Efficiency of some organic acids as safe control mean against root and stem rot disease of Coleus forskohlii
Coleus (Coleus forskohlii) is an important medicinal crop containing forskolin in their roots. Root rot is considered the most important disease in coleus, causing serious losses affecting growth and yield. Infected coleus plants showing root and stem rots were collected from Giza gardens and nurseries. The pathogenicity tests of the isolated fungi (Fusarium oxysporum, F. roseum, F. semitectum, F. solani, Macrophomina phaseolina, Pythium splendens and Rhizoctonia solani) revealed the ability of these fungi to cause infection. Application of three organic acids (Ascorbic, oxalic and salicylic acid) each at 250 and 500 ppm, against R. solani, F. semitectum, F. oxysporum and F. solani was performed in the greenhouse. All the tested organic acids reduced significantly disease incidence when used as dipping unrooted cuttings and/or spray plants 30 days after planting or soil drenching under greenhouse conditions particularly at 500 ppm compared with untreated plants. In general, oxalic acid at 500 ppm was more efficient in reducing infection with root and stem rot diseases. As for plant growth parameters, soil drenching with oxalic acid was the best treatment in increasing plant height and branch number compared with the other treatments. However, ascorbic acid was the least effective treatment compared with the other treatments. On the other hand, dual combination of three organic acids was superior on the other treatments and also recorded superiority in peroxidase and polyphenol oxidase enzyme activities.
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