Parthenium is an exotic invasive weed that originated in South America, and has formed severe infestations in Ethiopia. This weed is known to be host to various micro-organisms such as the rust pathogen Puccinia abrupta var. partheniicola that may be used as a component of integrated parthenium weed management. Field surveys were conducted in 2008 and 2009 cropping seasons in eastern Ethiopia to determine distribution, incidence, and severity of the rust (P. abrupta var. partheniicola) on this weed. In addition, the effect of this pathogen on morphological parameters of parthenium was studied both in the field and in the greenhouse at the Plant Protection Research Center, Ambo. A total of 218 fields were surveyed in four districts (Chiro, Gemechis, Kuni and Tullo) of Western Hararghe Zone, eastern Ethiopia. All the fields surveyed were infected with the pathogen, indicating that the disease was widely distributed in the zone. The incidence of rust in the surveyed area ranged from 25 to 74% while severity ranged from 18 to 55%. The highest (74%) and the lowest (25%) disease incidence were recorded in Tullo and Chiro, respectively, while the highest (55%) and the lowest (18%) disease severities were encountered at Gemechis and Chiro, respectively. Altitude had significant effect on both disease parameters (p ≤ 0.05). The effect of this pathogen on morphological parameters of parthenium under field conditions was found to be significant (p ≤ 0.05) at all locations. The effect of the rust on parthenium dry matter and seed production was significant (p ≤ 0.05) at all locations. Also, the effect of the rust on morphological parameters of parthenium in the greenhouse was significant (p ≤ 0.05). In addition, there was significant variation in the number of rust pustules per leaf, leaf senescence, and number of leaves attacked per plant, disease incidence and severity both at 14 and 21 days after inoculation. In the greenhouse, comparison of isolates from Ambo, Kuni, and Tullo showed significant effect while isolates from Chiro and Gemechis performed poorly for all the studied morphological parameters of parthenium. This study indicated that P. abrupta var.partheniicola has the potential to reduce morphological parameters as well as dry matter and seed production capacity of parthenium weed. It also elucidated the presence of variation in aggressiveness of the isolates. However, more extensive studies need to be undertaken at molecular level to utilize this pathogen in combination with other host-specific insects and pathogens after importation and release, as a component of integrated parthenium weed management in Ethiopia.
Key words: Parthenium hysterophorus, Puccinia abrupta var. partheniicola, aggressiveness, biological control, disease incidence, disease severity, epidemiological factors.
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