Studies of pelargonium leaf curl virus

SUMMARY Pelargonium leaf curl virus (PLCV) was compared with nine other viruses with isometric particles: broad bean mottle, carnation mottle, carnation Italian ringspot (CIRV), cymbidium ringspot, raspberry ringspot, tobacco necrosis, tomato bushy stunt (TBSV), turnip crinkle and a virus from Trifolium repens . PLCV was serologically related to CIRV and TBSV, although cross‐reactions between the latter two viruses occurred only with sera from rabbits given one more injection of antigen than usual. Considerable antigenic differences were found among seven isolates of PLCV, and between these isolates and CIRV and TBSV. Cymbidium ringspot virus was serologically closely related to the virus from Trifolium repens , and both were similar but serologically unrelated to the PLCV‐CIRV‐TBSV group. No other serological relationships were found among the ten viruses. Serologically related viruses gave similar zones after centrifugation in sucrose density‐gradients and, usually similar sedimentation coefficients. The different viruses infected twenty‐three to forty‐four out of sixty plant species tested. Carnation mottle and turnip crinkle viruses were not eliminated from plants grown at 37d̀C. for 4–6 weeks, whereas the other viruses usually were. The properties of the viruses in vitro were broadly similar.