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Abstract

This trial set out to study the effectiveness of preimmunization for the control of PRSV-W in winter bush squash  (cv. Caserta) in São Manuel, SP. Four replications with ten plants each were set out in a randomized completed block design in order to evaluate five treatments: 1) Control submitted to natural infection; 2) Preimmunization with a mild strain; 3) and 4) Preimmunization followed by inoculation with a potent strain five and ten days after, respectively; 5) Inoculation with a potent strain. The potent strain reduced drastically the fruit yield, and all harvested fruits showed mosaic symptoms. Preimmunization, alone of followed by inoculation with a potent strain ten days after, increased the marketable immature fruit yield in relation to the control and plants inoculated with a potent strain, but when a challeng incoculation with the potent strain was carried out only five days after preimmunization, there was a reduction in the immature fruit yield. Most preimmunizated plants that showed mosaic symptoms were infected by ZYMV, detected by ELISA test. It was concluded that preimmunization was efficient, increasing fruit yield and quality, even when the plants were inoculated with a potent strain ten days after the inoculation of the mild strain.