Tomato Bacterial Diseases: Bacterial Cancer, Black Spot

2024 Author: Sebastian Paterson | [email protected]. Last modified: 2023-12-16 13:47

How to prevent bacterial diseases of tomatoes

Tomato is now one of the most popular and favorite vegetable plants by Russians. This very light and heat-loving culture is grown both in greenhouses and in the field. However, to obtain a stable tomato harvest, a whole range of agrotechnical measures is required. In our North-West region with its capricious weather due to changes in temperature and humidity, with some heat deficit during the summer, gardeners, as a rule, grow tomatoes in greenhouses and greenhouses.

But there are also such experienced amateur vegetable growers who rely on the warm summer, who get harvests of tomatoes in the open field. Of course, in the initial period of development, they still use temporary shelters. Moreover, now there is a wide selection of different films. Alas, tomato plants are affected by several bacterioses, the intensity of development of which depends both on the peculiarities of growing this plant and on their general condition.

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When grown indoors, there is often high humidity and sometimes insufficient light. This greatly weakens the plants, which as a result leads to damage by these pathogens. The spread and development of these diseases can be contained or completely excluded if the air humidity in closed ground is reduced to 65-70%, and the daytime temperature is tried to be maintained within 22 … 26 ° С or 24 … 28 ° С (in cloudy weather it can be 4 … 5 ° C lower). Nighttime temperatures should be 12 … 14 ° С and 17 … 20 ° С (before and after flowering, respectively). It is also necessary to regularly control the temperature of the soil in greenhouses - to maintain it equal to 19 … 21 ° C throughout the growing season.

Black bacterial spot of tomato

The prevalence of this disease is quite wide, the disease is very harmful, especially in greenhouses. It brings especially great harm in years with hot summers. In this case, the seedlings are affected by up to 50%, and the fruits - up to 20%, because the increased humidity at high temperatures contributes to the increase in the defeat of the greenhouse tomato. The disease manifests itself in the defeat of the ground part of the plants, as a result of which the tomato does not produce fruit at all or it is of low quality. The disease affects the cotyledons, leaves, petioles, stems and fruits of tomato, and young tissues are more susceptible to the pathogen than aging ones. Seedlings and young plants suffer greatly from bacteriosis. At the first stage, very small depressed watery brown spots of irregular shape appear on the leaf blades of young leaves,translucent in transmitted light. They quickly increase in size (up to 1-2 mm), then the center of the spots gradually turns black.

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Under favorable conditions for the development of the disease, the spots merge, often this affected tissue necrotizes and falls out, and after a while the leaves themselves curl and dry out. Black elongated spots are formed on the stems and petioles, but sometimes the lesion begins to appear on them in the form of strokes and even dots. Often, with the course of the disease, these spots merge, and the plant may die. The same picture is observed on the stalks, shoots and pericarp.

With a strong lesion of the pedicels, a massive fall of flowers occurs. In young fruits (up to 2.5-3 cm in diameter) bacteria penetrate through damaged hairs or, at later stages, through wounds. The incubation period for the development of bacteriosis often lasts only 3-7 days (depending on temperature). When fruits are affected in the early phase of development, dark convex points, surrounded by a watery border, first appear on their surface, which eventually take the form of ulcers. Unlike typical symptoms of bacterial bird's eye cancer, dark scab-like spots are not surrounded by a light border.

The development of black spot largely depends on meteorological conditions: the lower the temperature, the slower the development of black spot. The bacteriosis is transmitted by seeds and plant debris. On seeds, the infection can persist for more than a year. Even with a latent infection, seeds can give outwardly healthy seedlings, which in the future can serve as a source of spread of bacteriosis. For this reason, it is important to purchase guaranteed healthy seeds. During the growing season, bacterial infection can enter through the stomata of plants. The pathogen persists for a very long time in parts of plants that are difficult to rot.

Tomato bacterial cancer

It is also ubiquitous. This disease is typically of a vascular nature. Signs of this disease are manifested in the form of wilting of plants: bacteria, penetrating into the vascular system, cause wilting of tomato shoots. This process begins with the lower tiers of leaves: they have a loss of turgor (sometimes on one side of the leaf), while the wilting parts of the leaf turn yellow along the edge and curl. In some cases, such a manifestation of bacteriosis may be its only external symptom. From the beginning of wilting to the complete death of the plant, it can take 1.5-2 months.

In case of primary infection, the vascular ring is damaged (in the form of its darkening) in the stems and at the base of the petioles of diseased leaves. Early damage to fruits by the causative agent of the disease leads to their ugliness: at the same time, the seeds darken and lose germination. Infection of the terrestrial organs of fruiting plants manifests itself in the form of brown ulcers on young sepals, stems, petioles, especially on the stalks, which causes the fruit to fall off. With a later infection, the fruit may look healthy and have a normal pulp consistency.

Local manifestation of symptoms of bacteriosis on fruits occasionally occurs in the form of a characteristic spot, which is called the "bird's eye". At the first stage, small affected areas of green fruits look like white spots, at the next stage, when the fruits ripen and color, the center of the spots turns yellow. These signs of "bird's eye" can develop on both affected and unaffected by wilting of plants. Diseased fetuses are delayed in their development, usually unevenly colored in comparison with healthy ones. With a strong development of the disease in plants, light brown stripes, cracks and ulcers appear on the petioles and stems, from which yellow mucus protrudes. On the cross section of such affected organs, the browning of the bundles of the vascular system is clearly distinguishable.

The causative agent of bacteriosis enters plant tissue through mechanical damage: through injured roots, stems, leaves. At high air humidity, it is able to infect the plant through open stomata. Infection with bacterial tomato cancer is spread by plant debris, seedlings, soil, but the dominant role here belongs to infected seeds, infected superficially or from the inside. The pathogen is also transmitted by pinching and pruning of plant leaves. With a permanent tomato culture in the same place, the soil serves as a reservoir of bacterial infection. The most favorable conditions for the development of bacteriosis are a temperature of 20 … 28 ° C and a relative humidity of 80-85%.

Read part 2 Bacterial diseases of tomatoes: hollowness, mottling, apical rot of fruits

Photo by E. Valentinov