Broomrape is the enemy of a good harvest!
The largest group of obligate underground parasites is broomrape. Kind broomstick — ABOUTrobanche Compared with other genera of the family, it is characterized by an exceptional variety of species composition (up to 120 species are known). Representatives of the genus Broomrape parasitize on wild, cultivated and weed plants.
Within our country, there are more than 40 species of broomrape, including five parasites of cultivated plants. The most harmful are the following species that infect technical, fodder, decorative, vegetable, gourds: sunflower broomrape - O. Sitapa, branchy or hemp broomrape - ABOUT. ramosa, Egyptian broomrape, or melon, - O. aegyptiaca, mutant broomrape - O. mutellii and broomrape alfalfa - O. lutea.
In the process of evolution, all organs of plants of this genus, except the stem, flowers and fruits, underwent significant changes: the roots turned into short fleshy sucker fibers, sucked to the roots of the host plant, the leaves lost chlorophyll and became small brownish, yellowish or lilacous scales with the next arrangement . The broomrape stem is light brown, yellowish, pinkish or bluish, fleshy, erect, branching or not branching, with a club-shaped base equipped with suckers that penetrate the root tissue of the host plant. The height of the stem can reach 50 cm or more.
With a strong contamination of the soil with broomrape seeds and in the presence of an affected plant, up to 200 peduncles of the parasite and more can fall on one plant.
The broomrape flowers are axillary, five-membered, with a two-lipped German blue, whitish or purple in color, with four stamens, collected several dozen in an ear or spike-shaped panicle. They are capable of self-pollination in the event that there was no cross, which is carried out with the help of a broomrape fly-phytomysis - Phytomysa orobanchia and bumblebees. Ovary - upper, single-rooted. Fruit - a box opening with two or three leaflets and containing up to 2 thousand seeds or more. The seeds are tiny, 0.2-0.6 mm long, 0.17-0.25 mm wide, roundish or oblong, dark brown, with a cellular surface. On one broomrape plant, there can be up to 100 thousand.
Almost all broomsticks have a relatively high specialization. Each species is adapted to parasitize on a limited circle of nourishing plants belonging to only one or several specific families, genera and species.
Sunflower broomrape parasitizes mainly on sunflower; from other plants, tomato, tobacco, shag, safflower, wormwood, and others are affected. Egyptian or melon worm infects about 70 plant species, including potatoes, tobacco, cabbage, tomato, and pumpkin. Branched infection, or hemp, mainly infects tobacco, tomato, hemp, cabbage, carrots, melon, etc.
The specialization of broomrape changed in the process of evolution, which was facilitated by natural selection and human activity. Along with new forms of plants, in the process of constantly changing relationships between the parasite and the host, new physiological populations and races of the parasite emerged and spread, differing in virulence and ability to overcome the protective properties of the host plant organism. The number of races of a parasitic species in a given region is determined by the duration of cultivation of the host plant and the diversity of its genotypes. The emergence of new, most aggressive races of broomrape leads to the loss of immunity by varieties. For example, in sunflower-immune varieties of broomrape at the place of its introduction into the root of the host plant, swellings form that prevent the further development of the parasite. Affected varieties do not have such swellings.
The development of the parasite is determined not only by the immunological properties of the host plant, but also by the timing of sowing, soil fertility, the supply of its seeds in the soil, the depth of their seeding, the structure of the root system of the feeding plant, the amount of moisture in the soil, etc. Depending on the biology of the host plant, broomrape developed perennial, biennial, annual, and even ephemeral forms. Development, habit and their other features depend on the properties of the nourishing plant.
The distinctive features of certain types of broomrape are the morphology of the stem and flower, as well as parasitic specialization.
Sunflower infection differs from other types of broomrape with a branchless stem up to 30 cm in height and more. Her bracts are ovoid, acute; corolla 12–20 mm long, tubular, strongly bent forward, almost not expanded at the end, of brown color. The species develops well on cultural and wild-growing representatives of the nightshade and asteraceae families. Among them are sunflower, tobacco, shag, tomato, railing, safflower, sea wormwood, Australian wormwood, wormwood, common wormwood, common gooseberry, solonchak bighead, odorless chamomile, and salt marsh aster. Sunflower infection does not infect castor oil plant, soybean, lallemanthus, cabbage, potatoes, and mustard.
At egyptian broomrape, or melon, branching stalk with few ovate-lanceolate scales 20-30 cm long. Corolla 23-27 mm long tubular-funnel-shaped, significantly widened in the limb. The species mainly infects gourds, as well as shag, tobacco, potatoes, sunflowers, mustard, turnips, peanuts, sesame seeds, tomatoes, cabbage, eggplant and other vegetable, industrial and wild plants (up to 70 species). Does not infect cotton, beets, alfalfa, grapes. Physiological races are known.
Branched or hemp infection, has a thin, up to 4–5 mm in the middle part, with rare scales, a stem up to 15–25 cm long, thickened at the base, with a large number (up to several tens) of side shoots. The flowers are smaller than those of the above described species of broomrape, with a diameter of up to 10-15 mm. Branched infection is less specialized in comparison with other species of the genus. It infects many species of nightshade, asteraceae, cabbage (cruciferous), pumpkin, and others. Among them are tobacco, shag, hemp, hops, cabbage (cabbage, cauliflower, kohlrabi), mustard, turnip, saffron, horseradish, railing, pumpkin, melon, carrots, dill, coriander, sunflowers, lentils, medicinal sweet clover, nightshade, peanuts, ropes, etc. Does not infect beets, parsnips, lallemanthus, parsley, eggplant, peppers. Physiological races are known.
