supposed that Rz1 selected for this resistance‐breaking mutation, because another resistance source, Rz2 (Scholten et al ., ), in combination with Rz1 still effectively reduces replication of mutated strains (Liu et al ., ; Pferdmenges et al ., ; Bornemann & Varrelmann, ). Both Rz1 and Rz2 resistant plants display a phenotype of quantitative resistance (Scholten et al ., ; Heijbroek et al ., ).…”

Occurrence ofPolymyxa graminisRibotypes in Germany and Their Association with Different Host Plants and Viruses

“…For example, the difference in aggressiveness between BNYVV isolates was found to be independent of the Polymyxa betae vector population (Bornemann and Varrelmann 2011). Tuitert et al (1994) found that the total number of P. betae resting spore clusters formed in roots of partially BNYVV-resistant cultivars and a susceptible cultivar did not differ at 6 and 12 weeks after inoculation.…”

Ability of Non-Pathogenic Fusarium oxysporum Strain Fo47 to Suppress Rhizomania Disease of Sugar Beets in Morocco

“…In addition, the manifestations of rhizomania on tolerant varieties were reported at several sites (ITB, 2010). This situation was partially explained by the lack of tolerance of some varieties, or higher pressure of the disease, due to one hot and wet spring and a more important presence of the Polymyxa, or even the appearance and increase of virulent pathotypes in the pathogen population (Schmit et al, 2002;Rush, 2003;Bornemann and Varrelmann, 2011).…”