Studies on the leaf blight disease of clove caused by Cylindrocladium sp.

Abstract

Leaf blight disease of clove caused by Cylindrocladium cuinqueseptatum Boedijn et Roitsma was investigated. The fungus infected clove leaves at all stages of maturity, but the seedlings were found to be more susceptible to the disease than mature plants. Injury of the host tissue was found to be a pre-requisite for successful infection by the fungus. The organism infected a wide variety of plants including some of the weed plants on artificial inoculation. Good growth and sporulation of the fungus was obtained on potato dextrose agar followed by Coon’s agar and Czapek’s agar. In liquid media, maximum dry weight of the mycelium was obtained on potato media, maximum dry weight of the mycelium was obtained on potato dextrose broth, followed by Czapeks’ broth. Maximum growth of the fungus was obtained on medium amended with gingelly oil followed by coconut and clove oils. In liquid media, maximum dry weight of the mycelium was obtained in the medium amended with gingelly oil followed by coconut clove oils. Optimum pH range for the growth of the fungus was found to be 7 to 9. Richards’ broth was found to be the best medium for the production of toxin followed by Czapek’s and Fries’ media. Exotoxin production was found to be more than endotoxin. The toxic metabolite is found to be thermostable. Diluting the culture filtrate to 4 times its volume showed a reduction in the toxic effect. However, the treatments did not completely eliminated the toxic effect of the preparation. The toxic effect of the culture filtrate translocated by defoliation on the cut twigs of plants. Culture filtrate of the fungus inhibited the spore germination of Colletotrichum glocosporioides and Curvularia sp. The culture filtrate as well as the mycelial extract produced lesions on clove leaves of different maturity, with pronounced effect on tender leaves. Spore germination of the fungus could be completely inhibited with all the eight fungicides in all concentrations on the first day of observation. Daconil-2767, Dithane M-45, Fytolan and Thride were able to cause 94,97,94 and 95 per cent inhibition of spore germination respectively upto 12th day at maxium concentration tested ( 3000 ppm). Growth of the fungus was completely inhibited with Bavistin 250, 500 and 1000 ppm, Dithane M-45 1000, 2000 and 3000 ppm; Mildothane 500, 1000 and 2000 ppm and thride 1000, 2000 and 3000 ppm; when tested in czapeks’ agar medium. In czapeks’ solution Bavistin, Difolatan, Dithane M-45 and Mildothane at all concentrations tested, there was complete inhibition of growth of the fungus. Bavistin at 250 ppm and Thiride at 1000 ppm were able to inhibit the growth of the fungus by 15 minutes immersion, when the culture dises were tested for the viability of the fungus, Mildothene and Dithane M-45 inhibited the growth of the fungus at 1000 and 2000 ppm respectively, When the culture discs were tested for the viability of the fungus after immersion for one hour in fungicidal solution. Fytolan and Difolaton were able to inhibit the growth of the fungus at the maximum concentration (both at 3000 ppm), only after 24 hours immersion in the fungicidal solution.