Cultivable bacteria isolated from apple trees cultivated under different crop systems: Diversity and antagonistic activity against Colletotrichum gloeosporioides.

João Frederico M Dos Passos,Murilo D Costa,Andréia Mara R De Oliveira,Gilberto Nava,José Itamar Boneti,Pedro B Da Costa,Gilmar R Zaffari,Luciane M.P Passaglia

doi:10.1590/s1415-47572014000400013

Abstract

This study evaluated the diversity of cultivable plant growth-promoting (PGP) bacteria associated with apple trees cultivated under different crop management systems and their antagonistic ability against Colletotrichum gloeosporioides. Samples of roots and rhizospheric soil from apple trees cultivated in organic and conventional orchards in southern Brazil were collected, together with soil samples from an area never used for agriculture (native field). Bacteria were identified at the genus level by PCR-RFLP and partial sequencing of the 16S rRNA, and were evaluated for some PGP abilities. The most abundant bacterial genera identified were Enterobacter (27.7%), Pseudomonas (18.7%), Burkholderia (13.7%), and Rahnella (12.3%). Sixty-nine isolates presented some antagonist activity against C. gloeosporioides. In a greenhouse experiment, five days after exposure to C. gloeosporioides, an average of 30% of the leaf area of plants inoculated with isolate 89 (identified as Burkholderia sp.) were infected, whereas 60 to 73% of the leaf area of untreated plants was affected by fungal attack. Our results allowed us to infer how anthropogenic activity is affecting the bacterial communities in soil associated with apple tree crop systems, and to obtain an isolate that was able to delay the emergence of an important disease for this culture.

Highlights

Apples are one of the most important cropped and consumed fruits in the world
A total of 300 bacterial strains were selectively isolated from the rhizospheric soil or roots of apple trees or from soil of a native field based on their growth in one of three semi-selective semi-solid media without nitrogen; i.e., NFb, LGI or LGI-P
Strains belonging to Enterobacter and Burkholderia genera were overrepresented in Native Field (NF), while strains belonging to the Pseudomonas genus were more abundant in the Conventional Orchard (CO) condition

Summary

Introduction

Apples are one of the most important cropped and consumed fruits in the world. According to Brown (2012), apples are the most produced temperate tree crop, and they are widely grown throughout almost the entire temperate climate region in the Northern and Southern hemispheres. Apple cropping has been expanding into subtropical and tropical zones (Karakurt and Aslantas, 2010). To achieve intensive fruit production, which requires very high productivity and fruit quality, large agricultural inputs are required. The excessive use of fertilizers, in addition to increasing production costs, leads to an increase in environmental pollution. The use of more sustainable technologies, such as biofertilization, is inevitable for the mitigation of environmental damage (Rodriguez and Fraga, 1999; Vessey, 2003; Karakurt and Aslantas, 2010)

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