SUMMARY

To evaluate the latex test for detecting distant serological relationships among plant viruses, latex coated first with antibody and then with virus was used to determine antiserum titres. In tests with latex coated with elongated viruses of the potato virus X group and with isometric viruses of the turnip yellow mosaic virus group the homologous titres of antisera were always much higher than in slide precipitin or agar diffusion tests. Usually, the heterologous titres were also increased and more heterologous reactions were found, especially when the pure y-globulin fraction was used instead of unfractionated sera, even though this y-globulin fraction contained relatively few antibodies. With both groups of viruses, the results corroborate previous observations made using conventional serological methods. In addition, turnip yellow mosaic virus was shown for the first time to be distantly serologically related to Andean potato latent and belladonna mottle viruses. The latex test may offer improved oppor-tunities to detect distant serological relationships among members of other groups of viruses