4.2 Monitoring and prognosis models for diseases

Typical symptoms caused by bacteria, fungi, viruses

The signs of diseases are called symptoms.
Symptoms can be local - occurring on individual plant parts - or can affect the entire plant (systemic). Local symptoms include physiological changes in plant structure such as leaf spots and proliferation. Systemic changes manifest as discoloration (e.g., yellowing) or growth changes (compression, broom growth). Symptoms may be primary or secondary regarding their mode of action. Primary symptoms are directly due to the interaction of the pathogen with plant tissue (proliferation). Secondary symptoms are a result of the pathogen's activity. Parts of the plant or the entire plant are affected. An example is wilting of the entire plant due to obstruction of the conduits in the roots by soil-borne fungi in horticulture (Verticillium, Fusarium). he plant or the entire plant are affected. An example is wilting of the entire plant due to obstruction of the conduits in the roots by soil-borne fungi in horticulture (Verticillium, Fusarium).

Symptoms can be microscopic or macroscopic. While microscopic changes are identified by specialists under the microscope, macroscopic symptoms are readily identifiable during visual crop inspection (Table 4.1.).

Table 4.1. Typical macroscopic symptoms caused by bacteria, fungi, viruses (rough symptom classification)

Pathogen group overview
Symptoms	Pathogen and Scientific name of the disease	Transfermode of the disease, Note	Examples
Local: mycelium, fruiting bodies and pustules, leaf spots, discoloration. Systemic: wilt, dieback	Fungi Mycosis	by wind and water (splashing) Pay attention to warning services!	Powdery mildew, downy mildew, Fusarium, Botrytis Viticulture: Erysiphe necator, Esca, Plasmopara viticola Orchards: pear rust, monilia, scab Arable crops: Phytophthora, Septoria,Rust Horticulture: Rhizoctonia, Verticillium, Phytium, Alternaria
Brown spots on leaf, flower or fruit Systemic: Wilt, dieback	Bacteria and phytoplasmas Bacteriosis Phytoplasmosis	by wind, water, vectors and contaminated work equipment. Observe forecast models and climate data	Viticulture: bacterial leaf spot, mildew fruit growing: fire blight, pear decay, curl disease Arable crops: Erwinia, Streptomyces, Stolbur, stone blight, bacterial blight, tuber blight Horticulture: Clavibacter bacterial wilt
Local: chlorotic spots, rings, necroses Systemic: dwarfism, stunted growth, yellowing, wilting, death	Virus Virosis	by vectors (aphid, cicada, beetles, fringed aphids, nematodes), contaminated plant material (rootstock, pollen, seeds, tubers), and contaminated implements	Viticulture: AMV, ArMV Fruit growing: apple mosaic virus, broomrape, bark canker Arable crops: Y- and S-virus, PNYDV (nanovirus) Horticulture: TSWV, CABYW

Pay attention to warning services!

Table 4.2. Symptom description of the most important/frequent pathogens in viticulture

