Control of Papaya Ringspot Virus-Type W in Zucchini Squash by Cross-Protection in Brazil

Abstract

Two mild strains of papaya ringspot virus-type W (PRSV-W) were tested under greenhouse and field conditions to study the potential of cross-protection for control of zucchini squash mosaic. Protected plants of zucchini squash cultivars Caserta and Clarinda were challenged with three severe strains from different geographic regions of the country in tests carried out in the greenhouse. Challenge inoculations were done mechanically 10 and 20 days after the protective inoculation. The mild strains did not have a visible negative effect on the development of the plants and offered effective protection against the severe strains. Field tests of protected Caserta plants were carried out in Piracicaba County, São Paulo. Comparative evaluation based on the symptoms and development of protected and unprotected plants of zucchini squash showed that both mild strains effectively protected the plants against the effects of the severe strain present in the field. Yield of marketable fruits harvested from protected plants was only 10% less than that of the healthy plants in one field trial. Compared with the yield from plants infected with the severe strains, protected plants showed an increase of 511 and 633% in the number and weight of marketable fruits, respectively, in a test in 1994. In a second experiment in 1995, an increase of 327% in the number and 344% in the weight of marketable fruits was recorded. These studies demonstrate the effectiveness of cross-protection for the control of the mosaic disease caused by PRSV-W in zucchini squash and offer growers a method for large-scale application of this technology.

Biomass, virus concentration, and symptomatology of cucurbits infected by mild and severe strains of Papaya ringspot virus

“…Rating 1 was assigned to plants without mosaic symptoms and leaf deformations and with good development; rating 5 was assigned to those exhibiting mosaic symptoms, blisters, severe leaf deformations and plant stunting; ratings 2, 3 and 4 were assigned to intermediate symptoms between the two extremes (Rezende & Pacheco, 1998).…”

“…In this case, the reduction in biomass was approximately 10 %. Field experiments have reported reductions of the order of 10 % as well, in total fruit yield of 'Caserta' zucchini squash and hybrid Tetsukabuto-type long-neck squash plants pre-immunized with strains PRSV-W-1 and PRSV-W-2 (Dias & Rezende, 2000;Rezende & Pacheco, 1998). Other authors have also reported yield decreases between 11 % and 15 % in plants pre-immunized by mild strains of other viruses, as Lecoq et al (1991) with ZYMV for zucchini squash and Montasser et al (1998) with CMV in melon.…”

“…ex Lam x C. moschata Duch.) plants showed that pre-immunization was efficient in controlling mosaic under greenhouse and field conditions (Dias & Rezende, 2000;Rezende & Pacheco, 1998;Rezende et al, 1999). This technology is already in use, at a small scale, to control this virus disease in commercial plantings, allowing significant yield gain.…”

“…This technology is already in use, at a small scale, to control this virus disease in commercial plantings, allowing significant yield gain. Despite the fact that a reduction in final yield of pre-immunized plants is known to happen and is even understandable (Dias & Rezende, 2000;Rezende & Pacheco, 1998), no specific reports exist on the effect of mild strains on the biomass of plants, nor on their concentration in infected tissues. In view of this, the objectives of the present work were to evaluate the concentration of mild and severe strains of PRSV-W in extracts of infected tissues of 'Caserta' zucchini squash, 'Menina Brasileira' long-neck squash and 'Crimson Sweet' watermelon (Citrullus lanatus (Thunb.)…”

Inheritance of resistance to the Papaya ringspot virus-watermelon strain (PRSV-W) from watermelon accession 'PI 595201'

“…Cross protection with mild strains of the virus has been tested with some success (Rezende and Pacheco 1998), but it needs further studies to be recommended to farmers, due to possible synergistic effect when the plants are infected by more than one virus. Genetic resistance is the ideal virus control strategy (Fraser 1992), both economically and environmentally.…”