Longan witches' disease (Figure)
Young shoots, leaves and flower spikes can all suffer and show obvious symptoms. The young leaves on the diseased shoots are small, light green, and the leaf margins are curled and cannot be unfolded. They are tubular; in severe cases, the entire leaves are linear and smoke-brown. The leaf surface of the growing leaves is uneven, the leaf margin is often curled toward the back of the leaf, the tip of the leaf is bent downward, and the veins are yellowish. Green, showing a phenomenon of light veins, inter-pulse mesophyll presents an amorphous, yellow-green mottle of varying sizes. The petiole is often flattened and slightly wider. Sometimes there are both types of malformed diseased leaves on the branches, or the spring and autumn shoots show obvious deformed leaves on the same shoots, but the summer shoots often grow normally and do not show symptoms. All kinds of deformed leaves on the tip of the disease soon fell off and became bald. Severe diseased plants, new shoots clustered, internode shortening, a variety of deformed leaves at the top, when the diseased leaves fall off, the entire branch shoots were broom-like, so there are witches' broom disease, ghost disease, broom disease said. The flower spikes are damaged and the internodes are shortened. The clumps are clustered, the flowers are deformed, and they are swollen. The quantity is large and the brown color is abnormally dense. Diseased flowers are not normally developed and often fall early and cannot be solid. Occasionally, if the fruit is a fruit, the fruit is small, the meat is thin and tasteless, and it is unbearable. After the ear is dry, it is not easy to fall off and often hangs on the branches.
Second, the pathogen
The disease is caused by Longan witches broom virus infection. The virions are linear and have a size of 121,000 nanometers; they are only present in the host screen, most of which are aggregates of many granules, and a few are isolated. Then a spherical body was isolated from the skin of the diseased branch, the petiole of the diseased leaf, and the veins, and the size was about 40 to 70 nm. Which type of granulosome is the virion of the disease remains to be further studied. According to the symptoms, it may be that the pathogen may be a mycoplasma, which needs further study. In addition to the longan eyes of the arbuscular virus, artificial inoculation can still infect litchi.
Third, the process of occurrence
The disease is mainly transmitted by grafting, grafting diseased branches with 2-year-old rootstocks, and onset of the incubation period of about 7-8 months. Seeds may be sick. Long-distance transmission is mainly through the transport of diseased seedlings, scions and seeds. The virus research of the Institute of Fruit Research of Fujian Academy of Agricultural Sciences showed that the natural pathogens of longan pteridopathiasis are Litchi Jingjing and Longan horned cheeks. The 1-2 instar nymphs of the litchi wax can not be transmitted, but the rate of transmission of 3-4 instar larvae is as high as 18.8% to 45.0%. Adults have long lifespan and can fly. Their disease transmission range and disease transmission period are both. More than nymphs. Litchi roasting adults and nymphs can spread the disease every year from January to November. The morbidity rate of adult cheek beetles in longan was 22.3%-37.8%.
Fourth, the incidence conditions
Young trees are usually more susceptible to disease than adult trees. The incidence of high-pressure seedlings is higher than that of seedlings. The disease resistance of longan varieties was different: red nucleus, cowboy, big grain, red shell, Youtanben, Puming, Blessing, banana eyes, flower shell, Qilongling and other species were more susceptible; The Shinsho version, Dongying longan, etc. are more disease-resistant or disease-resistant. Poorly managed orchards, spurs, and other sucking mouthparts have many pests, and plants with debilitating trees are prone to disease.
V. Prevention methods
1. It is forbidden to export seedlings, scions and seeds from the wards to prevent the spread of the disease to disease-free areas.
2. Cultivate disease-free seedlings. Use robust seedlings or scion nurserys that are disease-free and of good quality; scion or high-pressure seedlings are strictly forbidden on diseased trees. Once the disease is found in the nursery, it must be removed and burned in time.
3. The new areas and new orchards selected for planting resistant and resistant varieties should be selected for breeding and planting disease-resistant or disease-resistant varieties.
4. Intensify cultivation and management The newly-built orchards should appropriately loosen the row spacing to reduce the chance of natural contact. Fragmented orchards, especially those with severe diseases, should be immediately destroyed. Increase organic fertilizers to increase tree vigor and increase resistance to disease. Before and after applying fruit-bearing nitrogen fertilizer, it is necessary to use phosphorus and potassium fertilizers to promote the timely emergence and enrichment of autumn shoots, enhance the cold resistance, and reduce the incidence of autumn shoots. Mild disease trees should be cut off as soon as possible, diseased ear, to ease the condition, extend the results of a certain number of years.
5. Prevention and cure of insects in mediators and insect pests Refer to the section on prevention and treatment of litchi and figurines. The prevention and treatment of the corner cheeked hibiscus is overwintering and the first generation of incubating period; from May to June, it is necessary to spray insecticide.
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