In vitro Study on Physiological Growth and Effect of Different Artificial Inoculation Methods on Incubation Period of Alternaria porri (Ellis) Cifferi Causing Purple Blotch of Onion

Alternaria porri causing purple blotch of onion is major constrains in onion cultivation and causes a yield loss ranging from 2.5 to 87.8 per cent. The aim of this study was to find the effect of different inoculation methods on incubation period and to know the best solid media, temperature and pH for the mycelial growth of Alternaria porri. The maximum incubation period was observed for symptoms development in Soil inoculation (6.02 days) followed by Wound inoculation (4.93 days) and Syringe inoculation (4.47 days). The minimum incubation period was observed in Foliar spray inoculation (2.38 days). Among the solid media maximum radial growth of the fungus was recorded in PDA (89.97 mm) followed by Oat meal agar (89.67 mm) while minimum radial growth was observed in Corn meal agar media (53.82 mm). The result of pH indicated that pH 5 have maximum mycelial growth (87.0 mm) followed by pH 6 (84.0 mm) and the minimum growth was observed in pH 9 (61.0 mm). The results of temperature revealed that maximum growth (88.95 mm) of the pathogen was observed at 30℃ followed by 25℃ (85.97 mm). A sudden fall in mycelial growth was observed at 35℃ (78.95 mm) and 20℃ (61.22 mm).