Symptom Identification and Control Methods of Crown Gall Disease in Cherry Blossoms
Cherry blossoms are distributed in China's Liaoning, Hebei, Anhui, Jiangxi, Zhejiang, Jiangsu and Guizhou; they are also widely distributed in Japan and Korea. They prefer light and deep, fertile, well-drained soil, and have weak resistance to smoke and dust, harmful gases and sea breeze. They have a certain degree of cold tolerance, a relatively shallow root system, and are easy to cultivate. Cherry blossoms bloom profusely in spring and are very beautiful. They are suitable for planting on hillsides, in courtyards, in front of buildings and beside garden paths.
This disease is a common and serious disease of cherry blossoms, occurring widely in areas where cherry blossoms have been introduced. It occurs severely in Zhengzhou, Chengdu, Hangzhou, Jinan and Wuhan. Besides cherry blossoms, many other garden plants such as plum, plum apricot, peach, lilac, poplar, willow and dahlia are also affected. Infected plants develop poorly, with abnormal leaf color, which affects their ornamental value.
Symptoms: The disease mainly occurs on the root crown and lateral roots of the plant, mostly at graft wounds, and sometimes also at the base of the trunk. The affected parts usually produce tumors of varying sizes. The tumors are spherical, with a rough, uneven surface. They are initially grayish-white or flesh-colored, gradually turning brown or dark brown and cracking in a checked pattern. After the root system is infected, it develops poorly, with very few fibrous roots. The aboveground parts of infected plants grow slowly, the tree vigor declines, flowering is reduced and the flowering period is shortened; in severe cases the leaves yellow and drop early, and the entire plant may even die.
Pathogen: Caused by Agrobacterium tumefaciens (Smith et Towns.) Conn, a bacterium. The optimum temperature for the pathogen's development is 22°C.
Disease pattern: The pathogen survives and overwinters on the surface of tumors on infected hosts and in the soil. It can survive in soil for several months to about 1 year. The pathogen is mainly spread by rainwater and irrigation water, and can also be spread by tools or underground pests. Long-distance spread of the disease relies on the transportation of seedlings and plants. The pathogen invades the host through various wounds; after invasion it stimulates cells to divide rapidly, producing a large amount of meristematic tissue, thus forming tumors. From pathogen invasion to the appearance of symptoms takes as little as a few weeks or as long as more than 1 year. The disease is severe when the soil is moist, waterlogged and rich in organic matter. Alkaline soil favors the occurrence of the disease.
Control: ① When planting, strictly select healthy plants and avoid planting diseased plants. ② If diseased plants are found, destroy them immediately. After digging out the diseased roots, disinfect the surrounding soil by mixing in sulfur powder, at a rate of 50-100 g/sq m. For suspicious seedlings, soak them in 1% copper sulfate solution for 5 min before planting, then wash them with water and plant. ③ The nursery should be established in areas free of crown gall disease; in diseased areas, crop rotation of more than 2 years can be used.