by Sadul Islam
WWF-Pakistan survey team during its ecological assessment studies found several new species, some of these were new for Sindh, Pakistan and even for science. Striga gesnerioides is one of these species found during the natural vegetation assessment at Thatta district. The species was identified with the help of Dr Surraya Khatoon, Professor of Botany, University of Karachi.Striga gesnerioides is commonly known as witchweed, a root obligate parasitic plant which belongs to the family Orobanchaceae (previously was in Schrophulariaceae). The plant is still not included to the flora of Pakistan. It was discovered for the first time from the rocky area of district Thatta near Jhirk, Sindh where it was growing on the roots of another xerophytic and shallow rooted plant, Euphorbia caducifolia. The plant requires a living host for their initial development then it can survive without any host plant species.
The genus Striga has 40 species worldwide representing only by one in Pakistan. The species is native to Asia and Africa but have widely distributed to Arabia, Yemen, India, Nepal, Sri Lanka, Cambodia, Japan even in US and Australia. The species generally consider a very harmful parasitic weed for some crops such as cowpea, sugarcane, maize, rice, tobacco and sorgum in Africa because of its direct contact , which is established successfully through vascular connection to the roots of the crop plant. A system of chemical signaling between host and parasite is involved in the formation of this attachment.
Research reveals that the plant has range of host species and it generally attacks on dicotyledonous plants including member of the family Acanthaceae, Convolvulaceae, Euphorbiaceae, Fabaceae and Solanaceae. It produces plenty of seed which are viable for about ten years. During germination, the seed produces special modified organs called haustoria which penetrates roots cells of the host plant and the parasitic plant starts germination. Moist environment about 30 to 35oC temperature and nitrogen deficient soil is ideal for the seed germination of Striga. These seeds are also capable tp remain dormant for a longer period of time, waiting for the chemical and enzymatic signals sent by the host plant.
Stirga gesnerioides has reduced and scaly leaves with a pale-green or yellowish colour, the stem branches mainly below the soil and emerges as a cluster of generally unbranched, fleshy, erect shoots 10-20 cm high, the scaly leaves only a few mm long. Inflorescence is spike like. The flower colour when the plant is growing on cowpea is usually mauve but occasionally white, whereas in other forms it may be reddish, purple or even yellow. Seed production per plant is estimated to be over 60,000. Due to its very small size and weight, the dispersal mechanism of its seeds generally occurs by wind or water.
Very few uses of the plant are documented. The whole plant is consider as anti-diabetic. It is also used to color skins, the dry powder used as antiseptic for wounds in livestock as well. The species is not suitable for grazing.
Sadul Islam is Coordinator Conservation, WWF-Pakistan.