Mineral nutrition of crop plants is one of the major challenges faced by modern agriculture, particularly in arid and semi-arid regions. In alkaline calcareous soils, the availability of phosphorus and zinc is critically less due to their fixation and precipitation as complexes. Farmers use fertilizers to fulfill crop requirements, but their efficacy is less, which increases production costs. Plant growth-promoting rhizobacteria (PGPR) can improve the availability of crop nutrients through solubilizing the insoluble compounds of phosphorus and zinc in soil. In the present study, a total of 40 rhizobacterial isolates were isolated from cotton rhizosphere and screened for improving cotton growth through the solubilization of phosphorus and zinc. Out of these 40 isolates, seven isolates (IA2, IA3, IA6, IA7, IA8, IA13, and IA14) efficiently solubilized insoluble rock phosphate while seven isolates (IA10, IA16, IA20, IA23, IA24, IA28, and IA30) were more efficient in solubilizing insoluble zinc oxide. In liquid media, strain IA7 (2.75 μg/mL) solubilized the highest amount of phosphate while the highest concentration of soluble zinc was observed in the broth inoculated with strain IA20 (3.94 μg/mL). Seven phosphate-solubilizing and seven zinc-solubilizing strains were evaluated using jar trial to improve the growth of cotton seedlings, and the results were quite promising. All the inoculated treatments showed improvement in growth parameters in comparison with control. Best results were shown by the combined application of IA6 and IA16, followed by the combination of strains IA7 and IA20. Based on the jar trial, the selected isolates were further characterized by plant growth-promoting characters such as siderophores production, HCN production, ammonia production, and exopolysaccharides production. These strains were identified through 16S rRNA sequencing as Bacillus subtilis IA6 (accession # MN005922), Paenibacillus polymyxa IA7 (accession # MN005923), Bacillus sp. IA16 (accession # MN005924), and Bacillus aryabhattai IA20 (accession # MN005925). It is hence concluded that the integrated use of phosphate-solubilizing and zinc-solubilizing strains as potential inoculants can be a promising approach for improving cotton growth under semi-arid conditions.

农作物的矿物质营养是现代农业面临的主要挑战之一，特别是在干旱和半干旱地区。在碱性钙质土壤中，磷和锌的可用性极低，因为它们作为复合物固定和沉淀。农民使用肥料来满足作物需求，但其功效较低，从而增加了生产成本。植物促生长根际细菌 (PGPR) 可以通过溶解土壤中磷和锌的不溶性化合物来提高作物养分的有效性。在本研究中，共从棉花根际中分离出 40 株根际细菌，并筛选出通过增溶磷和锌来改善棉花生长。在这 40 个分离株中，有 7 个分离株（IA2、IA3、IA6、IA7、IA8、IA13、和 IA14) 有效地增溶不溶性磷酸盐岩，而 7 个分离株（IA10、IA16、IA20、IA23、IA24、IA28 和 IA30）更有效地增溶不溶性氧化锌。在液体培养基中，菌株 IA7 (2.75 μg/mL) 溶解最高量的磷酸盐，而在接种菌株 IA20 (3.94 μg/mL) 的肉汤中观察到最高浓度的可溶性锌。7株溶磷菌和7株溶锌菌对棉花幼苗生长的促进作用进行了瓶试评价，结果非常有希望。与对照相比，所有接种的处理都显示出生长参数的改善。IA6 和 IA16 的组合应用显示了最佳结果，其次是菌株 IA7 和 IA20 的组合。基于 jar 试验，选定的分离株进一步表征了植物生长促进特性，如铁载体生产、HCN 生产、氨生产和胞外多糖生产。这些菌株通过 16S rRNA 测序鉴定为枯草芽孢杆菌IA6（登录号 MN005922）、多粘类芽孢杆菌IA7（登录号 MN005923）、芽孢杆菌属。IA16（登录号 MN005924）和Bacillus aryabhattai IA20（登录号 MN005925）。因此得出的结论是，综合使用溶磷菌和溶锌菌作为潜在的接种剂可能是改善半干旱条件下棉花生长的一种有前景的方法。