Abstract
This work aimed to isolate and characterize plant growth promoting rhizobacteria (PGPR) from 10 Paspalum genotypes and evaluate the effect of their inoculation on P. regnellii, P. atratum, and P. malacophyllum genotypes. The bacterial population ranged from undetectable to 107 bacterial cells per gram of fresh matter in the Paspalum genotypes. Initially, we isolated 164 bacteria from rhizospheric soil and roots of the Paspalum genotypes using media N-free LG agar plate, semi-solid NFb, and LGI. The isolates were characterized genetically and physiologically. The sequencing of 16S rRNA showed the presence of many genera, and some are new in association with Paspalum. The most common was Bacillus followed by Rhizobium, Paraburkholderia, Enterobacter, Cupriavidus, Pseudomonas, Dyadobacter and Acinetobacter. Thirty-eight per cent of isolates produced siderophores, 25 % produced solubilized phosphate, and only 9 % produced indolic compounds. Three greenhouse experiments were performed in randomized blocks with six replicates using representative bacterial strains isolated from P. regnellii, P. malacophyllum and P. atratum cv. Pojuca. We also included strain Sp245 (Azospirillum baldaniorum), uninoculated control, and nitrogen control (150 kg N ha−1). There was an increase of up to 53 % in shoot dry matter in P. regnellii inoculated with strain Sp245 and the shoots accumulated more N. In contrast, only small effects were observed for the other Paspalum genotypes inoculated with PGPR from the host genotypes. This study shows a high diversity of diazotrophic rhizosphere bacteria and suggests no strain specificity between the bacterial isolates and the Paspalum genotypes.
Highlights
Brazil has the largest commercial cattle herd in the world, mainly pasture-based
This study shows a high diversity of diazotrophic rhizosphere bacteria and suggests no strain specificity between the bacterial isolates and the Paspalum genotypes
The number of plant growth promoting rhizobacteria (PGPR) ranged from not-detected to 107 bacterial cells per gram of fresh matter among the 10 Paspalum genotypes
Summary
Brazil has the largest commercial cattle herd in the world, mainly pasture-based. There are about 160 million ha of pastureland in Brazil cultivated with 80 % of Brachiaria The genus Paspalum is native to the Americas and is considered an alternative for diversification in Brazilian cultivated pastures (Manzur et al, 2020; Marques et al, 2020). Soil bacteria benefit soil properties and plants and can be an alternative N source in tropical grasslands. Many bacterial genera associated to various managed grassland ecosystems are classified as diazotrophic bacteria, belonging to genera Azospirillum, Azotobacter, Rhizobium, Bacillus, Pseudomonas, and others (Antunes et al, 2019; Döbereiner, 1966; Ribeiro et al, 2020; Souza et al, 2017)
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