Potential of fungal pathogens for biological control of water hyacinth

Abstract

A survey of fungal pathogens of water hyacinth were under taken in lakes Victoria and Kyoga and River Nile in Uganda and several potential isolates including Alternaria eichhorniae (Nag Raj and Ponnappa), 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 house. The disease incidence and severity progressed with time in both isolates although there was no (p>0.05) significant difference between the isolates, and overall disease incidence and severity was not (p>0.05) significant. However, Alternaria eichhorniae caused higher disease incidence than Cercospora sp. in the first and second week after inoculation while Cercospora sp. caused higher disease severity than A. eichhorniae after fourteen days. Both pathogens caused (p>0.05) significant reduction in overall plant fresh weight and no effects on number of living leaves and number of daughter plants. The disease infection also increased with increasing conidia concentration and as time progressed, and was significantly (p<0.01) 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.