Fenugreek root exudates show species-specific stimulation of Orobanche seed germination M FERNA ´ NDEZ-APARICIO*, A ANDOLFI  , A EVIDENTE  , A PE ´ REZ-DE-LUQUE* & D RUBIALES* *Instituto Agricultura Sostenible, CSIC, Co ´rdoba, Spain and  Dipartimento di Scienze del Suolo, della Planta, dellÕAmbiente e delle Produzioni Animali, Universita ´ di Napoli Federico II, Napoli, Italy Received 21 June 2007 Revised version accepted 29 October 2007 Summary Various Orobanche species are weedy and cause severe reduction in the yields of many important crops. The seeds of these parasitic weeds may remain dormant in the soil for many years until germination is stimulated by the release of a chemical signal from a host plant. In order to determine the effects of fenugreek root exudate on the induction of Orobanche crenata, Orobanche ramosa and Orobanche foetida seed germination, root exudate was collected from hydroponically grown fenu- greek seedlings. Fractionation patterns obtained from column and thin layer chromatography of the fenugreek root exudate showed a set of metabolites differing in their polarity with stimulatory activity on Orobanche seed germination. The crude root exudate stimulated both O. ramosa and O. crenata seed germination to the same level caused by the synthetic germination stimulant GR24 at 10 mg L )1 . It also stimulated O. foetida seed germination which did not respond to GR24. Active fractions of root exudate stimulated the germination of Orobanche species differentially. Keywords: broomrape, fenugreek, germination, Oroban- che, root exudate. FERNA ´ NDEZ-APARICIO M, ANDOLFI A, EVIDENTE A, PE ´ REZ-DE-LUQUE A&RUBIALES D (2008). Fenugreek root exudates show species-specific stimulation of Orobanche seed germination. Weed Research 48, 163–168. Introduction Plants have developed various mechanisms to ensure that germination occurs when conditions are favourable. One of the most specialised germination mechanisms can be found in the broomrapes (Orobanche species), which are holoparasitic plants devoid of chlorophyll and depending entirely on their hosts for all nutritional requirements. The germination of these obligate root parasites depends on the receipt of a chemical signal, which is present in the rhizosphere of potential hosts (Bouwmeester et al., 2003). This recognition system ensures that germination starts only when a suitable host root is available in the immediate vicinity, to which the young seedling has the chance to connect to the root and consequently be fed by its host. Various Orobanche species are weedy and cause severe reductions in the yields of important crops (Parker & Riches, 1993; Joel et al., 2007). Orobanche species vary in their host specificity, with Orobanche crenata Forsk. and Orobanche ramosa L. [syn. Phelipanche ramosa (L.) Pomel] having a rather wide host range and Orobanche foetida Poir. being far more specific. Orobanche crenata is parasitic on grain and forage legumes, but can be also parasitic on a wide number of cultivated and wild species belonging to Umbelliferae, like carrot, or Compositae, such as lettuce. Orobanche ramosa is mainly a parasite of Solanaceae (tomato, tobacco and potato), and also of Cannabinaceae (e.g. hemp) or Brassicaceae (e.g. oilseed rape). Orobanche foetida is however parasitic only on the wild species of Leguminosae (Pujadas-Salva´, 2002), and has only recently been reported to attack the cultivated legumes faba bean (Kharrat et al., 1992) and vetch (Rubiales et al., 2005). Seeds of these parasitic weeds may remain dormant in the soil for many years until germination is stimulated Correspondence: Diego Rubiales, CSIC – Institute Sustainable Agriculture, Apdo. 4084, Alameda del Obsipo, s ⁄ nCo´ rdoba 14080, Spain. Tel: (+34) 957 499215; Fax: (+34) 957 499252; E-mail: ge2ruozd@uco.es Ó 2008 The Authors Journal Compilation Ó 2008 European Weed Research Society Weed Research 48, 163–168