Bacterial disease of orchid: rotting disease

1. Harm: orchid rot can occur in many vegetables and ornamental plants, although it is not very common in orchids, but it may be one of the most destructive diseases. It is reported that in addition to infecting Cartland orchids, it also infects some species of the following genera, including orchid, orchid, Oncidium, Magnolia, Phalaenopsis and Magnolia. The disease has been reported in the United States and Japan. It occurred seriously in Fujian and caused a large number of orchid plants to die. Orchids are susceptible to diseases such as Cymbidium and Cymbidium. According to reports in Taiwan, the pathogen of orchid soft rot is the same as that of orchid sinister rot.

2. Symptoms: bacteria enter the plant through the wound and quickly form foul-smelling wet rot. In fresh and succulent tissues, decay develops rapidly, but in more mature tissues, especially in pseudobulbs and rhizomes, decay develops more slowly. The disease mainly occurred on the sinful buds of orchids, followed by leaves. At the initial stage of the disease, water-immersed mung bean-sized disease spots appeared at the base of the buds, which rapidly expanded upward and downward 2-3 days later, becoming dark green scalded patches, reaching the outside of the coleoptile, showing dark brown rot, and the diseased leaves were easy to pull out. The pathogen also infects the leaves, causing dark green water-stained patches on the leaves.

3. Pathogen: the pathogen of orchid rot is a soft rot Erwinia carotovora (Jones) Holland. Short rod-shaped, round at both ends, 1.2~1.9um X O.5~0.9um in size, Gram staining negative, periflagellum, 2-4, no capsule and spores. A small piece of tissue suffering from the disease is best cut off from the junction of the disease department and the health department, and placed in water droplets on the slide. after the cover glass is gently pressed, it is immediately placed in the microscope low power field of vision (120X) examination, the incision often has a large number of turbid bacteria overflow.

4. characteristics of the disease: the pathogen of orchid rot overwintered in the diseased tissue, and a large amount of accumulation in the diseased plant disease part was beneficial to the reproduction and survival of the pathogen. Germs are spread by water and can only invade from the wound. The disease occurs in July, with continuous rain of more than 15 days per month in summer and low temperature (25030 ℃), especially after typhoon and rainstorm. For fragile plants, heavy rain can damage the stratum corneum of new leaves, which is beneficial to bacterial infection, improper management of water and fertilizer, wet basin soil and excessive nitrogen application.

5. Prevention and control methods:

(1) Horticultural control: using acidic plant materials as the upper basin substrate can reduce the harm (because the bacteria like to grow under alkaline conditions), and the control basin is not too wet, because the bacteria can only be spread by water, so it is necessary to prevent splashing when dripping water. so that there is no free water in the matrix, seedlings and plants with fragile leaves should be covered to prevent direct rain.

(2) Chemical control: when the new buds unearthed 4~5cm, spray with 0.01% boric acid solution, or spray 50% Dikushuang, Shikujing and other fungicides 1000 times, have a certain control effect. As soon as infection is found, the diseased leaves should be removed and destroyed, and the 800-fold solution prepared by Physan can effectively prevent soft rot. If the disease develops rapidly, the whole diseased plant should be destroyed and the planting table should be disinfected with 10% Clorox (0.5% sodium hypochlorite). In order to prevent the soft rot of pseudobulbs and rhizomes, attention should be paid to the hygienic operation during ramet. The knife used for ramet should be disinfected in boiling water or 1 part of formalin plus 7-valent water solution, and the ramet section should be smeared with carbendan paste to prevent bacteria from invading from the wound. (Liu Zhongjian)