Comparative epidemiology of three tropical whitefly-transmitted geminiviruses.

Spatial and temporal patterns of spread of African cassava mosaic, okra leaf curl and tobacco leaf curl viruses in West Africa, East Africa and India share some general characteristics. By comparing the results and running new analyses on available data, it is shown that the epidemiology of these viruses is controlled by the same key variables. For instance, spatial spread is characterised by strong border effects due to accumulation of whitefly vectors (Bemisia tabaci) on the wind-exposed field borders under the influence of the prevailing wind. This results in pronounced environmental gradients of disease. Temporal patterns of virus spread are driven by the sinusoidal fluctuation of temperature over the year which correspond with changes of whitefly populations.

Evidence that the amino acid composition of the particle proteins of plant viruses is characteristic of the virus group. I. Multidimensional classification of plant viruses.

The amino acid (AA) contents of the coat proteins of 134 plant viruses and strains were classified by principal components analysis. The virus groupings that were obtained correlated well with the classification of Matthews. The relationships of each virus were dependent on the number of AA residues (axis 1) and on the percentage composition of each AA in the proteins (axes 2-4). The classification indicated which data were anomalous and needed confirmation. There seemed to be more anomalies in estimates of protein size than of protein composition.

Evidence that the amino acid composition of the particle proteins of plant viruses is characteristic of the virus group. II. Discriminant analysis according to structural biological and classification properties of plant viruses.

The amino acid composition (AAC) of the coat proteins (CPs) of 126 plant viruses or strains were analyzed by stepwise discriminant analysis. The criteria chosen for discrimination were: the structure of virus particles (3 clusters); the mode of of transmission of the viruses (6 clusters); and the grouping of viruses according to the classification of the International Committee on Taxonomy of Viruses (23 groups). Statistically significant correlations were obtained with different groups of discriminant amino acids. The results confirm that the AAC of the CPs contains all the information needed for a quantitative classification of plant viruses. These results and possible explanations of these clustering patterns are discussed.