Potato Virus Y (PVY) Potatoes South Africa / Introduction The causal agent of Potato Virus Y is a filamentous virus of the genus Potyvirus and family Potyviridae. Infected seed  potatoes, volunteer plants and some weeds can all be sources of this virus. Transmission is mainly by aphid vector, although  some mechanical transmission may also occur. There are three main groups of PVY strains: PVYO (ordinary type), PVYC   (stipple streak strain) and PVYN (tobacco veinal necrosis) . PVYNTN (potato tuber necrotic ringspot disease) is a new strain  that causes tuber necrosis. Symptoms Potato virus Y causes a range of symptoms from mild defoliation to death, depending on the virus strain, potato cultivar and  environmental conditions. It ranges from virtually none (latent), to noticeable stunting and mosaic symptoms to severe foliar  damage and even death of the entire plant.      Infection type   Virus strain Primary Secondary   PVYO 1. Mosaic & yellowing of leaves 1. Small brittle plants     2. Necrosis of stems 2. Leaves rugose     3. Leaf drop 3. Necrosis may occur       4. Mosaic difficult to distinguish     at low and high temperatures PVYC 1. Necrosis 1. Necrosis 2. Mosaic 2. Mosaic 3. Rugose leaves 3. Rugose leaves 4. Stipple streak (necrotic 4. Stipple streak also on tubers     lesions on leaves and stems)   PVYN 1. Milder mosaic and yellowing 1. Clear mosaic   PVYNTN  1. Usually moderate mosaic 1. Clear mosaic 2. Necrotic lesions 2. Necrotic lesions Transmission PVY is spread by aphids in a non-persistant manner. The stylets of the aphids carry PVY particles after feeding on an infected  plant and when they subsequently feed on a healthy plant they infect this with their contaminated stylets. In the case of non-  persistently transmitted viruses, aphids are virus-free again after 1 - 2 hours. The aphids thus acquire the virus from infected  plants and lose it quickly when they probe healthy plants. The green peach aphid, Myzus persicae, is the most effective  vector.  Hosts Potato virus Y (PVY) infects a range of solanaceous crops including potato, capsicum, tomato and tobacco. Carryover is  mainly via potato tubers (seed tubers or volunteers).  Control The use of insecticides is largely ineffective in the control of PVY, because they do not act fast enough to kill aphids quickly and thereby prevent virus spread. Methods of control include: Planting of certified disease free seed potatoes Spatial isolation of seed potato production from ware potato production Planting of border crops in order for aphids to lose their virus inoculum before moving into potato The eradication of aphid weed hosts especially other solanaceous plants Growing crops in regions where aphid pressure is low Refraining from growing new crops in proximity to established crops that might act as an infection source The destruction of volunteer potatoes as it may harbour the virus The destruction of haulms of seed potato crops before maturity, to prevent late infections spreading to tubers that are developing The application of non-toxic mineral oils have shown to reduce PVY transmission Roguing: the immediate removal and destruction of infected plants as well as adjacent plants
Viral disease