RESUMO
Nutrient deficiency in wild plant species, including quinoa (Chenopodium quinoa Willd), can be overcome by applying mineral-solubilizing bacteria. Quinoa is a gluten-free, nutritious food crop with unique protein content. The present study aimed to characterize mineral-solubilizing rhizobacterial strains and to evaluate their plant growth-promoting potential in quinoa seedlings. More than sixty rhizobacterial strains were isolated from the quinoa rhizosphere and found eighteen strains to be strong phosphate solubilizers. Most of these bacterial strains showed zinc solubilization, and more than 80% of strains could solubilize manganese. The selected strains were identified as Bacillus altitudinis Cq-3, Pseudomonas flexibilis Cq-32, Bacillus pumilus Cq-35, Pseudomonas furukawaii Cq-40, Pontibacter lucknowensis Cq-48, and Ensifer sp. Cq-51 through 16S rRNA partial gene sequencing. Mainly, these strains showed the production of organic acids, including malic, gluconic, tartaric, ascorbic, lactic, and oxalic acids in insoluble phosphorus amended broth. All strains showed production of gluconic acids, while half of the strains could produce malic, ascorbic, lactic, and oxalic acids. These strains demonstrated the production of indole-3-acetic acid in the presence as well as in the absence of L-tryptophan. The bacterial strains also demonstrated their ability to promote growth and yield attributes, including shoot length, root length, leave numbers, root and shoot dry biomass, spike length, and spikes numbers of quinoa in pots and field trials. Increased physiological attributes, including relative humidity, quantum flux, diffusive resistance, and transpiration rate, were observed due to inoculation with mineral solubilizing bacterial strains under field conditions. P. lucknowensis Cq-48, followed by P. flexibilis Cq-32, and P. furukawaii Cq-40 showed promising results to promote growth, yield, and physiological attributes. The multi-traits characteristics and plant growth-promoting ability in the tested bacterial strains could provide an opportunity for formulating biofertilizers that could promote wild quinoa growth and physiology.
RESUMO
Manganese (Mn) is an essential micronutrient for plant growth that is involved in the structure of photosynthetic proteins and enzymes. Mn deficiency is widespread mainly in dry, calcareous, and sandy soil, which leads to a significant decrease in crop yield. Mn-reducing bacteria promote the solubilization of Mn minerals, thus increasing Mn availability in soil. The present study aimed to assess the Mn solubilizing ability and plant growth-promoting potential of Bacillus spp. strains for maize plants with insoluble Mn compounds. Several Mn-solubilizing bacterial (MSB) strains were isolated from the maize rhizosphere using nutrient agar media amended with 50 mM MnO2. These strains were screened based on qualitative and quantitative solubilization of Mn, phosphorus, potassium, and zinc and production of ammonia. The majority of MSB strains were positive for catalase, protease, amylase, and oxidase activity, while more than 60% of tested strains were positive for lipase activity, and the production of indole-3-acetic acid and siderophores. Forty-five percent of the tested strains also showed solubilization of potassium. All the MSB strains were evaluated for their ability to promote plant growth and Mn uptake in the presence of MnO2 under axenic sand culture conditions. The results revealed that inoculation with MSB strains under sand culture significantly improved the growth of maize seedlings except for strains ASH7, ASH10, and ASH12. Comparatively, strains ASH6, ASH11, ASH19, ASH20, and ASH22 demonstrated a better increase in plant growth, fresh and dry biomass, and Mn uptake in roots and shoots than the other strains tested. All of these strains were identified as Bacillus spp. through 16S rRNA partial gene sequencing. Maize inoculation with these selected identified MSB strains also resulted in an increase in maize growth and nutrient uptake in maize roots and shoots under soil culture conditions in the presence of native soil Mn. The current study highlights the importance of MSB strain inoculation which could be a potential bioinoculants to promote plant growth under Mn deficiency.