INVASIVE OPUNTIA STRICTA: CASE STUDY IN SOUTHWESTERN SAUDI ARABIAYahya S. Masrahi and Osama H. Sayed
The stem succulent Opuntia stricta (How.) var. Dellinii (Cactaceae) is an alien invasive plant in Jazan Region southwest of Saudi Arabia. The plant spread into vast areas in the region affecting regional flora and competing with local crops. The plant large spines harm range and farm animals causing infections and reduced productivity. The present study is aimed at presenting a status report on presence and distribution of O. stricta in Jazan Region. Work involved survey of the plant along altitudinal gradient in the region. Work also included assessment of vegetative and reproductive aspects of O. stricta in both field and laboratory. Field studies indicated absence of the plant at altitudes lower than 200 meters above sea level and its rarity at high altitudes due to temperature extremes prevailing at these altitudes. The plant invaded vast areas at altitude of 300-400 meters. High invasiveness at these altitudes was reflected in increased number of individuals per unit area, number of cladodes per plant, plant surface area, plant fresh weight, and number of fruits per plant. Fruits contained large number of small and large seeds. Laboratory investigations indicated that both seed dimorphs have maximum germination rate at 35°C. Results also indicated that large seeds had germination potential higher than that of small seeds. Small seeds had a degree of physical and physiological dormancy that could be broken by scarification and gibberellic acid treatment. Results collectively indicated O. stricta has a high invasive potential due to successful vegetative growth and high reproductive effort. Results also point to temperature as an important factor affecting altitudinal distribution of the plant. Data represent a useful body of information for building a database for studies on progression of O. stricta invasion and control programs in the region.
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