The role of soil microbes in crop biofortification

Agronomic practices across the planet are becoming largely unsustainable in their current forms. With a growing population expected to reach ~9 billion by the year 2050, more sustainable ways to produce the world's main crops are needed. The main focus of current agronomic practices, especially in the case of cereal crops, is increased grain number and weight sometimes at the expense of nutritional content leading, in some instances, to micronutrient deficiencies. Micronutrient deficiencies are often termed hidden hunger, giving the false appearance that an individual is consuming sufficient amounts of nutrients. To counteract this problem, it is crucial that a sustainable solution to increase micronutrient concentration in a diverse range of crops is found. Plant growth-promoting microbes (PGPM) represents a sustainable solution to this problem. These PGPM can be divided into two main groups: Plant growth-promoting rhizobacteria (PGPR) and plant growth-promoting fungi (PGPF). These microbes are capable of increasing micronutrient concentrations in many crops worldwide. This chapter will focus on the use of these microbes to increase micronutrient content, in particular selenium, iron and zinc, using studies conducted over the last two decades right up to the present day, revealing how plant-microbe interactions and our ever-growing knowledge of these interactions can aid in the micronutrient biofortification of crops in a sustainable and environmentally friendly way.