Phosphorus is the second most critical macronutrient after nitrogen required for metabolism, growth, and development of plants. Despite the abundance of phosphorus in both organic and inorganic forms in the soil, it is mostly unavailable for plant uptake due to its complexation with metal ions in the soil. The use of agrochemicals to satisfy the demand for phosphorus to improve crop yield has led to the deterioration of the ecosystem and soil health, as well as an imbalance in the soil microbiota. Consequently, there is a demand for an alternate cost-effective and eco-friendly strategy for the biofortification of phosphorus. One such strategy is the application of phosphate-solubilizing microorganisms which can solubilize insoluble phosphates in soil by different mechanisms like secretion of organic acids, enzyme production, and excretion of siderophores that can chelate the metal ions and form complexes, making phosphates available for plant uptake. These microbes not only solubilize phosphates but also promote plant growth and crop yield by producing plant-growth-promoting hormones like auxins, gibberellins, and cytokinins, antibiosis against pathogens, 1-aminocyclopropane-1-carboxylic acid deaminase which enhances plant growth under stress conditions, improving plant resistance to heavy metal toxicity, and so on. Pyrroloquinoline quinine (pqq) and glucose dehydrogenase (gcd) are the representative genes for phosphorus solubilization in microorganisms. The content presented in this review paper focuses on different mechanisms and modes of action of phosphate-solubilizing microorganisms, their contribution to phosphorus solubilization, growth-promoting attributes in plants, and the molecular aspects of phosphorus solubilization.

Availability of Zn to plant is hampered by its immobile nature and adverse soil conditions. Thus, Zn deficiency is observed even though high amount is available in soil. Root-shoot barrier, a major controller of zinc transport in plant is highly affected by changes in the anatomical structure of conducting tissue and adverse soil conditions like pH, clay content, calcium carbonate content, etc. Zn deficiency results in severe yield losses and in acute cases plant death. Zn deficiency in edible plant parts results in micronutrient malnutrition leading to stunted growth and improper sexual development in humans. To overcome this problem several strategies have been used to enrich Zn availability in edible plant parts, including nutrient management, biotechnological tools, and classical and molecular breeding approaches.

Rice is inherently low in micronutrients, especially iron, which leads to severe malnutrition problems in rice-consuming populations. Different plant growth promoting rhizobacterial strains (PGPRs) (viz. Pseudomonas putida, Pseudomonas fluorescens, and Azospirillum lipoferum from a microbial collection and B 15, B 17, B 19, BN 17 and BN 30 isolated from the rhizospheric soils) were applied to field grown rice plants with an aim to increase the iron content of grains. 16S rRNA gene sequence showed that isolates belong to Enterobacteria species. Different parameters related to the increase in iron content of plants show an enhancement upon treatment of rice plants with PGPRs. Treatments with P. putida, B 17 and B 19 almost doubled the grain iron content. Besides this, the translocation efficiency of the iron from roots to shoots to grains was also enhanced upon treatment with PGPRs. It is therefore concluded that application of PGPR strains is an important strategy to combat the problem of iron deficiency in rice and consecutively in human masses.

Plant growth promoting rhizobacteria (PGPRs) improve growth of the host plants in a variety of ways. For this reason five bacterial strains isolated form the rice rhizospheric soil (B 15, B 17, B 19, BN 17 and BN 30) and three standard PGPR strains (viz. Pseudomonas putida, Pseudomonas fluorescens and Azospirillum lipoferum) were tested for plant growth promotion when applied to the rice plants as seedling treatments. The experiment was conducted for two rainy seasons of the years 2010 and 2011. Rice plants inoculated with the bacterial isolates recorded an improved plant growth and higher photosynthetic capacity signified by the higher chlorophyll content. Root and shoot dry mass was also found to be increased in the inoculated plants. Besides these iron and zinc content of the treated rice plants was also found to be higher in comparison with the uninoculated control plants. Hence, it can be concluded that application of PGPR has immense potential to be used as agricultural crop inoculants as they promote plant growth as well as improve the health and yield of the plants.

Global warming is rising as a serious concern affecting agricultural production worldwide. Rice is a staple food crop and the threshold temperature for its pollination is 35 °C. A rise in temperature above this value can cause pollen sterility and may severely affect fertilization. Therefore, a study emphasizing the rise in temperature with respect to pollen viability was conducted with eleven rice genotypes during kharif seasons of 2010 and 2011 in indigenous field conditions. Increasing mean temperature by 12 °C at full flowering was found to severely affect the spikelet attributes of the crop. All genotypes showed spikelet sterility above 90% during both seasons. The study indicated that increased temperature may limit rice yield by affecting spikelet fertility and grain filling. The net reduction in grain yield was 30.4% and 27.6% in 2010 and 2011, respectively. A clear reduction in pollen size under high temperature was shown by scanning electron microscopy.