Potato Leaf Roll Virus (PLRV) is a significant plant pathogen that impacts potato crops globally. This viral disease primarily affects potatoes, but can also infect other plants within the Solanaceae family. PLRV is a phloem-limited, positive-sense RNA virus, meaning it resides within the plant’s food-conducting tissues. First identified in 1916, PLRV remains a persistent challenge for potato growers worldwide.
Recognizing the Infection
The symptoms of potato leaf roll virus can vary based on the potato variety, environmental conditions, and the timing of infection. Plants infected during the current growing season, known as primary infection, often show symptoms first in their youngest leaves. These leaves may become pale green or yellow (chlorotic), and their margins can curl inwards towards the center.
For plants grown from infected seed tubers, referred to as secondary infection, symptoms are more severe and appear earlier. The entire plant may be stunted and exhibit an upright growth habit. Lower leaves show pronounced upward rolling, becoming stiff and leathery to the touch, often producing a cracking sound when crushed. These older leaves can also develop a purple or reddish discoloration, particularly along their edges, due to the accumulation of anthocyanin pigments.
Beyond the foliage, PLRV can cause internal defects in potato tubers. The most notable of these is net necrosis, characterized by small, brown, necrotic spots or strands scattered throughout the tuber’s vascular tissue. This internal discoloration may not be immediately visible at harvest but can develop and worsen during storage.
How the Virus Spreads
Potato leaf roll virus spreads primarily through insect vectors, particularly aphids. The green peach aphid (Myzus persicae) is the most efficient vector for PLRV transmission. Aphids acquire the virus by feeding on the phloem of infected plants. The virus then circulates within the aphid’s body, moving from its digestive system to its salivary glands, a process known as persistent transmission.
Once an aphid becomes viruliferous (capable of transmitting the virus), it can continue to transmit PLRV for the remainder of its life. This persistent nature means that even a single infected aphid can pose a significant threat to a healthy potato crop. Winged aphids can carry the virus over long distances, facilitating widespread infection, while wingless aphids contribute to plant-to-plant spread within a field.
Another significant way PLRV is propagated is through infected seed potatoes. If tubers from an infected plant are used for planting, they will produce infected plants in the subsequent growing season. This cycle of planting infected seed tubers provides a direct and consistent source of the virus within a field, making it an important factor in disease management.
Managing the Virus
Managing potato leaf roll virus involves an integrated pest management (IPM) approach that combines several strategies to minimize its spread and impact. Using certified virus-free seed potatoes is an important step, as this prevents the introduction of the virus from the outset.
Controlling aphid populations is another important management component, given their role as primary vectors. Insecticides, both systemic and foliar, can be applied to reduce aphid numbers. Reflective mulches can also deter aphids from landing on plants.
Removing and destroying infected plants, a practice known as roguing, helps reduce the source of the virus within a field. This includes volunteer potato plants from previous seasons and cull piles, which can harbor both the virus and aphid vectors. Selecting potato varieties that exhibit resistance to PLRV or are less susceptible to net necrosis can also significantly reduce losses.
Implementing good field sanitation practices, such as controlling weeds that can serve as alternative hosts for the virus or aphids, further supports overall disease management. Early detection of symptoms and prompt action are important, as infected plants cannot be cured.
Impact on Potato Production
Potato leaf roll virus can lead to substantial reductions in potato yield and quality, significantly affecting growers’ profitability. Infected plants often produce smaller and fewer tubers, leading to yield losses that can range from 33% to over 50% in individual plants. The overall global impact is estimated at around 20 million tons of potatoes lost annually due to PLRV.
Beyond reduced yield, the virus severely impacts tuber quality, making them unmarketable. The most significant quality defect is net necrosis, an internal browning that renders tubers unsuitable for fresh consumption, processing, or use as seed. This symptom occurs in susceptible varieties.
The presence of net necrosis can lead to significant economic losses for growers, as affected tubers are often rejected. This necessitates increased production costs due to disease management efforts, including scouting, aphid control, and the purchase of certified seed. The cumulative effect of yield reduction and quality degradation poses a considerable challenge to potato farming.