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Disease Control and Pest Management

Evaluation of Induced Mutants of Papaya Ringspot Virus for Control by Cross Protection. S. -D. Yeh, Graduate research assistant, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456; D. Gonsalves, associate professor, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456. Phytopathology 74:1086-1091. Accepted for publication 6 April 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1086.

Efforts to select naturally occurring mild strains of papaya ringspot virus (PRV) by field collection or single-lesion isolation from natural virion populations were not successful. In an attempt to induce mild strains, crude sap from PRV-infected squash was treated with nitrous acid (pH 6.0) and used to inoculate Chenopodium quinoa, a local-lesion host. Two mutants, designated PRV HA 5-1 and PRV HA 6-1, that produced no symptoms in papaya were obtained from 663 single-lesion isolations. Papaya seedlings inoculated with these mild mutants remained symptomless or showed diffuse mottling with no reduction in plant size. Under greenhouse conditions, protection was observed when PRV HA 5-1 was used to protect papaya against different mechanical challenge inoculations with a severe strain. The results indicate that the symptomless mutant could be used as a protectant for control of PRV.