Spruce snow blight

[distribution and harm] Foreign countries are distributed in North America, Northern Europe and Central Asia, harming European spruce (Piceaabies), white spruce (P.glauca), black spruce (P.mariana) and so on. It is distributed in Tianshan Mountain, Altai Mountain, Western Junggar Mountain and Kunqu Mountain in China. Damage to spruce (P.schrenkiana), Siberian spruce (P.obovata), Qinghai spruce (P.crassifolia) and Sichuan spruce (P.balfouria7la). In the late 1950s, at the beginning of afforestation activities, the disease only occurred sporadically in natural forests. At present, the disease has occurred widely in continuous cropping nurseries, and it has broken out in some areas, and it has also spread widely in regenerated young forests. The average incidence of artificial regeneration of young forests in various places is 10%-43%, and in severe cases it is as high as 88%.

[symptoms] in the early stage of the disease, the needles under the snow were dark grayish green and hot, with dirty white to light brown hyphae or bacterial membrane on the surface, and many small sclerotia from dark brown to reddish brown. After more than a month, near 1mm could be seen on both sides of the needles, dark brown swollen spots in the center, and sometimes spilled white glue droplets or tendrils. In the later stage, the diseased leaves appeared dark brown lines along the stomatal line, and then connected into a line segment, from depression to spread, and then uplifted, with a bubble-like appearance and straw color. the old diseased leaves of the previous year were grayish brown and the cortex ruptured intermittently in many places.

[pathogen] the pathogen is LophtphacodiumhyperboreumLagerb. Cotyledons abaxially or peripherally, more abaxially, Prophase buried, dispersed to clusters, 500 ~ 1000 μ m × 200 ~ 500 μ m, often several aspergillas fused, several millimeters long, some almost as long as needles. Intuitive stomatal lines are intermittent black dots or segments. The sporadic cortex is endogenetic and protuberant after maturity. Ascus disk longitudinally long, bubbly, straw-colored, longitudinally dehiscent apically or laterally. The false integument is a covering layer composed of host and fungal tissue. The outer layer is brown, spherical pseudo-parenchyma cells, and the inner layer is nearly colorless. The medial upper margin produces irregularly branched quasi-perifilaments, 40 μ m × 2.5 ~ 4 μ m. The wall is smooth, there is a septum, and the top center has a nuclear structure composed of dark brown and compact spherical cells, 40 ~ 150 μ m × 20 ~ 50 μ m. The seed layer is straw yellow and contains colloid. The ascus is rod-shaped, 89 ~ 22 μ m × 14 ~ 19 μ m, containing 8 spores, biseriate, and the top orifice turns blue with iodine solution. Ascospores are ovoid to fusiform, straight or slightly curved, often swollen on one side, containing 2 to 3 oil droplets, 14 ~ 21 μ m × 5 ~ 7 μ m, nearly colorless. Lateral filaments many, linear, 90-130 μ m, 2-diaphragm, sometimes branched. The asexual stage belongs to the genus Apostrasseria. Conidium of conidium, leaves abaxially or peripherally, mostly on abaxial surface of leaves, scattered, sometimes clustered. It is often associated with the sexual receptacle and buried in the needle cortex. At maturity, the top is slightly raised, 200 ~ 500 μ m × 130 ~ 220 μ m, subspherical to oblate, or concave at the bottom, irregular. A single chamber, or a labyrinth-shaped pseudo-multi-chamber, the wall is composed of brown pseudo-parenchyma cells, 15-20 μ m, rich in glia, sometimes spilling white droplets or tendrils. The sporogenous cells are gourd-shaped to nearly barrel-shaped, colorless, smooth wall, 9 ~ 15 μ m × 2 ~ 3 μ m, bottle pedicel sporulation. The conidia are immersed in colloid, not easy to disperse, colorless, unicellular, fusiform to oval, 2.5 ~ 40 μ m × 1 ~ 1.5 μ m, length / width ratio 2.5 / 2.7, with irregular glial appendages at the top. Superficial flocculent hyphae or bacterial membranes containing small black-brown sclerotia, mostly on the adaxial surface of leaves. Erect solitary, sometimes clustered, 10-25 needles per leaf, easy to fall off after melting snow. The small sclerotia is long, granular, slightly curved at the top or base, and the surface is rough. The thick-walled hyphae with brown longitudinal length and septum gather into bundles, which are easy to spread under light pressure, 80 ~ 320 μ m × 40 ~ 120 μ m.

[incidence regularity] pathogens are harmful to spruce plants. Long-term stable snow cover (above 40~50cm) in winter is the dominant ecological condition for the disease. Artificial snow-making inoculation of Tianshan spruce introduced and cultivated in Urumqi can also cause the disease. Because the susceptible hosts Snow Ridge spruce and Siberian spruce are widespread species in mountain forests, the pathogens are suitable for survival and growth in both ecological and host aspects. Therefore, spruce snow blight has become a widely distributed frequently-occurring disease. The disease is serious in areas with many obstacles, low-lying leeward valleys, deep snow cover, late snow melting and long snow melting period. Spruce snow blight and snow mildew often occur in the same area and on the same plant at the same time, and snow mildew often occurs in the lower part of the plant.

[prevention and control measures]

1. It is strictly forbidden to use diseased seedlings for bed transfer, afforestation out of the nursery and transfer them to other places.

2. Root out the disease center and remove the diseased plant in time from June to July. All the seriously diseased plants were removed, and the diseased branches were cut off from the mildly diseased plants. For other forest control and chemical control techniques, see "spruce snow mildew".