Taye Tessema, Monika Gossmann, Christian Obermeier, Carmen Büttner, Reinhard Metz, Gerhard Einhorn:
Importance of Parthenium (Parthenium hysterophorus L.) and the Role of Pathogens as Biological Control in Ethiopia

TAYE TESSEMA¹, MONIKA GOSSMANN¹, CHRISTIAN OBERMEIER¹, CARMEN BÜTTNER¹, REINHARD METZ², GERHARD EINHORN^2
1Humboldt University Berlin, Department of Phytomedicine, Germany
²Humboldt University Berlin, Department of Agronomy, 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 semiarid low altitude ([900]m) to humid high mid altitude ([2500]m) in the survey area. It grows on any type of soil: sand, loam or clay and in different habitats: roadsides, wastelands, rangelands, villages and gardens, and in crop fields. Experiments on diagnosis, incidence and distribution of pathogens associated with Parthenium, and further evaluation of the potential pathogens as biological control agents were carried out during 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. However, most of the isolates tested were non pathogenic except Helminthosporium isolate which resulted in a leaf blight symptom similar to the infected plants in the field. Its virulence was very limited and required high humidity for infection. Therefore, it was concluded that these non-obligate fungal pathogens showed insignificant potential for biological control of Parthenium. 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, being accidentally and possibly introduced together with Parthenium, was commonly found in high mid altitude (1400-[2500]m) while phyllody was observed in low to mid altitude regions (900-2300 m.a.s.l.) of Ethiopia, each with a disease incidence up to [75]% in some locations. Phyllody diseased plants were characterised by excessive branching, reduced plant height and leaf size, and alteration of floral structures into small leaf-like structures that lead the plant to sterility.

Study of the individual effects of the rust and phyllody disease on parthenium in different locations under field conditions 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. Virulence of parthenium rust collected from different locations showed that Ambo and Debre Zeit isolates were comparatively most virulent based on mean number of leaves infected per plant and mean number of pustules per leaf. From the distribution and effects on Parthenium, it can be concluded that Phyllody and rust diseases of Parthenium showed significant potential for use as a classical biological control of Parthenium weed in areas where the diseases are not present after the assessment of potential risk of specifity of Phyllody disease and identification of insect vector(s) that transmit phyllody disease.

Keywords: Biological control, Ethiopia, Parthenium hysterophorus L., pathogens

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Contact Address: Taye Tessema, Humboldt University Berlin, Department of Phytomedicine, Lentzeallee 55/57, 14195 Berlin, Germany, e-mail: taye thotmail.com