**1. Introduction**

The simulation results suggest that climate variability including storms, flooding, and other extreme weather with increases of temperature may ultimately disrupt crop yield [1]. By century's end, climate change with temperature increases could reduce 11–25% global crop productions [2]. Growth in the temperature and global population can result in shortage of water reserves [3]. Moreover, weather forecast uncertainty

will result in decrease of precipitation and increase of evapotranspiration relatively [4]. These factors can lead to drought and reductions in growth and crops yield. One of the main economic solution to increase stability in the production of agricultural products is the genetic modification of plants to withstand abiotic stresses [5]. Therefore, improving crops productivity under deficit irrigation is crucial and needed to ensure food security [6, 7].

As staple food, maize is an important cereal crop and main source of food security which plays a major role in the diets of millions of individuals, fodder, and bioenergy production in the world [8]. Drought stress as the most limitations to productivity of crops than any other abiotic stresses, substantially determines the maize production [9]. Maize is extremely sensitive and vulnerable to water-deficit stress at different growth and development stages that cause great yield reductions during grain fill [10]. Annually, 15–20% of maize production decreases due to climate change and drought. According to FAO statistics [11], maize production in 2016 decreased by 31% in comparison to 2015 due to drought stress and because of many problems of the global climate change and the expansion of maize yield under drought stress conditions. The development of drought-tolerant maize varieties are of high priority in plant breeding and crop science [12].

The knowledge inheritance of various morphological, biochemical, molecular, and physiological mechanisms of the drought maize tolerance is a key breeding strategy and helps the resistance of maize varieties against water-deficit stress [13, 14]. Water-stress tolerance is a complex quantitative trait that is controlled by many microeffective genes [15]. Relevant physiological traits include chlorophyll concentration, relative water content, leaf chlorophyll index, photosynthetic pigments, as well as biochemical traits such as protein content, synthesis of osmolytes, various enzymatic antioxidants, polyphenol oxidase which alters in response to drought and helps resistance of crops against stress [16, 17]. Breeders estimate the effects of genes controlling inheritance of traits in breeding populations, using different mating designs. According to the types of genetic material, the power of estimating additive, dominance, and epistasis gene effects are different [18]. Estimation of variance components of traits (additive, dominance, and epistasis) is important to determine which breeding method can optimize gene action more efficiently to recognize the need to produce hybrids or pure-line varieties [19, 20]. Additionally, levels of the additive effect and dominance degree are very important in designing a plant breeding for improving the trait of interest. Efficiency of selection majority depends on additive genetic variance, the environment, and the genotype × environment interaction effects and this encourages the breeders to understand to what extent the variation is heritable and how much of this variation is usable genetically. Knowledge of interact and gene act determine which breeding system can improve gene action and illustrate the role of this system in the crop plants evolution.

The main objective of this chapter was to determine the genetic control of various physiobiochemical traits which alter in response to water deficit and help the resistance of maize against stress. The knowledge of the physiobiochemical traits can be used to explore new genotypes of maize to increase grain yield under water stress conditions. The genetic component studies, inheritance pattern, and involvement of nonadditive, additive, and maternal genetic effects about various physiobiochemical traits were observed under water-deficit stress conditions. The obtained results will provide a source of potential genetic resources and inheritance patterns, which may be further studied to develop water-deficit tolerance maize varieties and, morphological and physiobiochemical markers.

*Genetic Interaction and Inheritance of Physiobiochemical Traits Can Predict Tolerance of Maize… DOI: http://dx.doi.org/10.5772/intechopen.111599*

### **2. Methods**

Various biometrical techniques, that is, North Carolina Model, generation mean analysis, diallel, and line × tester design could be used for understanding of gene action controlling of different plant traits. These methods give information on the importance of average additive and dominance gene effects in determining genotypic values of the generations. Among these, generation mean analysis is the one which determines the type of epistasis (nonallelic gene actions) at digenic level using scaling test, accurately and efficiently [20]. In other words, generation mean analysis model in addition to estimating the genetic parameters viz*.* mean, additive gene effects, and dominance gene effects, determines three types of nonallelic gene interactions viz. additive × additive, additive × dominance, and dominance × dominance [19]. In this method, the overall average for each trait is shown as follows:

$$\mathbf{Y = m + a\begin{bmatrix} d \end{bmatrix} + \beta\begin{bmatrix} h \end{bmatrix} + a\mathbf{2}\begin{bmatrix} i \end{bmatrix} + a\beta\begin{bmatrix} \mathbf{j} \end{bmatrix} + \beta\mathbf{2}\begin{bmatrix} \mathbf{l} \end{bmatrix} \tag{1}$$

where Y: the generation means, m: F∞ metric, d: additive effects, h: dominance effects, i: additive × additive interaction, j: additive × dominance interaction, 1: dominance × dominance interaction, and α, 2αβ and β2: coefficients of genetic parameters. All genetic parameters are tested using a *t*-test for significance. Then additive variance (VA), dominance variance (VD), and environmental variance (VE) are obtained as follows [19]:

