Tea cake disease harms tea tree growth

Tea cake disease, also known as blister leaf blight and leaf swelling disease, is an important disease of buds and leaves, distributed in tea areas all over the country, mainly harming tender leaves, tender stems, new shoots, flower buds, fruits and petioles. Young leaves infected with the initial appearance of light yellow to reddish brown translucent spots, and then expand into a round spot with a diameter of 0.3~1.25cm, the spot is sunken adaxially, light yellow to dark red, protruding on the back, showing steamed bread-shaped blister spots, there are gray-white or pink or gray powder on it, the late powder disappears, the protruding part shrinks to form brown withered spots, and there is a gray-and-white circle around the edge, like a cake, so it is called tea cake disease. When the disease is severe, there are several or dozens of obvious disease spots on a leaf, and then dry up or form ulcers. The diseased leaves are twisted or deformed, and the tea leaves are distorted, folded in half or irregularly rolled up. The petiole and tender stem are swollen and twisted, and the new shoots above the seriously diseased part are withered or broken. The disease has a great influence on the quality of tea.

The source of the disease is damaged exobasitic bacteria, which belongs to basidiomycetes subphylum fungi. The white powder on the disease spot is the fruiting layer of the bacteria, which is formed by the accumulation of many basidites. The basidium is cylindrical to clavate, the base is thin, the tip is slightly round, unicellular, there are 4 peduncles at the top of the basidium, and one spores are born on each peduncle. The basidiospores are oval in shape, produce septum before germination and turn into twin cells. during germination, each cell produces a germ tube, invading the host.

The pathogen overwintered or oversummer with mycelia on diseased leaves, and basidiospores could be formed in the first ten days of May or autumn in the next spring, when the average temperature was 15 ℃ ~ 20 ℃ and the relative humidity was higher than 80%. Basidiospores spread to young leaves or shoots by the wind and begin to germinate when there are water droplets. after 3-18 days of incubation, new disease spots are formed, and then the solid layer grows on them. After maturation, the basidiospores were scattered and re-infected for many times. The time of onset was different in different tea areas in China, from March to May and September to October in East and South China, from July to November in Southwest China, and from February and September to January of the following year in Hainan tea area.

The fungus spends the summer on the tea tree in summer. Basidiospores began to germinate in 2 hours under suitable temperature and humidity, and the germination rate was as high as 70% 80% in 24 hours. the germinated basidiospores produced two germ tubes, protruding from both sides of the spores, and the germ tubes invaded directly from the host epidermis. The temperature was 18 ℃ ~ 20 ℃, the relative humidity was 80% ~ 95%, the incubation period was 10 ~ 13 days, and the incubation period was 8 ~ 10 days at 20 ℃ ~ 23 ℃. It took 12 to 19 days to complete an infection process. Re-infection can occur 7-8 times a year in Sichuan and 15 times in Guizhou. The growth and development of basidiospores were inhibited and the disease stopped when the temperature was above 31 ℃ and continuous light for 4 hours. The tea garden has the advantages of less sunshine, long duration of dew, more fog, high humidity, easy to occur, partial application and over application of nitrogen fertilizer, excessive picking and pruning, extensive management, many weeds and serious disease.