Pictures of yam growth.

Usually, in the whole growth cycle of yam, it goes through germination, growth and dormancy. With the change of climatic conditions throughout the year, Chinese yam enters four stages in turn: germination stage, vine (strip) germination stage, tuber expansion stage and dormancy stage.

First, the budding period

The germination period is from the terminal bud (or adventitious bud) of yam tuber to emergence. Yam seedlings emerge quickly, which takes 20~30 days under field conditions; The germination time of yam segment is longer, lasting 40~50 days; Reiyoshi germinates faster, generally 20-25 days. In the process of germination, shoots are pulled up from the top of buds, and tubers are formed down from the base of buds.

At the same time, the root primordium is produced by the peripheral cells of each dispersed vascular bundle in the bud base, and then the root primordium passes through the epidermis, gradually forming the absorption root system of yam. When the tuber grows to 1~3 cm, the bud breaks through the soil. Generally, only one bud and one tuber can be formed from the seeds of Dioscorea opposita and Laiji, and multiple buds and tubers can be formed from the segments of Dioscorea opposita.

The germination and emergence of yam are closely related to weather conditions. If the weather is clear, the temperature is high, the soil moisture is suitable, the germination period is short, and the seedlings emerge quickly; On rainy days, the temperature is low, the soil moisture content is high (or the soil is dry), and the germination period is long. In the case of high soil humidity or early sowing and low temperature, it is often easy to cause seed potato to rot, leading to seedling shortage and broken ridge.

Second, the flowering period of yam

The period of Chinese yam from budding to budding to Lai Ji formation is 50-60 days. This period is the initial stage of tuber formation. Buds grow rapidly after being unearthed, reaching 1 m in 7~ 10 days. At this time, the first leaf unfolds, and then the stem and leaf continue to grow, and side branches appear.

The number of yam seed roots no longer increases, but fibrous roots appear in large numbers and develop in depth and breadth, and the main absorption roots of yam are initially formed. At the same time, yam tuber continued to grow downward, and a large number of adventitious roots appeared around the tuber.

During this period, the growth of yam plants changed from completely relying on seed potatoes to relying on the nutritional growth of yam stems and leaves. During this period, the growth centers were mainly overground vines and underground roots, and the tubers grew less, mainly in depth, with less thickening, and the tubers were light in color and milky white. In terms of cultivation measures, we should focus on loosening the soil and cultivating in the middle, promote the root system to be solid, remove weeds in the field, apply seedling fertilizer well, and promote the early growth and rapid growth of vines.

Third, the tuber expansion period of yam.

The tuber expansion period of yam from germination to stem and leaf growth is basically stable, lasting 60~80 days. It can also be divided into two stages: the peak of tuber expansion and the end of tuber expansion. This period is a period when the vines on the ground and underground tubers grow vigorously at the same time, but the growth center has shifted from vine growth to tuber. More than 85% of the dry weight of tuber was formed in this period.

The swelling of yam tuber to seed is different in different periods. Tubers began to elongate slowly in mid-May and basically ended in mid-September. The monthly elongation is August > June > July > September, and the average daily elongation is 7.2 mm, 6.5 mm, 6.4 mm and 1.3 mm respectively. In ten days, the fastest elongation is in late July and early August, and the average daily elongation is 10 mm, 8.5 mm and 9.5 mm respectively.

Fourth, the dormant period of yam.

The dormancy period is from the first frost when Chinese yam leaves begin to fall off to the second year when tubers germinate. Yam is not cold-tolerant. In autumn, when the temperature drops below 12℃, the vines of yam stop growing, the leaves further age, the protoplasm and chlorophyll of cells begin to disintegrate, most nutrients are transported to the tuber, and finally fall off in layers at the base of petiole.

During the dormant period of Chinese yam, tuber meat stores a lot of starch, protein and fat, and the intracellular water content decreases, the protoplasm viscosity increases, the terminal bud forms, the organs in the bud differentiate, and the tuber epidermis thickens, which is beneficial to safe wintering.

The dormancy of Chinese yam is affected by environmental factors such as light, temperature and plant hormones. Low temperature and short sunshine in late autumn are beneficial to the formation and accumulation of abscisic acid in yam, and the existence of abscisic acid inhibits germination. In the late dormancy stage of yam, abscisic acid in tuber gradually decreased, while gibberellin promoting germination gradually increased, and tuber could germinate and grow when the conditions were suitable in the next spring.

After Chinese yam enters dormancy, the tuber yield is the highest, the nutrients are the richest, the fragrance is the strongest and the quality is the best. We should seize the time to harvest and store, prevent freezing and rot, and do a good job in seed selection to ensure the supply of seed potatoes in the coming year.

Extended data:

First, the growth environment:

Yam requires fertile, well-drained sandy soil, and likes warm and sunny places, but it is afraid of frost and avoids continuous cropping.

Second, the geographical distribution:

Originated in Asia, it has been cultivated in China since ancient times, both in the north and south, and distributed in the wild. It is mainly produced in Henan, Shanxi, Shandong, Shaanxi and other places.

Third, the nutritional components:

Every 100g yam contains about 75g of water, carbohydrate 14.4~ 19.9g, protein 1.5~2.2g, fat 0. 1~0.2g, dioscin 50ug, B vitamins and vitamin C. The sticky substance in yam is mucin, which consists of mannan and globulin.

References:

Baidu encyclopedia-yam