Virions and Ultrastructural Changes Associated with Blueberry Red Ringspot Disease

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Abstract
An ultrastructural study of red ringspot-diseased specimens of highbush blueberry (V. corymbosum L.) revealed virus-like particles (VLP) in cytoplasm and nuclei of leaf cells. In the cytoplasm, the particles were embedded in circular inclusions composed of an electron-dense matrix with electron-lucent areas and surrounded by rough endoplasmic reticulum. In the nucleus, particles were associated with the nucleolus or lipid globules. Purified preparations from diseased blueberry leaves revealed large spherical VLP 42-46 nm in diameter. Density gradient centrifugation of purified preparations in sucrose or cesium chloride gradients always resulted in 2 absorbance peaks. Infectivity of purified preparations could not be demonstrated. Although the ultrastructural studies showed similarities to caulimoviruses, no serological reaction could be demonstrated with rabbit antiserum to cauliflower mosaic virus.