First detection of papaya ringspot virus-type W and zucchini yellow mosaic virus infecting Cucurbita maxima in Paraguay.
In July 2018, mosaic, leaf deformation, chlorosis and stunting were observed in plants of Cucurbita maxima var. Zapallito in an experimental area in San Lorenzo County, Central Department, Paraguay. The incidence of symptomatic plants was around 80% in an area of 2,500 m2. Preliminary transmission electron microscopic examination of ultra-thin sections of naturally infected plants revealed the presence of inclusion bodies typical of Potyvirus infections. Based on ELISA test, all samples reacted with antisera against papaya ringspot virus-type W (PRSV-W) and zucchini yellow mosaic virus (ZYMV), indicating a mixed infection with these potyviruses. Total RNA was extracted from symptomatic leaves, followed by RT-PCR using specific primers for the coat protein gene of PRSV-W and ZYMV, which amplifies fragments of 398-and 1186-bp, respectively. Four amplicons for each virus were sequenced. In BLASTn analysis, PRSV-W amplicons (MK751456-MK751459) shared 95.65–97.95% identity with PRSV-W isolates (DQ104819, AF344642). Similarly, ZYMV amplicons (MK751460-MK751463) shared 94.78–98.78% identity with ZYMV isolates (AB004641, AJ420019). This is thought to be the first detection of these potentially damaging viruses of cucurbitaceous crops in Paraguay.