What is parthenium plant

Humboldt University of Berlin - Faculty of Life Sciences - Albrecht Daniel Thaer Institute for Agricultural and Horticultural Sciences tEST

Investigation of Pathogens for Biological Control of Parthenium (Parthenium hysterophorus L.) in Ethiopia.

Dissertation for the award of the academic degree Doctor rerum agriculturarum (Dr. rer. Agr.) At the Agricultural and Horticultural Faculty of the Humboldt University in Berlin

Taye Tessema Wondimu ((B.Sc., M.Sc.)

Date of doctorate: 12.12.2002

ISBN 3–89820–456–1
Mensch & Buch Verlag, Berlin 2002

The competitive, climatically very adaptable, allergenic plant species Parthenium hysterophorus L. (Compositae) was introduced into Ethiopia via several routes in the 1970s and has colonized large parts of the country to this day. This affects road and river bank areas, pastureland as well as arable and horticultural areas. In a short time it was P. hysterophorus (Parthenium weed) in the north and east of Ethiopia to a dominant weed species with sometimes extreme plant densities in the fields.

To determine the spread of the plant and the infestation situation with pathogens, three country-wide studies were carried out from 1998 to 2001.
P. hysterophorus L. has spread from the hot, semi-arid areas of the lower regions (900 m above sea level) through medium altitudes to the humid high areas (2500 m above sea level).

Fungus species of the genera were made from different parts of the plant Helminthosporium, Phoma, Curvularia, Chaetomium and Alternaria isolated. In the pathogenicity tests under optimal conditions, they produced few symptoms, except for one Helminthosporium–Isolate with a low virulence. None of the species and strains appear promising for further processing with the aim of a bioherbicide.

As the two main diseases of P. hysterophorus became the native rust fungus Puccinia abrupta Diet. & Holw. var. partheniicola (Jackson) Parmelee and the faba bean phytoplasmosis called phyllody. The rust occurred in areas between 1500 and 2500 m above sea level. in a frequency of 5 to 100%, while the Phyllody between 900 and 2300 m above sea level. was found at a frequency of 5 to 75%.

Under optimal humidity conditions and 20 ° C, the uredospores of P. abrupta after 5 hours. An influence on germination by the mycoparasite Sphaerellopsis filum was not found.

From fresh and dried ones sick with phyllody P. hysterophorusThe DNA of the pathogen was isolated from plants and ribosomal sequences of 1800 bp were amplified with the aid of the PCR (primer P1 / P7). For all samples, restriction digestion of the PCR-amplified DNA and gel electrophoresis resulted in band patterns that are characteristic of the Faba bean phytoplasm group. Using the phytoplasma-specific PCR primer, the leaf bug suspected as a vector was identified Tylorilygus apicalis a DNA fragment isolated from the total DNA and amplified. The band pattern in restriction digestion with AluI however, it is not identical to that of the phyllody-afflicted Parthenium plants.

The effects of P. abrupta and phyllody on the morphological characteristics and seed production of P. hysterophorus were quantified in various infested areas in Ethiopia.
P. abrupta reduced the height, the number of leaves, the number of side shoots, the dry matter and the number of seeds by 11, 22, 28, 13, 25 and 43%, respectively.
Phyllody significantly reduced height, leaf area and seed count by 29, 81 and 85%, respectively; the number of leaves, the number of side shoots and the dry matter by 39, 40 and 18%, respectively.

In the virulence test of P. – abrupt- In isolates, the strains from the areas of Ambo and Debre Zeit showed the highest number of infected leaves and rust pustules per leaf.
When testing P. hysterophorus–Related crops and weeds on the host specificity of the rust were only there Guizotia abyssinica some small pustules.

Especially phyllody, but also P. abrupta have the competitiveness and the ability to reproduce P. hysterophorus considerably reduced in many areas. For this reason, these diseases are important components of an integrated control strategy. Further investigations must be made to find the phyllody vectors and to determine their host specificity towards important Ethiopian cultivated plant species.

