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

https://doi.org/10.1016/j.plaphy.2012.03.003Get rights and content

Abstract

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.

Highlights

Bacillus amylolequefaciens and Burkholderia cepacia as biocontrol agent of date palm disease. ► Both bacterial strains inhibited both growth and sporulation of the pathogen. ► The two bacteria triggered differently the phenylpropanoid pathways in infected root. ► They enhanced peroxidase activity and induced new isozymes in infected root. ► These changes were associated with a decrease of disease severity.

Introduction

Bayoud, a vascular disease of date palm, caused by Fusarium oxysporum f. sp. albedinis is the most damaging disease of date palm in Morocco and accounts for as much as 75% yield losses [1]. It has killed more than 10 million palm trees during the last 100 years [2]. Several control strategies such chemical treatments have been considered, but they remain inefficient and difficult to apply. The most effective measure to reduce the incidence of this disease would be to select and plant Foa-resistant cultivars. Unfortunately, date palm lines that are resistant to Bayoud disease usually produce low-quality fruits [2]. Recently, it was reported that Najda, a new line of date palm, was resistant to bayoud disease and produces high-quality dates [3]. However, repopulating oases only with Najda cultivar could lead to a massive reduction in date palm biodiversity within a short period of time. Therefore, more integrated management strategies are needed to tackle Bayoud disease on the long term. Such strategies should combine different alternatives to accommodate quality requirements as well as environmental constraints.

Biological control methods such as those using microorganisms that can suppress plant diseases [4], [5] represent a promising disease control alternative. They are based on the screening of plant extracts or antagonistic bacteria and fungi that can confer protection against plant pathogens [6], [7]. Several biocontrol agents were identified, including species of Trichoderma, Penicillium, Gliocladium, Sporidesmium, Burkholderia, Bacillus, Serratia, and many others. However, their efficacy has been often inconsistent when transferred into the field. Improving the success of such transfer relies on the elucidation of the mechanism of action and of how such mechanisms are affected by the environment. Several modes of action including antibiotic biosynthesis, parasitism, induced systemic resistance, and microbial competition were described [8]. Endogenous defense reactions were largely reported to be triggered in response to the attack by pathogens [9]. Hammerschmidt andKuc [10] have reported that induced resistance in plants was associated with the enhancement of the cell wall lignification, the stimulation of host-defense enzymes and the synthesis of pathogenesis-related (PR) protein. In the date palm-Foa interaction, little has been reported about the role of microbial agents in controlling Bayoud disease. El Hassni et al. [7] reported that the inoculation of date palm seedlings with a hypoaggressive isolate of F. oxysporum provided a degree of protection against further attacks by an aggressive isolate of Foa. Jaiti et al. [11] have tested the effect of root colonization with arbuscular mycorrhizal fungi, on the induction of date palm defense reactions against its pathogen. In this study, mycorrhizal plants showed a significant 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 [12].

Bacillus amyloliquefaciens and Burkholderia cepacia are known for their antifungal activity in several plant–microbe interactions. In coconut, B. amyloliquefaciens was found to be antagonistic against Phytophthora palmivora, the causal agent of bud rot disease [13]. In Arabidopsis seedlings exposed to bacterial volatile blends from B. amyloliquefaciens, disease severity by the bacterial pathogen Erwinia carotovora was significantly reduced [14].

B. cepacia can antagonize and repress many soilborne plant pathogens. It can prevent leaf and stem blight caused by the fungus Alternaria by inhibiting its spore germination. Economically important crop diseases such as blight due to A. solani and that caused by A. brassicae and A. brassicola, which affects the oil-producing plants rape and canola, can be controlled by B. cepacia [15]. Recently,Kelani-Feki and Jaoua [16] have reported that B. cepacia Cs5 can prevent Botrytis cinerea disease of vine plantlets. In addition, Kelani-Feki et al. [17] have described a broad spectrum of fungicidal activities of B. cepacia Cs5 against Alternaria alternata, Aspergillus niger, Fusarium culmorum, Fusarium graminearum and F. oxysporum. A strain of B. cepacia has been developed as a successful seed and root inoculant, which can suppress the pathogenic effects of fungi on a variety of conifers [18].

The objectives of this work were to i) determine the inhibitory effect of B. amyloliquefaciens and B. cepacia on the date palm pathogen F. oxysporum f. sp. albedinis, and ii) examine their potential role in triggering date palm defense reactions, including the accumulation of phenolic compounds and the activity of enzymes known for their involvement in date palm resistance such as peroxidase.

Section snippets

Effects of bacterial strains on Foa growth and sporulation in vitro

The two bacterial strains showed a significant antifungal activity (p < 0,05) against Foa. They inhibited its growth and sporulation on PDA medium. The maximum Foa growth inhibition was obtained after 6 days of co-culture with the bacteria; it was about 83% with Cs and 75% with Ag. After 13 days of co-culture, this inhibition decreased to 76% and 55% for Cs and Ag, respectively, due to a re-growth of the pathogen (Fig. 1).

The sporulation of Foa was also inhibited in co-culture with the bacteria

Discussion

The impact of the intensive use of chemical pesticides on the environment has resulted in the increased interest in biocontrol strategies for plant disease management.

In this work, we tested two bacterial strains, Ag and Cs, for their potential to control Bayoud in date palm, a disease caused by Foa. The two bacterial strains exhibited a significant degree of inhibition of Foa growth and sporulation in vitro. However, Cs was more effective in inhibiting Foa development than Ag. In addition, the

Microorganisms and in vitro tests

The Foa was isolated from bayoud-diseased rachis of date palm brought from Zagora in the south of Morocco [39]. The tested bacteria come from Laboratory of Biopesticides, Centre of Biotechnology of Sfax Tunisia, they were isolated from the rhizosphere of almond trees in the Sfax region.

Antagonism between bacteria and Foa was assessed by dual cultures on potato-dextrose medium. The inhibition of Foa growth was evaluated in PDA (potato-dextrose agar) medium. 10 μl of bacterial suspensions (1010

Acknowledgements

Financial support for this work was provided by PRAD 11-05-Egide N°24172UL and AI (Tunisie-Maroc) 24/02.

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