Early symptoms		Late stage and other associated symptoms		Pathogen
Rough symptom classification and example picture showing typical symptoms	Description	Rough symptom classification	Description
Leaf spots © biohelp	Bright spots on the top side of leaves that appear dark when backlit	Fungal growth	Whitish gray fungal mycelium layer on underside of leaves	Fungus:Downy mildew (Peronosporales): Plasmopara viticola
	Brown spots on leaf, flower or fruit	Fungal growth	Superficial gray coating; spreading to the whole plant	Fungus:Gray mold : Botrytis
	Chronic: Irregular yellow spots between leaf veins	Death	Leaf necrosis Acute: Death of the plant	Fungus:Esca (fungi complex)
Powdery cover © biohelp	Whitish-gray fungal mycelium layer on lower leaf surface. Later like powdery white lawn "powdery mildew" on the upper side of the leaf.	Fungal growth	Infestation of the previous year: Erysiphe necator figures on 2-year-old wood (extensor-shot) First symptoms of infestation on pointer shoots (= infected stingy shoots) Infestation of the grape: fungal edge on ridges (stems) spreads from there over the berries, seed breakage as a consequence	Fungus: Powdery mildew: (Erysiphe necator)
Discoloration and growth deformation © biohelp	Delayed budding in spring, partial or complete yellow discoloration of the leaf blade, various leaf deformations, shortened internodes and zigzag growth.		Weak growth, scimitar, broom growth; changes and abnormal branching of the vine wood, small berries and increased trickling.	Virus: Grapevine fanleaf virus + Arabis mosaic virus
	The oldest leaves curl downward, at the same time the leaf blades begin to turn yellow (white wine varieties) or dark red (red wine varieties) from the edges		In the final stage, only the main veins with their fringes remain green; symptom continuation along the shoots. Growth depression; increased trickling of the shoots	Virus: Grapevine leafroll virus GLRaV 1+3
	Light coloration of leaf veins in young leaves		Mosaic-like patterns on older leaves, curvature	Virus: Marbling of the vine (Grapevine fleck virus GFkV)
	Growth deformation: crippled shoots, shortened internodes, deformed, chlorotic leaf spots		Reduction quality and quantity of the yield	Virus: Ruländer disease (Grapevine Pinot gris virus)
	Stem and branch changes			Virus: Wood rot, corky bark disease (Grapevine virus A + B)

Table 4.3. Symptom description of the most important/frequent pathogens in orchards

Early symptoms		Late stage and other associated symptoms		Pathogen	Culture
Rough symptom classification and example picture showing typical symptoms	Description	Rough symptom classification	Description
Leaf spots © biohelp	Bright spots on the top side of leaf	Fungal growth	White fungal mycelium mostly on the top side of leaves - can be easily wiped off; spread to all parts of plant; stunted growth, brown discoloration and drying of leaves/plant	Fungus:Powdery mildew (Erisiphiaceae)	Orchards
	Bright spots on the top side of leaves that appear dark when backlit		Whitish gray fungal mycelium layer on underside of leaves	Fungus:Downy mildew (Peronosporales) - species group!	Orchards
	Brown spots on leaf, flower or fruit		Superficial gray coating; spreading to the whole plant	Fungus: Gray mold (Botrytis cinerea)	Orchards (strawberry)
	Rust colored spots	Pustules	Pustules on leaves, breaking open pustule-shaped spore deposits; death of plant parts	Fungus:Rust fungi (Pucciniales)	Apple, pear, plum
	Dull olive green, later brown or humped blackish spots on leaves	Necroses	Coalescence of spots, necrosis, leaf fall,cracked corked fruit skin	Fungus: Apple scab (Venturia inaequalis)	Apple
	Small, angular, watery spots bordered by the leaf veins, appearing translucent in backlight and black in incident light	Mucus secretion and death	Symptom spread to whole leaf, leaf dieback, mucus discharge	Bacterium: angular leaf spot (Xanthomonas fragariae)	Strawberry
	Shot-like, translucent symptoms with yellowish border	Lesions	Grooved, sunken, black-red lesions on bark of trunk and branches	Bacterium:Bacterial canker (Pseudomonas syringae pv. morsprunorum)	Stone fruit (plum, cherry)
Discoloration and growth deformation © biohelp	Curling and blistering of young leaves with partial red discoloration		Severe curling of leaves, chlorosis; reduction of fruit	Fungus:Curl disease (Taphrina deformans)	Peach, Nectarine
	Brown/black coloration and wilting from the petiole, bending of the shoot tips	Mucus secretion and death	Leakage of bacterial slime, death of the plant between a few weeks (young plants) and a few years	Bacterium: Fire blight (Erwinia amylovora)	Pome fruit
	Premature sprouting, chlorotic leaf rolling		Early leaf drop, Necrosis of phloem, Abnormal fruit development and early fruit drop	Phytoplasma:European Stone Fruit Yellows (ESFY, Candidatus phytoplasma prunorum)	Stone fruit
	Early shoots with red leaf tips, stipules enlarged		Autumn color already in summer, broom-like branching of one-year-old shoots "witches broom"	Phytoplasma: Apple shoot blight (Candidatus phytoplasma mali)	Apple
	Spots, ring spots (leaf, fruit, core), broom growth			Virus: E.g.: Cherry: hundreds of virus species, Raspberry 280 viruses)	Orchards
Wilt © biohelp	Shoot tip dieback		Gum flow; fruits turn brown, dry up and show white fruit bodies	Fungus: Monilia (Monilia spp.)	Orchards
Wilt © biohelp	Withered leaves	Death	Death of the entire plant	Fungus; soilborne: Verticillium wilt (V. dahliae)	Raspberry, Strawberry, cherry

