Abstract
The use of plant growth-promoting bacteria (PGPB), which aims to replace chemical fertilizers and biological control, is a goal for achieving agriculture sustainability. In this scenario, our goal was to identify and evaluate the potential of bacteria isolated from maize roots to promote plant growth and be used as inoculants. We evaluated 173 bacterial strains isolated from the maize (Zea mays L.) rhizosphere for the properties of their PGPB in vitro. Twelve strains were positive for siderophores, indole acetic acid (IAA) production, biological nitrogen fixation (BNF), and phosphate solubilization. Sequence analysis of 16S rRNA identified these strains as belonging to the genera Cellulosimicrobium, Stenotrophomonas, Enterobacter, and Bacillus. The elite strains were evaluated under greenhouse conditions upon the inoculation of two maize hybrids, ATL100 and KWX628. The ability of the isolates to promote plant growth was dependent on the maize genotype; Enterobacter sp. LGMB208 showed the best ability to promote growth of hybrid ATL100, while Enterobacter sp. strains LGMB125, LGMB225, and LGMB274 and Cellulosimicrobium sp. strain LGMB239 showed the best ability to promote growth of hybrid KWX628. The results highlight the potential of bacterial genera little explored as maize PGPB but indicate the need to investigate their interactions with different plant genotypes.
Highlights
Maize (Zea mays L.) is one of the most important cereal crops worldwide, with great economic importance in several countries (Yazdani, Bahamanyar, Pirdashti, & Esmaili, 2009)
63.4% (n = 59) strains were positive for biological nitrogen fixation (BNF), and 12.9% (n = 12) strains synthesized indole acetic acid (IAA)
In vitro screening of the 173 bacterial strains isolated from maize roots for properties commonly associated with plant growth-promotion revealed that 70.5% of the bacterial strains produced siderophores and 56.5% solubilized phosphate; both parameters are considered important microbial features of plant growthpromoting bacteria (PGPB) (Majeed et al, 2015)
Summary
Maize (Zea mays L.) is one of the most important cereal crops worldwide, with great economic importance in several countries (Yazdani, Bahamanyar, Pirdashti, & Esmaili, 2009). The species requires a high nutritional level to achieve economical yields, with nitrogen (N) and phosphorous (P) being the most limiting nutrients. The release of high-yield genotypes has increased the need for chemical fertilizers (Souza, Ambosini, & Passaglia, 2015). It is estimated that for an average yield of 7 - 9 t ha-1, applications of 110 - 140 kg ha-1 N and 20 - 50 kg ha-1 P2O5 are required (Montañez & Sicardi, 2013), the efficiency of fertilizer utilization by the plant rarely surpasses 50% efficiency (Halvorson, Peterson, & Reule, 2002). The poor efficiency of N use contributes to nitrate contamination of soil and groundwater, demanding alternatives to ensure competitive crop yields that are ecologically balanced (Majeed, Abbasi, Hameed, Imran, & Rahim, 2015). The use of microbial inoculants carrying plant growthpromoting bacteria (PGPB) is increasing (Hungria, Campo, Souza, & Pedrosa, 2010) but is still in the early stages of development (Souza et al, 2015)
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