① Short-lived seeds: the life span ranges from several hours to several weeks. Such as poplar, willow, elm, oak, cocoa, coconut, tea and so on. Willow seeds can only germinate within 12 hours after maturity. The life span of poplar seeds is generally not more than a few weeks.
② Intermediate seeds: life span is several years to several decades. The seed life of most cultivated plants such as rice, wheat, barley, soybean and kidney bean is 2 years; Corn for 2 ~ 3 years; Year of rape 3; Broad bean, mung bean, cowpea and Chinese milk vetch 5 ~ 1 1 year.
③ Long-lived seeds: the life span is more than several decades. Beijing Botanical Garden once accelerated the germination of lotus seeds dug out of peat soil for thousands of years, and later it actually blossomed. As far back as the Pleistocene (654.38+0 million years ago), the seeds of Arctic feather lentils buried in the permafrost of the Arctic can germinate rapidly in the laboratory after being dug out. These are the seeds of longevity.
Some manifestations of seed aging and deterioration are:
(1) seed discoloration: for example, the color of broad bean, peanut and soybean seeds becomes darker; The endosperm of cottonseed may turn green; The hypocotyl of cereal seeds turns brown in high humidity environment; White lentil seeds fluoresce with aging.
(2) The membrane system inside the seed was destroyed and the permeability increased.
③ Gradually lose the ability to produce hormones related to germination, such as GA, CTK and ethylene. (4) Slow germination, low germination rate, many deformed seedlings, poor growth potential and weak stress resistance, resulting in low biological yield and economic yield. The longevity of seeds is mainly determined by heredity, but it is also affected by environmental factors and storage conditions. According to the characteristics of storage period of plant seeds, they can be divided into two categories: normal seeds and stubborn seeds.
① Preservation of normal seeds: Normal seeds will enter the mature dehydration stage in the later stage of development, followed by the end of storage material accumulation. During this period, the seeds lose about 90% water and enter a dormant state, and the metabolic activities in the seeds basically stop. Most crop seeds fall into this category. This kind of seed has a strong tolerance to dehydration and can be preserved for a long time at a very low water content without losing its vitality. Generally speaking, seed moisture content and storage temperature are the main factors to preserve seeds. Harrington (1973) put forward two standards: ① every time the water content of seeds decreases 1%, the storage life of seeds doubles; ② Every time the storage temperature of seeds drops by 5.6℃, the storage life of seeds will be doubled. It has been suggested that the ideal storage conditions of seeds are: water content 4% ~ 6%; Temperature -20℃ or lower; Relative humidity 65438 05%; Moderate hypoxia; High carbon dioxide; The storage room is dark, away from light and high-energy rays, etc. It has also been pointed out that when the water content is 1% ~ 5% and the temperature is-18℃, the seed vitality can reach more than 1 century (International Commission on Plant Genetic Resources, 1976). Usually, the factors that can reduce respiration have the effect of prolonging the life of seeds. In addition, the seeds stored with skin at harvest are more protective, reduce mechanical damage and microbial invasion, and have longer life and higher vitality than those stored by threshing.
