Environmental and Experimental Botany 59 (2007) 224–234 Biological control of bayoud disease in date palm: Selection of microorganisms inhibiting the causal agent and inducing defense reactions Majida El Hassni a , Abdelbasset El Hadrami b , Fouad Daayf b , Mohamed Ch´ erif c , Essaid Ait Barka d , Isma¨ ıl El Hadrami a,∗ a Laboratoire de Biotechnologies, Protection et Valorisation des Ressources V´ eg´ etales ; Equipe Biotechnologies, Ecophysiologie et Valorisation des Plantes D´ epartement de Biologie, Facult´ e des Sciences Semlalia, BP. 2390, 40 000 Marrakech, MOROCCO b Department of Plant Science, 222 Agriculture Building, University of Manitoba, Winnipeg, MB, Canada R3T 2N2 c Laboratoire de Phytopathologie, Institut National Agronomique de Tunisie, 43 Avenue Charles Nicolle, 1082 Cit´ e Mahraj` ene, Tunis, Tunisia d Laboratoire de Physiologie V´ eg´ etale, UFR Sciences URVVC, Universit´ e de Reims Champagne-Ardenne, B.P. 1039, 51687 Reims Cedex 2, France Received 5 May 2005; received in revised form 6 October 2005; accepted 20 December 2005 Abstract Twenty-one isolates of microorganisms, including Bacillus spp., Rhizobium spp., Ulocladium atrum, Candida guilliermondii, Pseudomonas sp., Rahnella aquatilis and other bacteria not yet identified, were tested to determine their effects on the mycelial growth and the sporulation of Fusarium oxysporum f.sp. albedinis (Foa), the causal agent of bayoud on date palm. The potential of these antagonists in the induction of defense reactions in date palm seedlings was also studied. Four bacteria, B. pumilus W1, R. aquatilis W2, B. cereus X16 and n.d. S1, have exhibited a high inhibition toward mycelial growth of Foa (70–77%), and its sporulation (80–95% of the control). Moreover, cytological alterations have been detected in the Foa mycelium grown in the inhibition zone. Application of these antagonists into date palm seedlings has led to trigger defense reactions with an accumulation of non-constitutive hydroxycinnamic acid derivatives, such as the sinapic derivative I2, known to play a crucial role in resistance of date palm to Foa. This reaction was more pronounced in resistant cultivar (BSTN) than in susceptible (JHL). The combined effects of direct and indirect actions of Foa antagonists are discussed in the hope of providing a biocontrol strategy against bayoud. © 2006 Elsevier B.V. All rights reserved. Keywords: Date palm; Bayoud; Biocontrol; Fusarium oxysporum f.sp. albedinis (Foa); Phenols; Phytoalexins 1. Introduction The vascular fusariosis commonly named bayoud, caused by Fusarium oxysporum f.sp. albedinis (Foa), is the most destruc- tive fungal disease of date palm (Phoenix dactylifera L.). The impact of this disease is most severe in North Africa partic- ularly in Morocco where 2/3 of palm trees were destroyed so far (Fernandez et al., 1995). As for most vascular diseases caused by soilborne pathogens, fighting strategies are very lim- ited or quasi-inexistent. Among these strategies, the deployment of Foa-resistant cultivars appear to be the most suitable and economic approach (Djerbi, 1990; Louvet, 1991) but natural resistant genotypes are scarce with a poor quality of fruits and ∗ Corresponding author. Tel.: +212 24 439997; fax: +212 24 439997. E-mail address: hadrami@ucam.ac.ma (I. El Hadrami). the date palm breeding system is laborious and offered only as a long-term plan (El Hadrami et al., 2005). Alternative control measures such as the use of Foa antagonists are, therefore, nec- essary and need to be explored. This strategy is based, as shown in other pathosystems involving Fusarium species, on the use of microorganisms such as bacteria, yeasts or saprophytic fungi that have either a significant potential to inhibit disease causal agents or ability to enhance defense mechanisms (M’Piga et al., 1997; Larkin and Fravel, 1998; Benhamou and Nicole, 1999; De Boer et al., 1999; Ch´ erif et al., 2002; Silva et al., 2004). In the case of fusariosis biocontrol, most of the studies have reported the use of non-pathogenic Fusarium isolates alone or in com- bination with bacteria such as Pseudomonas fluorescens (Sneh, 1998; Duijff et al., 1999; Fuchs et al., 1997, 1999). Other biocon- trol agents belonging to the genera of Trichoderma, Penicillium, Gliocladium, Sporidesmium, Burkholderia, Bacillus, Serratia were also shown to confer some levels of protection against 0098-8472/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2005.12.008