Yam plants are composed of roots, stems, leaves, flowers, fruits and seeds. Botanical characteristics of yam roots. For a long time, people have often mistaken the yam they eat for the roots of yam.
In fact, the yam we eat is a metamorphosis of its stem, which is a tuber (some scholars believe it is a rhizome tuber), not a root. Where are the real roots of yam? People who eat yam are generally not seen. After the yam seed potatoes sprout, about 10 thick roots will grow from the lower end of the stem. At first, they mostly grow in transverse radiation, only 2 to 3 centimeters from the soil surface. Then most of the roots grow 5 to 10 centimeters underground. .
When each root grows to about 20 centimeters, it then extends to the lower soil. The deepest can extend to 60 to 80 centimeters underground, which is suitable for the depth of yam tubers into the soil, but generally very little. There are long yams that exceed the depth of the yam underground tubers. Schematic diagram of underground growth. Because these roots of yam all occur at the mouth of the yam, they are generally called mouth roots. This is the main root system that maintains the yam throughout its life. On the one hand, these roots of yam support the growth of above-ground stems and leaves; on the other hand, they absorb water and nutrients in the soil to supply the growth needs of the huge above-ground stems and underground tubers.
Therefore, it is also usually called absorption. As the underground tubers elongate and enlarge, many adventitious roots will grow on the new tubers. This is the annoying hairy roots we encounter when eating yams ( Also called fibrous roots). The adventitious roots at the upper end of the tuber, especially near the mouth root, are also quite long and can absorb water and nutrients in the soil layer to help the mouth root nourish the plant. But at the lower end of the tuber, especially the adventitious roots deep in the soil, they are very short and thin, and basically have no ability to absorb water and nutrients. When the soil is particularly dry, the tubers can grow a large number of fibrous roots and have the ability to absorb water.
The root system of yam is not very developed and is mostly distributed in the shallow layer of the soil, but it has a heavy task of absorbing water and nutrients. The stems and vines on the ground are up to 3 meters long, and some are even longer. They have to be climbed up and put on the shelves, and the leaves are covered with shelves. These rely on the roots to supply nutrients, so that the branches and leaves can flourish, and photosynthesis is used to produce more nutrients and continuously transfer nutrients. It is transferred and stored in underground tubers, and gradually forms a product organ weighing several kilograms - yam. Therefore, it is necessary to pay attention to deep plowing and root cultivation during cultivation in order to obtain high quality and high yield.
There are three types of yam stems, two above ground and one underground. There are two types of above-ground parts. The stems and vines on the shelves are the real stems of yam. The scattered seeds (commonly known as yam beans) growing between the leaf axils on the above-ground stems are also a metamorphosis of the stems. They are called above-ground tubers, also called bulbils or aerial tubers. The third type of stem is the yam we eat. It is also a metamorphosis of the stem and is called underground tuber.
The position and shape of underground tubers vary, but they are all yam stems or abnormal stems. Among the three types of yam stems, two are the product organs of yam, the reproductive organs used for seed propagation, and the harvest targets of human cultivated yam. If you need yams, harvest underground tubers, and if you need extra yams, harvest above-ground tubers, or both, or a combination of both. In yam cultivation, it is necessary to adapt to the botanical characteristics of yam stems and adopt corresponding technologies to achieve the above goals.
To this end, the botanical characteristics of yam stems are introduced as follows.
The top buds of the above-ground vine seed potatoes sprout out of the soil, and soon they will grow into purple soft stems more than 10 cm long. They are herbaceous vines, creeping, smooth and wingless, with a round cross-section and green color. Or purple with green streaks. The vines are 3 to 4 meters long and the stems are 0.2 to 0.8 centimeters thick. When the seedlings are 20 centimeters tall, the internodes of the stems and vines are elongated and have the ability to twine. At this time, a bracket should be set up. It starts with just one main branch. As the leaves grow, axillary buds grow between the leaf axils, and then the axillary buds form side branches. The curling direction of yam stems is certain, usually right-handed, that is, the tip of the new shoot rotates to the right and curls up in the same direction as the hour hand of the clock.
