Pear rotunda disease, also known as neodermal disease and coarse skin disease, occurs in Pear producing areas in China. After the harm of rotting disease, a large number of rotten fruits can be caused, pears, apples and other varieties are particularly prominent, and the fruit rate of general orchards is 20%-30%, and when it is serious, it can reach 50%-60%. In addition, rotunda can also harm the trunk and main branches, resulting in rough bark and weak tree potential, which seriously affects yield and fruit tree life.
Trunk infection with rotunda symptoms
First, the symptoms of rotifer disease in fruit trees
Rotifer disease mainly harms branches and fruits. After the branch is damaged, a slightly protruding brown spot is formed with the skin hole as the center, and the post-lesion gradually expands to form a nearly circular dark brown spot, and the central protrusion of the lesion is nodular, and the surrounding tissues are trapped in four places. Cracking of the edges. Most of the spots are limited to the cortex, and a few reach the xylem. In the following spring, small, illuminated dots (meristems or ascomycetes) are produced in the center of the lesion, and the margins are cracked and upturned in the shape of a saddle. On the perennial trunk or main branch, the spots are dense and joint, resulting in rough and cracked branches. The pathogen can also cause symptoms of dry rot after infection of the main trunk. The lesions are initially oval or irregular, purple-red, and the surface is moist, and as the spots expand, the dry and concave areas appear as dark brown spots. The junction of the plaque is cracked, the surface is upturned or peeled off, and the surface of the plaque has longitudinal and transverse cracks. Small black spots (conidia) are produced at the later lesions.
Apple fruit is affected by symptoms of rotunda disease
Fruit victimization shows symptoms in the near-ripening or double-gestational stages, initially forming water-like, nearly rounded small spots centered on the skin of the fruit, with a reddish-brown halo at the edges, and then rapidly expanding, forming a dark and light reddish-brown concentric chakra, rotting the flesh of the diseased part, and having tea-brown mucus oozing out. When the conditions are right, the disease develops rapidly, and within a few days, the whole fruit can rot and emit a sour odor. In the later stages of the disease, small black dots (conidia) gradually develop under the central epidermis of the spots of a few diseased fruits.
Second, the pathogen of rotifer disease in fruit trees
The pathogen is Staphylococcus staphylococcus. The unexual state is a species of Clostridium crustaceae.
The ovary is buried under the epidermis of the host, exposed through the epidermis when mature, dark brown, spherical or oblate spherical, with a perforated ascomycete stick-shaped, colorless, broad top, containing 8 ascospores. Ascospores are oval or ovate, unicellular, colorless to light brown. The conidia are spherical to oval in shape, with papillary orifices, dark brown. The conidia are colorless, single-celled, and the school-shaped contain oil droplet-like inclusions.
The optimal temperature for hyphae growth and conidia formation is around 27 °C and requires light. When the temperature is above 15 °C, the conidia can germinate, but it is most suitable for about 28 °C. Conidia germination has strict humidity requirements, and conidia cannot germinate in the presence of anhydrous membranes.
Third, the occurrence of rotifer disease in fruit trees
Pathogens overwinter as mycelium, conidia, and ascomycetes on the tissues of the affected branches, dead branches, piles, and branches scattered in orchards. In autumn, the diseased fruit that falls to the ground and decays or is buried in the soil has no disease transmission effect. After the temperature rises in the following spring, the overwintering mycelium continues to spread hazards on the branches; Wintering constellations produce conidia or ascomycete spores, which are released in the event of rain, which are spread by wind and rain and infect branches, fruits or leaves. The release of pathogenic spores is closely related to rainfall, and spore release peaks occur 2d after rainfall.
Pear fruit is affected by symptoms of rotunda
Conidia invade mainly from skin holes and wounds. From about 10 days after the flowering to the harvest of the fruit (the second sentence in April to September), as long as the climatic conditions are suitable, the bacteria can infect the fruit, and May to July is the period of concentrated invasion of the bacteria. Pathogens have the characteristics of latent infection. The anti-invasion ability of young fruits to pathogens is weak, and the anti-expansion ability is strong; With the growth of the fruit and the embolization of the epidermis, the rate of fruit infection continues to decline, but the incubation period of the pathogen gradually shortens. The resistance of young fruits is related to the content of phenols and sugars in the fruit When the phenol content in the fruit is more than 0.04% and the sugar content is less than 6%, the bacteria cannot expand. As the fruit ripens, the phenol content continues to decline, and the sugar content continues to rise, and when this limit is reached, the latent pathogen can expand to cause disease.
Conidia are generally not formed on the new spots formed in the branch, and by the 2nd and 3rd years, a large number of conidia are produced on the spots, and after the 4th year, the ability to produce conidia on the spots is gradually weakened, and the spots that are more than 13 years old no longer produce spores. Because the fruit in the field is very late and rarely forms fruiting bodies for re-infection, most of the fruit victims are primary infection.
