Abstract
A previously undescribed disease of the yellowing type was found to occur on cucumber and muskmelon in commercial greenhouses in Kanto area. Long, flexuous, rod-shaped virus particles, 12×1, 000nm approximately, were detected in dip preparations from diseased plants of cucumber and muskmelon. The detection was not easy, because the particles were small in number and labile in nature. The particles were also observed in thin sections prepared from both naturally and artificially infected plants of cucumber and muskmelon. Their presence was always restricted to phloem cells, but sometimes they were found in xylem parenchyma cells of vascular bundles. Virus-infected cells were also characterized by the development of amorphous granular structures and small vesicles containing fibrous materials in the cytoplasm. Both of them seemed to be closely related to virus multiplicaiton, and was considered to be viroplasms. Phloem necrosis was usually observed in diseased plants. It caused a remarkable accumulation of starch grains in chloroplasts in mesophyll cells. The virus was transmitted to healthy seedlings of cucumber and muskmelon by viruliferous greenhouse whiteflies, but not by inoculation of sap. From these results, the yellowing disease of cucumber and muskmelon was concluded to be caused by the long, flexuous, rod-shaped virus, which was named cucumber yellows virus.
