Rotten skin of Pinus koraiensis

[distribution and harm] the disease occurred in Korean pine (Pinuskoraiensis) plantations in three northeastern provinces. Yanji, Hunchun, Helong, Wangqing, Dunhua, Antu, Longjing and other cities (counties) in Yanbian area of Jilin Province had a serious disease, with a general incidence of 20% to 30%, a seriously diseased forest of 50% to 60%, and a few stands of Maoershan Forest Farm in Yanji City, with an incidence as high as 98.6%.

The pathogen invaded the phloem and cambium of young Korean pine trees and lateral branches, and even reached the surface xylem of sapwood, causing brown rot and death of the tissue, seriously affecting the growth of diseased trees, and some leading to death. According to the survey, the height growth loss of seriously diseased trees is 51.1%, and the DBH growth loss is 42.4%. The wood defect caused by the depression of the diseased part of the trunk, which affects the growth of wood, is an important disease to harm the young Korean pine plantation.

[symptoms] germs invade tree trunks and lateral branches from skin wounds. After the lateral branches were infected, the phloem turned brown and rotted, and local disease spots began to form, and the appearance of the whole branch did not change, which could be found by peeling examination. The pathogen quickly expanded the whole branch, and the needles turned yellowish green. The next spring, the whole branch withered, and there were fat droplets at the junction between disease and health. The primary disease site of the trunk is mostly in the dry skin or mechanical injury at the base of the diseased lateral branch. At the initial stage of the disease, the epidermis of the diseased part had no obvious change, and the cut phloem showed yellowish brown. After reaching the depths of the phloem, a lot of turpentine continued to spill from the lenticels and droplets hung on the bark. The disease part expanded laterally around the trunk to form a ring of rotten skin, and developed to the upper and lower direction and the depth of the cortex. The infected young trees suffered from the disease continuously for many years, and with the extension of the medical history, the overflowing fat accumulated more and more, so that the epidermis of the diseased part was covered with a layer of flowing fat. If the seriously diseased tree has been sick for several years, the disease part can be as long as 50~60cm, even more than 1m. Due to the destruction of the cambium of the diseased part and the loss of the ability of proliferation, the diseased part of the trunk is gradually sunken and thin, and the rotten skin is dry, cracked, rough and brown. At its worst, the trunk is thick at the top and thin at the bottom. When the cambium of the annular rotten skin completely rotted to death, the seriously diseased young trees withered and showed signs of death in April and May. By the middle of June, the papillae brown pseudoconidium and conidium were densely produced on the diseased branches and dry bark. Most of the natural withered branches and dried bark are sexual fruiting bodies. Sexual and asexual mixed together, it is difficult to distinguish with the naked eye. The dry skin of the seriously ill standing wood disease is also scattered with asexual and sexual fruiting bodies, and most of them are asexual, which are covered by flowing fat, and can be seen by careful examination of the flowing fat layer (color version 14).

[pathogen] the sexual type Leucostomakunzei (Fr.) Munk of the pathogen forms a pseudopodium, which is a flat-topped conical, initially buried in the skin, then exposed through the epidermal orifice and composed of dirty white loose tissue. More than 430 ovate-shaped and long-necked ascomycetes are closely arranged at the bottom. The neck is gathered together, and the nipple-shaped orifice is exposed outside the bark to form a disk-shaped outer seat. The boundary between the pseudoconstellation and the host tissue is clear, and the base has a black ribbon. The width of pseudosperm is 882 ~ 1311 μ m. The height is 694 ~ 977 μ m and the width of the outer seat is 240 ~ 700 μ m. The ascus is ovate with a long neck, leathery, mature green brown or brown, 244 ~ 330 μ m × 289 ~ 366 μ m in size, 599 ~ 688 μ m in neck length and 3355 μ m in diameter. The ascus is rod-shaped, thin-walled, colorless, thicker in the middle, obtusely round at the top, tapering at the lower end, sessile, 21.3 ~ 27.5 μ m × 4.3 ~ 5.0 μ m in size. There are 8 ascospores arranged in irregular double or three rows. Ascospores are sausage-shaped, monospore, colorless, 7.0 ~ 7.8 μ m × 1.0 ~ 1.5 μ m.

The asexual conidium is spherical or oblate, brown carbon, initially buried in the skin, and then breaks through the epidermis, only the orifice is exposed. The organ cavity is irregular multi-chamber communication, with a common orifice. The width is 696 ~ 1035 μ m and the height is 614 ~ 864 μ m. The conidiophores are peripherally branched in the organ cavity, with 1 to 3 dichotomous branches, tapering at the tip, colorless and without separation, 19.4 ~ 32.4 μ m in length and 1.1 ~ 1.6 μ m in diameter. The conidia is sausage-shaped, monospore and colorless, with a size of 3.0 ~ 5.1 μ m × 0.6 ~ 0.9 μ m.

The spore germination and colony growth of the strain were faster on PDA and other media, and the pure bacteria could be easily obtained by tissue and spore isolation by conventional methods. The colony is white felt at the beginning, and becomes brown when it is ripe. The granular conidia were produced on the surface of the colony after about 25 days of 23-27 ℃ side light culture, most of them were solitary and initially white, and then turned brown after 10-20 days of maturation, and the milky conidium horn overflowed from the orifice.

