Integrated control of water hyacinth with a mycoherbicide and a phenylpropanoid pathway inhibitor

Abstract

The fungus Alternaria eichhorniae isolate 5 (Ae5) is being developed as an effective mycoherbicide against water hyacinth in Egypt. To improve its pathogenicity, integration with 3,4-methylenedioxy trans-cinnamic acid (MDCA), a phenylpropanoid pathway inhibitor that weakens the plant's defense system, was explored. The severity of the disease induced by Ae5 increased when 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 a comparable level of total phenols to that in the untreated control plants. Phenol-storing cells were located at three sites in the leaf, within the adaxial palisade tissue, above the abaxial epidermis and in the vicinity of the vascular bundles. Dimensions of these three cell types were increased by infection with Ae5, decreased by MDCA treatment and, in the combined treatment, were similar to those in control leaves. Increased numbers of phenol-storing cells were found only in the region near vascular bundles of plants treated with either Ae5 or MDCA.

Keywords:

• Integrated control
• biological control
• bioherbicide
• Alternaria eichhorniae
• Eichhornia crassipes
• trans-cinnamic acid
• phenylalanine ammonia lyase

Acknowledgments

The authors wish to thank DANIDA (Danish International Development Assistance) through the Environment, Peace and Stability Facility (EPSF), Denmark for providing major financial support for this research. We are grateful to Alexander von Humboldt Foundation, Germany for its equipment grant that was helpful for conducting the present work. Thanks are due to Dr. Mike Greaves for reviewing the manuscript and Mr. Mohamed El-Metwally for his continued interest and generous technical assistance.