The highly competitive, adaptable and allergenic weed Parthenium hysterophorus L. (Compositae) is an invasive annual weed believed to be introduced to Ethiopia in 1970s and has currently spread to the most part of the country. Parthenium was observed growing in different habitats from hot arid and semi-arid low altitude (912 m) to high-mid-altitude (2500 m) of the study areas. It was observed that parthenium grows on roadsides, vacant sites, towns, villages, gardens, waterways, grasslands and in different crop fields both during the crop season and after harvest. It was detected as a major weed of crops in the north and eastern regions of Ethiopia with infestation of greater than 20 plants per m2 in some locations. Infestation of parthenium in the crop field varied from field to field depending on the time of parthenium intriduction into the area and the efforts made by the farmers to control the weed.

An exploratory field survey and laboratory studies on pathogens associated with parthenium was studied from 1998 to 2002 in order to provide information on future implementations of biological control in an integrated parthenium management system in the country.

A number of fungal isolates were obtained from seed and other plant parts of parthenium weed of which putative pathogenic fungal isolates were species of the genus Helminthosporium, Phoma, Curvularia, Chaetomium and Altenaria. However, in pathogenecity tests, most of these isolates showed no pathogenic effects exept one Helminthosporium isolate that showed limited virulence. It was, therefore, concluded that these pathogens could be opportunistic with insignificant potential for biological control of parthenium.

The two most important diseases associated with parthenium were the rust caused by Puccinia abrupta Diet. & Holw. var. partheniicola (Jackson) Parmelee and the phyllody caused by Faba Bean Phytoplasma Group (FBP). The rust was commonly found in mid altitude (1500 - 2500 m) with incidence from 5 to 100% while phyllody was observed in low to mid altitude regions (900 - 2300 m) of Ethiopia with incidence of 5 - 75%.

Spore germination test of P. abrupta showed that germination occurred 5 hours after incubation at 20 ° C and an increase of germination occurred with an increase in time of incubation suggesting that it requires low night temperature and occurance of dew for infection. A mycoparasite of the rust fungi, Sphaerellopsis filum has been found associated with P. abrupta on parthenium. But, the mycoparasite did not inhibit the germination of P. abrupta in this study.

Phyllody diseased plants were examined for phytoplasma infection by means of polymerase chain reaction (PCR) using universal primers for phytoplasma (P1 / P7) directed to ribosomal sequences. PRC products of about 1800 bp were obtained after amplification of DNA isolated from fresh and dried parthenium specimens showing phyllody symptoms. Digestion with AluI Restriction enzyme revealed restriction patterns for all samples corresponding to patterns typically observed for the faba bean phyllody phytoplasma group. A phytoplasma DNA was also obtained from suspected insect vector, Tylorilygus apicalis, which was not identical with the phytoplasma DNA obtained from diseased plant.

The individual effects of the rust and phyllody diseases on parthenium weed morphological parameters and seed production capacity were estimated by comparing the diseased and healthy plant samples collected from the field in different parthenium infested areas. Rust disease reduced mean plant height, number of leaves per plant, leaf area, number of branches, dry matter yield at maturity and number of seed produced by 11%, 22%, 28%, 13%, 25% and 43%, respectively . On the other hand, phyllody disease significantly reduced mean plant height, leaf area and seed production by 29%, 81% and 85%, respectively. However, mean number of leaves per plant, number of branches and dry matter yields were increased by 39%, 40% and 18%, respectively.

Virulence of parthenium rust collected from different locations showed that Ambo and Debre Zeit isolates were comparatively more virulent than the others based on the number of pustules per leaf and number of leaves infected. In the host specificity study of P. abrupta on weed and crop hosts related to parthenium, macroscopic and microscopic examination of inoculated tissue revealed that sporulation of P. abrupta was observed only on parthenium although limited numbers of poorly developed pustules were recorded on 3 varieties of niger seed (Guizotia abyssinica).

Phyllody phytoplasma and Puccinia abrupta were successfully infecting parthenium weed in many infested areas of Ethiopia with significant reduction on morphological parameters and seed production in the field. Hence, they are potentially useful as components of integrated parthenium management after further confirmation of insect vectors that transmit phyllody, and of host range of phyllody disease to related economic plants in Ethiopia.