TOMATO - FUNGUS

LATE BLIGHT

Pathogen: Phytophthora infestans
Host range: Tomato and potato may be severely affected.
Importance: Late blight is a most destructive disease of tomato, damaging both leaves and fruits. The pathogen spreads very quickly in cold and rainy weather. It occurs in all European countries and also in tropical and subtropical regions where tomato is cultivated at higher altitudes.
Under favourable conditions, leaves very rapidly die without previous yellowing.

33. Figure: Phytophthora infestans

Source: project number: HU/02/B/F/PP-136012

Symptoms:

When infested by late blight, leaves typically turn browning and necrotic and a brown, dry rot develops on the fruits. The first symptoms usually appear on leaf tips and margins where drops of water persist as indefinite water-soaked lesions. Infested leaves turn necrotic very quickly as the disease progresses, usually without any yellowing, and plants may die in a matter of a few days. In the mornings or after long wet periods, the sporangiophores may form a white layer on the underside of leaves, on the border between healthy and necrotized areas.

34. Figure: Phytophthora infestans

Source: project number: HU/02/B/F/PP-136012

Stems and petioles can also be affected; the disease manifests here in the form of dark brown spots. Infected fruits bear dark, olivaceous spots which may cover the entire fruit. At the beginning, these spots are dry to the touch, but secondary infections by other microorganisms may result in wet rot. A white layer of sporangiophores may also appear on fruits if weather is cold and wet, usually at the end of summer.
The symptoms of late blight may be confused with those of Alternaria. Main differences: the spots caused by Alternaria are darker, usually smaller and, most importantly, they feature concentric rings. Alternaria prefers a warmer and drier weather, compared to late blight.

35. Figure: Phytophthora infestans

Source: project number: HU/02/B/F/PP-136012

Late blight on fruits. When the fruit is only infested by Phytophthora infestans, the flesh stays rather firm; however, secondary infections may lead to the development of soft rot. White mycelial growth may also be present on infected parts in wet and cold weather.

36. Figure: Phytophthora infestans

Source: project number: HU/02/B/F/PP-136012

Late blight inside the tomato fruit. Note the dry rot and the white mycelial growth.

37. Figure: Phytophthora infestans

Source: project number: HU/02/B/F/PP-136012

Disease cycle: The overwintering oospores of the fungus in potato tubers and potato plants are probably the only source of infection. Overwintering as oospores in tomato plant debris has not been proven for all European countries. From potato stands and volunteer plants, sporangia are carried to tomato plants by wind. Sporangia form at high humidity (90-100 %), when the temperature is between 3-26 °C. Tissue infection only takes place in the presence of water, through either the upper side or underside of leaves. Zoospores released from sporangia germinate the most rapidly at 12-15 °C, but their further development requires temperatures above 20 °C. This is why cool nights combined with warm days are ideal for late blight development. If humidity is not so high, sporangia behave as conidia i.e. a single infective hypha emerges from them. Temperatures above 30°C are unfavourable for the fungus.

Control:
The main method of protection is the application of effective fungicides, but some other methods may also be helpful.
Cultivation practices:

avoid cultivation in wet localities (closed valleys, vicinity of forests and water surfaces) sunny fields should be preferred; sunshine is particularly important in the morning to dry the dew from the plants,
keep the canopy upright and provide for adequate spacing so that air can move freely among the plants.
if possible, avoid overhead irrigation,
do not grow tomato in the vicinity of potato,
remove and destroy infected plants,
varieties: the leaves of some varieties are partially resistant, yet the fruits can be infected. Consult your seed dealer.
chemical control (new systemic fungicides e.g Azol and sulphuric plant protection products)

EARLY BLIGHT

Pathogen: Alternaria solani
Host range: Potato and tomato.
Importance: Early blight occurs wherever tomatoes are grown, but it causes severe damage in a few regions only.
Symptoms: At the early stage, Alternaria spots are characterised by concentric rings and they are rather dry. Later on, the spots may be invaded by secondary microorganisms and develop wet rot. Early blight usually attacks older fruits at the beginning of ripening. Early blight on an older leaflet, in the early stage. Note the dark brown spots with concentric rings.

38. Figure: Alternaria solani on leaf

Source: project number: HU/02/B/F/PP-136012

Typically, large dark brown spots with concentric rings (up to 1 cm or even more) develop on the leaves, which may emerge to form large, necrotic zones. Spots may be covered by a dark layer formed by conidiophores with conidia. Spots may be surrounded by a yellow halo.

Early blight on old leaf, late stage. Note the yellowing tissue around spots and the necrotic zones on leaf, typically appearing in the final stage.

39. Figure Alternaria solani on leaf

Source: project number: HU/02/B/F/PP-136012

40. Figure Alternaria solani brown spot on leaf

Source: project number: HU/02/B/F/PP-136012

Eventually, infected leaves may die. The fungus attacks the older leaves first. On stems, the lesions are small, dark and slightly sunken at first, then they extend and develop concentric rings. In some cases, lesions may girdle the stem and kill the entire plant. Fruits develop dark brown to black spots, starting at the calyx.

