Working Party on Agricultural Quality Standard (WP.7)

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Working Party on Agricultural Quality Standards

LIST OF DISEASES AND PESTS

This text presents a list of the major diseases affecting potatoes, as well as a basic description of each disease and the extent of certification measures for each disease. More detailed information on the symptomology and epidemiology of the diseases can be obtained from the following textbooks:

Compendium of Potato Diseases (2001, 2nd edition). W.R. Stevenson and others, eds. St. Paul, Minnesota, USA, American Phytopathological Society.

European Handbook of Plant Diseases (1998). I.M. Smith and others, eds. Oxford, UK, Blackwell Scientific Publications.

Diseases, Pests and Disorders of Potatoes in Israel (2006, 2nd edition). L. Tsror and S. Warshavsky, eds. Israel Vegetable Growers Organization. Website: www.yerakot.il. E-mail: [email protected].

Fiches descriptives des maladies et ravageurs de la pomme de terre (2000). France, FNPPT (Fdration Nationale des Producteurs de Plants de Pommes de Terre)/GNIS (Groupement National Interprofessionel des Semence et Plants).

Kartoffel-Krankheiten, Schdlinge und Unkruter (2003). W. Radke, W. Reickmann and F. Brendler, eds. Gelsenkirchen, Verlag Thomas Mann.

Maladies et ravageurs de la pomme de terre (1991). W. Radke and W. Rieckmann, eds. Translated and adapted into French by M. Magnenat. Gelsenkirchen-Buer, Verlag Thomas Mann.

Pests and Diseases of Potatoes. A Colour Handbook (2008). Stuart Wale, Bud Platt & Nigel D. Cattlin. Manson Publishing.

Potato Diseases (2005). A. Mulder and L.J. Turkensteen, eds. The Hague, NIVAP. Website: www.nivap.nl.

Disease English	Disease French	Agent	Status in UNECE Standard	Recommended diagnostic method	General disease description	Tuber symptom	Plant syptoms	Comment

