Sclerotinia sclerotiorum

1. Harm: Sclerotinia sclerotiorum occurs every year in the orchid room of the Shanghai Botanical Garden, causing the whole bud of orchid leaves to die, with an annual incidence of about 1%. Although it is not very common, the orchid always dies of the whole bud or even the whole basin after infection. Among orchids, autumn orchids in Jianlan are more susceptible, and other cymbidium and spring orchids also occur.

2. Symptoms: the disease occurs in potted orchids placed indoors from March to April every year. At first, the base of the leaf shows water-soaked rot, which can extend upward to most or the whole leaf, showing reddish brown, but the undiscolored part of the leaf color can remain green for a short time, followed by grayish white, with black round or oval small sclerotia, sclerotia diameter 0.5~1.5mm, buried under the epidermis of orchid leaves, arranged in a vertical row. Parallel to the veins. In the plants with this disease, the base of the diseased leaves are delaminated and easily broken.

3. Pathogen: the pathogen of Sclerotinia sclerotiorum is a kind of stem and leaf sclerotiorum (Ectostroma sp.) fungi, which does not produce spores, sclerotia is black and glossy, small, 0.5~1.5mm in diameter. The sclerotia was dissected and the internal and external color was the same. On the potato, sucrose and Agar medium, the sclerotia was easily produced and buried under the surface of the medium, while the hyphae was not well developed. the appearance, color and size of the cultured sclerotia were completely consistent with the natural growth of the diseased leaves.

4. characteristics of the disease: Sclerotinia sclerotiorum has no spores, so it overwinters with sclerotia in diseased leaves or diseased fallen leaves. Mycelial infection will be caused by germination in the coming spring. The basin soil is too humid, and the disease occurs frequently when the temperature is cold. In the genus Orchid, the disease is serious in Cymbidium. The results showed that there were resistance differences among varieties.

5. Prevention and control methods:

(1) artificial control: it was found that the diseased orchid leaves were pulled out quickly. It is observed that in a pot of orchids, not all orchid plants suffer from disease at the same time, but successively, so it is found that they should be pulled out immediately, and a small amount of lime or sulfur powder can be disinfected in the hole.

(2) Horticultural prevention and control: orchids overwintering in greenhouse should not come out too early in spring. Generally, orchids can not be moved outdoors until after Qingming and breaking frost. Watering indoors in winter and spring should not be too much. Attention should be paid to the water permeability of pots. Watering should also be watered from the edge of the basin.

(3) Drug control: disinfection of culture medium with pentachloronitrobenzene (such as prevention and control of white silk disease) and application of 50% 1O00 solution of clonitramine at the initial stage of the disease had certain effect. (Liu Zhongjian)