Studies on Alternaria Spp.Causing Leaf Blight in Cauliflower and Its Management in Chotanagpur Region
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Date
1999
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Birsa Agricultural University, Ranchi
Abstract
Leaf blight disease of cauliflower (Brassica oleracea var, botrytis L.) caused by Alternaria brassicae is a widespread disease in Bihar. Spots were small, circular measuring 2-5 mm which gradually enlarged upto 10-25 mm in diameter. These spots were lighter in colour but later on changed to dark brown. Conspicuous zonations or concentric rings were formed on almost all the fully developed spots.
Alternaria brassicae: Conidia obclavate, muriform, bottle shaped, attenuated into a long conspicuous beak at the tip and slightly narrowed at the base.
Conidiophores - simple, erect or ascending straight, sometimes flexuous, more or less cylindrical. Mycelium-short, compact, septate, branched, hyaline at first, later on turned light brown to olivaceous gray, inter and intracellular, 4.8 μ wide and 3.6 u in diameter.
Alternaria brassicicola Conidia variable in shape, cylindrical to oblong, poorly developed beak, muriform, light olivaceous to dark olivaceous, in long chain of 6 to 8 spores Mycelium - short, compact, septate, branched, sometimes hyaline, olive gray to grayish black, inter and intracellular 4.2 µ in diameter.
Conidiophore simple, erect or ascending straight, cylindrical, olivaceous, septate, 5-7.5 x 35-45 μ, conidia born terminally on conidiophore.
Radial growth and biomass production was found significantly superior in Richards and potato dextrose compared to other media followed by leaf extract,
Czapek's agar and glucose asparagine.
Optimum temperature and pH for growth and sporulation of the fungus were found 25°C and 5.5, respectively. Sucrose 1% proved to be the best medium for germination whereas distilled water and rain water resulted the least percentage of germination of spores.
The fungus produced significantly maximum amount of 423.3 mg dry mycelial mat and sporulation in the standard Richard's medium containing sucrose and followed by glucose, mannitol and maltose.
Organic form of nitrogen as Urea and asparagine was found to be the best source of nitrogen as compared to inorganic source. Among the inorganic source the fungus had much more affinity with nitrate form of nitrogen as sodium nitrate and ammonium nitrate than ammoniacal form ie. Ammonium chloride.
Thiamine was found to be the best vitamin for maximum mycelial mat production and sporulation. Bavistin was found most efficacious at 200 ppm whereas 'karanj and neem oil completely inhibited the growth at 10,000 ppm. In field condition also this fungicide was found significantly superior at 0.05% concentration. Spore germination of the fungus was completely suppressed at 75 ppm.
KT 9, Pusa subhra, Improved Japanese, Pusa Katki, Aghani and Poosi varieties: of cauliflower were found moderately resistant to Alternaria leaf blight disease.