Striga asiatica

Abstract: Summary: A series of synthetic germination stimulants for the plant parasites Striga and Orobanche has been prepared. These compounds, analogues of the natural Striga germination stimulant, strigol (I), (Cook et al., 1966, 1972) cause signiticant germination of Striga hermonthica (Del.) Benth. seed at concentrations as low as 10−9 M, and an even greater activity against species of Orobanche has been demonstrated. Initial outdoor box trials of the compounds against Striga asiatica (L.) O. Ktze. in Hyderabad, India, have shown a reduction of up to 65% of the seed after a single treatment of the soil 6 weeks before the planting of the sorghum host. Resume: Une possibilite nouvelle de lutte contre les Striga et les Orobancbe par l'utilisation des stimulants synthetiques de la germination. Une serie de stimulants syntbetiques de la germination pour les plantes parasites Striga et Orobanche ont ete prepares. Ces composes, analogues au stimulant naturel de la germination chez les Striga, le strigol (I), (Cook et al., 1966,1972) ont provoque une germination significative des semences de Striga hermonthica (Del.) Benth. a des concentrations aussi faibles que 10−9 M; une activite superieure a meme ete demontree sur des espeices d'Orobanche. Les premiers essais en pots, a l'exterieur, de ces composes contre Striga asiatica (L.) O. Ktze, a Hyderabad en Inde, ont montre une reduction atteignant 65% des semences aprees un seul traitement du sol, 6 semaines avant la plantation du sorgho, hote de ces plantes parasites. Zusammenfassung Ein neuartiger Weg in der Bekampfung von Striga und Orobanche durch die Anwendung synthetischer Keimungsstimulan-tien Es wurde eine Reihe von synthetischen Keimungsstimulantien fur die Pflanzenparasiten Striga und Orobanche hergestellt. Diese Verbindungen, Analoge des naturlichen Keimungsstimulans von Striga, Strigol (I), (Cook et al., 1966, 1972) bewirken bei so niedrigen Konzentrationen wie 10−9 M, eine beachtliche Keimung der Samen von Striga hermonthica (Del.) Benth. Fur Orobanche-Arten wurde sogar noch eine grossere Aktivitat nachgewiesen. Es wurden erste Gefass-versucbe mit diesen Verbindungen gegen Striga asiatica (L.) O. Ktze. in Hyderabad, Indien durcbgefuhrt. Dabei konnte bei einmaliger Behandiung des Bodens, 6 Wocben vor der Aussaat der Wirtspflanze (Hirse), ein Ruckgang der Samenzahl bis zu 65% festgestellt werden.

Abstract: While witchweed is nearing eradication in the United States, it continues to thrive in other parts of the world, especially in Africa, together with other witchweed species. The continuing problems from witchweeds and other parasitic weeds, the broomrapes, dodders and mistletoes, are outlined, including their extent, the degrees of damage caused, and the difficulties in their control. While a small minority are being successfully controlled by the use of immune varieties, most are currently controlled by existing techniques only partially, or on a local basis, and they may even be spreading or intensifying. The challenges they present are emphasised. Nomenclature: witchweed, Striga asiatica (L.) Kuntze; dodders, Cuscuta spp.; broomrapes, Orobanche spp.; mistletoes, Viscaceae, Loranthaceae.

Abstract: The germination of Striga sciatica, a root parasite of many cereal and leguminous crops, is stimulated by several host and nonhost plant derived stimulants. HPLC revealed the presence of three active composeds in root exudates from Striga host plants, maize and sorghum, and also from proso millet. A fourth active composed was present in sorghum exudates Acetate and heptafluorobutyrate derivatives were prepared and analyzed by HPLC and mass spectrometry. Each step involved in the isolation, chromatographic purification, and derivatization was followed by a sensitive Striga seed germination bioassay. We report the isolation of strigol as the major Striga seed germination stimulant in maize and proso millet root exudates and as a minor component of the total activity in sorghum root exudates