The early nutrient supply comes from the nutrient supply process during the growth of adventitious buds. Later, while differentiating vascular molecules, the parenchyma cells located around the adventitious buds also differentiated vascular molecules and connected with the vascular molecules of the mother's base to transport nutrients to the young buds. Through cross-section anatomy, it can be seen that the yam stem has three parts: epidermis, epidermis and vascular column. The epidermis is a layer of neatly arranged cells. The periphery of the cortex is parenchyma tissue, and the inside is thick-walled tissue. Inside the thick-walled cells is a vascular column, and the outermost layer of the vascular column is a round of larger outer tough limited vascular tubes. Within the large vascular tubes, scattered small vascular tubes can be seen in some parts. Inside are the marrow and medullary rays, which are filled with large parenchyma cells. The morphological characteristics of the above-ground stems and vines of yam are different from ordinary monocots, but similar to dicots.
While the Lingyuzi yam forms tubers in the underground part, many Lingyuzi yams grow between the axils of the above-ground leaves. Lingyuzi is a deformation of axillary buds, that is, deformation of side branches, called aboveground tubers, also called aerial tubers or bulbils, commonly known as yam beans. Lingyuzi is oval in shape, 12.5 cm long, 0.8-2 cm in diameter, brown or dark brown, with a yield of 200-600 kg per 67 square meters. Under normal circumstances, yam fragments grow after the 20th node of the stems and vines, and begin to occur in the leaf axils of the third node downward from the top of the yam main stem or side branches. Anatomically, the remainder is called a bulbil.
The 1 to 2 layers of cells under the epidermis of the leaf axil often undergo pericircular division to increase the number of cell layers. A bulge in the leaf axil can be seen on the fifth to sixth nodes. Viewed from a longitudinal section, the cells in the second and third layers under the epidermis continue to divide at the periphery and at the periphery, forming a bulbil primordium of meristematic tissue. When small green bulbils are seen on the outside, terminal buds begin to differentiate internally, and root primordia are formed at the same time. Due to the circumferential division of the cells in the bulbil meristematic zone, the number of cells increases and the volume increases, and the bulbil becomes a spherical ball. The outermost layer of the ball is neatly arranged thin-walled cells, and within it are several layers of tightly arranged cells.
The parenchyma cells in the middle part of the bulbil contain abundant starch and protein granules, and the outer tough and limited vascular vessels are scattered between the parenchyma cells. Due to the continuous proliferation and increase of cells in the meristematic zone, the volume of bulbils increases rapidly until it stops growing in mid-to-late August. From the perspective of the whole yam plant, the remaining parts from the fifth to tenth sections from the top bud downward are the largest in size. Mature Lingyuzi has a rough epidermis. The outermost layer is a more fissured cork epidermis, and the inside is a periderm formed by the cork cambium layer. From the external appearance, it can be seen that there are bud eyes and degenerated scale leaves like potato tubers, and the terminal buds are buried in the periderm, making the appearance difficult to detect.
This is similar to underground tubers. There are no obvious nodes. If you look closely, you can see that the buds of Lingyuzi are arranged as regularly as potatoes. From an anatomical structure point of view, Lingyuzi only has root primordium and root differentiation, but no lateral root differentiation, and the terminal buds of that year are also in a dormant state. Lingyuzi contains a special substance called yam, which is not found in other parts.
The edible part of underground tuber yam is not a fat root, but a fat stem, so it is called a tuber. Figure 4 Yams grown in a natural state are called underground tubers because they grow underground. Because tubers grow like roots, they are sometimes called rhizomes, but they cannot be called roots. How are yam underground tubers formed? After the seed potatoes germinate, they first grow adventitious buds, which extend out of the ground and grow into stems and leaves. At the base of this new above-ground stem, you can see the division of parenchyma cells around the vascular tissue, which is the tuber primordium. As a result of continued division, scattered vascular molecules are differentiated.
At the lower end of the tuber, there is always a group of cells with a certain volume and strong meristematic ability. This is the basal meristem group of the yam tuber. The basal meristem tissue gradually differentiates and matures. The epidermis of young tubers is formed. There are basic tissues in the epidermis and scattered vascular bundles in the basic tissues. When the small tubers grow to 3 to 4 centimeters, the brown new yams can be clearly seen with the naked eye. The hypertrophy of the tuber is completely accomplished by the increase in the number and volume of the basal meristem cells. As can be seen from the cross section of the epidermis, the outermost layer is brown epidermal suberinized epidermis.
