Potato leafroll

Potato leafroll is a viral disease of potato caused by Potato leafroll virus (PLRV). Infected plants may become upright, stunted, pale and stiff, with leaf margins rolling upward. Symptoms from infected seed tubers usually begin in the lower leaves, while aphid-transmitted infections often appear first in young upper leaves. Some cultivars develop internal tuber net necrosis, reducing yield and market quality.

Potato leafroll is most important in potato production because infection can reduce plant vigor, tuber yield and tuber quality. Disease expression varies with virus isolate, potato cultivar, plant age and infection timing.

Plants arising from infected seed tubers generally show the most severe symptoms. Aphid-transmitted infections may be less obvious, particularly when infection occurs late in the season. Visual diagnosis can overlap with other causes of leaf rolling, chlorosis and stunting, so laboratory testing is advisable for seed-production, certification or uncertain cases.

Plants from infected seed tubers:

• Upright, rigid or slightly stunted growth.
• Lower leaves roll upward along the margins, become stiff, brittle or leathery, and may yellow or die prematurely.
• Leaves may produce a dry, parchment-like rattling sound when shaken.
• Symptoms can progress from older lower leaves toward the upper canopy.

Current-season aphid infection:

• Young upper leaves may become pale, upright and upward-rolled.
• Leaf margins can show reddish or purplish discoloration, depending on cultivar and conditions.
• Late infections may produce weak or unapparent foliar symptoms.

Tubers: Some cultivars develop internal phloem or vascular net necrosis, seen as brown, net-like strands or translucent brown discoloration, often concentrated near the stem end. Tubers may look normal externally.

The causal organism is Potato leafroll virus, a virus that moves through the plant’s phloem. The main sources are infected seed tubers, volunteer potatoes, cull piles and infected plants left in or near the crop.

PLRV is transmitted persistently by aphids. The green peach aphid, Myzus persicae, is generally the most efficient vector; the potato aphid, Macrosiphum euphorbiae, can also transmit it. After acquiring the virus from an infected plant, an aphid retains it for life and can transmit it while feeding on healthy potato plants. PLRV is not normally spread by routine mechanical contact or pruning tools, unlike some mechanically transmitted potato viruses.

PLRV survives between seasons mainly in infected living potato tissue, especially seed tubers and volunteer plants. In spring, infected tubers produce infected plants that serve as virus reservoirs. Aphids acquire the virus while feeding in phloem tissue; after a latent period within the aphid, the virus reaches the salivary glands and can be inoculated into another plant during feeding.

Winged aphids can carry PLRV into fields over considerable distances, while wingless aphids contribute to local plant-to-plant spread. Virus movement within the potato plant follows the phloem. Daughter tubers produced by infected plants may carry the virus into the next crop.

There is no treatment that cures a potato plant after it becomes infected. Remove and discard infected plants and do not use their tubers as seed. In commercial production, protect future crops by combining certified seed, early roguing, volunteer and cull-pile management, cultivar selection and aphid monitoring.

Aphid control can reduce secondary spread, particularly when directed at colonizing vector populations, but it cannot reliably prevent every introduction by migrating aphids. For valuable seed lots or uncertain diagnoses, submit symptomatic tissue or tubers to a state plant diagnostic laboratory or qualified plant virology laboratory.

• Use certified disease-free seed and remove volunteer potatoes, cull piles and symptomatic plants.
• Use reflective or aluminized mulch where appropriate for the crop and site; it may reduce aphid landing and virus spread but is not a complete control.
• Maintain weed sanitation around potato plantings.
• Conserve lady beetles, lacewings, syrphid larvae and parasitoids by avoiding unnecessary broad-spectrum insecticide use.
• Use insecticidal soaps or horticultural oils only when specifically permitted and practical for the crop, understanding that they may suppress aphids but do not cure infected plants and may not stop transmission by every incoming aphid.

• Plant only certified, virus-tested seed potatoes from a reputable supplier; do not save planting tubers from symptomatic garden plants.
• Choose cultivars with useful resistance or tolerance where locally available, recognizing that susceptibility and symptom expression vary by cultivar.
• Remove volunteer potatoes and destroy cull piles before crop emergence.
• Rogue clearly symptomatic plants early, bagging and removing them rather than leaving them in the field.
• Control weeds and unmanaged solanaceous hosts around production areas when they can harbor aphids or virus.
• Monitor aphids with regular crop scouting and use regional extension thresholds and recommendations.
• Separate seed-production areas from home-garden or cull-potato areas whenever practical.

• PLRV is the type species of the genus Polerovirus.
• Secondary infections from infected seed tubers are often more severe than infections acquired late through aphid feeding.
• Internal net necrosis may develop during storage even when the tuber looked normal at harvest.
• Some infected potato plants show few visible symptoms, so appearance alone is not reliable for seed certification.
• PLRV differs from many potato viruses because it is not normally mechanically transmitted by handling or cutting equipment.