29th September 2019 By Daana 0

Dodder is a dangerous neighbor Part 2

The seeds of many species of dodder are very similar in weight, shape, and often color to the seeds of cultivated plants on which they 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 carmine 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 rotate 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.

So sales break the skin of the sucker, deeply enters the body of the nourishing plant and goes to its conducting bundle. Having reached the wood, the central cells of the article turn into tracheids, and the phloem elements, in turn, are connected 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 at the expense of 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 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.

Prevention measures

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 with sowing is the soil, in which large stocks of seeds of the parasite accumulate. 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, the germination of seeds is stimulated by provocative autumn and spring irrigation.

From alfalfa and clover crops that are most often infected with dodder, the parasite spreads to other crops, especially those that follow them in 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.