Puzuqin

It is a single-stranded deoxyribonucleic acid, non-enveloped, spherical conjoined genome virus. The name of this group comes from the Latin Gemini, which means twins. The diseases caused by conjoined viruses have a long history, but the understanding of the properties of this group of viruses began in the 1970s. Bok et al. (Bock et al., 1974) first purified maize stripe virus (MSV) and found that its particles were two spherical symbionts. Harrison (B.D.Harrison, 1977) and Goodman (197 1) both proved that the genome of maize stripe virus is ssDNA, and in the same year Harrison and others proved that ssDNA is a circular structure. 1978, ICTU formally agreed to set up a group and named it Geminivirus. In the fifth report made by Francki et al. (199 1) on behalf of the International Committee on Virus Classification, the components of conjoined virus were divided into three subgroups according to the genome structure, host range and vector types.

Viral characteristics

Virus particles consist of two small (less than 20 nanometers in diameter) incomplete icosahedron. The associated dimer is 18 ~ 20× 30 (nanometer). The subunits are arranged in a lattice shape of t = 1, forming 22 penta-adjacent subunits. Sedimentation coefficient (s20 w) is 69 ~ 76s, and its molecular weight is about 2.6× 106. Coat protein contains a polypeptide with a molecular weight of 27 ~ 34× 103. The molecular weight of ssDNA is 7 ~ 8× 106, which is the smallest nucleic acid molecule in the self-replicating virus found at present. Nucleic acid accounts for about 18% ~ 20% of the particle weight, sedimentation coefficient (S20.w) is 16S, and the buoyancy density in cesium chloride is 1.7 17g/cm3. SsDNA has two forms: circular and linear. Linear DNA may be the precursor of synthetic circular DNA, and closed circular DNA is infectious. There are reading frames (putative genes) on the nucleic acid chain of the virus and its complementary nucleic acid chain, and the host tissue extract contains three kinds of ssDNA dsDNAs. Therefore, it is speculated that the prophase of replication is to synthesize cDNA with the help of the host system, and drum or bidirectional replication is carried out with DSDNA as a template. Virus particles exist in the nucleus of the host, forming large aggregates. It is speculated that DNA replication and particle assembly are carried out in the nucleus.

Members of the conjoined virus group can survive for 2 ~ 3 days at room temperature at the passivation temperature of 40 ~ 60℃, and the dilution limit is 10-2 ~ 10-4.

Characteristics and correlation of subgroups

The conjoined virus consists of three subgroups, and their main characteristics are as follows:

Subgroup I: The typical member is maize stripe virus (MSV), the genome is single-stranded DNA with molecular weight of 7 ~ 8× 105, and the molecular weight of polypeptide in protein shell is 28 ~ 34× 103. Cicada is persistent and cannot be spread by machinery. The host is limited to Gramineae. There is no serological correlation among the members of the subgroup.

Subgroup Ⅱ: The typical member is beet top curl virus (BCTV), whose genome is molecular DNA with molecular weight of 8× 105, and the molecular weight of polypeptide in protein shell is 30× 103. Cicadas and horned cicadas continue to spread, and mechanical inoculation is difficult. Some members have far serological correlation with subgroup III.

Subgroup Ⅲ: The typical member is bean golden mosaic virus (BGMV), which has a genome of ssDNA and two molecules. The molecular weight of each nucleic acid is 7 ~ 8× 105, and the molecular weight of coat protein is 27 ~ 30× 103. It is continuously transmitted by Bemisia tabaci under natural conditions and can be mechanically transmitted under experimental conditions. The host range varies with different members, which is harmful to dicotyledonous plants.

The A molecule of the DNA of subgroup III has homology with the nucleotide sequences of subgroup I and subgroup II, so it is considered that there is a far evolutionary relationship among these three subgroups.

