Detection of Multiple Potato Viruses in the Field Suggests Synergistic Interactions among Potato Viruses in Pakistan

Abstract

Viral diseases have been a major limiting factor threating sustainable potato (Solanum tuberosum L.) production in Pakistan. Surveys were conducted to serologically quantify the incidence of RNA viruses infecting potato; Potato virus X (PVX), Potato virus Y (PVY), Potato virus S (PVS), Potato virus A (PVA), Potato virus M (PVM) and Potato leaf roll virus (PLRV) in two major potato cultivars (Desiree and Cardinal). The results suggest the prevalence of multiple viruses in all surveyed areas with PVY, PVS and PVX dominantly widespread with infection levels of up to 50% in some regions. Co-infections were detected with the highest incidence (15.5%) for PVX and PVS. Additionally the data showed a positive correlation between co-infecting viruses with significant increase in absorbance value (virus titre) for at least one of the virus in an infected plant and suggested a synergistic interaction. To test this hypothesis, glasshouse grown potato plants were challenged with multiple viruses and analyzed for systemic infections and symptomology studies. The results obtained conclude that multiple viral infections dramatically increase disease epidemics as compared to single infection and an effective resistance strategy in targeting multiple RNA viruses is required to save potato crop.

Keywords: ELISA; Synergism.

Fig. 1

Viral sampling areas in potato growing regions of northeastern and central Punjab, Pakistan. Sampling areas Pie charts show the detected overall viral prevalence % in two cultivars in each area. One recorded GPS value from a sampling region is shown

Fig. 2

Mixed virus prevalence in samples collected from all locations. Bars with the same letter (b, f and g) are not significantly different (P<0.001) according to LSD All-Pairwise Comparisons Test. The mixed viral infections are compared within each collected leaf sample for general co-infection prevalence.

Fig. 3

Absorbance values for singly and co-infected potato plants cv. Desiree. Detection of (A) PVX, (B) PVY, (C) PVS, (D) PVA, (E) PVM and (F) PLRV. The results are grouped according to viruses present in plants. Positive and negative controls were provided with the kit. Bar represents standard deviation of three replicates and represented with the same letter (a, b and d) are not significantly different (P<0.001).

Fig. 4

Potato plants showing viral symptoms in field condition (A) Desiree; PVX infected (mild mosaic and mottling, greening and vein thickening) (B) Cardinal; PLRV infected (severe upward leaf curling, rugosity) (C) Desiree; PVX and PVS mix infection symptoms (severe leaf thickening, yellowing, mosaic and leaf crinkling) (D) Desiree; plant infected with PVX, PVY and PVS (severe leaf thickening, leaf yellowing and severe upward curling, necrotic lesions, sunken veins and mosaic) (E) Desiree; plant symptoms inoculated with PVX and PVS in glasshouse (Leaf thickening, necrotic lesions, mottling and leaf curling) (F) Desiree; Control healthy plants in glasshouse.