Table 4.4. Symptom description of the most important/common pathogens in arable crops

Early symptoms		Late stage and other associated symptoms		Pathogen	Culture
Rough symptom classification and example picture showing typical symptoms	Description	Rough symptom classification	Description
Leaf spots © Penn State Dpt. of Plant Pathology	Bright spots on the top side of the leaf	Fungal growth	White fungal mycelium mostly on the top side of the leaves- can be easily wiped off; spread to all parts of plant; stunted growth, brown discoloration and drying of leaves/plant	Fungus:Powdery mildew (Erisiphiaceae)	Arable farming
	Brown irregular spots on leaves		Brown spots on stems and fruits; White-gray fungal mycelium on underside of leaves; Rotting or withering of leaves, rotting of fruits and tubers	Fungus: Downy mildew: Late blight; (Phytophthora infestans)	Tomato, potato
	Brown spots on leaf, flower or fruit		Superficial gray coating; spreading to the whole plant	Botrytis, gray mould (Botrytis cineraria)	Arable farming
	Rust colored spots and pustules on leaves	Pustules	Breaking open pustule-shaped spore deposits; death of plant parts	Fungus:Rust fungi (Pucciniales)	Cereal, asparagus, bean, pea, leek
Leaf spots © biohelp	Oval, yellow-green, chlorotic spots on the lower leaves	Necroses	Gray-green streaky necrosis, leaf drought, black fruiting bodies on upper and lower leaf surfaces	Fungus: Septoria leaf spot (Septoria tritici)	Cereals
Wilt © biohelp	Fading and/or wilting of leaves or fruit clusters	Sporenbelag	Discoloured spikelets and orange coloration of lemmas due to spore coatings in cereals; yield reduction	Fungus; soilborne: Fusarium head blight and stem and ear rot	Cereals, corn
	Withered leaves	Death	Death of the entire plant	Fungus; soilborne: Verticillium wilt (V. dahliae V. longisporum on cabbage)	Sugar beet, hops, sunflower. Peas, beans, cabbage
	Withered leaves	Death	Death of the entire plant	Fungus; soilborne: Fusarium wilt	Onion, cabbage, spinach, cucumber, pea, bean
	Necrosis and strangulation of seedlings, wilting symptoms	Death	Overturning of seedlings, death of above- and below-ground plant parts	Fungus; soilborne: Rhizoctonia falling sickness, stem rot (R. solani, R. sp.), beet rot (R. solani* AG 2-2)*	Arable farming
Discoloration and growth deformation © Howard F. Schwartz, Colorado State University, Bugwood.org	White stem base (whitelessness), curling of the top leaves		Air nodules, nodule deformation, Dry core	Fungus; soilborne: Rhizoctonia(R. solani AG 3)	Potato
	Chocolate-brown necroses on the leaves (drought spots, spray spots)	Necroses	Coalescence of necroses, destruction of leaf mass, partial stains on stems	Fungus; soilborne: early blight (Alternaria sp.)	Potato
Growth deformation © Central Science Laboratory, Harpenden , British Crown, Bugwood.org	Cauliflower-like cell growths on the tuber	Spore covering	Black spore powder from growths; yield loss, crop failure	Fungus: Potato canker (Synchytrium endobioticum)	Potato
Smell © Howard F. Schwartz, Colorado State University, Bugwood.org	Fishy odor in wheat	Spore covering	Instead of spikes, black-brown spore deposits are formed	Fungus: stinking smut (Tilletia spp.)	Cereals
Rot © Howard F. Schwartz, Colorado State University, Bugwood.org	Muddy, slimy rot on tuber, turnip, stem or leaves, unpleasant odor	Death	Complete rotting of the stored part of the plant	Bacterium: Bacterial, tuber wet rot, soft rot, blackleg of potato (Pectobacterium carotovorum)	Potato,carrot, cabbage, celery
Discoloration and growth deformation © biohelp	Leaf yellowing, dwarfism, leaf deformation and curled leaves	Necroses	Necrosis, dieback	Virus: Pea necrotic yellow dwarf virus (PNYDV)	Native legumes. alfalfa and soybean not affected!
Discoloration and growth deformation © biohelp	Discoloration, necrotic spots on leaf and stem		Flesh discolored such brown	Virus: tobacco rattle virus (TRV)	Potato

