Diagnostics and control methods for bacterial canker of pepper in greenhouses

®’ and CANKER ON PEPPER. G “ * a №. E. ch r AFUKH u ь Z A. u ^ ь 3 cha I) ‚9 h r ’,.! r ь 4 4 # m % u

Before the start of the current season, all seed should be treated by soaking in a 0.05% potassium permanganate solution for 10 minutes with stirring, followed by thorough rinsing. Seed treatment is carried out immediately before sowing. To protect plantings, Phytolavin-300 or copper-containing preparations are usually applied, although they are not sufficiently effective. 2.4.2.2. Bacterial canker

Pathogen — Clavibacter michiganensis subsp. michiganensis (Smith) Davis et al. Harmfulness. The disease is rarely encountered in greenhouses, causing local damage to pepper leaves, shoots, and fruit. Symptoms. Bacteria cause the formation of small spots on fruit, which merge into larger ones reaching 1-3 cm in diameter. With severe development of the disease, leaves become discolored and fall off easily when the plant is shaken. Pathogen biology. Cells are non-motile, appear as short rods, 0.3-0.4 x 0.8-1.0 µm in size. Cultural properties. Aerobic, non-spore-forming bacteria. On meat-peptone agar, colonies grow slowly, are round, smooth, raised, initially colorless (almost transparent), and later cream-yellow. When glucose is added to the medium, colony growth accelerates, they become significantly larger and pale yellow in color. Infection can be transmitted via seed, but plant debris serves as the primary source of infection, and soil to a lesser extent. Protection measures. To limit the spread of infection before the start of plant formation, weeding of diseased plants from the plantings is carried out (at least twice a month). Unnecessary shoots and leaves are removed using a special tool. To reduce the spread of bacteriosis throughout the greenhouse, work with diseased plants should begin after treating healthy ones.

Biological agents. To reduce the reservoir of pathogens, seed is soaked in a 0.2% working solution of Phytolavin-300 for two hours. Subsequently, transplants are sprayed twice, starting from the 1-3 true leaf stage, with a 0.2% suspension of Phytolavin-300. Dipping the roots of transplants into the same suspension yields good results. During the period of intensive fruiting, it is recommended to spray plants with Planriz.

Chemical agents. For seed treatment, pre-sowing (on the day of sowing) seed soaking in a suspension of TMTD (thiram) is used. In hotbeds and greenhouses, it is advisable to replace the soil or disinfect it with methyl bromide or Basamid granulate (from 20 to 60 g/m). To protect plants during the growing season, copper-containing preparations are used: copper oxychloride, copper oxychloride and copper sulfate (Dzhalilov, 2000). Considering circadian rhythms of susceptibility, treatments should be carried out in the morning hours (10-12 a.m.) or in the evening (4-6 p.m.).

Brown bacterial wilt Pathogen — Ralstonia (Pseudomonas) solanacearum (E.F.Smith) Yabuuchi.

Harmfulness. A quarantine disease, not yet noted in Russian greenhouses. Potentially extremely harmful.

Symptoms and control measures for bacterial wilt

Symptoms. Bacterial wilt begins with yellowing and wilting of leaves, ending in the rapid death of the plant. When stems are cut, a light-brown sticky slime is released from the vessels, which resembles Erwina infection. Bacteria are easily detected by microscopic examination of plant sap taken from roots and stems. The symptomatology is similar to verticillium wilt infection of pepper, but in the latter case, one-sided leaf wilting is observed first.

Host plants: tomato, eggplant, pepper, potato, etc.

Protection measures. Seed may be the source of primary infection, but more often it is infected potato tubers, transplants, plant debris, and soil; therefore, of primary importance are:

• quarantine measures;
• spatial isolation from potato plantings;
• adherence to cultivation technology;
• soil disinfection.

Soft bacterial rot and damping-off of seedlings

2.4.2.4. Soft bacterial rot

Pathogen — Erwinia carotovora subsp. carotovora (Jones) Bergey, Harrison.

Harmfulness. Mainly fruits are affected during storage and transportation.

Symptoms. Internal tissues soften, the fruit turns into a watery mass and acquires a sharp unpleasant odor.

Pathogen biology. The pathogen is a wound parasite. The disease develops rapidly during hot and humid weather. Sucking and leaf-eating pests are passive vectors of the pathogen.

Protection measures. Pest control during the growing season contributes to a significant reduction in fruit damage by rot. It is recommended to perform spraying of plants with copper-containing preparations before harvesting, which also reduces losses during storage. If fruits are washed after harvesting, chlorinated water should be used (the water chlorination level must be at least 0.005%). Fruits should not be stored at temperatures above 21°.

Damping-off of seedlings

Pathogens — species of the genera Pythium sp., Rhizoctonia solani, Phytophthora sp.