FUNGUS

Potato wart disease	Galle verruqueuse	Synchytrium endobioticum	Zero tolerance	Visual observation of tubers and stem base	Tuber: tumours Plant: tumours and galls on stolons and stem base
Late blight	Mildiou	Phytophthora infestans	Tolerance for wet or dry rot	Visual observation of plants and tubers	Tuber: rot at harvest and in storage. A reddish-brown granular rot develops under the skin into the centre of tubers. Plant: necrosis of leaves and stems. Stem lesions of late blight resulting in stem cracking.
Dry rot	Fusariose	Fusarium solani var. coeruleum	Tolerance	Visual observation of tubers and identification on specific medium	Tuber: storage rot. Circular rot with concentric wrinkles and white, orange or blue mycelial growth on surface of rot. Light brown rot with a diffuse edge develops from skin inwards. Plant: non-emergence or weak plants
Dry rot	Fusariose	Fusarium sulphureum	Tolerance	Visual observation of tubers and identification on specific medium	Tuber: storage rot. Small lesions develop at wounds and expand producing symptoms externally similar to gangrenei.e. slighty depressed with a wavy edge. Internally lesions develop cavities filled with grey powdery tissue. Plant: non-emergence or weak plants
Dry rot	Fusariose	Fusarium avenaceum and other F. spp	Tolerance	Visual observation of tubers and identification on specific medium	Tuber: storage rot. Symptoms tend to be similar to those for F.solani var. coeraleum although rots are often smaller and affected tissue is dark brown as illustrated for F.avenaceum Plant: non-emergence or weak plants
Gangrene	Gangrène	Phoma foveata and other Phoma spp.	Tolerance for dry rot	Visual observation of tubers and identification on specific medium	Tuber: storage rot. Initial lesions are round, dark and slightly depressed, often like a thumb mark. As lesions develop they become black and sunken with an irregular wavy edge. Black pycnidia can form on the surface. Rotted tissue is generally brown or black with a well defined margin between healthy and diseased tissue. Cavities are usually lined with purple, yellow or white mycelia. Plant: non-emergence or weak plants			May be regulated without tolerance in some regions
Leak (watery wound rot)	Pythiales	Pythium spp	Tolerance for wet rot	Visual observation of tubers and identification on specific medium	Tuber: rots develop at wounds soon after harvest when growing conditions are hot. Tubers are discoloured with greasy feel. Rots develop in flesh of tuber with a clear dark line separating healthy outer tissue from spongy, soft brown diseased tissue which turns dark on exposure to air.
Pink rot		Phytophthora erythroseptica	Tolerance for wet rot	Visual observation of tubers and identification on specific medium	Tuber: rots develop at lenticels and eyes soon after harvest when conditions have been wet and warm just before harvest.
Rubbery rot		Goetrichum candidum	Tolerance for wet rot	Visual observation of tubers and identification on specific medium	Tuber: rot develops at or soon after harvest in tubers from waterlogged soils. Tuber surface is discoloured with patches of white mycelium developing on surface which feels damp. Internally, a grey, watery rot develops rapidly inwards from skin with a sour milk smell.
Rhizoctonia Black scurf (on tuber)/ Stem canker (on the plant)	Rhizoctone brun	Perfect state: Corticium; imperfect state: Rhizoctonia solani	Tolerance on tubers (black scurf)	Visual observation of plants and tubers	Tuber: blemish caused by dark brown or black sclerotia forming on tuber surface; coverage may be difficult to assess accurately on unwashed dirty tubers. Plant: uneven emergence, wilting and stunting. Stem canker: brown slightly sunken, sharp-edged lesions develop on stem bases. A superficial white powdery collar of fungal growth may be seen on stems just above soil level.			Stem canker regulated in some regions. No need for general regulation because regulation of black scurf is seen as more effective
Silver scurf	Gale argentée	Helminthosporium solani	Controlled indirectly through tolerance for shrivelled tubers	Visual observation of tubers and identification on specific medium	Tuber: skin blemish. Disease starts as small, round, silvery patches on skin. In humid conditions, dark sooty conidiophores can develop around the edge of lesions. Large silvery patches develop as individual lesions expand and merge during storage.			Regulated with tolerance in some regions
Black dot	Dartrose	Colletotrichum coccodes	Controlled indirectly through tolerance for shrivelled tubers	Visual observation of tubers and identification on specific medium	Tuber: skin blemish. Silvery, irregularly shaped lesions present at harvest quickly darken. Lesion is less well defined than silver scurf. Oval, pinhead black bodies (microsclerotia) are often visible on the skin. Growing plant: may contribute to early dying disease in warm climates			Regulated with tolerance in some regions
Skin spot	Oosporiose	Polyscytalum pustulans	Not regulated	Visual observation of tubers	Tuber: skin blemish and death of eyes. Small (1-2 mm), brown-black pimples develop on the skin, usually 2-3 months after harvest, eyes may be killed. Plant: uneven and non-emergence			Regulated with tolerances in some regions. No need for a general regulation, not a barrier to trade.
Early blight	Alternariose	Alternaria solani and Alternaria alternata	Controlled indirectly through tolerances for dry rot	Visual observation of leaves and tubers	Tuber: largely superficial rot Plant: necrosis of leaves
White mould	Sclerotiniose	Sclerotinia sclerotiorum	Controlled through tolerance for dry rot	Visual observation of stem	Tuber: rot at heel end, rare. Internal rot is pale brown with fluffy white mycelia and black sclerotia developing in cavities. Plant: wilting and death of individual stems. Pale green to white, water-soaked lesions develop at base of stem, reddish brown zones develop on these lesions accompanied by growth of woolly, white mycelia in humid conditions.			Not to be regulated. Infection is from soil inoculum and not from the tuber
Powdery scab	Gale poudreuse	Spongospora subterranea	Tolerance	Visual observation of tubers with confirmation by microscope	Tuber: round individual raised scabs present on tubers at harvest, lesions erupt exposing brown powdery tissue (sporeballs) leaving tattered fragments of skin along edge of lesion. Infection at time of eye development can result in outgrowths (cankers) of varying sizes developing at rose end of tubers. Powdery scab spore balls at 250 times magnification.			May be regulated with tolerance in some regions
Verticillium wilt	Verticilliose	Verticillium dalhiae and V. alboatrum	Not regulated	Visual observation of leaves and plant	Tuber: vascular discolouration Plant: wilting and death			No need for regulation in UNECE standard because path of infection is primarily though infested soil and not the seed tuber.

