The role of rice rhizobacteria in plant growth promotion and defense against Magnaporthe oryzae infection
Date
2012
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
The natural interactions between plant roots and their rhizospheric microbiome
are vital to plant fitness, modulating both growth promotion and disease suppression.
Naturally occurring root-associated rhizospheric bacteria were isolated from
California field grown rice plants (M-104), eleven of which were taxonomically
identified by16S rRNA gene sequencing and fatty acid methyl ester (FAME) analysis.
Using an experimental hydroponic set-up, the isolates were inoculated into the rice
growth media to test for growth promotion properties. A cocktail of all eleven isolates
increased rice biomass by 91%. Treatment with a single isolate identified as an
Arthrobacter oxydans species (EA201) increased biomass, as well as shoot
phosphorus (P) and iron (Fe) concentration.
Bacterial isolates were tested for biological control activity against the
devastating foliar rice fungal pathogen, Magnaporthe oryzae pathovar 70-15. In vitro,
a Pseudomonas isolate, EA105, displayed antibiosis through impairing 70-15
appressorium formation, the specialized structure needed for infection. EA105 also
displayed inhibition of fungal growth through diffusible compounds (65% inhibited)
and through volatile compounds (51% inhibited). Although hydrogen cyanide (HCN)
is a volatile commonly produced by biocontrol Pseudomonads, the activity of EA105
seems to be independent of its HCN production. Characterization of volatiles
produced by EA105 was done using SPME-GC-MS and included alcohols,
hydrocarbons, ketones, and sulfur-containing compounds. During in planta
experiments, an induced systemic resistance (ISR)-like response was seen in soilgrown rice by priming roots with EA105 and a Pantoea agglomerans isolate (EA106).
EA105 reduced the number of blast lesions formed by 33% and EA106 by 46%. The
application of natural bacteria as biocontrol agents in combination with current disease
protection strategies could create a synergistic and long-lasting approach to
sustainable agriculture.