Abstract
Plant growth promoting rhizobacteria Pseudomonas aeruginosa strain MF-30 isolated from maize rhizosphere was characterized for several plant growth stimulating attributes. The strain MF-30 was also evaluated for antifungal properties against Rhizoctonia solani causing banded leaf and sheath blight in maize (Zea mays L.) under in vitro conditions and was found to have higher mycelial growth suppression in the culture suspension (67.41%) followed by volatile organic compounds (62.66%) and crude extract (51.20%) in a dual plate assay. The endophytic and epiphytic colonization ability was tested using Green Fluorescent Protein (GFP)-tagging. Visualization through confocal scanning laser microscope clearly indicated that strain MF-30 colonizes the root and foliar parts of the plants. Further, the effects of seed bio-priming with P. aeruginosa MF-30 was evaluated in the induction and bioaccumulation of defense-related biomolecules, enzymes, natural antioxidants, and other changes in maize under pot trial. This not only provided protection from R. solani but also ensured growth promotion under pathogenic stress conditions in maize. The maximum concentration of hydrogen peroxide (H2O2) was reported in the root and shoot of the plants treated with R. solani alone (8.47 and 17.50 mmol mg−1 protein, respectively) compared to bioagent, P. aeruginosa MF-30 bio-primed plants (3.49 and 7.50 mmol mg−1 protein, respectively). Effects on total soluble sugar content, total protein, and total proline were also found to enhanced significantly due to inoculation of P. aeruginosa MF-30. The activities of anti-oxidative defense enzymes phenylalanine ammonia lyase (PAL), ascorbate peroxidase, peroxidase, superoxide dismutase, and catalase increased significantly in the plants bio-primed with P. aeruginosa MF-30 and subsequent foliar spray of culture suspension of MF-30 compared to pathogen alone inoculated plants. qRT-PCR analysis revealed that seed bio-priming and foliar application of P. aeruginosa MF-30 significantly increased the expression of PR-1 and PR-10 genes with the simultaneous decrease in the disease severity and lesion length in the maize plants under pathogenic stress conditions. A significant enhancement of shoot and root biomass was recorded in MF-30 bio-primed plants as compared to untreated control (p < 0.05). Significant increase in plant growth and antioxidant content, as well as decreased disease severity in the P. aeruginosa MF-30 bio-primed plants, suggested the possibility of an eco-friendly and economical means of achieving antioxidants-rich, healthier maize plants.
Highlights
Maize is one of the important cereal crops grown throughout the world for food, feed, and fuel.Maize production is often affected by the biotic and abiotic stresses devastatingly affecting the yield and quality of the produce and interferes in achieving the potential yield of a cultivar [1,2,3,4,5]
Pseudomonas aeruginosa strain MF-30 used in this study showed prominent antagonistic reactions aeruginosa strain used in this study showed antagonistic reactions againstPseudomonas test pathogens
67.41%in inaadual dual plate plate assay assay using using culture. This indicated the possibility of production of water-soluble antimicrobial compounds in MF-30 due due
Summary
Maize is one of the important cereal crops grown throughout the world for food, feed, and fuel.Maize production is often affected by the biotic and abiotic stresses devastatingly affecting the yield and quality of the produce and interferes in achieving the potential yield of a cultivar [1,2,3,4,5]. Among various diseases, banded leaf and sheath blight (BLSB) caused by Rhizoctonia solani (formally known as Rhizoctonia sasakii) is considered as one of the emerging and severe pathogens limiting the crop production under a changing climatic scenario [10,11,12]. The pathogen R. solani is a necrotroph which produces phytotoxins during the infection process causing necrotic spot on the leaf, sheath, and stem, preferably [1,2,6]. For the management of BLSB, the major focus is on host plant resistance where maize germplasm is evaluated against R. solani at different agro-climatic zones to identify resistant sources [6,13,14,15,16]. A small number of germplasm/donor parents have been identified as having resistance gene(s)/quantitative trait loci (QTLs), but the breakdown of resistance in due course of time is of great concern and poses a major challenge for plant breeders [17,18,19,20,21]
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