Garlic continuous cropping, like other field crops, often causes disasters with the adaptation and prevalence of diseases, insects and weeds. In particular, there is no specific medicine for preventing and treating viral diseases in the world at present. Generally, the incidence of symptoms in the field is about 30%, and the severity rate is 100%. Not only various viruses, but also various vectors. It is generally spread by vector pests such as aphids, leafhoppers, mites and nematodes, which makes people hard to prevent. It has developed into the number one "killer" of garlic in the world. There are many kinds of garlic viruses, which often cause dwarfing, mosaic, distortion, non-bolting or short and thin stems, small garlic heads, low yield, poor quality and heavy losses, which is the primary factor that causes the degradation of garlic varieties at present.
In order to effectively prevent and control plant virus diseases, people have made arduous explorations for decades, but they have never found an effective medicine to prevent and control virus diseases. So scientists turned their attention to the study of cell cloning and virus-free tissue culture of plant meristem (due to genetic and species evolution reasons). ), made epoch-making achievements and entered the stage of industrialization. According to Xu Peiwen's research report, the average weight of four generations of virus-free garlic in Cangshan, Shandong Province is 37 grams per garlic bolt, which is 2.55 times that of poisoned Cangshan garlic (control). Garlic that meets the export standard (head circumference ≥ 15cm) accounts for 6 1.25% on average, which is 8.8 times that of the control. The yield per 667 m ~ 2 of young garlic shoots and garlic heads were 958.75 kg and 1560 kg, respectively, which were higher than the control 155.5% and14.0%, respectively, and the yield-increasing effect could be maintained for 5 ~ 10 generations. According to the research, the biological basis of yield increase of virus-free garlic is that the leaf area of virus-free garlic increases by 765,438+0.0% ~ 65,438+005.0%, and the chlorophyll content increases by 65,438+08.1%~ 47.1%. It can be seen that virus-free and rapid propagation of garlic is the key technical measure to restore and improve its varieties.
It is precisely because the virus-free tissue culture and rapid propagation technology of garlic can fundamentally treat virus diseases, restore and improve garlic varieties, and increase production and income, so the international community has always attached great importance to the research and development of its technology and the industrialization of its achievements in the past two or three decades. The research on tissue culture of virus-free garlic in China began in the early 1980s. Shandong Cangshan garlic took the lead in successfully organizing virus-free garlic and applied virus-free garlic seeds to field production. However, due to its low micropropagation coefficient, it is necessary to carry out generation propagation in insect-proof net room, which will inevitably increase the chances of virus infection and production cost of virus-free garlic seedlings, resulting in low quality and high price of seedlings, which is difficult to popularize and apply in a large area. The rapid propagation coefficient of virus-free garlic in indoor tissue culture is the bottleneck technical link that restricts its industrialization. Therefore, around the key link of improving the coefficient of micropropagation, Professor Li, the doctoral supervisor of Vegetable Research Institute of Nanjing Agricultural University, led his graduate students to tackle key problems step by step, and was finally conquered by his disciple Xiong Yi 1999. The explosion of virus-free garlic tissue produced new growth points and formed miniature test-tube bulbs, which were directly used for field sowing. The micropropagation coefficient was as high as 70-80, which laid a technical foundation for the industrialization of virus-free garlic and greatly accelerated its industrialization process. This technology has obtained the national patent.
There are many kinds of garlic viruses. Since Brierley and Smith in the United States first reported that almost all cultivated varieties were infected with garlic mosaic virus in 1994, according to incomplete statistics reported in the literature, there are as many as 16 kinds of viruses naturally infecting garlic, which are divided into 10 groups, among which there are three groups of viruses mainly distributed in China, including potato Y virus group, tobacco mosaic virus group and carnation latent virus group.
Garlic virus can be transmitted by insect vectors or juice, among which insect vectors are an important transmission route, and many garlic viruses can be transmitted by aphids, mites and nematodes. Garlic virus has a strong specificity to insect vectors, and there are differences in virus transmission between the same insect vectors. For example, Myzus persicae can transmit GLV-G and GMV, while Myzus brassicae, Myzus tritici and Myzus tritici cannot transmit these two viruses. The spread of juice is due to the friction between the leaves of healthy plants and sick plants, or people working in the field, which makes the healthy leaves slightly injured and the virus spreads from the wound. Garlic virus spreads and infects through the above two ways, and then passes to the next generation of asexual offspring through bulbs, thus accumulating in garlic nutrition for a long time, leading to the decline of yield and quality.
The distribution of virus in plants is uneven. In infected plants, the apical meristem is usually virus-free or has only a very low concentration of virus. In older tissues, the number of viruses increases with the distance from the shoot tip. According to related tests, the content of OYDV-G in bulbs is higher than that in leaves, and the content of old leaves is higher than that of young leaves. Except for the outgrowth bulb in garlic plants, all other tissues contain viruses, but their distribution is uneven.
In the process of garlic virus identification and virus-free tissue culture seedlings, many detection methods can be used, such as visual inspection, indicator plant identification, serum melon and electron microscope observation.
Virus-free tissue culture of garlic is an effective method to prevent and control garlic virus diseases and restore and improve garlic varieties. Virus-free tissue culture of garlic includes the micropropagation process of culture medium, virus-free materials, test-tube seedling and bulb culture, virus-free and purity-preserving.
Up to now, garlic vegetative stem tips, reproductive stem tips, root tips, leaf tips, garlic petals, storage leaves, vegetative leaves, flower stems, scale buds, flower primordium, aerial root bulbs and garlic somatic cells have been successfully used for tissue culture to form virus-free garlic test-tube seedlings. Among them, stem tip virus-free tissue culture is the majority, and the size of stem tip is usually 0.1~ 0.9 mm. The smaller the stem tip, the better the virus-free effect. Garlic stem tip culture combined with heat treatment can greatly improve the virus-free rate. Bear (1999) directly organizes virus-free test-tube bulbs by using reproductive stem tips, and the propagation coefficient is ten times that reported before, which lays a technical foundation for the industrialization of virus-free garlic seeds.