Abstract
Photosynthetic bacteria (PSB) possess versatile metabolic abilities and are widely applied in environmental bioremediation, bioenergy production and agriculture. In this review, we summarize examples of purple non-sulfur bacteria (PNSB) through biofertilization, biostimulation and biocontrol mechanisms to promote plant growth. They include improvement of nutrient acquisition, production of phytohormones, induction of immune system responses, interaction with resident microbial community. It has also been reported that PNSB can produce an endogenous 5-aminolevulinic acid (5-ALA) to alleviate abiotic stress in plants. Under biotic stress, these bacteria can trigger induced systemic resistance (ISR) of plants against pathogens. The nutrient elements in soil are significantly increased by PNSB inoculation, thus improving fertility. We share experiences of researching and developing an elite PNSB inoculant (Rhodopseudomonas palustris PS3), including strategies for screening and verifying beneficial bacteria as well as the establishment of optimal fermentation and formulation processes for commercialization. The effectiveness of PS3 inoculants for various crops under field conditions, including conventional and organic farming, is presented. We also discuss the underlying plant growth-promoting mechanisms of this bacterium from both microbial and plant viewpoints. This review improves our understanding of the application of PNSB in sustainable crop production and could inspire the development of diverse inoculants to overcome the changes in agricultural environments created by climate change.
Highlights
In the 20th century, the emergence of the green revolution triggered a worldwide boom in the agriculture industry [1]
This research group reported that treating Chinese pak choi with R. palustris can enhance soil microbial metabolic activity and alter the abundances of some bacterial groups [47,48]. They found that the abundances of the operational taxonomic units (OTUs) related to the acceleration of carbon and nutrient cycling in soil, such as those phyla belonging to the Proteobacteria, Planctomycetes, Acidobacteria, Actinobacteria, Verrucomicrobia and Nitrospirae, were significantly increased following treatment with R
purple non-sulfur bacteria (PNSB) are widely found in nature, especially in submerged environments, such as underlying Plant Growth Promoting (PGP) mechanisms of PS3 from the viewpoint of microbes and plants; (4) develop optimal fermentation and formulation processes for commercialization; (5) perform field experiments to verify the efficacy and performance of the PS3 inoculant under conventional and organic farming conditions; (6) obtain regulatory approval and certification of the PS3 inoculant as a biofertilizer or plant biostimulant
Summary
In the 20th century, the emergence of the green revolution triggered a worldwide boom in the agriculture industry [1]. Yoshida and colleagues reported that treating rice seedlings with a PNSB inoculant three weeks before the heading stage increased the grain yield and panicle number by 200%. Sakpirom and colleagues reported that treating rice seedlings with the formulated R. palustris TN110, Ru. gelatinosus TN414 or mixed inoculants significantly increased the weight and length [65]. Ge and colleagues reported that treating cucumber seedlings with R. palustris strain G5 (isolated from the mud and water of the Qingshui River in Zhoukou city, Henan Province, China) could reduce the damage caused by cadmium and salt stress and enhance the agronomic traits and activities of reactive oxygen species of the plants [68,69]. Co-inoculation with KE149 and biochar could help to promote plant growth and strengthen the antioxidant system of soybean plant while grown under normal and stress conditions [79]
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