In situ localization of cacao swollen shoot virus in agroinfected Theobroma cacao.
An alternative method for the infection of T. cacao cv. Amelonado with cacao swollen shoot badnavirus (CSSV) was investigated. A greater-than-unit length copy (1.2) of the CSSV DNA genome was cloned into the Agrobacterium binary vector pBin19 and was transferred into young plants via A. tumefaciens. Typical leaf symptoms and stem swelling were observed 7 and 11 weeks post-inoculation, respectively. Viral DNA, CSSV coat protein and virions were detected in leaves with CSSV symptoms. Agro-infected plants were used to study the in situ localization of CSSV by dot-blot hybridization and its histopathologic effects in planta. In both leaves and petioles, virions were only seen in the cytoplasm of phloem companion cells and of a few xylem parenchyma cells. Light microscopy showed that stem swelling resulted from a proliferation of the xylem, phloem and cortex cells.