Distribution and harm

The distribution of virus is related to the distribution of vectors, which is more common in tropical and subtropical regions. It is an important pathogen of food and cash crops and often causes serious economic losses. Corn stripe virus has been raging in Africa for a long time. It and Setaria viridis mosaic virus are important pathogens that harm tropical gramineous crops and are also very popular in India. African cassava mosaic virus and Indian cassava mosaic virus cause serious mosaic disease of cassava, and even lead to extinction. Bean golden mosaic virus was first discovered in Brazil and widely distributed in tropical and subtropical America. Tobacco leaf wrinkle virus is distributed in Indonesia, and tobacco leaf curl virus identified in China is distributed in Yunnan and Fujian tobacco-growing areas.

The symptom types of diseases are related to the distribution of virus particles in the host. The particles of maize stripe virus and foxtail mosaic virus infecting Gramineae plants are distributed in the leaves of the host (except epidermal cells), and stripes and star mosaic appear in the leaves. The particles of other members of conjoined virus are distributed in phloem, causing two main types of symptoms. The first one is spread by leafhoppers, which is characterized by leaf shrinkage, leaf distortion, deformity and leaf area reduction. The second is the transmission of whitefly, which first shows yellow veins, and finally all veins turn into golden yellow and yellow nets, while the tissues between veins are still green. This unique symptom is very obvious in the wild.

Meat paste

desert-living cistanche

Xu Zhigang

A generic term for a class of listed plants parasitic on the roots of herbs or woody plants. In a narrow sense, Orobanche refers to the plants of Orobanche and Orobanche. Sorghum seeds can spread far with the transportation of host seeds, and once introduced, it is difficult to eradicate, so it is listed as the quarantine object of imported plants. The leaves of Ofentine are degraded and there is no chlorophyll, so they live a completely parasitic life.

Distribution and harm

There are more than 40 species of Robinia pseudoacacia/kloc-0, and there are 23 species in China, which are mainly distributed in temperate regions, especially in temperate regions and high altitude regions north of 30 north latitude. China's northeast, north and northwest provinces are more common.

Phragmites communis can be parasitic on the roots of more than 70 kinds of dicotyledonous herbs, most of which are Polygonaceae, Solanaceae, Leguminosae, Cucurbitaceae and Compositae, and it is harmless to monocotyledonous plants. Different species of beaks have different host species. Stimulated by the root exudates of the host plant, the seeds germinate and grow bud tubes when the water is sufficient, and the top of the bud tubes are adsorbed on the lateral roots of the host to absorb the nutrients and water of the host. Affected plants grow poorly, the pressure of cell expansion is reduced, and they are often in a wilting state, thus reducing the host's resistance to other unfavorable conditions such as pests and diseases. The damaged plants are thin and short, unable to bloom or have few flowers, the number of grains increases, the yield decreases 10% ~ 30%, and the seriously damaged plants can be completely destroyed. Sometimes as many as 100 ~ 150 plants are parasitic on a single host plant.

