PPDL Picture of the Week for
October 29, 2012

Papaya Ring-Spot Virus on Pumpkin

Dan Egel, Extension Vegetable Specialist, SWPAC, Purdue University

I was delighted when I first observed the pumpkins in Figure 1.  These mini pumpkins, each about the size of the palm of your hand, are colored the expected yellow/orange. In addition, however, each pumpkin is streaked with a unique green pattern. The green mosaic designs that so fascinated me caused distress to the grower who could not sell the pumpkins to a retail outlet. The grower wanted to know what caused the green areas of the pumpkin that did not mature to the proper color.

The green symptoms on these pumpkins are caused by a virus known as Papaya Ring-Spot Virus (viruses are named for the plant in which it was first found). The virus is spread from plant to plant by an aphid, a small green insect with piercing-sucking mouthparts. Research at Purdue University, however, has indicated that applying insecticides to kill the aphid cannot stop spread of the virus to neighboring plants. The virus can be transmitted to the plant in seconds, making insecticide applications ineffective. Instead, planting early in the season may result in fewer virus symptoms since pumpkins are formed before virus symptoms become severe. In addition to mosaic patterns shown in figure 1, symptoms of virus on pumpkins include bumpy/uneven surfaces (Figure 2) and reduced yields. Viruses may also cause a mosaic symptom on leaves (Figure 3).

Whether one finds the appearance of the pumpkins in figure 1 enchanting or scary, know that the virus doesn’t affect humans or cause the pumpkin to become rotten. It’s just the appearance of the pumpkin that is changed...like a costume!

Click image to enlarge

Figure 1. Mini pumpkins with green streaks

Figure 1

Figure 2. Green bumpy pumpkin

Figure 2

Figure 3. Mosaic symptoms in leaves

Figure 3

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service