VIRUS

Severe mosaic	Virose grave	Potato viruses Y (all strains), A, V and M, and in combination with PVX and S	Tolerance for severe virus	Visual observation of plant and ELISA test	Plant: distortion or deformation of leaves or plants. This can be rugosity, crinkle, rolling and rigidity of the leaves. Mottling of leaflets may also occur. Tuber: superficial necrosis caused only by PVY strains			Tuber symptoms, regulated with tolerance in some regions
Mild mosaic	Virose légère	PVX, PVS and PVY strains, especially PVY^N	Tolerance for mild mosaic	Visual observation of plant and ELISA test	Plant: discolouration or mottle of leaves without distortion Tuber: superficial necrosis caused only by PVY strains			Tuber symptoms, regulated with tolerance in some regions
Leafroll	Enroulement (Virus E)	Potato leafroll virus (PLRV)	Tolerance for severe virus	Visual observation of plant and ELISA test	Plant: rolling of leaves and stunting Tuber: net necrosis in flesh
Mop top (Spraing in tubers)	Mop top	Potato mop-top virus (PMTV)	Not regulated¹	Visual observation of plant and tubers, ELISA test and PCR	Plant: marked mottling of leaves and stunting of all or some stems. Yellow chevrons and blotching on leaves and stunting of all or some stems. Tuber: necrotic rings or arcs on surface and in flesh			Regulated with a zero tolerance in some regions
Tobacco rattle virus (Spraing in tubers)	Rattle	Tobacco rattle virus	Not regulated¹	Observation of tubers and PCR	Plant: mottling and distortion of leaves and stunting of some or all stems Tuber: brown, corky arcs and spots in the tuber flesh which are sometimes visible on the skin surface			Regulated in some regions with tolerance
Tomato spotted wilt virus	TSWV	Tomato spotted wilt virus	Not regulated		Plant: leaf spotting and necrosis Tuber: skin blemish and internal necrotic spotting			Regulated in some regions with zero tolerance

BACTERIA

Blackleg	Jambe noire	Pectobacterium atrosepticum (syn. Erwinia carotovora subsp. atroseptica) and Pectobacterium carotovorum (syn. E. carotovora subsp. carotovora), Dickeya spp. (syn. E. chrysanthemi)	Tolerance for crop and tuber for wet rot	Observation of plant and tuber	Plant: yellow, rolled upper leaves on blackleg plant; black slimy rots developing on stems. Tuber: watery, soft rot of disintegrating flesh and pungent smell
Ring rot	Flétrissement bactérien, pourriture annulaire	Clavibacter michiganensis subsp. sepedonicus	Zero tolerance	Observation of plant and tuber, test by IF and PCR	Tuber: vascular soft rot Plant: wilting and death
Brown rot	Pourriture brune	Ralstonia solanacearum	Zero tolerance	Observation of plant and tuber, test by IF and PCR	Tuber: vascular soft rot Plant: wilting
Common scab	Gale commune	Streptomyces scabiei and other S. strains, e.g. Streptomyces europaeiscabiei and S. stelliscabiei	Tolerance on the tuber	Observation of tuber	Tuber: superficial, corky, irregular-shaped scabs on tuber surface; in severe cases, cracks may develop on the affected surfaces
Netted scab	Gale plate	Streptomyces europaeiscabiei and Reticuliscabiei	Tolerance on the tuber	Observation of tuber	Tuber: superficial netted scabs

VIROID

Potato spindle tuber viroid	Viroïde des tubercules en fuseau	Potato spindle tuber viroid (PSTV)	Zero tolerance	Observation of plant and tuber. Test by molecular hybridization and PCR	Tuber: elongation of tuber Plant: stunting and leaf rolling

PHYTOPLASMA

Stolbur	Stolbur	Phytoplasma [The principal vectors are leafhoppers (Macrosteles spp, Hyalestes spp)];	Zero tolerance	Visual observation of leaves and tubers	Plant: stunting and leaf rolling			In some regions regulated, zero tolerance

NEMATODES

Cyst nematodes	Nématodes à kystes	Globodera rostochiensis and Globodera pallida	Zero tolerance	Visual observation of the field and testing of soil	Plant: wilting and death
Root knot nematodes	Nématodes à galle	Meloidogyne chitwoodi and fallax	Zero tolerance	Observation of tuber, microscopic examination of cut tuber, and PCR test	Tuber: surface galls and internal necrotic spots			In some regions regulated, zero tolerance
Potato rot nematode	Nématodes libres	Ditylenchus destructor	Zero tolerance	Observation of tuber	Tuber: surface cracking and cortical spotting			In some regions regulated, zero tolerance

PESTS

Colorado beetle	Doryphore	Leptinotarsa decemlineata	Unregulated	Visual observation of eggs, larvae and adults	Plant: leaf damage			In some regions regulated, zero tolerance
Wireworms/ slugs	Taupin	Agriotes sp.: A obscurus, A. sputator, A. lineatus/ Tandonia budapestensis, Arion hortensis	Unregulated	Visual observation of tubers	Tuber: tunnels and holes
Tuber moth	Teigne	Phthorimea opercullella	Unregulated	Visual observation of leaves and tubers	Tuber: leaf Plant: tunnels in flesh damage			In some regions regulated, zero tolerance

1. According to experience in certain areas, the disease can eradicate itself due to low transmission rates