**1. Introduction**

By 2050, around 9.9 billion people will be living on earth, with an expected concurrent doubling of the global food demand; hence agricultural production must increase at the same rate [1, 2]. This exponential population growth comes with an expected doubling of meat consumption; hence, demand for cereals-based feeds such as maize (*Zea mays* L.) will follow the same trend [3]. Therefore, modern breeding programs must double current genetic gains [2, 4]. However, a 2013 study alerted that current yield increase trends of most staple crops, including maize, are

insufficient to meet the 2050 food demands [5]. Several biotic and abiotic factors are determinant limitations to crop yield despite breeding efforts, and climate disturbances will further compound these yield-reducing stressors [2, 6].

With this background, it is apparent that crop improvement programs targeting only the inherent genetic makeups of plants to increase yields are not efficient enough to increase crop production sufficiently to meet future food and feed demands [4]. Furthermore, it is necessary to achieve the desired crop production without increasing production surfaces since land degradation will likely worsen shortly [3]. This alarming situation calls for re-orienting plant breeding programs to adopt new climate-smart breeding approaches to boost crop productivity sufficiently to levels that would match the current and expected population growth rates [4, 7]. Instead of just focusing on increasing crop yields through improving its inherent genetic makeup, plant breeders should explore the immediate growing environment of the crops they seek to improve.

One of the components of the immediate growing environments of crops is the soil microbiota composed of microorganisms including fungi, archaea, and bacteria that have co-evolved with plants, among which some form highly beneficial symbiotic relationships with plants helping them in nutrient uptake, growth regulation, biotic and abiotic resistance, which ultimately results in increased yields [8–10]. The soil microbiota is relevant since most plant traits of interest, including nutrient use efficiency, tolerance to drought, salt, pest, and diseases, and yield, are part of a system comprising complex plant-associated microorganisms [11]. Plants have developed the ability to modulate the composition and activity of their microbiota through the secretion molecules and other signaling compounds [12]. Plant breeders would greatly benefit from understanding the genetic basis of this interaction and its influence on traits of interest and using this knowledge during selection and stability studies [11].

Among these microorganisms, arbuscular mycorrhizal fungi (AMF) are significant elements of the soil–plant system and constitute 5 to 50% of the microbial biomass of soils (Olsson et al., 1999). Arbuscular mycorrhizal symbiosis (AMS) is the most widespread and oldest terrestrial symbiosis [13], formed by 80–90% of terrestrial vascular plants, including grasses such as maize [14]. Plants benefit from AMS better mineral nutrition, especially phosphorus uptake [15], which improves mycorrhized plants biomass compared to non-mycorrhizal plants [13, 16], through colonization of plant roots, production of large networks of extra-root mycelium in the soil, and aid in the uptake of mineral nutrients by hosts in exchange for carbohydrates [17]. Elements such as nitrogen, magnesium, calcium, potassium, and trace elements such as copper [18], zinc, or even iron, are better absorbed by the plant through the AMF symbiosis [19, 20].

Furthermore, AMF are also a significant component of soil fertility improvement [21], playing an essential role in the soil's physical, chemical, and biological components. They increase soil water holding capacity by improving its structure and inherent enzymatic activity by activating other microorganisms such as nitrogen-fixing bacteria [22]. AMF also participate in the nitrogen, phosphorus, and carbon cycles while correcting soil acidity [23, 24]. Regarding plant bioprotection, AMF play an essential role [25, 26] through, for instance, helping plants to thwart root-damaging nematodes [27, 28], pathogenic fungi such as verticillium wilt [29], and various pathogenic bacteria [30]. In addition, AMS provides plants with better resistance to abiotic stresses such as water and salt stress or the presence of heavy metals [31, 32].

Maize (*Z. mays* L.) is one of the essential staple food crops, therefore, essential to food security [33, 34]. Along with rice and wheat, it provides at least 30% of the food calories to more than 4.5 billion people in 100 countries [35, 36]. Maize is *Climate-Smart Maize Breeding: The Potential of Arbuscular Mycorrhizal Symbiosis… DOI: http://dx.doi.org/10.5772/intechopen.100626*

grown in more than 166 countries in the world, including tropical, subtropical, and temperate regions from mean sea level to 3000 m AMSL [37], and among cereals, it ranks highest in terms of grain yield per hectare worldwide [38]. Furthermore, besides its revenue generation as a cash crop, maize utilization is diversifying and joining new markets such as biofuel production and livestock feed [33, 34]. Therefore, maize productivity and production need to increase exponentially to support future food and feed demands as a food security crop. This increase will be required to occur under less inorganic input, severed land degradation, and aggravated climate disturbances that will profoundly disadvantage maize in its interaction with its biotic and abiotic environments. Considering the tremendous benefits of AMS to crops such as maize, we believe future maize research and breeding should adopt a more climate-smart approach by focusing more on understanding maize-AMF interaction and improving symbiotic capacity to boost yields. Therefore, in this chapter, we first review the components relevant to maize-AMF interaction, then present benefits of AMS in terms of biotic and abiotic stress tolerance and improvement of yield and yield components, and finally summarize pre-breeding information related to maize-AMF interaction and trait improvement avenues based on up-to-date molecular breeding technologies.