Harmfulness. A localized disease of seedlings, resulting in their failure to emerge (pre-emergence damping-off), or the cessation of growth in seedlings due to root or root collar rot. Under conditions favorable to the pathogens, the disease can completely destroy the transplants.

Symptoms. Infection can cause symptoms similar to Phytophthora root rot.

Biology of pathogens. The disease develops most severely in unsterilized soil containing peat, during periods of cold, wet weather, or when using overhead irrigation. Additional causes of seedling losses include poor seed quality, deep sowing in waterlogged soil, and extremely low or high salt concentrations.

Diagnosis of root rot pathogens

The presence of Pythium on affected plants is easy to diagnose. To do this, the rotten root is washed in water, the surface is treated with alcohol, and placed on an agar medium in a Petri dish. After 2–3 days at a temperature of 25°, fluffy white mycelium grows on the surface of the medium without conidiophores; sclerotia are never formed in culture.

Rhizoctonia is easy to identify when examining roots under a microscope by the presence of brown mycelial strands.

Fusarium forms mycelium on an agar medium slightly later than Pythium. Its color is initially white, then pink; sickle-shaped conidia characteristic of this genus develop on it, followed later by black microsclerotia.

Control measures for pepper pathogens

Protection measures. To prevent the disease, certified seed is sown, treated with one of the preparations (trichodermin, pseudobacterin-2, planriz, TMTD); soil temperature and humidity are controlled, the air in the greenhouse is ventilated, and seedlings are culled upon the appearance of the first disease foci. To create favorable conditions in the root zone, the surface of seedling containers is covered with a layer of vermiculite or washed river sand.

Basic preventive practices include:

• Application of trichodermin to seedling trays at least one week before seed sowing.
• Soaking seeds in a solution of immunocytophyte to increase resistance to root rots.
• Preventive drenching of the soil with sulfur-based preparations (Thiovit, Kumulus, colloidal sulfur) or a 0.4% working solution of Oxichom.

In the event of a complex infection, which can be diagnosed by microscopic examination of the roots of affected plants, tank mixtures of preparations with different modes of action are used for drenching. For example, a mixture of Oxichom or Ridomil MC (Curzate, Ordan) and preparations from the benzimidazole group is used.

Fusarium stem rot

Pathogen — Rhizoctonia solani (Kühn) Dupe, et al.

Harmfulness. Disease most severely affects the stems of pepper plants, less frequently ripening fruits. Affected plants die prematurely.

Symptoms. The fungus causes darkening and softening of tissues at the nodes. Damage on fruits is concentrated around the peduncle. Affected tissue darkens and takes the form of a depressed spot with thin red circles. If the dead plant remains in place, under humid conditions, diffuse pinkish sporulation appears on its surface. Protection measures. Application of trichodermin at all stages of crop cultivation. Removal of affected plants along with the soil ball or mineral substrate. Maintenance of normal air humidity in the greenhouse to prevent epiphytotics of fungal diseases 2.4.3.3. Phytophthora blight Pathogen — Phytophthora capsici Leonian. Harmfulness is more often associated with damage to transplants. The disease is rarely encountered when plant cultivation technology is followed. Symptoms. Tissues of the root collar darken, a constriction forms, and seedlings lodge. A white silky coating of sporulation develops on the affected tissue. On adult plants, the disease develops on leaves, petioles, stems, and fruits, where brown, rapidly enlarging spots with a watery zone, covered with sparse mycelium, may appear. In the final stages of disease development, affected fruits dry out completely, and the pericarp takes on the appearance of dry films (Fig. 143 27; р }, -, | ь ь о у -“. \ К \. - = Х, #: 2$ | у. } Га ‚ $ (м | в‘ ы ^^ | Л | } Г $ 1 г | р ' м % | 5) < к ГВ, > Ч —. РА. 7; | 5 и. _ 2% = Fig. 143. PHYTOPHTHORA BLIGHT ON PEPPER FRUITS Fig. 142. FUSARIUM WILT OF PEPPER Biology of the pathogen. Zoosporangia are oval, obpyriform, or irregular in shape, 26-68 x 18-38 µm, with one clearly visible protruding papilla, less often 2-3. Oospores are spherical and rounded, 20-42 µm in diameter, colorless or yellowish. Protection measures. Spraying transplants with a 0.3-0.4% working solution of Oxichom. The same solution can be used to drench the substrate in which the transplants are grown. The appearance of disease symptoms on adult plants is possible during periods of sharp fluctuations in temperature and air humidity; therefore, to prevent its development in the greenhouse, an optimal hygrothermal regime should be maintained 2.4.3.4. Gray mold Pathogen — Botrytis cinerea Pers. Harmfulness. On peppers, the disease is rare because the optimal conditions for the development of the pathogen and the plant differ significantly. Under conditions favorable to the pathogen, the disease can cause serious harm due to damage to stems, flowers, and pepper fruits. Gray mold rarely leads to mass mortality of pepper plants.

