Diagnostics and prevention of diseases in tomatoes and eggplants

Viral and phytoplasma diseases of eggplant and tomato: symptoms and vector control

Physiological disorders and viral infections can significantly reduce the yield of solanaceous crops. On tomatoes, symptoms of infection manifest as the leaves curling upward along the midrib, and the leaf blade does not return to its shape over time. Affected bushes produce small fruits, which reduces the overall productivity of the plantings. At low temperatures, silvering (chimera) is also activated on tomatoes: small angular silvery spots form on young leaves, and in adult plants, half of the lobes of a compound leaf become discolored.

Eggplants often suffer from the tobacco ring spot virus. The disease begins with the appearance of solitary necrotic rings on the leaves, which then turn brown. Later, the ring spot takes on a concentric shape, and the leaves thicken and become leathery. This pathogen belongs to the group of nepoviruses with isometric virions and is transmitted by mites, nematodes, beetles, thrips, and orthopteran insects.

Another serious threat to eggplant is stolbur, caused by RAGO-phytoplasma. The disease is widespread mainly in open ground, and is less common in plastic and glass greenhouses in the second half of summer. Infected plants lag in growth, their stems stand upright, thicken, and break easily, and the leaves acquire a purplish-red tint. The flowers become deformed, sterile, and fall off, and the fruits develop abnormally. Leafhoppers transmit the infection.

The basis for protection against these infections consists of agrotechnical measures. It is necessary to destroy weeds around greenhouses, paying special attention to bindweed — the main host of phytoplasma vectors. Leafhopper vectors are destroyed chemically using neonicotinoids: the preparations Aktara, Confidor, and Mospilan. Additionally, for seed treatment of eggplant and to increase their resistance, pre-sowing thermal seed treatment is applied.

• Virus host range — 250 species
• Families of host plants — 54
• Neonicotinoid protection period — 2–3 weeks

Fungal diseases of eggplant: control of Verticillium wilt and gray mold

Verticillium wilt of eggplant (causative agent — Verticillium dahliae Kleb) leads to a delay in plant growth and a sharp drop in yield, up to the complete loss of plantings. In the initial stages, the lower leaves acquire a grayish-green color due to interveinal necrosis. Then the tissue between the veins turns brown and dries out, the leaves turn yellow, curl, and fall off from the bottom up. A cross-section of the stem reveals browning of the vascular tissue, which is clogged with the pathogen's fine multicellular mycelium.

To reduce the infectious background of Verticillium wilt, a set of preventive measures is used:

• thorough destruction of crop residues;
• observance of crop rotation;
• disinfection of soil and seed treatment;
• use of resistant cultivars and hybrids.

The causative agent of Verticillium wilt persists in the soil in the form of microsclerotia for several years. Because the pathogen develops inside the plant's vascular system, most standard fungicides do not show effectiveness during the growing season. The biology of the pathogen imposes strict limits on the conditions for its development in the soil.

For chemical prevention of Verticillium wilt, soil steaming or disinfection with Basamid-granules or methyl bromide is carried out.

Gray mold is another dangerous infection that usually manifests with the onset of the fruiting phase of eggplants. Although this pathogen rarely leads to the complete death of the bush, it causes the drying out of parts of the stems. The incidence of fruit gray mold increases sharply in the autumn period, which is directly related to an increase in humidity.

Gray mold of eggplant: symptoms and complex control measures

Gray mold (causative agent — fungus B. cinerea / Botrytis cinerea) belongs to wound parasites and can quickly destroy the eggplant harvest in a greenhouse. The disease primarily affects the stems, and in humid weather, it quickly spreads to fruit sets and fruits. If the infection penetrates the fruit set, the fruit stops its development and dies. On ripening fruits, the disease manifests as a fluffy grayish-olive coating, which later turns into dry rot with concentric spots.

On stems, the first signs of the disease usually appear in April–May at the points where leaf petioles and fruit clusters break. Within 3–5 days, brown spots expand along the stem up to 4–5 cm, gradually encircling it. During the first 6–8 days, there is no sporulation; the center of the spot lightens to a straw color, and blurred ring-like bands appear on it. Due to the necrosis of internal stem tissues, the vessels die, water supply ceases, and the shoot above the affected zone wilts rapidly.

The infection spreads mainly through the air and by contact during plant care or harvesting. Spores are also dispersed by water splashes during irrigation. By the end of the season, a multitude of small black sclerotia form on plant debris, which serve as a source of infection for subsequent plantings. In greenhouse conditions, the fungus can also affect cucumber, tomato, pepper, cabbage, and lettuce.

The basis of prevention is maintaining low air humidity in greenhouses. When shaping the bush and removing leaves and fruits, it is important to act carefully to minimize the wound surface. All plant debris must be removed from the greenhouse immediately and without fail.

1. Regularly inspect plantings during the growing season for early detection of primary grey mold foci.
2. In dry weather, carefully excise the affected sections of stems and fruit stalks with a sharp knife.
3. Coat the wounds and spots with a medicinal paste based on CMC glue with the addition of Trichodermin or chemical fungicides (Rovral, Ephal, Tecto, Sumilex).

Post-harvest disinfection significantly reduces the number of surviving spores and sclerotia in the greenhouse. It includes cleaning structures and glazing, as well as steaming or fumigating the soil with methyl bromide or dazomet granules. This prepares the greenhouse for the safe cultivation of the next crop.

