Abstract:
Aqueous extracts of Parthenium hysterophorus leaf and flower seriously inhibited
seed germination and seedling growth (root and shoot length) of lettuce. Extracts of the root
and stem had much less effect. Lettuce roots were more sensitive to the allelopathic effect
than shoots. It appears that early removal of Parthenium weed from lettuce fields is essential
to avoid poor germination and seedling growth. Copyright © 2005 John Wiley & Sons, Ltd.Parthenium (Parthenium hysterophorus) is an aggressive weed, native to the Americas but
now widely spread in Asia, Africa and Australia (Evans 1997). It was introduced accidentally
into Ethiopia in the 1970s and it spread rapidly in all regions of the country, along roads and
railways, through grazing areas and arable lands, adversely affecting crop production and
animal husbandry (Tefera 2002). It has an allergic effect which makes the weeding usually
used by subsistence farmers more difficult. The successful spread of Parthenium in so many
parts of the world has been attributed to its allelopathic properties, which enable it to
compete effectively with otherwise strong crop or pasture species (Mersie and Singh 1987;
Swaminathan et al. 1990; Stephen and Sowerby 1996).
Lettuce is an important cash and food crop in Ethiopia, the area grown in the 2001/02
cropping season being 128 ha, with an average yield of 89 q/ha (CSA 2002). A major threat to
good lettuce production is competition from annual grasses and broad-leaved weeds against
which it is not a good competitor. The rapid spread of Parthenium in Ethiopia is a bigger threat to
the expansion and sustainable production of lettuce. Little is known of the allelopathic potential
of Parthenium weed on lettuce seed germination and seedling growth, the subject of this paper.