Biological characteristics

It is classified as a completely parasitic plant, which has no real root, only the sucker is adsorbed on the root surface of the host, and it is connected with the vascular bundle of the host root with a short-whisker-like secondary haustorium. The tender stem with fleshy hair stands upright outside the ground and occasionally branches. The tender stems are covered with villi or glandular hairs, light yellow or purple-brown, about 65,438+00 ~ 20 cm high, up to 40 cm. The succulent stem is rich in various amino acids, especially phenylalanine, which is a valuable herb with the effects of strengthening yang and tonifying kidney. The leaves degenerate into small scales, sessile and chlorophyll-free, and the degenerated leaves are spirally arranged on the stem. Amphoteric flowers, symmetrical left and right, petals in a tube, white or purple, beige and blue-purple. It varies from species to species. The corolla is symmetrical, often curved with two lips, the upper lip is 2-cleft, the lower lip is 3-cleft, and there are 4 stamens, which are born in the corolla tube, the upper part is narrow and the base is enlarged. The pistil ripens first and is pollinated by insects. The stigma of pistil is enlarged and the style is bent downward. Lateral placentation, each stem has 30 ~ 50 flowers, up to 80 flowers. Each flower has a capsule, which splits longitudinally and contains 500 ~ 5000 seeds. Each plant can produce 5000 ~ 65438+ ten thousand seeds, up to 450 thousand seeds. The seeds are oval, very small, about 0.2 ~ 0.5 mm, dark brown, hard, with reticulate or concave spots on the surface. When it is ripe, it can be scattered in the soil, or it can be scattered with the wind and attached to the seeds of the host. Seeds falling into the soil can survive for 5 ~ 10 years in the depth of 5 ~ 10 cm. Seed germination is very irregular, and seeds germinate every day in suitable seasons. Sorghum seeds have special germination conditions, which require sufficient water, suitable temperature (about 25℃), high soil alkalinity (pH > 7.0) and host root exudates. It can't germinate when the temperature is too high or too low, and it can't germinate in acidic soil (pH < 6.5). Secretion from the root of the host can stimulate its germination. The root exudates of some non-host plants can also induce seeds to germinate, but the germinated bud tube can not establish a host relationship with the roots of the induced plants. This non-host plant that induces seed germination and is not parasitic is called "induced plant", and pepper is a common one.

Major groups

Taxonomically, there are more than 40 species of/kloc-0, but the classification system is incomplete. The more important species are as follows. (1) Bender column when (Orobanche cernua). Symmetrical two-color orphans or Eurasian orphans, commonly known as sunflower orphans or single grass. The stem is erect and solitary, fleshy, with a diameter of about 1cm, densely covered with fine hairs, light yellow to purple brown, with a height of about 30-40cm, spikes, tubular flowers, smaller, and a length of about10-20 mm. There are 20-40 flowers on each stem, up to 80. The corolla tube is enlarged and the upper part is narrow. It takes about 4 ~ 1 1 day from tender stem excavation to flowering, 5 ~ 7 days from flowering to fruiting, and 30 days from excavation to seed maturity. Seeds can survive in soil for 5 ~ 10 years. The seeds are dark brown, with a size of 0.16 ~ 0.18× 0.1(mm) and longitudinal wrinkles on the surface. In Europe, it is distributed in all Asian countries, especially in the area north of 40 north latitude. The main host plants are sunflower, tobacco, tomato and safflower. But it can also grow parasitically in the roots of broad beans, peas, carrots, celery, melons, flax and absinthe, and induce plants to be peppers. (2) Aedes aegypti, also known as branches or melons. The stem is erect and firm, with 3 ~ 5 branches above the middle. The height of the stem is about 15 ~ 30 cm, and the stem is densely covered with glandular hairs, which are yellow-brown. Spike, about 8 ~ 1 5cm long, cylindrical, bracts ovate, lanceolate, 8mm long, calyx bell-shaped,1cm long, 4 or 2 stamens at the top, superior ovary, placentation of lateral membrane. Corolla lip-shaped, blue-purple, about 20 mm long, funnel-shaped tube. The seeds are small, ovoid, narrow and sharp at one end, yellow-brown, about 0.2 ~ 0.5 mm long and 0.2 ~ 0.3 mm wide, with reticulate wrinkles on the surface (see figure). Each plant bears 65,438+0,000 ~ 50,000 seeds. It is distributed in Asia, Europe and the United States. In China, Xinjiang and Gansu are the most harmful. There are about 50 species of plants belonging to 17 family. The main hosts are cantaloupe, watermelon, melon and cucumber. Followed by tomatoes, tobacco, sunflowers, carrots, cabbage, eggplant and some weeds. The most common occurrence period in Gua Tian is from June to July, and the parasitic rate can reach 100%. The germination rate of seeds in alkaline soil is low, and the survival period in soil is as long as 10 ~ 15 years. The induced plants are corn, clover, alfalfa and sesame. ③ Pennisetum, with erect and stout stems, 7 ~ 10 mm in diameter, unbranched and solitary, up to 20 ~ 60 cm. The first flower is white, and gradually turns pale yellow, with dense spikes. The flowers are large, about 30mm, and the flowering period is June-July. The seeds are larger, 0.3 ~ 0.5× 0.25 (mm). Mainly distributed in the Middle East, Mediterranean coast, West Asia and North Africa. Host plants are mainly silkworms and peas, also known as beans. A large number of seeds are often piled up in the soil of diseased fields, which can grow 2 million to 3 million plants per hectare every year, posing a serious threat to agriculture and often leading to crop failure. ④ biennial or perennial herbs, with erect stems, yellowish brown, slightly enlarged base, plant height 10 ~ 50 cm, unbranched, densely covered with spider-like white hairs on inflorescences, thick stems, scaly leaves, spikes, long 10 ~ 15 cm, lilac flowers and no bracts. The seeds are grayish brown and irregular, and the epidermis has reticular wrinkles. The main hosts are Artemisia plants of Compositae, such as Artemisia capillaris, Artemisia scoparia, Artemisia scoparia, etc. In recent years, it has been found that it can also parasitize sunflower, with flowering period from April to July and fruiting period from July to September. The whole stem can be used as medicine, which has the effect of tonifying kidney and strengthening yang. Most of them are distributed in the area north of 30 north latitude. ⑤ The plant height of O.sinensis var.sinensis is 20 ~ 40 cm, and the whole plant is densely covered with yellow-brown glandular hairs mixed with pilose hair. The stem is stout, with a diameter of 0.5 ~ 1 cm. The leaves are ovate-lanceolate, 1 ~ 2 cm long and 4 ~ 6 mm wide. The dense spike is 10 ~ 30 cm long, with cup-shaped calyx, lavender, blue or blue-purple corolla, rarely yellow, 2.5 ~ 3.5 cm long, upright tubular, slightly curved upper part, enlarged funnel-shaped, hairy anthers, keel-shaped upper corolla, equal to lower lip. The capsule is oblong, with a length of 1 ~ 1.2 cm, a diameter of 4 mm, an oblong seed of 0.4×0.25 mm, a reticulate pattern on the surface and a honeycomb pit at the bottom of the mesh. The flowering period is from May to June, and the fruiting period is from June to August. Distributed in slopes, roadsides and forests around Sichuan, Qinghai and Tibet in China, with an altitude of 1, 600 ~ 3500m. Artemisia is the main host.