• Consumption of CMC glue per 10 l of water — 300–340 g
• Dose of fungicide in paste per 10 l of water — 30–40 g
• Concentration of Bayleton for spraying — 0.05%
• Interval for repeated stem treatment — 12–15 days

To prepare the medicinal coating, water, CMC glue, and fungicide are mixed, after which the mixture is brought to a paste-like consistency using chalk. In case of mass damage to plantings, spraying of eggplant stems with a 0.05% solution of the preparation Bayleton is practiced.

Phomopsis and anthracnose of eggplant: features of manifestation

Phomopsis (pathogen — Phomopsis vexans, synonym Phyllosticta hortorum) rarely affects eggplants in greenhouses, activating mainly in hot weather. The disease damages all plant organs at different stages of development. At the early stage of seedling development, it leads to damping off. At later stages, Phomopsis can cause wet ring rot of the stem near the soil surface.

On leaves, the disease manifests as sharply defined round brown spots with a light center, located mainly on the veins. Fruits become covered with concentric dry light-brown spots. Rotting often begins at the base of the fruit in the form of dry black spots, which later turn into soft rot that completely engulfs the fruit.

The pathogen forms groups of black pycnidia that break through the epidermis of the affected tissues. The diameter of pycnidia on leaves and stems is 60–200 µm, and on fruits, it reaches 120–350 µm. Inside them, unicellular colorless pycnospores of two forms mature: cylindrical with two oil drops (measuring 5–10 × 2–4 µm) and slightly curved thread-like ones (13–28 µm in length). The source of infection is ascospores in perithecia, pycnospores in pycnidia, and viable mycelium in seeds and plant debris.

Anthracnose of eggplant is more common in open field conditions, and is recorded rarely in greenhouses. On leaves, the disease forms oval grayish-brown spots with concentric zones. On fruits, depressed grayish-brown spots appear, which can merge, crack, and cover a large part of the surface.

Pathogen biology. Acervuli are densely arranged along the edges of the spots and often merge. Setae are grayish-brown, located along the edge and in the center of the acervulus, with 1-3 septa, tapering towards the apex. Conidiophores are short, pigmented, 21-29 x 3.3-4.2 µm. Conidia are elongated-ovoid or club-shaped, straight or slightly curved, 19-25.2 x 4.2-4.6 µm. Plant protection measures. Affected plants are sprayed with a 0.3-0.4% working solution of copper oxychloride or Oxychom. 2.3.3.5. Black mold of eggplant fruit Pathogen — Rhizopus nigricans Ehrenb. Harmfulness. The disease occurs mainly in open soil, but sometimes affects plants in greenhouses during the summer period. Symptoms. The affected tissue is watery; the mold is gray with black sporangia, through which the fungus survives unfavorable conditions. Pathogen biology. Sporangia are hemispherical, 100-350 µm in diameter, spores are irregular in shape. Plant protection measures. If necessary, plants are sprayed with Oxychom or Ridomil MC. Effectively spraying plants with a Trichodermin suspension is effective, but this technique has not yet been developed in detail. Fig. 133. BLACK MOLD OF EGGPLANT. 2.3.4. Nematode diseases 2.3.4.1. Meloidogyne infection

Pathogen: Meloidogyne incognita (Kofoid et White) Chitwood — southern root-knot nematode, M. javanica (Treub) Chitwood (Javanese), and M. arenaria (Neal) Chitwood (peanut).

Harmfulness. A dangerous and extremely harmful disease. In extended crop rotation, plants are affected to a significant degree; total harvest loss is possible.

Symptoms. Rounded swellings (galls) are visible on the roots of affected plants, inside which, under microscopy, female root-knot nematodes with characteristic egg sacs can be found. Galls are usually small; syngalls are rarely formed. Affected plants lag in growth and wilt on sunny days.

Biology and control measures are described in Chapter 1.

Non-parasitic diseases 2.3.5.1. Discoloration of eggplant fruit Symptoms. Lightening of the fruits manifests during periods of low light, both in the summer and (especially) in the autumn. The ripening eggplant fruit does not acquire the color characteristic of the given cultivar (it lightens). Fruits that are normally purple or black become brownish or tan. These symptoms must be distinguished from the lightening of the eggplant fruit that occurs upon reaching the stage of biological maturity, which is characteristic to a large extent of cultivars and hybrids with white flesh (for example, the Sirenevyi Tuman and Alekseevskii cultivars). Cause. A decrease in light intensity combined with a drop in temperature. Methods for eliminating the disease. In summer, light-colored fruits are rare, occurring primarily in dense plantings. With the onset of inclement weather in the autumn period, plants should be thinned by removing some leaves from the upper canopy so that sufficient light reaches the fruits. In greenhouses with supplementary lighting, the light is switched on, not to extend the day length, but to increase light intensity, because under short-day conditions, fruit set and fruit quantity increase sharply in the autumn period. 2.3.5.2. Fruit cracking Symptoms. Formation of a longitudinal crack on the side of the ripening fruit, where not only the skin but also the parenchyma of the fruit ruptures down to the seed chambers. Observed, as a rule, only in ground-level greenhouses and hotbeds. Fig. 135. CRACKING OF EGGPLANT FRUIT.