The inner part is composed of several layers of flat cork cells, cork cambium and cork inner layer. In older tubers, there are some large parenchyma cells within the periderm, which are loosely arranged and have large gaps. The parenchyma cells in the center of the tuber are scattered with outer tough limited vascular tubes. Between the two layers of parenchyma cells, there are several layers of cells with the ability to divide. The cells divide circumferentially to form a circle meristematic zone. The skin differentiates inwardly from the cells dividing in the meristematic zone. As a result, the tube molecules and alcohol wall cells are pushed out, so the tuber continues to grow thicker.
It can be seen that the yam tuber has neither the radiating vascular tubes characteristic of plant roots nor the double tough vascular tubes characteristic of plant stems. It only has parallel vascular bundles, so it has root and Intermediate nature of stem. Therefore, people also call this type of tubers basilis. Cross section of yam tuber From an evolutionary perspective, the organ differentiation of some types of Dioscoreaceae plants is relatively vague. It is difficult to call it a tuber because it has both the nature of a stem and the instinct of a root. It also looks like a middle type.
There are many variations in the shape of yam tubers. Although they can be roughly divided into elongated yams, flat yams and round yams, there are intermediate types of variation in each type. Especially for flat yams, the tubers vary the most, including palm-shaped, fan-shaped, splayed, and even elongated ones. The variation in yam tuber shape is mainly affected by genetics and environment, with soil environment having the greatest impact. Even among locally separated breeds, individual variation is complex. Precisely because of the variability of tubers, it is possible to continuously select according to established guidelines to obtain high-quality varieties of long stick-shaped yams, with a very thin upper end and a thicker middle and lower part. The general length is 60 to 90 cm, and the longest one can reach 2 meters. Its diameter is generally 3 to 10 centimeters, and the base weight of a single plant is 0.5 to 3 kilograms, and the heaviest one can reach more than 5 kilograms.
Yam planting technology:
1. Land preparation and trenching
Yam is a shallow-rooted crop with a long growth period and is cropped once a year. Generally, in spring, the ground temperature reaches Planted in the field at 10℃. For yam planting, you should choose fields with high, dry terrain, good drainage, deep soil, soft sandy loam or light loam. The soil quality above and below is required to be consistent, and the soil should be slightly acidic to neutral. Yams are not suitable for continuous cropping and should generally be rotated every 2-3 years.
When digging cultivation ditches, the distance between them is generally about 1 meter, the depth is 0.6 to 1.0 meters, and the width is 25 centimeters. When digging trenches, stack topsoil and subsoil separately to allow the soil to be fully weathered. After the soil thaws in spring, first fill the trench with the lower soil and then the topsoil to keep it stable. Combined with ordinary acres of filled soil, Streim microbial inoculant, 50kg-70kg of phosphate fertilizer, 25kg-30kg of ammonium bicarbonate, and 25kg-30kg of potassium sulfate are applied on it.
Avoid applying a large amount of immature organic fertilizer to prevent root burning and tuber branching.
2. Seed block treatment
20-25 days before planting, select the hard root of the disease-free block that meets the characteristics of the planted variety for seeding, and cross-section one end of it. Dip it in slaked lime powder and put it in the sun for a few days to sterilize and promote germination. To increase the reproduction coefficient, the roots must be cut off for reproduction. That is to say, select a thinner root tuber about 1m long and 2.4-4.5cm in transverse diameter, cut it into several small sections 15-20cm long, and mark the upper and lower ends with a brush. Then dip each section in lime and place it horizontally in the sun to dry the seeds. Sun dry until there are fine cracks at the end of the section. During the drying period, handle the seeds with care to prevent scratches. At the same time, protection from wind, rain and frost should be done.
3. Yam cultivation
After the yam cultivation ditch is filled with soil and fertilizer, a flat border of about 1 meter wide is made on the ditch. When planting, open a planting ditch about 10 cm deep and wide in the middle of the flat border, and then water it. After water seeps in, spread the yam seeds into the ditch in single rows with a spacing of 15 to 20 centimeters, and plant about 4,000 yam plants per acre. Cover with 8 to 10 cm of soil, and then cover with mulch to protect moisture, increase soil temperature, and promote seedling emergence. If you use "yam beans" to propagate yam seeds, you can use two rows in one border to increase the reproduction coefficient. The row spacing is 40 to 50 cm, and the plant spacing is about 10 cm. About 12,000 plants are planted per acre.