Tomato rot caused by early blight (Alternaria solani). Note that the symptoms first appear around the calyx. It starts as a dry rot, but secondary infections later on may turn it into a wet rot.

41. Figure Alternaria solani on fruit

Source: project number: HU/02/B/F/PP-136012

Disease cycle: A.solani usually survives in plant debris and on seeds, although in regions with mild winters volunteer plants, potato and Solanaceous weeds may also serve as overwintering hosts. Heavy dew or frequent rains favour the germination of spores. Temperatures between 25-30 °C are optimal for disease development.

Control:

avoid overhead irrigation, if possible,
crop rotation,
use pathogen-free seeds,
proper fertilization,
the most effective control is provided by fungicides. Use fungicides complying with EU regulations, e.g. Polyram DF contact treatment or material containing metiram as active ingredient.

DAMPING OFF

Pathogen: Several fungi (Pythium, Phytophtora, Fusarium, Botrytis, Sclerotinia, Alteraria)
Host range: A broad range of cultivated dicot plants.
Importance: Damping off is a very common condition that severely affects transplants.
Symptoms: Seedlings fail to emerge or a large number of them suddenly die. The stems and leaves of young plants appear water soaked and soft. Often, they become discoloured, greyish or brown. Young leaves wilt. Roots are missing or covered with brown lesions.
Disease cycle: The fungi causing damping off easily survive in soil and plant debris and on improperly cleaned and sanitized tools, equipment etc. used in the previous growing season. Pythium in particular is often transmitted by contaminated tools and hands. Spores may by carried by the wind and infect plants from splashing water (rain, irrigation).
Control: General sanitation methods are of paramount importance. When growing transplants, use clean, sterilized pots, tools and medium. Do not use garden soil. The planting medium should be light and fast draining. Provide for sufficient air circulation and illumination. When planting outdoors, make sure the temperature has reached the optimal range for young plants. Irrigate in the early hours so that the plants can dry before the evening.

LEAF SPOT OF TOMATO

Pathogen: Septoria lycopersici

Host range: most commonly found on tomato
Importance: A devastating and globally occurring disease of tomato, able to infest plants at any stage of their development.
Symptoms: The spots caused by Septoria typically appear on the older leaves first. The disease then spreads upwards, towards the younger parts. The spots are circular or somewhat angular, 2-5 mm in diameter, with dark brown margins and lighter brown to grey centres (they look like rings). Unlike those caused by early blight, Septoria spots do not have concentric rings.

42. Figure Septoria lycopersici

Source: project number: HU/02/B/F/PP-136012

Typical Septoria spots with a dark ring around the pale central part on older leaves.

Disease cycle: The fungus overwinters in plant debris incorporated into the soil which will be the most important source of infection in the next season. It may also survive on solanaceous weeds or even on tools and equipment such as stakes etc. Spores are spread by water drops such as splashing rain or irrigation water, by cultivation equipment and workers (hands, clothes) and insects (e.g. aphids, the Colorado potato beetle etc.) Seeds may also be contaminated. Septoria prefers warm (20-25 C), wet, humid conditions; under favourable conditions the spores may germinate within 2 days. The spots appear within 5 days after the initial infection, followed by pycnidia in 7 to 10 days. The next generation of spores are released within 10-13 days.

Treatment:

crop rotation (avoid plant members of the family Solanaceae )
thoroughly eliminate sources of inoculum (plant debris) after harvest
in large fields, plant debris may be incorporated into the soil by deep ploughing
use healthy, disease-free seeds/transplants
avoid overhead irrigation; water plants early in the day
fungicides are effective against the disease. The use of fungicides depends on the rate of infection, and the on the plant protection products complying with EU regulations.

Material with sulphuric content used against Phytophthora might be effective against Septoria too.

GREY MOLD

Pathogen: Botryotinia fuckeliana (Botrytis cinerea)
Host range: Extremely broad (vegetables, strawberries, wine grape, ornamentals)
Importance: B. fuckeliana is ubiquitous. Even under unfavourable conditions, it may cause serious damage in stands with injured or weak plants.

Symptoms:

43. Figure Botryotinia fuckeliana

Source: project number: HU/02/B/F/PP-136012

First symptoms: The most common symptom caused by B. fuckeliana on tomatoes are lighter rings on fruit surface.

The most serious symptom caused by B. fuckeliana on tomato is the production of light-coloured rings (“ghost rings”) with a darker centre on both immature and ripe fruits.

44. Figure Botryotinia fuckeliana

Source: project number: HU/02/B/F/PP-136012

"Ghost rings" caused by grey mould. In some varieties, the inside parts of the rings ripen later than the surrounding tissue. Not to be confused with the symptoms caused by Tomato spotted wilt virus.

