Taye Tessema:
The Role of Pathogens as Natural Biological Control Agents of Parthenium Weed in Ethiopia

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TAYE TESSEMA
Humboldt-Universitšt zu Berlin, Institute for Horticultural Sciences, Section Phytomedicine, Germany

Parthenium is an exotic invasive weed that originated in tropical America, now occurs widely in India, Australia, and Africa. In Ethiopia, it is also known to affect crop, animal and human health. Parthenium was observed growing in different habitats from hot, arid and semi arid low altitude (912m.a.s.l.) to humid high mid altitude (2500m). Experiments on diagnosis, incidence and distribution of pathogens associated with Parthenium and further evaluation of the potential pathogens as biocontrol agents were carried out from 1998-2002. Several fungal isolates of the genus Helminthosporium, Phoma, Curvularia, Chaetomium, Alternaria, and Eurotium were obtained from seed and other plant parts of Parthenium although the isolates tested were non-pathogenic except Helminthosporium isolates. The two most important diseases associated with Parthenium were the rust, caused by Puccinia abrupta var. Partheniicola and the phyllody, caused by phytoplasma of fababean phyllody group (FBP). The rust was commonly found in high mid altitude (1400 -- 2500m.a.s.l.) with disease incidence up to 100% in some locations while phyllody was observed in low to mid altitude regions (900 -- 2300m.a.s.l.) of Ethiopia with up to 75%. Individual effects of the rust and phyllody diseases on parthenium in different locations under field condition showed that weed morphological parameters were significantly affected. Seed production capacity of Parthenium was reduced by 42 and 85% due to rust and phyllody, respectively. Host specificity tests against the weed and crop hosts related to Parthenium revealed that sporulation of P. abrupta was observed only on Parthenium though limited number of poorly developed pustules were recorded on varieties of niger seed. Phyllody and rust diseases of Parthenium showed significant potential for use as a classical biological control.



Keywords: Ethiopia, non-obligate fungi, Parthenium, phyllody, rust


Footnotes

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Contact Address: Taye Tessema, Humboldt-Universitšt zu Berlin, Institute for Horticultural Sciences, Section PhytomedicineLentzeallee 55/57, 14195 Berlin, Germany, e-mail: tayetessema@yahoo.com
Andreas Deininger, September 2004