Effect of Mycoherbicides on Waterhyacinth [Eichhornia Crassipes Mart. Solms]

Abstract

One of the major problem accompanying water resource development in Sri Lanka is the explosive proliferation of water hyacinths (Eichhornia crassipes). A survey of plant pathogenic fungi associated with naturally infected water hyacinth was conducted in different waterways in the Eastern part of Sri Lanka and potential isolates including Alternaria alternata, Cercospora rodmanii, Aspergillus sp.and Trichoderma sp. were identified. The four identified fungi were evaluated for their pathogenicity on water hyacinth at laboratory conditions. The first pathogenicity trial indicates, the leaf area affected by the fungal pathogen changes with the intensity (days). The changes in leaf area affected by the pathogen across intensity levels depend upon inoculation method (p=0.003). But there was no statistically significant effect in the inoculation methods on the leaf area affected by the fungal type (p=0.06). All fungal types had different levels of dead lesions formed in water hyacinth. After seven days of inoculation, Alternaria sp. revealed to have the highest affected area, followed by Aspergillus sp. and Cercospora sp. but, all four fungal species had similar level of effects in term of dead lesion formed in leaves after 22 days of inoculation. During the confirmation test, observed diseased symptoms also similar to first laboratory trial which confirmed that the disease syndromes of first lab trial were caused by the inoculated pathogenic fungi, not from the other factors and also indicate that, after one week of inoculation A.alternata revealed to have the higher affected area followed by C rodmanii and Aspergillus sp. and the Trichoderma sp. did not give a significant effect on confirmation test. The selected three pathogenic fungi including Alternaria sp., Aspergillus sp., and Cercospora sp. can easily culture and disease can cause by conidia, mycelial fragment or mycoherbicidal preparation. Different carriers produced different levels of affected leaf area upon infection by the fungal type (p<0.0001). However, fungal types alone did not show differences in the formation of dead lesions in the leaf surfaces of water hyacinth (p=0.31). Moreover, the carrier type and fungi do not combine to influence the overall area affected by the fungus (p=0.49). A better and quick infection caused by the mycoherbicidal preparation with oven ash. The extent of infection depends on the concentration of mycoherbicide and the 60% of oven ash concentration showed better result on water hyacinth control. We concluded that, A. alternata and Cercospora rodmanii could be used as effective biocontrol agents against water hyacinth following performance evaluation under natural environmental conditions and their host specificity test.