cotton seedling anthracnose

Symptoms can occur in both seedling stage and adult stage. Seed rot could be caused by infection and germination at seedling stage, reddish-brown stripes appeared at the base of stem after emergence, and seedling death was caused by expansion constriction. Orange-red sticky substance (conidia) is produced on the disease spot when it is damp. Round or semicircular chloasma appeared at the edge of the cotyledon, and then dried and fell off, leaving the edge of the cotyledon incomplete. In the initial stage of cotton boll infection, the cotton boll showed a dark red spot, and after expansion, it showed a brown spot, and the disease part was sunken, with orange powder, that is, conidia. In severe cases, the whole bell rotates and cannot be cracked, and the fiber turns into a black stiff flap. The disease spot of the leaf is irregular and nearly round, and it is easy to dry and crack. Stem spot reddish brown to dark black, oblong, central depression, epidermis rupture often exposed xylem, easy to break in case of wind. In the later stage of production, the cotton boll was seriously injured and suffered a lot of losses.

Pathogen ColletotrichumgossypiiSouthw. It is called Colletotrichum gloeosporioides, which belongs to the subphylum fungus. Glomerellagossypii (Southw.) Edgerton is called cotton clump shell, which belongs to ascomycete subphylum fungi and is rare. The ascus shell is dark brown, spherical to pear-shaped, 100-160 × 80-120 (μ m) in size, buried in the host. The ascus contains 8 ascospores, single cell, oval, slightly curved, size 12-20 × 5-8 (μ m). The asexual conidia are placed on the conidiophores and arranged in a shallow basin, with bristles on the conidial disc, dark brown setae and 2-5 septum. The conidiophores are short and conidia can be produced continuously on them. Conidia colorless, unicellular, long oval or short stick-shaped, size 9-26 × 3.5-7 (μ m), mostly aggregated, pink. Conidia germinate and often produce 1-2 septum, with a germ tube growing at the top of the germ tube and an invading filament invading the host. The optimum temperature for conidia germination was 25-30 ℃. The conidia germinated less and grew slowly at 35 ℃, but did not germinate at 10 ℃. The suitable soil temperature is 24-28 ℃ and the relative humidity is more than 85%.

The pathogens of transmission and disease conditions overwintered mainly by conidia on cottonseed velvet, and a few of them overwintered by mycelium in cottonseed coat or cotyledons. Seed carrier is an important source of primary infection. The conidia of the pathogen can survive on cottonseed for 1-3 years. Because the initial temperature of cottonseed germination and spore germination are both about 10 ℃, the pathogen is easy to invade during cottonseed germination, and then the conidia can be spread by wind and rain, insects and irrigation water. The pathogen of cotton boll infection invaded the cottonseed, and the carrying rate was 30%, 80%. The diseased leaves, stems and bolls fall into the soil, causing bacteria in the soil, which can not only cause the disease in the seedling stage, but also infect the cotton boll by Rain Water.

The selection of disease-free seeds and seed disinfection are the two keys to the prevention and control of the disease. The main results are as follows: (1) choose disease-free seeds or interannual seeds with good quality. (2) seed treatment was carried out before sowing. Seed dressing with 40% double wettable powder 0.5kg and 100kg cottonseed, 70% methyl topiramate wettable powder 0.5kg and 100kg cottonseed, 70% wood manganese zinc wettable powder 0.5kg and 100kg cottonseed, and 1kg 10% Lingfu mixture and 50kg cottonseed coating have good control effect. (3) sowing at the right time, cultivating strong seedlings, promoting the early development of cotton seedlings and improving disease resistance. (4) reasonable close planting can reduce the humidity in the field, prevent cotton seedlings from growing too vigorously, and pay attention to prevent the premature senescence of bolls. (5) spraying 70% methyl thiophanate (methyl thiophanate) wettable powder or 70% chlorothalonil wettable powder, 70% mancozeb wettable powder, 1500 carbendazim wettable powder and 25% carbendazim wettable powder at the initial stage of the disease.