Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2013
Publication Date: 4/2/2013
Citation: Sobolev, V.S., Orner, V.A., Arias De Ares, R.S. 2013. Distribution of bacterial endophytes in peanut seeds obtained from axenic and control plant material under field conditions. Plant and Soil. 371(1-2):367-376.
Interpretive Summary: Frequent contamination of peanuts with highly carcinogenic aflatoxins under drought conditions is a significant food safety issue. A strategy of biological control through the application of soil bacteria to the peanut is one that may find a practical application. However, the bacterial strains cannot compete with the less water-demanding fungi under drought conditions in the soil. The situation seems to be different with bacteria that live inside peanut seeds. These bacteria are sheltered from environmental stresses and microbial competition by the host plant, seem to better tolerate drought, and may prevent fungal invasion when similar soil bacteria fail. A new experimental approach allowed us to grow bacteria-free young peanut plants, and demonstrated that both, experimental and control peanut seeds accommodated selected species of nonpathogenic bacteria that originate from soil. Among all species, the highly insecticidal B. thuringiensis and antifungal B. amyloliquefaciens, were dominant. The toxicity of these bacteria may explain their selection by the host peanut plant. We plan to clarify the issue on whether among the plant-associated bacteria that colonize the soil internal bacteria play a considerable role in protecting plants from fungal invasion under drought conditions. The research is planned, and the results will be reported in a due course.
Technical Abstract: Since endophytic bacteria may play a role in the defense mechanism of peanut from fungal invasion, the internal bacterial colonization of peanut seeds was investigated. Bacteria-free young peanut plants from seed embryos were successfully grown to maturity in the field. Mature seeds from these plants contained several species of nonpathogenic endophytic bacteria, which were identified by the analysis of DNA sequences of their 16S-ribosomal RNA gene. Among the eight bacterial species isolated, Bacillus thuringiensis, which is known to produce insecticidal Bt-toxins, was dominant. There was no significant difference in number and relative occurrence of the two major bacterial species between the experimental seeds grown from axenic planting material and the conventionally grown control seeds. This fact suggests that the endophytic bacterial colonization derives from local soil and not from the seed source, and that the peanut plant accommodates only selected species of bacteria from diverse soil populations.