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Symptoms and Control Methods of Tea Tree Crown Gall

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Symptoms It occurs in Anhui, Zhejiang, Guangdong and other provinces. It mainly damages the roots. When the main root and lateral roots are infected, light brown spherical small protrusions first appear on the diseased part, then expand into tumor-like growths, small ones resembling grains of rice, large ones resembling broad beans, and multiple small tumors gather together into large tumors. In the later stage, the diseased tumors turn brown and become lignified, with a rough surface and hard texture. When cuttings and seedlings are infected, they have few fibrous roots or fail to develop roots, causing the seedlings and plants to become weak or the leaves to turn yellow and fall off, and the plants die. Pathogen Agrobacterium tumefaciens

Symptoms It occurs in Anhui, Zhejiang, Guangdong and other provinces. It mainly damages the roots. When the main root and lateral roots are infected, light brown spherical small protrusions first appear on the diseased part, then expand into tumor-like growths, small ones resembling grains of rice, large ones resembling broad beans, and multiple small tumors gather together into large tumors. In the later stage, the diseased tumors turn brown and become lignified, with a rough surface and hard texture. When cuttings and seedlings are infected, they have few fibrous roots or fail to develop roots, causing the seedlings and plants to become weak or the leaves to turn yellow and fall off, and the plants die.

Pathogen Agrobacterium tumefaciens (Smith Townsend) cinn, called Agrobacterium tumefaciens, belongs to the kingdom Prokaryotae. The pathogenic bacterium is short rod-shaped, size 1-1.5 x 0.4-0.8 (Ftm), with 1-3 peritrichous flagella, has a capsule, and is Gram-negative. On agar medium, the colonies are white to grayish white. This bacterium has a wide host range and can infect more than 300 kinds of plants. The optimum temperature for development is 25-30°C, and it is killed at 51°C after 10 minutes. The optimum pH is 7.3. It dies after 25 minutes in 10% lime milk.

Transmission routes and conditions for disease occurrence The pathogen overwinters in the soil or on diseased tissues, and is spread by irrigation water or rainwater. It can also be spread by underground pests and contaminated tools. It can also spread over long distances with diseased soil and diseased seedlings. After the pathogen invades the cortical tissue through wounds or cuts, it grows and reproduces. The cells around the wound divide rapidly due to stimulation by the pathogen, forming a large number of proliferated tumors. In production, whether seedlings have wounds and cuts is an important condition for whether this disease can break out severely. Nurseries with low-lying terrain, high soil moisture, and heavy clay soil are prone to the disease.

Control methods (1) Strict quarantine, and it is strictly forbidden to transport seedlings from diseased areas. (2) Choose a leeward and sunny plot with good drainage, loose soil, and no previous tea tree planting to establish a cutting nursery. (3) Strengthen tea garden management, promptly control underground pests, and make every effort to reduce root wounds. (4) When diseased plants are found, dig them out promptly, then disinfect the diseased holes with 1% 96% copper sulfate solution or 1:1:100 Bordeaux mixture, or drench with 80% antibacterial agent 402 emulsifiable concentrate 1000 times solution.

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