Isolation screening and characterisation of local beneficial rhizobacteria based upon their ability to suppress the growth of Fusarium oxysporum f. sp. radicis-lycopersici and tomato foot and root rot

Authors: KAMOU, NATHALIE - Aristotle University Of Thessaloniki; KARASSALI, ELENI - Benaki Phytopathological Institute; MENEXES, GEORGIOS - Aristotle University Of Thessaloniki; KASIOTIS, KONSTANTINOS - Benaki Phytopathological Institute; BON, MARIE-CLAUDE - European Biological Control Laboratory (EBCL); PAPADAKIS, MANOLIS - Aristotle University Of Thessaloniki; TZELEPIS, GEORGIOS - Aristotle University Of Thessaloniki; LOTOS, LEONIDAS - Aristotle University Of Thessaloniki; LAGOPODI, ANASTASIA - Aristotle University Of Thessaloniki

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2015
Publication Date: 4/11/2015
Citation: Kamou, N., Karassali, E., Menexes, G., Kasiotis, K., Bon, M., Papadakis, M., Tzelepis, G., Lotos, L., Lagopodi, A. 2015. Isolation screening and characterisation of local beneficial rhizobacteria based upon their ability to suppress the growth of Fusarium oxysporum f. sp. radicis-lycopersici and tomato foot and root rot. Biocontrol Science and Technology. Vol. 25, Nos. 7–8, 928–949.

Interpretive Summary: Tomato crown and root rot or tomato foot and root rot (TFRR) caused by a phytopathogenic Fusarium fungus (FORL) is one of the most damaging soil-borne diseases of tomato and it is becoming more common in greenhouse tomato production. The disease initially reported in 1974 in Japan, is now found worldwide. The disease occurs in both the greenhouse and the field on tomato worldwide and causes significant losses in tomato production. In closed systems, with recirculation of nutrient solution and rock wool as a growing medium, TFRR can cause serious problems. The disease is not effectively controlled with the existing fungicides, and therefore alternative methods such biological control are needed. The purpose of the present study was to evaluate the potential for biocontrol of TFRR of bacterial strains isolated from natural agro-ecosystems in Greece where lower disease incidence and severity were observed. Seven strains of rhizobacteria, out of 384 strains tested, showed impact in multiple and dual culture testing and were further tested for their biocontrol and growth-promoting effects on tomato plants, and their antifungal properties in test tube trials. All seven strains significantly reduced disease severity under controlled conditions, and the bacterial strain of Pseudomonas chlororaphis named ToZa7 appeared to be the most promising strain that could be potentially used as a biofungicide, especially under Greek (Mediterranean) conditions. This strain may provide a new method to effectively control TFRR and reduce losses to tomato production.

Technical Abstract: Tomato crown and root rot or tomato foot and root rot (TFRR) is caused by the phytopathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici (Forl). The disease occurs in both greenhouse and outdoor tomato cultivations and cannot be treated efficiently with the existing fungicides. We conducted a study to search for bacteria that attack this fungus, which might be able to be developed as new biocontrol agents. Beneficial rhizobacteria isolated from natural agrosystems in Greece were selected based upon their ability to control the pathogen. Seven out of 384 strains tested in multiple and dual cultures showed strong antagonism to TFRR, and they were identified as Pseudomonas chlororaphis, Bacillus cereus, Serratia marcescens and S. rubidaea, by sequencing the 16S rRNA or the 16S and 23S rRNA inter-spacer regions. The seven strains were tested for their potential biocontrol and growth-promoting effects in planta, and their antifungal properties in vitro. All strains significantly reduced disease severity under controlled conditions, in a gnotobiotic system and in flower pots. Moreover, one P. chlororaphis and one S. marcescens strain significantly decreased disease severity to the level of the uninfected control plants under natural conditions in the flower pot experiment. The inhibitory activity of bacterial liquid cultures on the fungus was demonstrated for all seven strains in vitro, using filter paper, thin layer chromatography and microtiter bioassays. Genes encoding phenazines were tentatively detected by PCR in the P. chlororaphis strain and chitinase-encoding genes were detected in one S. rubidaea and all three S. marcescens strains. Production of phenazine-1-carboxamide and hydrogen cyanide was evidenced for the P. chlororaphis strain while protease activity and production of siderophore-like compounds was confirmed in all bacterial strains. The present study opens the door for possible use as biofungicide of these strains and in particular the P. chlororaphis strain (ToZa7) to control TFRR, especially under Mediterranean conditions.