Studies on the cross-protection among strains of papaya ringspot virus.
The present study showed that cross-protection occurred between the different strains of PRV. The protecting strains did not completely inhibit the invasion of the challenge strains into the protected plants and not the spread of the challenge strains in the protected plants either, but it did inhibit the multiplication of the challenge strains. It was further found that the more closely related the protecting and challenge strains were, the greater the degree of cross-protection was. The efficiency of cross-protection between the closely related PRV strains of South-China was positively related with the rate of multiplication and spread and the concentration of the protecting strains in the plant, but negatively related with those of the challenge strains. The results mentioned above suggested that in order to control papaya ringspot virus disease by means of cross-protection either with a classical method or with CP genetic engineering method, the local dominant strains or severe should be used as the experimental materials in the work of induction and screening of mild strains or obtaining transgenic plants. In this way, better results might be expected.