Flowering plants-parasites - General phytopathology

Flowering plants-parasites

It is known that most plants are photosynthesizing autotrophs, but among them there are many species that partially or completely use for their nutrition the products created by other plants, since it is more energy-efficient to draw products than to produce them independently.

According to the type of parasitic , flowering plants can be divided into half parasites that have retained the ability to photosynthesize, but mineral salts and water are obtained from host plants, and full parasites , which also lost the ability to photosynthesize. Both semiparasites and complete parasites are found stem and root.

Among the stem parasites , the species mistletoe ( Viscum spp.), whose bushes with stiff dark green leaves on branching stems are noticeable, especially in the impersonal period, in the crowns of deciduous trees. Green leaves and branches of mistletoe are capable of photosynthesis, but instead of roots in the base of the mistletoe bushes, suckers are formed-haustoria embedded in the branches of a tree and sucking out solutions of mineral substances from it. Seeds of mistletoe form in white or yellowish berries, which eagerly eat thrushes, waxed and other birds. Thrush deryaba even got a specific name viscivorus, ie. a devil mistletoe. The seeds of mistletoe are covered with a sticky jelly-like substance and therefore adhere to the surface of the beak. Trying to get rid of them, birds clean the beak of the branch, damaging their skin, so that the seeds adhering to the twigs give germs that penetrate into the finished wounds on the tree. Consequently, birds not only spread the seeds of mistletoe, but also contribute to infection.

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Among the root sex parasites there are a lot of plant species widely distributed in meadows and pastures - , mariannik "Ivan-da-Marya" and others. Their seeds germinate in the soil, the stem is brought to the surface and forms a normal shoot with leaves and flowers, and the spine is introduced into the root of the growing plant next to it. Consequently, like the mistletoe, the root half parasites consume only water and minerals from the host plant. However, they often significantly weaken plants and damage feed production and grazing livestock.

Complete parasites are much more harmful.

The most common stem parasites are dodder (genus Cuscuta). Yellow or reddish, strongly branching stems of the dodder tangle the stems of the host plant and with using suckers-haustorium suck nutrients out of them. The dodder is devoid of roots and leaves, there is no chlorophyll in its cells, all the nutrients it receives from the host plant. Therefore, the defeat of the dodder greatly weakens the plants, reduces the yield of seeds and green mass. On the stems of the dodder, small flowers are formed, and then - boxes with seeds, often similar in shape and size to the seeds of the host plant, so they are difficult to separate during sorting, and they fall into batches of harvested seeds. When sowing, the seeds of dodder come into the soil and germinate. The lower root part of the shoot penetrates into the soil, and the upper part, leaving the soil, makes circular motions. Touching the stem of the growing plant next to it, the stem of the dodder twists around it. Then Haustoria are formed, the juices of the host plant begin to feed, the root part dies, and the overground grows stronger, entangling its prey. The branches of the stem are transferred to nearby plants, so the dodder can entangle a large number of them.

Among root parasites the greatest harm to agriculture is caused by broomrape (genus Orobanche). Colorless shoots of broomrape with chlorophyll-deprived leaves that look like scales, grow on the roots of the feeding plant, to which they are attached with the help of Haustorium. Dozens of broomrape can parasitize one bush of tobacco or of sunflower . The affected plant gives them too many nutrients, so it lags behind in growth and sometimes does not form seeds at all. The shoots of the broomrape end with purple or pinkish inflorescences, in which a huge number (up to half a million) of small seeds is tied. After shedding, the seeds are able to remain in the soil for a long time (up to several years) without loss of germination. Germination of seeds stimulates root secretions of susceptible plant species. The seedlings grow in the direction of the concentration gradient of these secretions and, in contact with the roots, form the haustoria implanted in them. Many species of flowering plants parasitize on the roots of trees. Especially great is their diversity in the rainforests, where they often have the appearance of lignified lianas.

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