Siderophore-positive bacteria present in the rhizosphere and in bulk soil assist plants by either inhibiting phytopathogen proliferation or increasing plant growth. The bacterial diversity of the Shisham forest ecosystem in the Tarai region of the Western Himalayas was studied and used for siderophore production, taking into account the large-scale dieback and wilt-induced mortality in Dalbergia sissoo (common name: shisham) plantation forests and the importance of soil microbes in tree health. In addition, Pseudomonas, Burkholderia, and Streptomyces were prominent siderophore-positive bacteria in Shisham forests. Pseudomonas species are known for their remarkable siderophore-producing ability. Bacterial siderophores inhibit pathogen growth by rapidly lowering the number of ferric ions in the rhizosphere. The Pseudomonas monteilii strain MN759447 was isolated from a D. sissoo plantation forest at the Agroforestry Research Centre, Pantnagar, Uttarakhand (28°58'N 79°25'E/28.97°N 79.41°E). It produces a significant number of siderophore units (80.36% in total). A two-stage optimization of growth factors was attempted in the strain MN759447 for better siderophore recovery. In the first-stage single-factor experiment, among the five variables studied, only pH, NH4NO3 concentration, and Fe concentration affected siderophore synthesis. In the second stage, an optimization of pH, NH4NO3 concentration, and Fe concentration for improved growth and enhanced siderophore production was carried out using a Box-Behnken design with response surface methodology. By using LC-MS, two derivatives of pseudomonine, salicylic acid, and kynurenic acid were detected as siderophores in the purified XAD-2 methanol extract of the P. monteilii strain MN759447. In addition to siderophore production, the P. monteilii strain MN759447 also exhibited a broad range of antagonistic activity against Aspergillus calidoustus (65%), Fusarium oxysporum (41.66%), Talaromyces pinophilus (65%), and Talaromyces verruculosus (65.1%) that are linked to sissoo mortality. To our knowledge, this is the first report on siderophore-producing bacteria isolated, identified, and characterized from the D. sissoo Roxb. forest habitat. This strain can also be developed as a commercial product.
It is well-known that phosphate-solubilizing bacteria (PSB) promote crop growth and yield. The information regarding characterization of PSB isolated from agroforestry systems and their impact on wheat crops under field conditions is rarely known. In the present study, we aim to develop psychrotroph-based P biofertilizers, and for that, four PSB strains (Pseudomonas sp. L3, Pseudomonas sp. P2, Streptomyces sp. T3, and Streptococcus sp. T4) previously isolated from three different agroforestry zones and already screened for wheat growth under pot trial conditions were evaluated on wheat crop under field conditions. Two field experiments were employed; set 1 includes PSB + recommended dose of fertilizers (RDF) and set 2 includes PSB - RDF. In both field experiments, the response of the PSB-treated wheat crop was significantly higher compared to the uninoculated control. In field set 1, an increase of 22% in grain yield (GY), 16% in biological yield (BY), and 10% in grain per spike (GPS) was observed in consortia (CNS, L3 + P2) treatment, followed by L3 and P2 treatments. Inoculation of PSB mitigates soil P deficiency as it positively influences soil alkaline phosphatase (AP) and soil acid phosphatase (AcP) activity which positively correlated with grain NPK %. The highest grain NPK % was reported in CNS-treated wheat with RDF (N-0.26%, P-0.18%, and K-1.66%) and without RDF (N-0.27, P-0.26, and K-1.46%), respectively. All parameters, including soil enzyme activities, plant agronomic data, and yield data were analyzed by principal component analysis (PCA), resulting in the selection of two PSB strains. The conditions for optimal P solubilization, in L3 (temperature-18.46, pH-5.2, and glucose concentration-0.8%) and P2 (temperature-17°C, pH-5.0, and glucose concentration-0.89%), were obtained through response surface methodology (RSM) modeling. The P solubilizing potential of selected strains at <20°C makes them a suitable candidate for the development of psychrotroph-based P biofertilizers. Low-temperature P solubilization of the PSB strains from agroforestry systems makes them potential biofertilizers for winter crops.