|FAN, BINQUAN - Chinese Academy Of Agricultural Sciences
Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2014
Publication Date: 8/12/2014
Citation: Roberts, D.P., Lakshman, D.K., Maul, J.E., McKenna, L.F., Buyer, J.S., Fan, B. 2014. Control of damping-off of organic and conventional cucumber with extracts from a plant-associated bacterium rivals a seed treatment pesticide. Crop Protection. 65:86-94.
Interpretive Summary: Soilborne plant pathogens cause diseases that result in major economic losses to farmers in the United States. Biologically based control measures for these diseases need to be developed for conventional crop production systems due to environmental problems associated with existing chemical controls. Biologically based control measures also need to be developed for organic crop production systems as existing disease control measures are often inadequate. We analyzed ethanol extracts of five biological control agents for suppression of damping-off of cucumber caused by the important soilborne plant pathogen Pythium ultimum. We demonstrated that cell-free extracts from cell mass of strain N4-5 effectively suppressed damping-off of cucumber caused by P. ultimum when applied as a seed treatment to conventional or organic cucumber seed. These ethanol extracts were as effective as a synthetic pesticide applied to cucumber seed and superior to a commercially available biological control treatment for this disease. These seed treatment extracts also had a shelf-life of at least three months. None of the extracts from the other biological control agents were effective. Since this application of ethanol is allowed in organic crop production we have developed a promising control measure for use in organic cucumber production. These ethanol extracts can also be used in conventional cucumber production systems for control of P. ultimum. This information will be useful to scientists devising strategies for control of soilborne plant pathogens.
Technical Abstract: Environmentally friendly control measures are needed for soilborne diseases of crops grown in organic and conventional production systems. We tested ethanol extracts from cultures of Serratia marcescens N4-5 and N2-4, Burkholderia cepacia BC-1 and BC-2, and B. ambifaria BC-F for control of damping-off of cucumber caused by the soilborne pathogens Pythium ultimum and Rhizoctonia solani; ethanol being an OMRI-approved solvent for use in certain applications in organic crop production. Ethanol extracts from strains N4-5 and N2-4 inhibited mycelial growth and germination of sporangia of P. ultimum in vitro but those from strains BC-1, BC-2, BC-F, and the ethanol control did not. Ethanol extracts from strains BC-2 and BC-F inhibited mycelial growth of R. solani in vitro while ethanol extracts from strains BC-1, N2-4, N4-5, and the ethanol control did not. Thin-layer chromatography and PCR experiments demonstrated that ethanol extracts from strain N4-5 contained prodigiosin while ethanol extracts from strains BC-2 and BC-F contained pyrrolnitrin; extracts from strains N2-4 and BC-1 did not contain either of these compounds. Prodigiosin was previously implicated in inhibition of P. ultimum while pyrrolnitrin has been shown to inhibit R. solani. Organic cucumber seed treated with ethanol extracts of strain N4-5 was the only extract treatment from any of these five microbial strains to effectively suppress damping-off caused by P. ultimum in growth chamber pot experiments. No extracts applied as treatments of organic cucumber seed suppressed damping-off caused by R. solani in greenhouse pot experiments. These ethanol extracts from strain N4-5 provided suppression of P. ultimum on cucumber that was similar to that provided by a commercially available seed treatment pesticide and greater than that provided by a commercially available biocontrol agent for this pathogen. The inhibitory factor(s) in ethanol extracts of strain N4-5 responsible for suppression of P. ultimum damping-off of cucumber was stable for 14 weeks when seeds coated with these extracts were incubated at 4 °C in the dark. Experiments reported here suggest that certain natural products from microbial strains as seed treatments are promising alternatives for control of soilborne diseases in conventional or organic cucumber production systems.