Potential of Fungal Pathogens for Biological Control of Water Hyacinth

Abstract

Surveys were undertaken in lakes Victoria, Kyoga and River Nile in Uganda between 2000 and 2001 to detennine fungal pathogens associated with water hyacinth. Several potential pathogen isolates including Alternaria eichhorniae, Cercospora sp. and Acremonium zonatum were identified. Isolates of Cercospora sp. and A. eichhorniae were evaluated for their effectiveness on water hyacinth plants in the screen bouse. The disease incidence and severity progressed with time in both isolates although there was no significant difference (P>0.05) between the isolates and overall disease incidence and severity was not significant (P>0.05). There was no significant (P>0.05) effect of pathogens on overall plant fresh weight, number of living leaves and daughter plants, but linear regression analysis showed a significant (P<0.01) decrease in fresh weight of water hyacinth plants. Disease infection increased with increasing conidia concentration and was significantly (P<0.05) lower at the lower conidia doses. Host range tests on 9 cultivated plant species showed that sorghum was highly susceptible to Cercospora sp. while A. eichhorniae did not cause disease symptoms on any of the plants. This study suggests that both pathogens have potential for biological control of water hyacinth, but A. eichhorniae is safer to use than Cercospora sp.

Keywords: Fungal pathogens, water hyacinth control.