45. Figure Botryotinia fuckeliana

Source: project number: HU/02/B/F/PP-136012

A much more important symptom is fruit rot, that usually starts at the stalk. The fungus causes a soft rot with a grey growth developing on the lesions in later stages. In the final stage, small (3 mm) black sclerotia appear. On the stem, large, pale necrotic lesions may be present with a grey growth of conidiophores. Above the necrotic spot, the stem dies. B. fuckeliana can also be part of the damping-off complex. B. fuckeliana lesions on the green parts are rather unique with their grey, fuzzy growth of mould, but the ghost rings on fruits are often confused with those caused by viruses, although rings caused by viruses are often accompanied by malformations.

Disease cycle: The fungus survives either in plant debris as mycelia or in various substrates as sclerotia and also on various dying parts of living plants i.e. some inoculation source is always present in the stand. Being a weak pathogen, B. fuckeliana is usually unable to enter intact green tissues (it needs some injury) but it may infect healthy flowers and fruits, under wet conditions in particular. Plants weakened by insufficient light and cold weather are more susceptible to the infection. Infections are more important during autumn, winter and early spring in glasshouses, but if the summer weather is cold and rainy, plants may also be infected in the open field.

Control:

increasing the calcium content of soil reduces susceptibility,
proper spacing of plants,
sunny locality,
avoid overhead irrigation wherever possible,
application of fungicides in compliance with EU regulations.

FUSARIUM WILT OF TOMATO

Pathogen: Fusarium oxysporum f. sp. lycopersici
Host range: The pathogen is the fungus Fusarium oxysporum f. sp. lycopersici, which infects the roots of tomato and, to a lesser extent, pepper and eggplant.
Importance: Fusarium is a fairly common disease of tomato. The pathogen damages vessels, blocking circulation in the water transporting system, and hence causing the infected plants to wilt, temporarily first (only for a day) and then permanently.

46. Figure Fusarium oxysporum f. sp. lycopersici

Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

https://www.forestryimages.org/browse/detail.cfm?imgnum=1234206

Symptoms:

Young plants turn yellow when infected:

47. Figure Fusarium oxysporum f. sp. lycopersici

Source: https://gd.eppo.int/taxon/FUSALY/photos

The first symptoms are leaf spots, followed by lesions on the fruit stem. Initially, leaves take a very bright yellow colour, with the veins becoming even lighter. The canopy loses its characteristic form and the leaves begin to curl and wither quickly.

The infection starts from below, but eventually also attacks the younger leaves. The fungus may kill the plant. Often only a single branch or side branch shows symptoms.

48. Figure: Fusarium oxysporum f. sp. lycopersici

Source: Clemson University - USDA Cooperative Extension Slide Series , Bugwood.org

Disease cycle: Fusarium produces conidia. It may survive in the soil for several years. The conidia are spread by water, insects and infected tools. Warm weather provides optimum conditions for development and reproduction; the fungus is favoured by soil temperatures around 27^oC or higher.

Control: The production of resistant varieties should always be considered.

Plant debris or even the soil itself may serve as sources of infection.

a) Mechanical control:

Remove and destroy infected plants and disinfect utensils. Proper crop rotation is advisable

b) Biological control:

Use of resistant species is advisable

c) Chemical control:

Use plant conditioners, and fungicides permitted for use in tomato in the EU.

VERTICILLIUM WILT

Pathogen: Verticillium dahliae Kleb.
Host range: Veticilium . dahliae has a very wide host range among economically important crops and ornamental plants, native species and weeds, including both woody and herbaceous plants. (CABI 2020)
The primary economic hosts of Verticilium. dahliae include: artichoke, aubergine, bell pepper, potato, strawberry and tomato and etc.

Distribution:

49. Figure Distribution of Verticillium dahliae Kleb.

Source: https://gd.eppo.int/taxon/VERTDA/distribution

Importance: Verticillium is a soil-borne pathogen. The optimum soil temperature for infection is 12-13°C, with an air temperature of 19-23°C. The pathogen causes a vascular disease, by clogging vessels. The optimum temperature for producing conidia is 25-28°C.

Verticillium causes severe outbreaks in hot areas. It rarely infects plants under moderate climates, with the damage limited to crops grown on dense soils.

Symptoms: A characteristic initial symptom is the appearance of yellow spots on the lower leaves. As the spots spread, the veins of the leaves turn brown. The leaves then become completely brown and fall off. The disease spreads upwards in the stem until it eventually infects the entire plant.

50 Figure: Verticillium dahliae Kleb. symptoms on leaves

Source:

https://www.growingproduce.com/vegetables/tomatoes/vigilance-required-to-tame-verticillium-wilt-of-tomato/

51. Figure Verticillium dahliae Kleb. symptoms on leaves

Source:

http://www.omafra.gov.on.ca/IPM/english/tomatoes/diseases-and-disorders/verticillium-wilt.html

Disease cycle: Verticillium dahliae is soil borne. While not a true soil dweller, it can persist in the soil for up to 15 years in the form of masses of hardened mycelium known as microsclerotia. The fungus penetrates the water transporting vessels in the root tip and then invades the entire plant, through the vascular system.

Control:
Chemical control and crop rotation are ineffective.

Cultivation practices