Citrus tristeza virus ultrastructure and associated cytopathology in Citrus sinensis and Citrus aurantifolia

Abstract

Citrus tristeza virus ultrastructure and associated cytopathology was documented with three isolates and two hosts, sweet orange 'Madam vinous' (Citrus sinensis (L.) Osbeck) and Mexican lime (Citrus aurantifolia (L.) Swingle). Virions were long, flexuous, and disorganized or in swirled, parallel masses. Infection was common in phloem parenchyma and companion cells and less frequent in mature sieve elements. Immunogold labeling confirmed previous findings that the major coat protein encapsidated the length of purified virions, while the minor coat protein encapsidated one terminal. Three types of inclusions were observed: (i) viral arrays that reacted with antibodies against the major (p25) and minor (p27) Citrus tristeza virus coat proteins, (ii) fibrous inclusions that reacted with antibodies against the Citrus tristeza virus p20 gene product but were sparsely labeled with antibodies against either coat protein, and (iii) accumulated cytoplasmic vesicles associated with aggregated, vesiculating mitochondria. The latter resembled Beet yellows virus-like vesicles, which are typical of closterovirus infection, but did not react with any of our antibodies. Cytopathology did not differ between isolates and plant hosts. Most effects were observed in phloem parenchyma cells, including chloroplast degradation, mitochondria vesiculation, and nuclear membrane invagination. Multivesicular bodies and lipid-filled vesicles were abundant in the cytoplasm. Masses of electron-lucent vesicles and electron-dense bodies were present between the cell membrane and cell wall.Key words: immunolocalization, CTV major coat protein, CTV minor coat protein, CTV p20 gene product, inclusions, isolate severity.