The fungus Alternaria eichhorniae isolate 5 (Ae5) is being developed as an
effective mycoherbicide against water hyacinth in Egypt. In order to improve its
virulance, an integration with MDCA, a phenylpropanoid pathway inhibitor, which
weakens the plant defence system, was explored. The disease severity induced by
Ae5 increased when its formulation was applied to water hyacinth plants pretreated
with MDCA. Infection with Ae5 amplified the total phenol concentration in diseased
water hyacinth leaves whereas MDCA reduced it. Plants treated with both Ae5 and
MDCA contained level 0 f total phenols comparable tot hat i n the untreated control
plants. Anatomically, phenol-storing cells were recorded at 3 locations within leaf
tissues: within the adaxially-Iocated palisade tissue, above the abaxial epidermis and
in vicinity of vascular bundles. Dimensions of the all three types were increased in
response to infection with Ae5, decreased in response to MDCA treatment and nearly
resume the dimensions of those in control leaves in response to the combined
treatment. Among the three types of phenol cells, the number of only bundle-
associated phenol cells was responded to either Ae5 or MDCA treatment.