The knowledge of ecology and epidemiology of rhizomania is particularly useful to understand the means and practices able to limit or avoid its further diffusion. Some promising methods of biological control using coexisting and non-pathogenic organisms could potentially help improve the action of the not completely effective genetic resistances. This integrated protection would be valuable, especially in the even more frequent development of resistance¿breaking strains in the BNYVV, where the known types of resistance, alone or in combination, seem to have lost part of their original ability to protect the crop. Therefore, further efforts will be needed to discover new traits likely still present in the wild species of the genus Beta. The availability of large collections of germplasm stored in the International Beta gene-banks should ensure the enhanced efficiency of genetic resistance by means of conventional and marker-assisted selection methods. Some almost immune transgenic varieties seem already to be waiting for release where and when it will be possible. The introduction chapter describes briefly the sugar beet crop, the more common diseases, and the damage caused by rhizomania. The following chapters discuss biological properties of the causal virus, BNYVV, and its vector, Polymyxa betae, and their interactions with the environment and the host-plant. In particular, the great advances in research of the molecular biology of BNYVV should be noteworthy, which have been established by a wide range of the most modern methods. Recent work focused on the genetic diversity and evolution of BNYVV is moving forward our understanding of the dramatic worldwide epidemics of rhizomania. Newly developed molecular techniques also lead to practical applications, such as quantification of inoculum in ecological and epidemiological research.

The book treats theoretical and practical aspects

1   Introduction      1.1  Beets and Sugar Beets    1.2  Abiotic Stresses     1.3  Pests and Diseases    1.4  Rhizomania and Economic Damages2   Rhizomania: History and Current Status     2.1  First Observations and Investigations     2.2  Etiology     2.3  Histological Observations     2.4  Spreading of the Disease3  The Causal Agents: Beet Necrotic Yellow Vein       Virus     3.1  Host Range and Symptoms    3.2  Strains    3.3  Transmission by Vectors     3.4  Properties of Virus Particles    3.5  Properties of Genome    3.6  Effect of Small RNA Species on Root             Symptoms    3.7  Cytopathological Effect    3.8  Detection and Diagnosis     3.9  Other Soil-Borne Viruses Associated with            Rhizomania4  Molecular Biology and Replication of Beet         Necrotic Yellow Vein Virus     4.1  Replication and Cis elements    4.2  Origin of Assembly      4.3  Movement    4.4  Pathogenicity Determinants and Counter            Defense Mechanisms    4.5  Silencing Suppression and Movement of             BNYVV       4.6  Future and Prospects: RNA-RNA Network in the              Regulation of ¿a BNYVV Life¿5  Genetic Diversity of Beet Necrotic Yellow Vein     Virus       5.1  Benyvirus    5.2  Variation    5.3  Geographical Origins and Migration    5.4  Emergence of Resistance-Breaking Variants    5.5  Conclusions6  The Viral Vector Polymyxa betae     6.1  Taxonomy    6.2  Life Cycles of Plasmadiophorids    6.3  Infection and Germination of Polymyxa betae    6.4  Host Range and Genetic Diversity    6.5  Virus-Vector Relationship    6.6  Detection and Discrimination    6.7  Conclusions  7  Ecology and Epidemiology     7.1  Inoculum    7.2  Dispersal    7.3  Factors Affecting Infection and Disease              Development    7.4  Modeling for Infection and Spread 8  Control      8.1  Disease Effects and Damages     8.2  Agronomic Control     8.3  Chemical and Thermal Control     8.4  Biological Control 9  Genetic Resistances      9.1  Sources of Resistance     9.2  Resistances to BNYVV     9.3  Multiple BNYVV Resistance    9.4  Resistance to Polymyxa betae     9.5  Resistant Varieties    9,6  Mechanisms of Resistance     9.7 Germplasm Conservation in the Service of Plant          Breeding10 Engineering Transgenic Rhizomania Resistance     10.1  Introduction        10.2  Pathogen-derived Resistance    10.3  RNA Silencing-Mediated Resistance    10.4  Resistance Based on Genes of Non-viral Origin    10.5  Concluding Remarks    11 Breeding Methods    11.1  Screening for Resistance     11.2  Breeding for Resistant Varieties    11.3  Field Trials and Release of Varieties12  Assisted Selection