Abstract
The bacterium Pseudomonas entomophila has been recognized as an exceptional species within the Pseudomonas genus, capable of naturally infecting and killing insects from at least three different orders. P. entomophila ingestion leads to irreversible gut damage resulting from a global blockage of translation, which impairs both immune and tissue repair systems in the insect intestine. In this study we isolated a P. entomophila bacterial strain from soil samples which displayed a strong activity against Xanthomonas citri subsp, citri (Xcc), the etiological agent of citrus canker disease. The antagonism potential of isolated bacteria against Xcc and its ability to reduce citrus canker severity was assessed both ex planta and in planta. Our findings show that pathogenicity assays in Citrus x limonia by pressure infiltration and spray with a mixture of P. entomophila and Xcc leaded to a significant reduction in the number of canker lesions in high susceptible citrus leaves, at 21 days post-infection. To the best of our knowledge this is the first report of antibacterial activity of P. entomophila against a phytopathogenic bacterium. Collective action of P. entomophila factors such as diketopiperazine production and the type 6 secretion system (T6SS) may be involved in this type of biological control of citrus canker. The results suggest that the P. entomophila strain could be a promising biocontrol agent acting directly against Xcc.
Highlights
IntroductionSustained world population growing has forced farmers to implement unfriendly practices toward the environment (i.e., arbitrary use of pesticides and chemical fertilizers) to attend to rising demand for higher yields of agricultural products
Sustained world population growing has forced farmers to implement unfriendly practices toward the environment to attend to rising demand for higher yields of agricultural products
Because the Gammaproteobacteria Pseudomonas and Xanthomonas, have been the bacterial genera most consistently detected by metagenomic approaches in several phyllospheres (Vorholt, 2012). it is reasonable to think that there might be a competitive relationship between these two bacterial genera in this environmental niche where resource availability is greatly reduced. In accordance with this and the findings of our previous study (Meneghine et al, 2017; Villamizar, 2017), carried out using a whole metagenomics sequencing approach of soil samples from São Paulo Zoo, it which shown genes that encode several metabolites with antibacterial activity, which were mainly associated to genome of gamma-proteobacteria group specially from Pseudomonadaceae family, we suggest that Pseudomonads bacteria recovered from soil samples from São Paulo Zoo could display antagonism against Xanthomonas citri subsp. citri 306 (Xcc 306), the etiological agent of citrus canker disease
Summary
Sustained world population growing has forced farmers to implement unfriendly practices toward the environment (i.e., arbitrary use of pesticides and chemical fertilizers) to attend to rising demand for higher yields of agricultural products. The increasing gap between supply and demand and the unfavorable impact on the environment has encouraged researchers to develop alternative strategies, searching to promote a sustainable agriculture. Several genera of both soil and plant associated bacteria became in powerful tools in sustainable agriculture, since these bacteria display extremely versatile secondary metabolisms, which provide useful sources of many diverse metabolites with valuable biological activities, including antibiotic activity (Raaijmakers and Mazzola, 2012). Others have the capacity to establish themselves as natural inhabitants of the rhizosphere and phyllosphere, acting as commensals or providing beneficial activity to their host They can promote suppression of pathogen infection and/or directly facilitate host growth and fitness (Mercado-Blanco and Bakker, 2007)
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