Draft:Soybean anthracnose

The first reported was in 1917 in Korea, the disease reduces stands, seed quality, and yields by 16-20% or more in the United States, by 30-50% in Thailand and by 100% in certain areas of Brazil and India.

Symptoms and signs
Soybeans are susceptible to anthracnose pathogens at all stages of development. Foliar symptoms, which develop after a prolonged period of high humidity, include necrosis of laminar veins, leaf rolling, petiole cankering, and premature defoliation. During the early reproductive stages, symptoms typically appear on stems, petioles, and pods as irregularly shaped, brown areas and may resemble pod and stem blight. In the advanced infected tissues are covered with black fruiting bodies (acervuli) that produce minute black spines (setae). The setae are diagnostic for preliminary identification of pathogen. Preemergence and postemergence damping-off may occur when infected seeds are planted. Dark-brown, sunken cankers often develop on the cotyledons of emerging seedlings. These cankers gradually extend up toward the epicotyl and down toward the radicle. During humid conditions, one or both cotyledons become water soaked, quickly winter, and fall off. Premature defoliation may occur throughout the canopy when cankers girdle the leaf petioles. Seeds colonized by Colletotrichum truncatum may not show symptoms or may develop brown staining or small, reregulation shaped, gray areas with black specks. Infected seeds may die during germination, if germinate, they produced infected seedlings.

Causal Organisms
The most common pathogen associated with anthracnose is Colletotrichum truncatum. Other Colletotrichum spp. also reported on soybeans are C. chlorophyti, C. coccodes, C.gloeosporiodes (syn. Glomerella cingulata), C. graminicolla (syn.G. graninicolla), C.incanum, and Glomerella glycines (syn. Colletotrichum sp.). The host ranger for C. Chlorophyti and C. incanum are not known or other pathogen have wide host ranges. All the species are known or presumed to be seedborne in soybean. Disease Cycle and Epidemiology The anthracnose pathogens over season as mycelia, sclerotia and acervuli in crop residue and in seeds. Seedborne inoculum may result in pre or postemergence damping-off of seedlings or failed seed germination if the embryos are infected. Mycelium may also became established in infected seedlings without symptoms developing until the plants begin to mature. Stem and pod infection usually occur in the reproductive stages of soybean development during warm, moist conditions. Detailed information about the environmental conditions that promote disease development is lacking. conidia of C. truncatum and G. glycines germinate and form appressoria at temperature below 35ºC when the plant surface is wet. The conidia are short lived and sensitive to drying, 5 h of air drying can reduce germination by 98%. Infections typically occur if rain, dew, or fog provides free moisture for a period of 12 h or more.

Management
Soybean germplasm varies in susceptibility to anthracnose. Sources of resistance have been identified in some soybean germplasm, but not in commercial, private cultivars. Using high-quality seeds that are free of pathogens and have a treatment with a recommended fungicide may reduce the levels of inoculum associated with the pathogens that cause anthracnose. Crop residues should be plowed under in situations in which soil erosion is not a concern, and rotating crops may also reduce the inoculum load. Applying fungicides during the mid to late reproductive growth stages may also be effective, especially under conditions known to favor disease development and when needed for seed production fields.