② Preservation of recalcitrant seeds: recalcitrant seeds are not resistant to dehydration, and drying and low temperature should be avoided during storage. These seeds still have high water content (30% ~ 60%) when they are mature, and they can automatically enter the germination state soon after harvest. Once dehydrated (even if the water content is still high), it will affect the germination process and lead to the rapid loss of vitality. Many fruit trees in tropical and subtropical regions, such as litchi, longan, mango, cocoa, rubber, coconut, chestnut and oak, and some aquatic herbs, such as water hyacinth, water chestnut and water bamboo, are stubborn seeds. If these seeds are harvested and placed in a ventilated place indoors, their life span is often only a few days or longer. For example, the suitable storage conditions of cocoa seeds are: water content 33% ~ 35%, temperature 65438 07 ~ 30℃, storage period at least 70 days; However, when the water content is lower than 27% and the temperature is 65438 07℃, the germination ability is rapidly lost. Seeds of mango, litchi, longan and pineapple have good storage effect at 65438 05℃, but they will be damaged at 5 ~ 65438 00℃. ⑴ Sunshine length: This is the most important factor to induce and control bud dormancy. For perennial plants, long-term sunshine usually promotes growth, while short-term sunshine will stop elongation and form dormant buds. In chestnut, storax and other plants, sunshine-induced bud dormancy has a critical sunshine length. When the sunshine length is shorter than the critical sunshine length, it can cause dormancy, but when it is longer than the critical sunshine length, it will not happen. For example, Robinia pseudoacacia, Betula platyphylla and Larix gmelinii seedlings stopped growing and went into dormancy after a short day 10 ~ 14. Short sunshine and high temperature in winter can induce the formation of dormant buds of aquatic plants (such as Plantago asiatica, Trionyx sinensis and Utricularia). Short sunshine also promoted the dormancy of hibiscus flower buds. However, lily of the valley and onion are the opposite, and long-term sunshine induces dormancy.
⑵ Dormancy promoter: abscisic acid is the most important substance to promote dormancy, followed by hydrogen cyanide, ammonia, ethylene, mustard oil and various organic acids. The reason why short sunshine can induce bud dormancy is that short sunshine promotes the increase of abscisic acid content. The birch extract (containing ABA) can inhibit the growth of birch seedlings in short day, and the buds with all the characteristics of dormant buds in winter can be formed by prolonging the treatment time.
When dormant buds resumed growth, the activity of cytokinin in the extract increased. The dormancy formation of perennial herbs is the same as that of woody plants mentioned above. In dry season areas, these herbs go into dormancy in dry season. (1) Release the dormancy of buds
① Low temperature treatment: Many woody plants need to go through a low temperature of 0 ~ 5℃ for 260 ~ 1000 hours to break their dormancy. Plants released from dormancy can germinate and grow in a warm environment. Some dormant plants can also be given long-term sunshine or continuous illumination without low temperature treatment to relieve dormancy. However, once the bud dormancy of most woody plants in the north temperate zone is fully induced by short-term sunlight, it can not resume growth after long-term sunlight, and usually only low temperature can relieve dormancy.
(2) Warm bath method: soak the whole overground parts or branches of plants in warm water at 30 ~ 35℃ 12 hours, then take them out and put them in the greenhouse to relieve the dormancy of buds. This method can make clove and forsythia blossom early.
(3) Ether fumigation: the whole plant or isolated branches are fumigated with a certain amount of ether in a sealing device 1 ~ 2 days to germinate. For example, 1 1 month, put the roots of clove and lily of the valley into a closed container with a volume of 1 liter, put 0.5 ~ 0.6 ml of ether into the container, take it out after 1 ~ 2 days, and store it at 15 ~ 20℃ for 3 ~ 20 days.
④ Plant growth regulator: Gibberellin is effective in breaking bud dormancy. Spraying 1000 ~ 4000μ L/L GA solution on peach seedlings and grape branches, or spraying 100 ~ 200μ L/L kinetin on peach seedlings can break the dormancy of buds. Soak potatoes in 0.5 ~ 1.0μ l/L GA solution 10 ~ 15 minutes, and the buds will germinate quickly and orderly.
⑵ Prolonging the dormancy period of buds: In agricultural production, the dormancy period of storage organs should be prolonged to make them resistant to storage and avoid losing market value. For example, potatoes are easy to germinate during storage, and at the same time, they will produce toxic substances called solanine, which cannot be eaten. 2 ~ 3 weeks before harvesting, 2 000 ~ 3 000 μ L/L of fresh green pigment can be sprayed in the field, or 1% sodium naphthylacetate solution or methyl naphthylacetate clay powder can be evenly coated on the tuber to prevent germination during storage. Bulb vegetables such as onions and garlic can also be treated in a similar way.