Studies on purple blotch of onion, garlic and fungicide tests for control

Symptoms of purple blotch disease appearing on onion, shallot, multiplier onion, leek and garlic are similar except that the levels of susceptibility are different. Most conidia produce germ tubes and penetrate wounds on leaves within 8 hr. after inoculation. Using a freezing microtome for thin sectioning, plenty of mycelium conidiophores and conidia were found under epidermal cells of the infected leaves. Most conidia observed are club-shaped with cross and longitudinal septa. In an attempt to find out how the fungus produces spores, various kinds of media, and many types of lights (UV, fluorescent, incandescent, sun light) were used in cultivation of the fungus. The most important factor is temperature. This fungus produces spores when the temperature is between 18 - 26 deg.celsius. The fungus grown on CMA at this temperature in the dark will produce the highest number of spores. The fungus produces more conidia on PA than on PDA and PA is suggested for culturing this fungus because it is cheaper than the others. Needles, carborundum, or breaking the leaves to create wounds were used to find the most suitable method for inoculating the host plants with this fungus. Inoculum was applied to the test plant by spraying with a hand spray or using a cotton swab soaked with inoculum smeared on wounded and unwounded leaves. All test plants were covered with plastic sheets to retain moisture. The cotton swab method is the most successful one. The effectiveness of ten selected fungicides against the fungus was tested using fungus cultures on PDA, artificially inoculated plants and infected plants in the field. It was proved that Manzate-D is the most effective one while Dithane M45 and Antracol come the second. Azinmag and Delsene MX also showed satisfactory results