Table 4.5. Symptom description of the most important/common pathogens in horticulture

Early symptoms		Late stage and other associated symptoms		Pathogen	Culture
Rough symptom classification and example picture showing typical symptoms	Description	Rough symptom classification	Description
Leaf spots	Bright powdery spots on the top side of the leaf	Fungal growth	White fungal mycelium mostly on the top side of the leaves - can be easily wiped off; spread to all parts of plant; stunted growth, brown discoloration and drying of leaves/plant	Fungus:Powdery mildew (Erisiphiaceae)	Horticulture
	Bright spots on the top side of leaves		Whitish gray fungal mycelium layer on underside of leaves	Fungus:Downy mildew (Peronosporales) - species group!	Horticulture
	Brown irregular spots on leaves		Brown spots on stems and fruits; White-gray fungal mycelium on underside of leaves; Rotting or withering of leaves, rotting of fruit	Fungus:Late blight (Phytophthora infestans) - type of downy mildew!	Tomatoe
	Brown spots on leaf, flower or fruit		Superficial gray coating; spreading to the whole plant	Fungus: Gray mold rot (Botrytis cinerea)	Strawberry, Cucumber
Leaf spots © biohelp	Yellowish, blurred brightenings on the upper side of the leaf	Fungal growth	Patches of gray-brown to olive-green mycelial coating on the underside of leaves	Fungus: Velvet spot	Tomato
Leaf spots © biohelp	Slight lightening of the veins, faintly visible concentric rings on the leaf, stem and fruit. Depending on the variety, the color and shape of the spots differ	Growth deformation	Fruit deformation	Virus: Tomato spotted wilt virus (TSWV)	Tomato, bell pepper
Discoloration and growth deformation © biohelp	Older leaves become chlorotic, leaf thickening and brittle leaves		Entire plant may become chlorotic, Reduced fruit set, Fruit shedding	Virus: Cucurbit aphid-borne yellows virus (CABYV)	Horticulture
Wilt © biohelp	Withered leaves	Death	Death of the entire plant	Fungus; soilborne: Verticillium wilt (V. dahliae* and V. albo-atrum)*	Cucumber, tomato
	Welken von B Withered leaves lättern			Fungus; soilborne: Fusarium wilt	Cucumber, tomato
	Discoloration and strangulation of seedlings and young plants at the root neck			Fungus; soilborne: Pythium root rot (Pythium sp.)	Horticulture
	Necrosis and strangulation of seedlings, wilting symptoms		Overturning of seedlings, death of above- and below-ground plant parts	Fungus; soilborne: Rhizoctonia damping-off (R. solani, R. sp.)	Horticulture
	Leaf parts wilting		Dieback of plant parts, bird's eye spots on fruit	Bacterium: Bacterial wilt (Clavibacter michiganensis)	Tomato, bell pepper