Extracted metabolites from the biocontrol agent Pseudozyma aphidis inhibit phytopathogenic fungi and bacteria using a dual mode of action: antibiosis and induced resistance


Raviv Harris Maggie Levy
Department of Plant Pathology, The Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel

Natural product-based pesticides may serve as an alternative for traditional synthetic pesticides. Microorganisms are a prospective source of such biological pesticides.

A unique strain of P. aphidis (designated isolate L12, Israel 2004) that was isolated in our laboratory was previously established as a potent biocontrol agent against diverse phytopathogens. This work demonstrates that metabolites extracted from the biocontrol agent P. aphidis (isolate L12) can inhibit fungal and bacterial phytopathogens, and in addition can activate an induced resistance in plants.

Biologically active metabolites were extracted from P. aphidis biomass, and the antimicrobial activity of the extract was demonstrated for diverse plant pathogens. Growth inhibition was demonstrated in vitro on bacterial phytopathogens such as: Pseudomonas syringae pv. tomato, Xanthomonas campestris pv. vesicatoria, Clavibacter michiganensis subsp. michiganensis, Erwinia amylovora and Agrobacterium tumefaciens. Strong inhibition of fungal mycelial growth was also demonstrated in vitro on phytopathogenic fungi such as: Botrytis cinerea, Rhizoctonia solani, Sclerotinia sclerotiorum, Fusarium oxysporum f. sp. lycopersici and Alternaria alternata and on the oomycete Pythium spp.

Additionally, in planta experiments demonstrated a dose-dependent inhibition of B. cinerea infection on tomato plants. Significant reduction of 70-95% in B. cinerea infection was obtained when the spore suspension was pre-treated with extract concentrations higher than 4.2mg ml-1. Similar results were obtained in preventative assays. Spraying the plants with 5mg ml-1 of the extract two hours prior-inoculation with B. cinerea, reduced the disease symptoms by 68%.

Furthermore, preliminary results demonstrated that application of P. aphidis crude extract can systemically decrease B. cinerea infection by 20%, along with up-regulation of pathogenesis related genes such as: PR1a (2-fold), LOX (13-fold), GlucA (12-fold), Chi3 (14-fold), Chi9 (5-fold), PIN1 (3-fold) and AOS (2-fold).

These results suggest that the extracted metabolites from P. aphidis L12 may serve as natural pesticides using a dual mode of action: antibiosis and induced resistance.