The temperature range of ascospore and conidia germination was 15: 30 ℃, and the optimum temperature was 20: 25 ℃. The temperature range of colony growth was 5: 35 ℃, and the optimum temperature was 25 ℃. The pH range of ascospore and conidia germination was 3.5-8.5, and the optimum pH value was 4.5-6.0. The pH range of colony growth was 3.0-8.0, and the optimum pH value was 3.5-4.0. The germination rate of spores was closely related to nutritional conditions, and ascospores and conidia could not germinate when cultured in water. In 25 ℃ culture for 48 hours, the medium used 2% Agar, the germination rate was 53%, the Agar 2% plus pine bark juice 98%, the germination rate was 78.6%, and the Agar 2% plus potato juice 78%, plus pine bark juice 20%, the germination rate was 91.8%. When the nutrition is sufficient, the conidia become round when they germinate, and the ascospores are gourd-shaped. The nutrition is poor, the conidia and ascospores are long oval or thicker and elongate when they germinate, and bud tubes grow from both ends or one end of the spores.

The pure bacteria and spore suspension obtained from isolation and culture were used to inoculate disease-free young trees such as Pinus koraiensis, Pinus sylvestris var. mongolica, Larix gmelinii and other young trees by means of drilling, acupuncture, burn, etc. The results showed that the inoculation rate of Korean pine was 100%, and the incubation period of other tree species was about 100 days from inoculation to the occurrence of rotten skin.

[incidence regularity] the bacteria overwintered with mature and immature pseudoconidia, conidia and hyphae. After the end of April, the average temperature of the day was more than 10 ℃. On rainy days, the mature Pseudoconidia and conidia released spores, which were transmitted by wind and Rain Water, which was the primary infection source of the disease. At the beginning of June, the dry bark of diseased branches, dry stems and seriously diseased trees formed new pseudoconidia and conidia, which gradually matured and released spores in early July, which was the source of repeated infection of the disease. The period of spore transmission lasted for 5 months from the end of April to the end of September. The number of spore transmission is closely related to rainfall, temperature and humidity. From mid-June to late July, heavy rainfall, high temperature and humidity are the peak period of spore transmission, during which there are several transmission peaks. The spores captured by slides in the forest and microscopic examination of sections showed that the production and maturity of sexual and asexual fruiting bodies were irregular, and the maturity of each ascus in the same ascus and the mature stage of each ascus in the same ascomycete were irregular. When the ascus matures, the wall disintegrates and dissolves, and a large number of single ascospores and many ascomycetes can be seen in the mature ascus shell. Diseased young trees can release sexual and asexual spores from July of that year to July of the third year.

The occurrence and prevalence of the disease are closely related to forest age, slope aspect, soil, stand composition, canopy density, tree growth, management measures and so on. The disease can occur at the age of 10 to 30 years, and the disease is serious in the stand of 15 to 25 years old. The disease of sunny slope and semi-sunny slope was more serious than that of shady slope, and that of pure forest was more serious than that of mixed forest. The forest with heavy soil and low content of available nitrogen was seriously diseased. The distribution disease of the forest with canopy density of about 0.8 was mild, while the stand with too large canopy caused poor growth and serious disease. For the stand with low canopy density, due to the strong light in the forest, it is beneficial to the occurrence of pests such as Korean pine aphid and pine aphid, resulting in many small wounds in the dry bark of the forest, which is conducive to the invasion of the disease, so the disease is also serious, and there is no thinning and tending for a long time after afforestation. As a result, many compressed and dying trees in the forest, or thinning and tending are carried out too late, and some stands with unreasonable intensity pruning, the disease is serious. On the other hand, thinning and tending should be carried out in time to keep the canopy density of about 0.8, the incidence of the disease is mild. Therefore, all the factors that cause poor growth of trees and a large number of wounds in weak trees are the causes of the occurrence and epidemic of the disease.

[control measures] the pathogen is a weak parasite, and the control methods are mainly forest management measures, supplemented by chemical control. The tending management of Pinus koraiensis plantation should be strengthened, thinning and tending should be carried out in time according to the law of growth and development of young forest, maintain suitable density, improve the sanitary environment in the forest, and strengthen the tree potential to prevent the occurrence of the disease. According to the investigation, the coarse-skinned Korean pine not only grows faster than the fine-skinned Korean pine, but also has stronger resistance to the rotten skin of Korean pine. Attention should be paid to the breeding of resistant and fast-growing Korean pine varieties to provide production and application. Afforestation should be suitable for land and trees, and great efforts should be made to build mixed forests.

In combination with thinning and tending, diseased branches, dried trees and dying seriously diseased trees were removed and burned out of the forest, so as to reduce the source of infection. For the preserved diseased tree, the ideal effect can be obtained by scraping the rotten skin with NaOH1% and Ca (OH) 225% water solution in spring. When scraping, you should pay attention to protect the cambium, scrape to the junction of disease and health, and extend 5~10cm to the healthy area. With strict operation, the disease can be controlled after prevention and treatment in the first year, and can be cured by proper supplementary treatment in the second year. This method is especially suitable for seriously diseased young trees with DBH below 10cm in a large area, and the trees are safe and harmless. It can also be smeared with pine tar, pine tar plus diesel oil at 1:1, chlorothalonil 10% oil, etc., and good results can be obtained. However, attention should be paid to the application of oil to control seriously sick young trees whose length exceeds 50cm, which is easy to cause drug damage and even die, and can be treated stage by stage.