Branch pillar

1 ~ 2. Plants; 3. Corolla unfolding; 4. Stamens; 5. pistil; 6. Calyx unfolding; 7. Bracteoles; 8. Bracts (Imitation of Wang Wencai: Flora of China, Volume 69)

Prevention and treatment

Sorghum is a malignant weed in panicum miliaceum. Once the parasite is colonized, it is difficult to remove the seeds scattered in the ground. No epidemic areas should be strictly quarantined. When introducing in the same latitude area, we must prevent the introduction. In the ward, it is effective to implement rotation for more than 7 ~ 8 years, but it is difficult to implement. In view of the fact that it takes only 10 ~ 15 days from digging to flowering, it can be killed by artificial rooting or spraying herbicides. During the rotation period, some induced plants can be planted to stimulate the germination of sorghum seeds in the soil, thus accelerating the decrease of sorghum seed density.

Forest (19 10 ~ 1980)

Shen

Plant pathologists and pathologists. Minhou county, Fujian province. 1933 graduated from the Agricultural College of Jinling University, and served as an assistant and senior in the Agricultural College of Fuzhou Union Medical College. 1937 went to the graduate school of Cornell university in the United States for further study, and 1940 received a doctorate in philosophy. In the same year, he returned to China and successively served as an associate professor at Jinling University, director of the Agriculture and Forestry Department, professor and head of the Department of Plant Pathology in Peking University. After 1949, he served as a professor at Beijing Agricultural University, director of the Department of Plant Protection, and deputy director of the Institute of Plant Protection, Chinese Academy of Agricultural Sciences.

