Alternaria leaf spot .pptx

A presentation on Alternaria leaf spot ,a foliar disease of brassica crops caused by fungal pathogen Alternaria brassicicola.

1. Plant Pathology Maida Nazeer MSc. Botany Semester 02 Alternaria leaf spot

2. Alternaria Leaf spot is caused by the fungus Alternaria dauci , survives between carrot crops as a pathogen of wild and volunteer carrot, in infected crop debris, in the soil for up to one year and in or on contaminated seed. Alternaria Leaf spot is also common disease of cabbage caused by fungal pathogen A. brassicicola . Microscopic Characteristics : Alternaria spp. have septate, brown hyphae. Conidiophores arise singly or in clusters, usually 2-6 ,may be long or short, they are also septate and brown in color, occasionally producing a zigzag appearance. They bear simple or branched large conidia which have both transverse and longitudinal septation. Pathogens

3. Macroscopic Characteristics: Surface; Texture downy to wooly, color pale gray to olive brown on surface. May eventually becomes covered by short, grayish, aerial hyphae. Reverse; Brown to Black Growth Rate; Rapid growth. Hosts: Alternaria leaf spot describes a broad group of fungal diseases that infect several common garden plants. As with many common diseases, several species of closely related fungi cause this leaf-spotting disease. Some target specific plants, but others strike entire plant families. In case of brassica vegetables such as Cabbage Broccoli Cauliflower Brussels sprouts A. brassicicola cause Alternaria leaf sprout. HOSTS

4. Alternaria leaf spot symptoms first appear as greenish brown, water-soaked lesions. Lesions quickly become dark brown to black with or without yellow halos. Under disease-favorable conditions, lesions coalesce and cause entire leaves to become yellow, collapse, and die. Older leaves are most susceptible to infection and often the first to develop symptoms, but all leaves can be infected. Petiole lesions appear like leaf lesions but are more elongated; petiole lesions quickly kill entire leaves. Disease symptoms are often confused with Cercospora leaf spot and bacterial blight, and microscopic examination is often necessary for accurate diagnosis. Symptoms

5. Carrot seedlings can also be attacked by A. dauci within 2 to 3 weeks after emergence. Infected hypocotyls and upper roots become girdled and shrivel, turning a gray or black color. Seedling infection appears similar to Pythium damping-off, but A. dauci infection and decay is drier than that of Pythium.

6. Cultural Control; Plant high quality seed are free of the Alternaria leaf spot pathogen. Hot water treatment can reduce seed contamination but may reduce seed storability and germination. Select varieties resistant or tolerant to Alternaria leaf spot, such as ‘Orlando Gold,’ if available. Practice a three-year or longer crop rotation to other than hosts such as small grains. Eliminate potential sources of the pathogen by deeply burying crop debris after harvest and controlling wild and volunteer carrot. Avoid prolonged periods of leaf wetness by avoiding dense planting, orientating rows parallel to the prevailing wind direction, and timing irrigations to end before dusk. Avoid overhead irrigation if possible. Chemical Control; Fungicides are rarely necessary for Alternaria leaf spot control in many high plain's carrot production regions, but are essential in warm, humid environments. Disease forecast models have been developed that can improve the timing and efficiency of sprays. Chemical controls are most effective when combined with as many cultural control strategies as possible. control