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Abstract: This study evaluated root endophyte bacteria and rhizobacteria in terms ofmultifaceted plant growth promotion (PGP) traits and antagonistic potential against majorfungal pathogens of rice (viz. Rhizoctonia solani, Bipolaris oryzae, Pyricularia oryzae,Ustilaginoidea virens and Sarocladium oryzae). Twenty bacterial isolates from each group(viz. endorhiza and rhizosphere) were isolated from different rice types of North EastIndia. Cultivated rice types were Upland rice (Mima, Kochi and Minil), Lowland HYV rice(Ranjit and Jaya) and Lowland scented rice (Keteki Joha and Kunkuni Joha). Thepopulation of rhizospheric bacteria was higher than the endophyte isolates. Thepopulation counts of endophyte bacteria were the highest in scented rice cultivar(Kunkuni Joha) and for rhizobacterial isolates; the population density was maximum inthe lowland HYV rice (Jaya). The endophytes were more efficient than the rhizobacteria interms of the activity of cellulase, pectinase, ACC-deaminase, production of IAA- likesubstances, solubilization of zinc and mineralization of organic phosphates. In contrast,the rhizobacterial isolates were more efficient in solubilization of inorganic phosphatesand antagonism against major rice fungal pathogens. Through 16S rDNA sequenceanalysis, the promising rhizobacterial isolates showing antagonism against all the fungalpathogens were identified as Brevibacillus reuszeri 12R, Lysinibacillus xylanticus 48R,Bacillus megaterium 58R and Serratia marcescens 79R. These results suggest that the rootbacterial endophytes and rhizobacteria characterized in this study could be successfullyused to promote plant growth and induce fungal resistance in rice plants and can be usedas bioinoculants for enhancing rice growth in the acid soil regions.
ABSTRACT
ABSTRACT The application of beneficial bacteria has recently been used for sustainable agriculture. In current research, 71 bacterial isolates were obtained from rice plant and the rhizosphere soil of different paddy fields in Guilan province, Iran. After primitive investigation, 40 bacteria with typical predominant characteristics were selected. By PCR-RFLP of their 16S r-DNA gene, 8 Operational Taxonomic Units (OTUs) totally consisted of 33 isolates were obtained. From all of them, 8 isolates were selected for rice seed germination experiment, then, effective isolates were used for pot experiment to evaluate their ability for promoting rice growth. All of them were able to increase rice growth and yield, but in different potential. These tested isolates were identified as Alcaligenes faecalis (DEp8, O1R4), Pantoea ananatis (AEn1), Bacillus vietnamensis (MR5), Bacillus idriensis (MR2) and Stenotrophomonas maltophilia by partial sequencing of their 16S r-DNA gene. Among them, AEn1 and MR5 produced indole-3- acetic acid (IAA) in larger amounts than the other isolates and the isolates AEn1 and O1R4 were able to solubilize phosphate in higher amounts. According to the results obtained, it can be concluded that AEn1, O1R4 and MR5 can be considered as bacterial inoculants to use as alternatives for chemical fertilizers.
ABSTRACT
ABSTRACT The main objective of the present study was to isolate phytohormone-producing, phosphate-solubilizing strains of Azospirillum from wheat to be used as inoculants for plant growth promotion. Five Azospirillum strains were isolated from the rhizosphere of field-grown wheat (Triticum aestivum L.), and it was confirmed by BOX-polymerase chain reaction (PCR) that the isolates were different and not re-isolates of the same strain. Sequence analysis of the PCR-amplified 16S rRNA gene indicated that four isolates showed maximum similarity to Azospirillum brasilense and one isolate showed maximum similarity to Azospirillum zeae. This is the first report indicating the presence of an A. zeae like isolate in the wheat rhizosphere in Pakistan. The bacterial isolates were characterized for their plant growth-promoting traits, phosphate solubilization, and indole-3-acetic acid (IAA) production. None of the isolates showed phosphate solubilization activity in the commonly used Pikovskaya medium. However, all strains (except AzoK4) exhibited ability to solubilize tricalcium phosphate (TCP) in modified Pikovskaya medium in which sucrose was replaced by Na-malate, as well as in TCP-supplemented Luria-Bertani (LB) medium. Organic acids, such as acetic, citric, lactic, malic, and succinic acids, were detected in culture supernatants of the tested Azospirillum strains. All strains exhibited ability to produce IAA in the growth medium, except Azospirillum sp. AzoK1. Among the strains tested, the maximum IAA production (30.49 ± 1.04 mg L-1) and phosphate solubilization (105.50 ± 4.93 mg L-1) were shown by a pure culture of Azospirillum sp. AzoK2. In pot experiments, single-strain inocula of Azospirillum sp. AzoK1 and AzoK2 improved wheat plant growth.