Broomrape seeds, light as dust, are freely carried by wind, water, stick to the feet of people who work with tools, store organs of plants, and are carried by dust storms over vast distances.
The germ in the broomrape seed, like in many other parasitic plants, is underdeveloped, not divided into root, stem and cotyledons, but consists of groups of cells surrounded by storage tissue containing the nutrients necessary for the seedling until it sucks to a nourishing plant. The optimum temperature for germination of broomrape seeds is 22–25 ° С. They do not germinate at temperatures below 20 ° C and above 45 ° C, some above 50 ° C. The temperature optimum for seed germination of Egyptian broomrape and branched broomrape is higher than that of sunflower broomrape.
Broomrape seeds can germinate at any depth of the arable horizon under the influence of root secretions of certain species of host plants. If there are no such plants near the broomrape seeds, then they do not germinate, however, they can remain viable for 8-12 years. According to some researchers, with an increase in the concentration of root secretions to a certain limit, the percentage of sprouted seeds also increases. In less moist soil, the concentration of root excretion will be higher, therefore, especially severe depletion of sunflower by broomrape is observed in dry years.
A substance secreted by host plants that stimulates the germination of broomrape seeds was found not only in their roots, but also in the leaves and in the bark of the stem (sunflower). This substance is resistant to boiling and drying. It was possible to isolate its crystalline fraction containing a concentrate of stimulating substances.
Root secretions of lettuce, flax, corn, soybeans, perennial leguminous herbs (alfalfa, clover, horned lamb), tomato, earthen pear and others stimulate the germination of broomrape seeds, but since these crops are not susceptible to broomrape, its seedlings, not finding suitable nourishing plants are dying. The use of provocative crops in the fight against broomrape is based on this phenomenon.
The number of germinated broomrape seeds and their germination energy depend not only on the root secretions of the host plant, but also on a number of other conditions: the type of the feeding plant, its immunological properties and the concentration of cell juice, the virulence of the broomrape and the proximity of its seeds to the root of the plant the host, from the reaction of the environment, temperature and soil moisture, etc.
Germination, suction of broomrape to the roots of the nourishing plant and its initial development occur secretly in the soil. During germination, a slightly crimped sprout with a club-shaped thickening at the end emerges from the seed, growing in the direction where the concentration of root secretions of the blinking plant is higher. Touching the root of a plant susceptible to broomrape, the thickening begins to grow, and the rest of the sprout atrophies, turning into a thin thread; then the connection with the seed coat is interrupted.
Soon, the thickening at the root of the host plant is covered with tubercles giving it the appearance of a star. One of the haustoria, pushing apart the cells of the parenchyma of the root cortex, penetrates into it and reaches the xylem. Tracheids developing inside the haustorium merge with the conducting elements of the host plant into a single whole so that it is difficult to find a border between them. At the opposite end of the broomrape, a kidney is formed, covered with numerous scales, which later turn into modified leaves. The bud develops into a flower-bearing stem that carries inflorescence to the surface of the soil.
Germination of broomrape seeds scattered in the soil, its absorption and development occur gradually as the root system of the nourishing plant grows. Therefore, on the roots of one host plant, one can observe all phases of the formation of the parasite; from seed germination to pod ripening. From the moment of germination of broomrape seeds to the appearance of its plants on the soil surface, at least 1.5-2 months pass. You can evaluate sunflower varieties for broomrape resistance without waiting for the broomrape flower stalks to leave the soil by the presence of sucking broomrape on the roots of the host plant.
Broomrape Control Measures
A complex of techniques is used to protect against flowering parasites.
- protection from the entry of broomrape seeds into farms and areas where it does not occur, and thorough cleaning of seeds in infected farms;
- the systematic weeding and elimination of broomrape before it forms seeds and inflorescences to prevent new infections of the soil. Weathered broomrape is carried out of the field, burned or buried deeply;
- the introduction of crop rotation, excluding the affected crops for a long period (at least 6-8 years).
Since broomrape infects various wild plants, the fight against it is an indispensable link in the system of protective measures.
You can free the soil from broomrape with the help of thickened sunflower crops (provocative crops), which cause massive germination of broomrape seeds. During the appearance of the largest number of inflorescences of the broomrape or at the beginning of its flowering, the culture is harvested for silage. The broomrape does not have time to spread, and when harvesting the next crop of its seeds will be much less. For the same purpose, clover or clover is sown. Especially good results are obtained by introducing into the culture new broomrape-resistant and broomrape-tolerant varieties of sunflower and other crops.
- Popkova. K.V. / General phytopathology: a textbook for high schools / K.V. Popkova, V.A. Shkalikov, Yu.M. Stroykov et al. - 2nd ed., Revised. and add. - M .: Drofa, 2005 .-- 445 p.: Ill. - (Classics of domestic science).
- Key to broomrape flora of the USSR (from atlases of fruits and seeds). / E.S. Teryokhin, G.V.Shibakina, etc. - St. Petersburg: SCIENCE, 1993 .-- 127 p.