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.