Symptoms. The fungus causes sudden browning of the succulent tissues of young leaves, shoots, flowers, and fruits. The infection spreads rapidly, forming zones of irregular, water-soaked spots. Later, a grayish-white mycelium of the fungus appears on the water-soaked spots; the infected tissues dry out, and a dark gray pathogen sporulation forms on them. The plant dies, and the younger the plant, the faster this happens.

On fruits, the infection initially manifests as olive-green spots, which may soon spread over the entire fruit, on which sporulation later forms (p. 145)

Biology of the pathogen. High humidity combined with the presence of wounds on plants contributes to the development of the disease. Plants in dense plantings and those damaged by chewing pests are most often affected. The pathogen more often infects the most developed plants.

Source of infection: plant residues and sclerotia present in the soil.

Protection measures. Observe the planting density and number of shoots recommended for each cultivar or hybrid. Minimize plant injury during periods of high air humidity. When the first outbreaks of gray mold appear, increase greenhouse ventilation. The affected areas are cleaned with a knife and smeared with a thick suspension of a mixture of chalk and fungicides (bayleton, topsin-M, efal...)

Powdery mildew

Pathogen — Oidium ambrosiae Thüm., sexual stage — Leveillula taurica Arn.

The harmfulness of the disease under greenhouse conditions is low.

Symptoms initially appear on the leaves as light green spots of irregular shape. Later, under favorable conditions, the spots expand and turn yellow; a sparse whitish mycelium with conidia appears on them. In the final stage, the entire leaf turns yellow, dries up, and falls off. Biology. Conidia on long conidiophores, colorless, solitary, elongated-elliptical in shape. The pathogen develops well at low relative humidity of the air. An epiphytotic development occurs at temperatures from 15 to 25°. In the absence of plant residues of infected plants in the greenhouse, the pathogen spores die within 10-14 days, which should be taken into account when planting plants of a new crop rotation. Excess moisture has an adverse effect on spore development; under its influence, the spores swell prematurely and burst before they can germinate.

Dissemination and survival of the pathogen. The infection spreads aerogenically via conidia, which are easily carried by air currents. Humans play a certain role in the spread of infection during plant care. The pathogen survives in plant residues.

Protection measures. When the first signs of the disease appear, plants can be sprayed with a 0.02-0.03% solution of the preparation Strobi. It is possible to use such preparations as Quadris, Topaz, Thiovit, and Kumulus, although they are not yet registered for this crop. 2.4.3.6. Cercospora leaf spot of pepper

Pathogen — Cercospora capsici Heald et Wolf.

The harmfulness of the disease is low; it manifests only during periods of high air humidity.

Symptoms. The disease can manifest on stems, lateral shoots, and fruits. On the leaves, light brown, round spots with a dark border appear, surrounded by chlorotic tissue, up to 1 cm in diameter. The leaf tissue dries out and often crumbles, forming holes. With severe infection, the leaves die and fall off.

Biology of the pathogen. The disease actively develops in moist conditions. Conidiophores are brownish, 10-15 in a fascicle, straight or geniculate-curved. Conidia are colorless or pale-colored, awl-shaped or club-shaped, straight or slightly curved, with a truncate base, 30-200 x 2.5-4 mcm.

Cercospora leaf spot is often found on leaves simultaneously with bacterial leaf spot and Alternaria blight, which is due to the similarity of conditions favorable for their development.

The pathogen is transmitted mainly through seeds. Protection measures. To prevent the development of the disease, seeds obtained from healthy plants are used and, if necessary, treated with fungicides from the benzimidazole group or TMTD. 2.4.3.7. Alternaria blight Pathogen — Alternaria solani Sor. [syn.: Macrosporium solani Ell. et Mart.] and Alternaria capsici-annui Sav. et Sand. Harmfulness. The disease occurs in greenhouses sporadically and, as a rule, becomes most noticeable only in the autumn period. Affected plants rarely die; more often, as the disease develops, the photosynthetic surface of the leaves decreases slightly. Occasionally, fruits are also damaged, becoming unsuitable for sale.

Symptoms. The pathological process begins on old leaves with the appearance of angular black or dark brown spots on the leaves, limited by veins.

Subsequently, the disease more often spreads to fruits and less often to stems. No pattern is observed in the arrangement of the spots; they grow up to 20 mm in diameter, acquiring a round shape. On fruits, the spots are initially watery, gradually darkening, with a lighter center covered with a black moldy coating. Biology of the pathogen. Conidia in chains, club-shaped, elongated or spindle-shaped, brown, 32-82 x 7—

24 µm, with 3-7 transverse and 1-3 longitudinal septa.

The pathogen persists until the new season on plant residues, where it develops saprotrophically. Under favorable conditions (in the presence of droplet moisture), the pathogen is capable of penetrating the plant, where it develops not only in the surface tissues but also in the deeper ones.