Dodger is a dangerous neighbor
The parasitic genus includes the most dangerous flowering parasitic plants for cultivated plants, combining great viability with high fecundity. The dodger comes from tropical America and Africa, from where it spread north and south, gradually adapting to new conditions and plants and isolating new species (up to 100 species are described). There are thin and thick stalked forms.
Dodder (Cuscuta) - a genus of parasitic plants, all species of which are classified as quarantine weeds. Previously, a separate family of Povilikovy (Cuscutaceae), consisting of one genus - Dodger. Modern genetic studies have shown that it is more appropriate to assign this genus to the tribe of the Felicidaceae family Convolvulus (Convolvulaceae).
In our country, there are more than 30 species of dodder. All of them are objects of internal quarantine. The most common and malicious: Field dodder (Cuscuta campestris), Clover (Cuscuta trifolii), Hop-like (Cuscuta lupuliformis), Linseed (Cuscuta epilinum), Short-flowered dowel (Cuscuta breviflora), Lehman's Cow (Cuscuta lehmaniana).
Dodgers are aboveground parasites whose body has turned into a filiform or cord-like, curly, yellowish, greenish-yellow or reddish smooth or warty, chlorophyll-free stalk with barely visible traces of leaves in the form of scales. Plants are devoid of roots, feed and attach to the host plant with the help of suction cups - haustoriums that are formed in places of contact with the nourishing plant and deeply embedded in its tissue. The extraction of nutrients occurs due to the higher osmotic pressure of the parasite's cell juice.
The stalk of the dodder is covered with numerous rather small, sessile or short-peduncle flowers with a double pericarp of white, pinkish or greenish color, collected in glomerular, spike-like or spherical inflorescences. The fruit is a box with four, rarely two or one spherical, oval or slightly elongated (sometimes irregularly shaped) seeds; on the inside they are angular, covered with a solid cellular, pitted-rough shell.
Dodgers parasitize on annual and perennial grasses, shrubs and trees (fodder legumes, industrial, vegetable, melons, ornamental crops, vineyards, fruit trees, berry plants, wild grasses, shrubs and tree species). In addition to the main host plants, certain species of dodder are able to infect very many plants belonging to diverse families. Only a few species are specialized for certain nourishing plants.
Sucking water with organic and inorganic compounds dissolved in it, grafts cause metabolic disorders in host plants, weaken and delay their growth and development. Rapidly growing, the parasite encompasses entire arrays of susceptible culture, often causing the death of affected plants. Not only the crop is reduced, but also the winter hardiness of plants, and the quality of the products is deteriorating. Grass cut by hay, infected with dodder, does not dry well, grow moldy, lose its nutritional value, can cause animal diseases, and sometimes their death. Dodger also serves as a carrier of viral plant diseases.
The spread of these flowering parasites occurs mainly with seeds of cultivated plants with poor cleaning. In addition, they are carried by animals, cars, water, wind; fall into the fields with manure if cattle fed plants infected with dodder; distributed with planting material, packaging. Wild plants and weeds infected with this parasite can serve as a source of infection.
The distinctive features of different species of dodder are the morphology of the stem and flowers, as well as specialization in parasitization on certain nourishing plants.
At thyme thin yellowish or reddish filiform branching stems up to 1 mm thick, developing mainly on the lower part of the stems of the feeding plant, often forming dense felt near the ground. The flowers are pink-white on very short peduncles, collected in dense spherical bundles. Fruiting is plentiful. It infects clover, alfalfa, vetch, beetroot, flax, potatoes, timothy and many weeds.
Field dodder has filiform pale yellow branching stems developing in the middle and upper parts of affected plants. The flowers are white. It infects tobacco, shag, beets, clover, vetch, alfalfa, lentils, peas, soy, cabbage, carrots, watermelon, pumpkin, potatoes, yellow clover and many weeds.
At alfalfa or close stems, hairy-thin, yellow with a pink hue or greenish, smooth, glabrous, white flowers, gathered in dense glomeruli with bracts at the base. Strongly affects alfalfa and many herbaceous plants.
Clover has filiform, up to 1 mm thick, branched red stems. Before flowering, it spreads in the lower part of the stem of the feeding plant, where it forms a dense felt of branches, and only subsequently rises higher. The flowers are pink, less often - white, on very short pedicels, collected in dense spherical bundles. Parasitizes on clover, alfalfa, nick, beets, flax, potatoes and a number of weeds.
Linseed has greenish-yellow, medium thickness, juicy, unbranched stems. A cup of yellowish flowers is almost equal in length to the corolla. Seeds are single or double. Infects flax, camelina, clover, alfalfa, hemp, beets and other cultivated and weed plants.
European dodder similar to thyme, which differs from the thicker (2.5 mm) reddish stem. Her flowers are pinkish. Seeds are spherical or pear-shaped. It infects alfalfa, clover, sainfoin, hemp, beans, tobacco, hops, potatoes, lupins, testes of vegetable crops, numerous weeds, as well as shrubs and trees.
