Affiliation:
1. School of Biotechnology, Institute of Agricultural Technology, Suranaree, University of Technology, Nakhon Ratchasima, Thailand
2. The Center for Scientific and Technological Equipment, Suranaree University of Technology, Nakhon Ratchasima, Thailand
Abstract
ABSTRACT
Bradyrhizobium
encompasses a variety of bacteria that can live in symbiotic and endophytic associations with leguminous and nonleguminous plants, such as rice. Therefore, it can be expected that rice endophytic bradyrhizobia can be applied in the rice-legume crop rotation system. Some endophytic bradyrhizobial strains were isolated from rice (
Oryza sativa
L.) tissues. The rice biomass could be enhanced when supplementing bradyrhizobial strain inoculation with KNO
3
, NH
4
NO
3
, or urea, especially in
Bradyrhizobium
sp. strain SUTN9-2. In contrast, the strains which suppressed rice growth were photosynthetic bradyrhizobia and were found to produce nitric oxide (NO) in the rice root. The expression of genes involved in NO production was conducted using a quantitative reverse transcription-PCR (qRT-PCR) technique. The
nirK
gene expression level in
Bradyrhizobium
sp. strain SUT-PR48 with nitrate was higher than that of the
norB
gene. In contrast, the inoculation of SUTN9-2 resulted in a lower expression of the
nirK
gene than that of the
norB
gene. These results suggest that SUT-PR48 may accumulate NO more than SUTN9-2 does. Furthermore, the
nifH
expression of SUTN9-2 was induced in treatment without nitrogen supplementation in an endophytic association with rice. The indole-3-acetic acid (IAA) and 1-amino-cyclopropane-1-carboxylic acid (ACC) deaminase produced
in planta
by SUTN9-2 were also detected. Enumeration of rice endophytic bradyrhizobia from rice tissues revealed that SUTN9-2 persisted in rice tissues until rice-harvesting season. The mung bean (
Vigna radiata
) can be nodulated after rice stubbles were decomposed. Therefore, it is possible that rice stubbles can be used as an inoculum in the rice-legume crop rotation system under both low- and high-organic-matter soil conditions.
IMPORTANCE
This study shows that some rice endophytic bradyrhizobia could produce IAA and ACC deaminase and have a nitrogen fixation ability during symbiosis inside rice tissues. These characteristics may play an important role in rice growth promotion by endophytic bradyrhizobia. However, the NO-producing strains should be of concern due to a possible deleterious effect of NO on rice growth. In addition, this study reports the application of endophytic bradyrhizobia in rice stubbles, and the rice stubbles were used directly as an inoculum for a leguminous plant (mung bean). The degradation of rice stubbles leads to an increased number of SUTN9-2 in the soil and may result in increased mung bean nodulation. Therefore, the persistence of endophytic bradyrhizobia in rice tissues can be developed to use rice stubbles as an inoculum for mung bean in a rice-legume crop rotation system.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
18 articles.
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