CHAYOTE MOSAIC, A NEW DISEASE IN SECHIUM EDULE CAUSED BY A TYMOVIRUS

A sap-transmissible virus was isolated from chayote (Sechium edule) in Costa Pica. Infected plants showed chlorotic spots and rings, and blo tchy mosaics, which often coalesced to give a complete mosaic and leaf deformation. By electron microscopy, spherical virus-like particles o f approximately 29 nm in diameter were visible, and cytological change s associated with the chloroplasts were observed. The virus particles sedimented in sucrose density gradients as two components, a top compo nent of empty protein shells and a bottom component of electron-dense particles. Electrophoretic analysis showed a single-stranded RNA of ap proximately 5.7 kb and capsid protein (CP) subunits of -22 kDa. The vi rus was identified as a member of the tymovirus group on the basis of particle morphology, size, sedimentation in sucrose gradients, cytopat hological effects, and capsid protein and genome properties, and it wa s tentatively named chayote mosaic virus (ChMV).