Degradation of Cocoyam (Xanthosoma Sagittifolium L.) by three Isolates of Sclerotium Rolfsii Sacc. and its Control

Abstract

The morphological characteristics of three isolates of Sclerotium rolfsii from Aburi (AB), East Legon (EL) and Legon campus (LC) were studied on PDA at an incubation temperature of 28oC. Radial growth of mycelia and the production of sclerotia were more pronounced in the East Legon (EL) and Legon campus (LC) isolates. When the red and white cormels of cocoyam (Xanthosoma sagittifolium) were inoculated with the various isolates of Sclerotium rolfsii, the white cormels were more resistant to infection by the fungus as compared to the red cormels. After cultivating the red and white types of cocoyam on soils inoculated with sclerotia of the three isolates, phenotypic development was more suppressed in the red type of cocoyam than the white type, whilst the yield of cormels was greater in the white type than the red type of cocoyam. The effects of ethanol and aqueous leaf extracts of plantain, cassava and cocoyam were studied as related to the physiology of the fungus, Sclerotium rolfsii on solid and liquid culture media amended with varying dilutions of the extracts. The studies made were in relation to the radial growth and vegetative growth of mycelia as well as sclerotia production. There were clearly differing responses produced by the three isolates of the fungus to the heat-sterilized phytotoxins present in the solid PDA and liquid PDB even though they all showed dose-dependent responses to the active compounds in the leaves. Clearly the ethanol and aqueous extracts of cocoyam proved to be very effective in the control of radial and vegetative growth of mycelia as well as sclerotia production. The Aburi (AB) isolate in both the solid and liquid media proved to be more responsive to the phytotoxins with the Legon campus (LC) isolate being the least responsive with regards to radial and vegetative growth of mycelia as well as the production of sclerotia. Higher concentrations of the heat-sterilized ethanol and aqueous leaf extracts proved to be more effective than the least concentrations due to the greater amount of phytotoxins present. The results of the current study have been discussed on the possible effects of the three isolates of Sclerotium rolfsii from Aburi (AB), East Legon (EL) and Legon campus (LC) on corm, cormel and pseudostem development of the red and white types of cocoyam as well as the possible use of the various extracts in an integrated control of the fungus and that further studies are recommended to augment these research findings.