Single Column has cord-shaped branched stems with a thickness of 2 mm or more. Her flowers are sessile or on short pedicels, collected in loose spike-shaped inflorescences. Corolla tube short, not protruding from the cup. Parasitizes on grapes, tree and shrub species, can infect sunflower, cotton, beets, as well as some weeds (nettle, wormwood, quinoa).
Fodder fruits (capsules) contain from 2 to 5 small, 1-3 mm in diameter seeds, covered with a hard shell with a cellular, pitted, rough surface.
The germ in the dodder is not differentiated into cotyledons, the root and stem are a spirally twisted thread immersed in a gelatinous protein nutrient mass.
The seeds of many species of dodder are very similar in weight, shape, and often color to seeds of cultivated plants.on which parasitize. So, the seeds of field dodder and creeping clover are so similar that they can be discerned only upon careful examination. Masking the seeds of the parasite under the seeds of a cultivated plant is the result of parasitic adaptation. This makes it difficult to use conventional methods for separating clover and alfalfa seeds from dodder seeds.
Seed cleaning must be carried out on special sortings, the action of which is based on a combination of sieves and carminer with the subsequent use of special electromagnetic machines. Fodder seeds having a cellular surface are mixed with magnetic powder and separated by electromagnets from seeds of cultivated plants in which the powder does not linger on the smooth seed skin.
Dodder seeds germinate on the 5-15th day after sowing. Unripe seeds swell and germinate sooner than mature ones.
When the seed swells, the spirally twisted embryo straightens, its thickened end, devoid of a cap and provided with colorless hairs, grows into the soil and absorbs water. The opposite end of the seedling is freed from the seed peel, rises vertically and begins to make rotational movements clockwise in search of a nourishing plant.
In the initial period of development, seedlings receive nutrients from stocks of seeds. The seedling can "crawl" a short distance due to the movement of nutrients from its base to the apex. Such an independent existence can last 16-25 days, while there are cases when the length of the seedling reached 30 cm or more.
If the parasite does not meet a plant suitable for infection, it dies.
Attachment of the parasite to the host and its nutrition are carried out with the help of haustoria, which are formed on the threadlike stalk of the dodder from the side adjacent to the stem of the host plant. The substances secreted by the suction cups soften the epidermis, which facilitates the penetration of the parasite into the tissue of the nourishing plant. If the conditions are acceptable, the inside of the sucker grows, forming a wedge-shaped toe.
Sosalets breaks the skin of the suction cup, deeply enters the body of the feeding plant and goes to its conducting bundle. Having reached the wood, the central cells of the salsicle turn into tracheids, and the phloem elements, in turn, combine with the corresponding elements of the host plant into a common system that allows the parasite to receive water and nutrients.
After the mole attaches itself to the nourishing plant, its connection with the soil is broken and it begins to live off the nutrients extracted from the host plant. In this case, the parasite develops surprisingly quickly, throwing huge yellowish or orange-tinged lashes, in the stem nodes of which the lateral shoots are laid. Soon, the plants in the foci of infection become heavily entangled with long stalks of the dodder. From one seed, a lesion with a diameter of up to 6 m2 can form. The vegetative body of the dodder has high turgor pressure, which allows fragments of shoots not to fade for several days.
Due to the shells with different permeability, the seeds of the grafting germinate at the same time, so the emergence of seedlings can be extended for several years.
In the fight against dodder, preventive measures are of great importance. Sowing is carried out with seeds cleared of dodder. They carry out testing of root crops, phytopathological examination, quarantine measures. According to state standards, sowing by seeds littered with dodder is prohibited.
The main source of infection by sowing is the soil, in which large stocks of parasite seeds are accumulated. Therefore, non-clogged areas are selected for sowing (according to field testing) or they clean the soil. The arable horizon is cleaned either by plowing the seeds of the dodder to a greater depth by plowing with plows with skimmers, or by stimulating their germination, followed by the destruction of seedlings by surface treatment. In areas of irrigated agriculture, germination of seeds is stimulated by provocative autumn and spring irrigation.
From the crops of alfalfa and clover, the most frequently infected with dodder, the parasite spreads to other crops, primarily to those that follow them in the crop rotation. Therefore, on infected fields from the crop rotation, affected crops are excluded for 5-6 years.
If the dowel appeared in the crops of perennial grasses (clover, alfalfa), they are mowed before flowering or seeding of the dowel. Timely mowing is especially effective against field dodder, 95% of the stems of which are located at a distance not exceeding 5 cm from the soil surface, and with a low cut are easily removed from the field along with hay.
- Popkova. K.V. / General phytopathology: a textbook for high schools / K.V. Popkova, V.A. Shkalikov, Yu.M. Stroykov et al. - 2nd ed., Rev. and add. - M .: Drofa, 2005 .-- 445 p.: Ill. - (Classics of domestic science).