The fungal physiology, rice diseases, physiological diseases, phytoncide, potato late blight and its degradation were deeply studied, and outstanding results were obtained. In the study of fungal physiology, it is found that short wave is an effective light for the germination of chlamydospores of false smut. In conidia germination, it is clear that the sensitivity of Sclerotinia sclerotiorum to copper toxicity is greatly improved after the interference of unknown substances is eliminated. In the physiological study of oomycetes, it was found that organic acids are beneficial to amino acid synthesis, but increasing cell permeability can be solved by increasing calcium concentration. In the study of potato degeneration, the law of host disease resistance change after virus infection was put forward as a guide to formulate seed potato production system, and this research achievement won the 1978 National Science Conference Award; In the study of potato late blight, according to the formation process and quantity of central diseased plants, the control methods focusing on reducing the rate of diseased plants and planting disease-resistant varieties in the field were put forward.

His main works are General Plant Pathology, Plant Pathogenic Fungology and Plant Immunology, and he has translated Diagnosis and Identification of Plant Diseases-Pathogenic Fungi and phytoncide, and published nearly 100 academic papers.

Lin Kongxiang (19 10 ~ 1985)

Luo zhida

Plant pathologist and citrus Huanglongbing expert. Minhou county, Fujian province. 1934 graduated from Fujian United University. 194 1 received a doctorate from Cornell University and was employed as an associate researcher at California State University. He returned to China in September of the same year and served as an associate professor and professor in Lingnan University, Sichuan University, Yunnan University and Jinling University. After 1952, he served as professor and director of plant protection department of South China Agricultural University (now South China Agricultural University). He used to be the chairman of Guangdong Plant Pathology Society, the head of Guangdong Citrus Huanglongbing Research Group, and the consultant of the National Citrus Huanglongbing and other viral diseases prevention and control research cooperation group.

For more than 40 years, he has made unremitting investigation and study on citrus Huanglongbing, and made it clear that Huanglongbing virus is highly contagious, which provided a theoretical basis for implementing quarantine, cultivating disease-free seedlings, digging out diseased plants and strengthening pest control. Later, he devoted himself to the research of thermal disinfection and the cultivation of disease-free seedlings, which effectively eliminated the pathogen of Huanglongbing in citrus tissues and obtained reliable disease-free propagation materials. This achievement was the first in the world at that time and was valued by experts in the same industry. The United States quickly successfully disinfected other citrus virus diseases and promoted them. In the 1970s, he put forward the technical method of "citrus cultivation without pests and diseases", which was mainly detoxified by heat treatment. The above research results have won many national and ministerial scientific and technological achievement awards. His main works include virus-free cultivation of citrus and more than 20 academic papers.

Li Ling (19 1 1 ~)

Fang zhangzhao

Plant pathologist. Hangzhou, Zhejiang. 1927 studied at the Agricultural College of Nanjing Central University. 1937 received his doctorate from the University of Minnesota. After returning to China, he worked in Chengdu Institute of Plant Pest Control, Sichuan Institute of Agricultural Improvement and Chongqing Ministry of Agriculture and Forestry. 65438-0945, went to Taiwan Province Province and served as the director of Taiwan Province Agricultural Laboratory. He was the editor-in-chief of Journal of China Agricultural Society, the president of Plant Pathology Society and the editor-in-chief of Scientific Agriculture. 1947 After August, he served as the deputy director of the Plant Production and Protection Department of FAO for 25 years. 1948 was elected as an academician of the Washington Academy of Sciences. From 1948 to 1976, he was invited to be a member of the editorial boards of Sydowia-Anna EES mycologi-CI II (published in Vienna) and Phytopathologia Mediterranea (published in Italy).

