Induction of Systemic Resistance against Sheath Blight in Rice by Different Pseudomonas Isolates

Abstract

Sheath blight disease is a fungal pathogen that causes leaf blight in rice plants, resulting in significant yield losses throughout the growing season. <i>Pseudomonas</i> spp. have long been used as biocontrol agents for a variety of plant diseases. Four <i>Pseudomonas</i> isolates were tested for their ability to promote rice growth and generate systemic resistance to <i>Rhizoctonia solani</i>, the causal pathogen of sheath blight disease. In vitro, <i>Pseudomonas</i> isolates produced the growth hormone indole acetic acid (0.82-1.82 mg L^-1). Additionally, seed treatment with <i>Pseudomonas putida</i> suspension outperformed <i>P. brassicacearum</i>, <i>P. aeruginosa</i> and <i>P. resinovorans</i> in terms of germination and vigor evaluation. The maximum seed germination of 89% was recorded after seed treatments with a fresh suspension of <i>P. putida</i>, followed by 87% germination in <i>P. aeruginosa</i> treatment, compared with only 74% germination in the untreated controls. When compared with the infected control plants, all <i>Pseudomonas</i> isolates were non-pathogenic to rice and their co-inoculation considerably enhanced plant growth and health by reducing the disease index to 37% and improving plant height (26%), fresh weight (140%) and dry weight (100%). All <i>Pseudomonas</i> isolates effectively reduced sheath blight disease incidence, as well as the fungicide carbendazim, which is recommended for field management of <i>R. solani</i>. In comparison to untreated control seedlings, treatment with <i>Pseudomonas</i> isolates enhanced the production of peroxidase and polyphenol oxidase enzymes and the expression of the <i>phenylalanine ammonia lyase</i> (<i>PAL</i>) and <i>NPR1</i> genes, which could be involved in disease incidence reduction. In conclusion, the use of <i>Pseudomonas</i> spp. has been demonstrated to improve rice growth and resistance to <i>R. solani</i> while also providing an environmentally acceptable option to the agroecosystems.