Use of two bacteria for biological control of bayoud disease caused by Fusarium oxysporum in date palm (Phoenix dactylifera L) seedlings.

The Bayoud, caused by Fusarium oxysporum f. sp. albedinis (Foa), is the most destructive disease of date palm (Phoenix dactylifera L) in Morocco and Algeria, with no effective control strategy yet available. In this work, two bacteria, Bacillus amyloliquefaciens strain Ag1 (Ag) and Burkholderia cepacia strain Cs5 (Cs), were examined for their potential to control this disease. Both bacterial strains inhibited both growth and sporulation of Foa. They released compounds into the culture medium, which resulted into cytological changes in Foa's mycelial structure. When Jihel-date palm plantlets, a susceptible cultivar, were induced with these bacteria, the size of the necrosis zone, which reflected the spreading of the pathogen, was reduced by more than 70%, as compared with uninduced controls. To further investigate the mechanisms of such disease reduction, phenolic compounds and peroxidase activity were assessed. One month after inoculation, date palm defense reactions against Foa were different depending on the bacterium used, B. cepacia led to higher accumulation of constitutive caffeoylshikimic acid isomers while B. amyloliquefaciens triggered the induction of new phenolic compounds identified as hydroxycinnamic acid derivatives. Peroxidase activity has also been stimulated significantly and varied with the bacterial strain used and with Foa inoculation. These results add to the promising field of investigation in controlling Bayoud disease.