Root cancer of fruit trees is an important root disease on fruit trees and seedlings. The host has a wide range of diseases and can infect 1 983 heads of plants including 138 families including peach, plum, apricot, cherry, pear, apple, grape, jujube, papaya, chestnut and walnut. The pathogenic bacteria inhabit the roots of the plants, forming tumors, weakening the tree vigor, and causing death of fruit trees in severe cases. Roots of grapes, peaches, almonds, and big cherries are the most susceptible hosts.
I. Hazardous conditions The occurrence of root cancer in fruit trees in China is quite common, but the obvious hazards of the disease occur in the roots. Many farmers have lacked awareness of it, and they have paid less attention to prevention and control, and the quarantine measures when the seedlings are transferred and introduced, resulting in the spread of germs. The condition has been increasing year by year.
Second, the pathogenic and hazardous symptoms The root cause of fruit tree disease is Agrobacterium tumefaciens, belonging to bacteria. The optimum development temperature is 22°C, the highest is 34°C, the lowest is 10°C, the lethal temperature is 51°C, the optimum pH is 7.3, and the humidity of 60% is most suitable for the formation of tumors.
Root cancer mainly occurs in the root and neck, but also occurs in lateral roots and branch roots. It is common at the grafted sites. The roots are damaged and form cancerous tumors. The shape, size and texture of cancerous tumors vary from host to host. In general, the woody host's tumor is large and hard and lignified; the herb host's tumor is small and soft, fleshy. The shape of the tumor is generally spherical or oblate spheroidal, but also heals each other into irregular shapes. The size of the tumor is not very different. It is as small as a bean, as large as a walnut or a fist. The vast majority occur in the healing parts of scion and rootstock. The tumor is milky or slightly reddish, smooth and supple at birth, gradually brownish, lignified and hard, with rough or uneven surfaces.
The diseased plants were cancerous in the roots, and the circulation of water and nutrients was hindered. The tree vigor declined, the leaves were yellow, and the trees were severely dead. Seedlings are hindered from development after the victim's development, and the growth is slow, the plants are short and the leaves are yellow and premature. The fruit trees suffer, fruit is small, and the tree age is shortened.
Third, the pathogenesis of the root cancer disease in the cancer tissue in the cortex winter, or when the cancer rupture, enter the soil in the winter. Rain and irrigation water are the main vectors for disease transmission. In addition, underground pests such as cockroaches, cockroaches, and nematodes also play a role in disease transmission. Seedlings carry the bacteria is the main way of distant disease transmission.
Pathogens invade the host through wounds, and grafts, stomata, insects, or wounds caused by human factors can become pathogenic invasion pathways. When bacteria invade, they can cause abnormal division of host cells and cause cancer. Once the host cell divides, even if the pathogen is removed, it cannot stop the development and increase of the cancer. The time from the invasion of the bacteria to the appearance of the tumor usually ranges from several weeks to one year or more. Severe onset occurs when wood seedlings, fruit seedlings, and vegetables are plucked.
Fourth, the incidence of conditions 1. Temperature, humidity suitable temperature and humidity is the basis of infection of the root cancer bacteria. The incidence of pathogenic bacteria infection and disease increases with the increase of soil moisture, and vice versa. In terms of temperature, according to the tomato inoculation test, the formation of the tumor was best at 22°C, and the formation of tumors at or below 18°C ​​was fine, and the nodules were not easy to form at 28°C to 30°C, and nodules above 30°C could form. .
2. Physical and chemical properties of the soil Soils that are alkaline are favourable to disease and acidic soils are detrimental to disease. In the range of pH 6.2 to 8, soil pathogenicity can be maintained. When the pH drops to 5 or lower, the soil with bacteria cannot cause plant diseases, and no bacteria with pathogenicity can be isolated from this soil. Land masses with poor soil mass and bad drainage have a high incidence of root carcinogenesis, and there is less incidence of sandy loam with loose soil and good drainage.
3. The grafting method, the interface size, and the speed of healing can affect the degree of the disease. After cutting, the seedlings have large wounds and heal slowly. After that, they need to cultivate soil. The contact time between the wound and the soil is long and there are many infection opportunities. Therefore, the incidence is high. The bud grafted seedlings interface above the surface, the wound is small, healing faster, rarely infected afterwards. In addition, accidental rooting or infestation of soil pests can increase the incidence of disease.
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