Abstract
The biosurfactants produced by Bacillus atrophaeus L193 was examined by their use in the control of the aphid Rhopalosiphum padi in order to suggest a friendly alternative to chemical pesticides. A screening of different culture media demonstrated the highest biosurfactant production by L193 in TSB supplemented with colloidal chitin. Surfactants, which are produced in large quantities (2.04 g/L), reduce surface tension to 33 mN/m. Electrospray Q-TOFS MS analysis demonstrated that lipopeptides, such as surfactins, fengycins, bacillomycins and iturins, are the predominant metabolites present in biosurfactants produced by strain L193. Treatment with L193 surfactants led to an aphid mortality rate of 59.8% within 24 h. Microscopy analysis showed that these compounds caused insect death by affecting cuticle membranes. An evaluation of aphid feeding activity also demonstrated that aphid feeding capacity is affected by treatment with surfactants. Moreover, microbial cultures of strain L193 and their supernatants also showed high levels of activity against R. padi, which is probably due to the presence of surfactants and hydrolytic enzymes such as proteases and glucanases. This study demonstrates that B. atrophaeus L193 is an effective treatment for plants affected by aphids.
Highlights
Aphid species Rhopalosiphum padi affects several cereal crops, resulting in severe economic losses in agriculture
The strain used in this study showed 16S rRNA gene-sequence similarity of 99.5% to its closest relative B. atrophaeus
The most common Bacillus species tested against M. persicae is the entomopathogenic bacterium Bacillus thuringiensis (Torres-Quintero et al, 2015)
Summary
Aphid species Rhopalosiphum padi affects several cereal crops, resulting in severe economic losses in agriculture. R. padi leads to plant decline and transmits different phytopathogenic viruses including the barley yellow dwarf virus (BYDV) which causes chlorosis, stunting and yield loss (Biurrun et al, 2010; Liu et al, 2014). It promotes the growth of fungi, such as Cladosporium sp. On leaf surfaces through the excretion of sugars, and decreases the rate of plant photosynthesis (Dhami et al, 2013). This pest is managed through the application of chemical insecticides.
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