VIEW ARTICLE

Squash Mosaic Virus Variability: Nonreciprocal Cross-Protection Between Strains. J. Albersio A. Lima, Professor de Fitopatologia, Centro de Ciencias Agrarias, Universidade Federal do Ceara, Fortaleza, Brasil; Merritt R. Nelson, Professor of Plant Pathology, University of Arizona, Tucson. Phytopathology 65:837-840. Accepted for publication 20 February 1975. DOI: 10.1094/Phyto-65-837.

Interactions between strains IH and IIA of squash mosaic virus (SMV) in pumpkin (Cucurbita pepo) and cantaloupe (Cucumis melo) plants were studied. Complete reciprocal interference was observed in pumpkin. In cantaloupe, strain IH dominated in mixed infections, and was able to overcome initially suppressive effects from prior infection by IIA. The latter phenomenon is believed related to the fact that in cantaloupe the multiplication rate of strain IH is twice that of strain IIA. In pumpkin, the relative extent of multiplication of the two strains is equal. The detection of interference, when the challenge strain is the milder of the two, was accomplished by utilizing host range differences and the serological intragel absorption technique. When opposite cotyledons of pumpkins were inoculated simultaneously with equal concentrations of different strains of virus, each strain dominated in roughly 50 percent of the plants to the exclusion of the other. When the concentration of one strain was reduced in relation to the other, the number of plants in which it dominated was reduced proportionately. Identical experiments with cantaloupe resulted in more complete dominance of strain IH even when the concentration was much less than strain IIA.