POTATO LEAF ROLL

Causal organism: Potato leaf roll virus (Acronym: PLRV)
This virus rarely exterminates the plant like Virus Y, but causes hard yield losses and is responsible in part for the decline of potato.

Host range: Potato and all crops and weeds from the family Solanaceae.

Occurrence and importance:
This virus occurs everywhere within the EU and in other European and neighbouring states. The virus may cause serious yield losses, very small and few tubers, but exterminates the whole plant like Virus Y only rarely. Leaf roll is responsible along with other viruses for the decline of potato and the retiring of old potato varieties.

Symptoms and mistakable diseases:
The potato leaf roll virus (known from its name) causes a very well visible leaf rolling up: the leaflets are curled up to form a small boat. Infected plants are dwarf, the leaves are very fragile, and the whole plant is light, etiolated, just like antocyanotic varieties (Symphonia, Dura). Some varieties have a hard yellowing reaction. Leaf rolling usually begins at the top of the plant. Cutting across the stems, there are some necroses in the external part, under the skin of the stem.

Leaf roll symptom has several causes: appearance of potato stollbur phytoplasma, root infection by Fusarium spp., Rhizoctonia solani or Colletotrichum atramentarium often cause leaf roll, but always with a smaller-bigger wilt. This symptom occurs at a hard cyst- or root-knot nematode attack. Fragile leaves, leaf roll and lighter colour together ease detection, in presence of these 3 symptoms the potato leaf roll virus infection is absolutely sure. Leaf roll virus may occur in the plant together with other viruses, so their symptoms may be mixed.

Disease cycle:
The potato leaf roll virus overwinters in infected seed potato tubers and in perennial solanaceous weeds. The overwintering form, the egg of the aphids is not infected. The virus is persistent but not propagation persistent; infected vectors keep their infection ability until the end of their lives. Infected, overwintered plants and stored tubers are infection sources; aphids, first of all green peach aphid (Myzus persicae) are vectors. The virus is persistent, so transmission needs longer time, but the vector keeps its ability upto the end of its life.

Control:
The control of the potato leaf roll virus depends on variety, agri-technical and chemical base. Resistance against this virus is not complete, there are no absolutely resistant (immune) varieties, but there are a lot of registered varieties that have good resistance against the virus. The Santé, White Lady and other resistant varieties have very small virus infection rates year after year. Use of such varieties an inexpensive and very effective method. The use of state-certified seed material is a useful way too. These seed potatoes have a low pathogen infection guaranteed by the state.
In seed potato production, good isolation may be useful. Greater distance between seed potato and other solanaceous planted fields may slow down the spreading of virus infection. Taking care to perennial solanaceous weeds (Lycium halomifolium, Solanum dulcamara) is also advantageous.
Chemical control against aphids is useful against this virus. Since the potato leaf roll virus is persistent, the transmission of the virus is particularly much slower than the effect time of insecticides. So these products can kill aphids during suction, before the start of virus transmission. Effective insecticide seed dressing materials and spraying products are listed in the table on aphids.