The occurrence of rotunda disease in fruit trees is closely related to climatic conditions, cultivation management measures and host disease resistance.
1. Climatic conditions
During the period of bacterial infection, rain and high humidity are the dominant factors in the epidemic of diseases. When the temperature is above 20 °C, the relative humidity is above 75% or the rain is continuous for 3-4 days, there are spore releases, spreads and infestations in the field. April to July is the most susceptible period for fruits and new branches, when the temperature conditions are suitable for the onset of the disease, and the amount of rain and the number of rainy days become the key factors in the development of the disease. During this period, the amount of rainfall is large, the number of rainy days is large, the release of pathogen spores is large, the probability of host infection increases, and the occurrence of disease is heavy; Conversely, in years with little rain or region, the amount of spore release in orchards is small, and the occurrence of disease is light.
Pear leaves are affected by symptoms of rotunda
2. Cultivation management
The pathogen is a weak parasitic fungus, and the weakening of the tree is closely related to the occurrence of diseases. Extensive orchard management, insufficient fertilizer, partial nitrogen fertilizer, excessive ring peeling, excessive fruit hanging, and serious damage to borer and dry borer pests can lead to tree weakness and thus facilitate disease. In addition, since the germs that infect the fruit mainly come from the affected branches, the orchard fruits with heavy branches are also seriously ill
3. Host disease resistance
There are obvious differences in the resistance of different varieties of pears to rotunda. The differences in disease resistance between cultivars are mainly related to the size, quantity, epidermal tissue structure and phenol content of the skin pores of cultivars. Varieties with many skin holes and loose epidermal structure are more susceptible. Among the apple varieties, red star, Fuji, golden crown and green banana are the most susceptible to diseases, followed by Guoguang, Marshal, Zhuguang and other varieties, and the vodka peel is more resistant to disease. Pears have the strongest resistance in different populations, followed by white pears, Xinjiang pears and Western pears with the worst resistance, but there are also large differences in resistance between varieties within species.
Pear high quality fruit performance
Fourth, fruit tree rotifer disease prevention and control measures
The prevention and control of rotifer disease in fruit trees should take comprehensive measures such as selecting disease-free seedlings, strengthening water and fertilizer management, removing disease residues, and combining spray protection during the growth period.
1. Agricultural prevention and control
(1) Breeding and selecting disease-free seedlings: the nursery land should be far away from the old orchard and the ward, and it is necessary to avoid raising seedlings in the open space between the rows of the diseased orchard to cultivate disease-free seedlings. The introduced seedlings should be carefully inspected and the sick seedlings and weak seedlings should be eliminated. Pick scion from a healthy, disease-free tree.
(2) Strengthen cultivation management: rational fertilization, balanced application of nitrogen, phosphorus and potassium fertilizers, and pay attention to increasing the application of organic fertilizers to control the amount of fruit hanging in the tree body to prevent the occurrence of large and small annual phenomena. Timely control of leaf diseases and borer pests to avoid early leaf defoliation and the decline in resistance of branches and fruits due to the harm of other pests and diseases, aggravating the incidence of disease. During the growth of seedlings, frequent inspection, found that the diseased seedlings are immediately uprooted, and sprayed in time to protect. In winter, pruning is combined to remove diseased and insect branches, and the outside of the garden is burned intensively.
2. Chemical control
(1) Eradicate the source of overwintering bacteria: scrape off the lesions on the trunk and main branches in early spring in time, and apply a fungicide to protect the inhibition. Scraped bark and diseased tissue should be taken out of the park and burned in a concentrated manner. During the dormant period, spray 50-100 times liquid of crystalline stone sulfur compound or 3-5 baumedu stone sulfur compound and other eradicating fungicides to eradicate latent pathogens.
Pear tree high quality fertility garden performance
(2) Plant treatment: rational use of drugs, master the application period and frequency to improve the control effect. According to the infestation characteristics of rotunda pathogens, pharmaceutical control should be carried out regularly from the fall of flowers to protect the fruit. The first spray should be carried out about 10 days after the flowering, and then the number of applications and the time of application are determined according to the rainfall, the growth of spore growth in the orchard and the length of the residual period of the agent. In addition to spraying the canopy, branches should also be sprayed. The optional agents are oxyazole, phenoxymethozole, ether ester, fluosilazole, zinc manganese, Bordeaux liquid and so on. Attention should be paid to the alternating use of different agents to avoid germs developing resistance.
(3) Post-harvest treatment of fruits: After the fruit is harvested, the fruits are strictly screened and stored, the diseased fruits and injured fruits are removed, and then the fruits are immersed in the fruit with sec-butylamine, methylthiopramine or immastat and other medicinal solutions for 3 minutes, and the low temperature (1-2 ° C is appropriate) after packing is stored.