title: Isolation and identification of Desmodium root exudates from drought tolerant species used as intercrops against Striga hermonthica.
abstract: Plants from the genus Desmodium, in particular D. uncinatum, are used on sub-Saharan small-holder farms as intercrops to inhibit parasitism of cereal crops by Striga hermonthica and Striga asiatica via an allelopathic mechanism. The search for Desmodium species which are adapted to more arid conditions, and which show resilience to increased drought stress, previously identified D. intortum, D. incanum and D. ramosissimum as potential drought tolerant intercrops. Their potential as intercrops was assessed for resource poor areas of rain-fed cereal production where drought conditions can persist through normal meteorological activity, or where drought may have increasing impact through climate change. The chemical composition of the root exudates were characterised and the whole exudate biological activity was shown to be active in pot experiments for inhibition of Striga parasitism on maize. Furthermore, rain fed plot experiments showed the drought tolerant Desmodium intercrops to be effective for Striga inhibition. This work demonstrates the allelopathic nature of the new drought tolerant intercrops through activity of root exudates and the major compounds seen in the exudates are characterised as being C-glycosylflavonoid. In young plants, the exudates show large qualitative differences but as the plants mature, there is a high degree of convergence of the C-glycosylflavonoid exudate chemical profile amongst active Desmodium intercrops that confers biological activity. This defines the material for examining the mechanism for Striga inhibition.
authors.affiliation: Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK. Electronic address: tony.hooper@rothamsted.ac.uk.
authors.forename: A M
authors.initials: AM
authors.lastname: Hooper
authors.affiliation: Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK. Electronic address: john.caulfield@rothamsted.ac.uk.
authors.forename: J C
authors.initials: JC
authors.lastname: Caulfield
authors.affiliation: Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK. Electronic address: bing.hao@rothamsted.ac.uk.
authors.forename: B
authors.initials: B
authors.lastname: Hao
authors.affiliation: Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK. Electronic address: john.pickett@rothamsted.ac.uk.
authors.forename: J A
authors.initials: JA
authors.lastname: Pickett
authors.affiliation: International Centre of Insect Physiology and Ecology, P.O. Box 30772, Nairobi, Kenya. Electronic address: cmidega@icipe.org.
authors.forename: C A O
authors.initials: CAO
authors.lastname: Midega
authors.affiliation: International Centre of Insect Physiology and Ecology, P.O. Box 30772, Nairobi, Kenya. Electronic address: zkhan@icipe.org.
authors.forename: Z R
authors.initials: ZR
authors.lastname: Khan
mesh_terms: D002851:Chromatography, High Pressure Liquid; D018556:Crops, Agricultural; D055864:Droughts; D005122:Exudates and Transudates / Q000737:chemistry*; D007887:Fabaceae / Q000737:chemistry; D005419:Flavonoids / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification; D013058:Mass Spectrometry / Q000379:methods; D010675:Pheromones / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology; D018517:Plant Roots / Q000737:chemistry*; D034362:Striga / Q000187:drug effects*
chemical_list: D005419:Flavonoids; D010675:Pheromones
keywords: Desmodium incanum; Desmodium intortum; Desmodium ramosissimum; Desmodium uncinatum; Di-C-glycosylflavone; Parasitic weeds; Root exudate; Striga hermonthica; Striga inhibition