Mainly engaged in the prevention and control of pests and diseases of cotton, wheat and vegetables, and carried out fruitful activities to promote international assistance and cooperation in the United Nations Food and Agriculture Organization. For example, formulate international plant protection conventions, formulate international plant epidemic prevention certificates, establish regional plant protection contracts and organizations in Europe, the Middle East, the Far East, Central America, South America, the West Indies and Africa, assist Southeast Asian countries in establishing plant protection centers, assist in establishing locust control institutions in the Middle East and Africa, set up expert groups, advocate reasonable plant pest control technologies, and send experts to assist countries in studying plant protection issues.

He published a monograph on the identification and distribution of head smut in China, and published more than 10 papers on head smut internationally. 197 1 year, the board of directors of the university of Minnesota awarded him a special achievement award. His main works are Storage and Drying of Grains, Weed Control, Persistent Insecticides and Environment and Their Unexpected Effects, International Plant Pest Control, China Smut Fungi, etc.

Popular animals

Epidemiological regional system

Ceng Shimai

Pathogens overwinter and overwinter in areas with different geographical and climatic conditions, and are linked together through long-distance transmission, completing a one-year cycle and forming a regional system with widespread diseases. Known as the epidemic bacteria group. The term "endemic flora" was put forward in the study of the epidemic law of wheat stripe rust in China in the 1960s. Wheat stripe rust is widespread in North China and Northwest China. Stripe rust likes cold and is not resistant to high temperature. We can't spend the summer in the winter wheat areas of Huang-Huai-Hai and the middle and lower reaches of the Yangtze River. We can only spend the summer on wheat plants and autogenous seedlings in cold late-maturing winter wheat areas such as Gansu, Qinghai, Sichuan and Ningxia. Summer spores spread to the above-mentioned winter wheat areas with the wind to infect autumn seedlings, reproduce and overwinter, and develop into spring epidemic in the next spring, but there is no local overwintering bacteria source in spring wheat areas and northern winter wheat areas with severe winter. In this way, the wheat areas in North China, the middle and lower reaches of the Yangtze River, Shaanxi, Gansu and Qinghai are connected into an epidemic area of wheat stripe rust. The flora can be divided into several epidemic areas, such as Longnan fungus source base area, Ganqingxia area, Longdongqiao area, Guanzhong-Jinnan, southern Henan-northern Hubei prone area, northern Henan-southern Hebei prone area, Beijing-Tianjin-Tangshan-Baoding accidental area and so on. Each endemic area plays a different role in the epidemic flora, each area has its own characteristics, and the interval has different bacterial source relationships. The study of epidemic flora provides a theoretical basis for formulating the overall control strategy of diseases and the rational distribution of disease-resistant varieties. For example, planting varieties with different disease resistance genes in Longnan, Guanzhong and Henan can slow down the directional selection of new varieties, and the disease resistance of varieties is expected to last. In addition to wheat stripe rust, wheat stalk rust and wheat yellow dwarf disease in the border area of winter and spring also have local problems.

Equivalence principle in epidemiology

Equivalence theorem of epidemiology

Xiaoyueyan

The influence of different epidemiological factors on the epidemic of diseases and the losses caused by them are quantitatively expressed by changing epidemiological parameters, and the changed coefficients become unified equivalent values, which is the equivalence principle. This is one of the basic principles of plant disease epidemiology. This principle was first put forward by J.E. Van der plank in 1963. It is of great significance in comparative epidemiological research and system simulation modeling. Because the epidemic rate, or daily infection rate, incubation period, infection period, spore production and so on can comprehensively represent the dynamic characteristics of disease epidemic, various environmental factors, human measures, host disease resistance, pathogen pathogenicity and so on also affect the epidemic dynamics of diseases. Therefore, the pathogen with lower toxicity is the equivalent value of these factors in the epidemic process compared with the corresponding parameters measured under the most suitable environmental conditions and high resistance (or high sensitivity) varieties. Usually calculated by correlation analysis.