spruce blight

[distribution and harm] the disease occurred in Songhua River area and Yichun forest region of Heilongjiang Province. It was harmful to the 16-year-old 21-year-old plantation of Piceakoraiensis. In the damaged stand, the young trees of Abiesnephrolepis and Pinuskoraiensis were also susceptible to the disease. A felt-like mycelium grows on branches and leaves, causing withering and felt blight. It spreads upward from the lower part of the crown and extends in a conical shape along the trunk. In 1/4 places in the lower part of the crown, the damage rate of branches and leaves can reach more than 50%; in 1/3 places in the lower part of the crown, the damage rate of branches and leaves can reach 30% to 50%; in 1/2 places in the crown, the damage rate of branches and leaves is less than 30%. When the victim is serious, almost the whole crown and leaves are withered and withered.

[symptoms] at the beginning of the disease, cobweb mycelium grew on the branches and leaves in the dense part of the lower crown, wound leaves and branchlets, and gradually formed hyphae. A felt mycelium layer was formed under the base of branches and leaves, which was about 1~2mm thick and gradually spread to green branches and leaves. The first gray-white, gradually changed to gray, the upper surface of the injured branches, forming a black mildew layer. The stripped mycelium and cortical tissue are still green, and the transport tissue is intact, so the top branches and leaves are normal. When seriously injured, the branchlets and leaves are completely covered by a felt mycelium layer to form a mycelial membrane, which can even form a mycelial membrane under the skin, blocking and suffocating the lenticels and stomata, causing branches and leaves to wither and wither and die, followed by groups or concomitant black globules in or above the mycelium, that is, the ascomycetes.

[pathogen] is RoselliniaherpotrichioidesHepting&Davidson. The ascomycetes are grouped or coexisting, concentrated on the felt mycelium or buried in the mycelium. Nearly spherical, dark brown, carbonaceous, 501 ~ 855 μ m in diameter, with obvious black papillary pores. The ascus is cylindrical, with a short handle, a thickened tip, a small pore and a starchy apical ring (plug) in the middle. The dye turned blue with Melze solution, 180 ~ 207 μ m × 10.5 ~ 13.6 μ m. Ascospores are single-row oblique, unicellular, unequilateral oval to square, with bud slits on one side, sometimes pointed at both ends, containing 1 × 2 oil balls, 20 ~ 24 μ m × 8.5 ~ 10 μ m.

Ascospores did not germinate in water droplets, but could germinate in 2% glucose, sucrose, maltose and other nutrient solutions. 2% maltose Agar membrane was used for spore germination test, and the germination rate was significantly increased.

[incidence regularity] the pathogen overwintered in the host mycelium in ascomycetes. Ascospores are the source of primary infection and are usually attached to the host surface. When the seedlings or stands are too dense, continuous rain and high humidity in summer, the bacteria can grow, reproduce and spread rapidly, causing harm to the host. According to the investigation of Suiling Forestry Bureau of Heilongjiang Province, under the same site condition, the greater the canopy density of Picea koraiensis plantation, the more serious the disease occurred in shady slope, under slope, in forest and unnurtured stand.

[control measures] for over-dense stands, timely measures such as forest cleaning, pruning and transparent cutting can reduce diseases, among which transparent cutting has a significant effect on disease control. The incidence and disease index have decreased significantly, and the prevention and control effect can reach 91.2%. When there are conditions, use 75% chlorothalonil smoke scavenging agent for control, the dosage is 15kg/ha, has a certain control effect.