$$\text{VA} = 2\,\text{V} \text{F} \text{2} - \text{VBC1} \text{-} \text{VBC2} \tag{2}$$

$$\text{VID} = 4\left(\text{VBC1} + \text{VBC2} - \text{VF2} \cdot \text{VE}\right) \tag{3}$$

$$VE = 0.25(\text{VP1} + \text{VP2} + 2\text{VF1})\tag{4}$$

Broad sense ( <sup>2</sup> h*bs* ) and narrow sense ( <sup>2</sup> h*ns* ) heritability are estimated using the following equations:

$$\mathbf{h}\_{ho}^{2} = \left(\mathbf{VA} + \mathbf{VD}\right) / \left(\mathbf{VA} + \mathbf{VD} + \mathbf{VE}\right);\\\mathbf{h}\_{w}^{2} = \left(\mathbf{VA}\right) / \left(\mathbf{VA} + \mathbf{VD} + \mathbf{VE}\right)\tag{5}$$

The North Carolina (NC) mating designs permit determination and/or estimation of variance components (additive and dominance components) by using the information from half-sib families. The experimental material of North Carolina designs I, II, and III is developed from F2 generation as a base material. The design III (NCIII) involves backcrossing the F2 plants to the two parental inbred lines from which the F2 were derived. The NCIII design was extended to include a third tester. This third tester is the F1 from the two parental inbred lines: in this extended form, this design is known as the triple test cross [21]. Line x Tester mating design uses inbred lines as the base population. The design is useful in deciding the relative ability of a number of female and male inbreds to produce desirable hybrid combinations [22]. When the same parents are used as females and males in breeding, the mating design is called diallel. Parents used the range from inbred lines to broad genetic base varieties to clones. The design is the most commonly used in crop plants to estimate general combining ability (GCA) and specific combining ability (SCA) and variances. Analysis of the diallel for GCA and SCA are based on the Model I, which is proposed

by Griffing [23]. The GCA/SCA ratio reveals that different characteristics show an additive or nonadditive gene action. AGCA/SCA ratio with a value greater than one indicates additive gene action, whereas a GCA/SCA ratio with a value lower than one indicates dominant gene action. Furthermore, high additive gene action indicates higher heritability and fewer environmental influences [24].

### **3. Water deficit as the most serious abiotic stress**

Among all other abiotic stresses (such as floods, salinity, temperature extremes, heavy metals), water deficit or drought is a significant restricting factor for global agricultural production. Additionally, drought stress is a primary limitation effecting crop yield due to complexity of fresh water limiting and climate change [25, 26]. Water stress occurs when turgor and water potential are reduced to the point where they disorder normal metabolic functions and reproductive capacity of plants [27]. Drought severity depends on several variables, for example, precipitation rate and distribution, evaporative demands and water-maintaining ability of soils [28]. Drought is predicted to become severe owing to global warming, low precipitation, and high evaporation particularly in arid and semiarid regions due to climate change [29]. Moreover, depletion of available water resources, growing world population rise, increasing food demand and climate changes cause water availability less predictable in many areas that exacerbate impacts of drought on global agriculture [30]. Therefore, water scarcity has become a great concern and brought more and more investigations on the drought-resistant crops and knowledge of the water-saving mechanisms of plants under water limitation conditions, especially in arid and semiarid environments [31]. Variety of physiological, biochemical, morphological, and molecular traits of the plants are impaired in water-limiting environments [32].

Water deficit significantly reduces development, grain yield, and yield components of maize at vegetative and reproductive growth stages [33]. Since the heritability of grain yield is low and strongly influenced by the environment, direct selection for it in the different generations is unreliable. Taking this matter into consideration, it is essential for breeders to identify traits that have high heritability, high correlation with grain yield, and low-cost measurement. Then, in the breeding programs, indirect selection for grain yield using these traits could be easier than selection based on direct grain yield [34, 35].

### **4. Genetic variation of the water-deficit tolerance-associated traits**

Understanding about the genetic variation for traits relating to water stress tolerance has great importance in developing breeding program strategies. Depending on the stress duration and severity and the stage of plant development and plant species, water stress causes many morphological, physiological, biochemical, and molecular changes in plants [36]. Plants respond to survive under water deficit condition through the induction of both regulatory and functional sets of genes [37]. The selection of drought-tolerant genotypes and associated traits is globally recognized as an effective strategy to maintain the growth and survival of agricultural crops exposed to future drought periods. A better knowledge of the physiobiochemical traits can be used to create new varieties of crops to increase productivity in water scarcity conditions [38]. Due to the complex genetic basis of water deficit tolerance and poor

*Genetic Interaction and Inheritance of Physiobiochemical Traits Can Predict Tolerance of Maize… DOI: http://dx.doi.org/10.5772/intechopen.111599*

heritability of the crop yield trait, individual trait components, is more frequently identified and characterized due to its better heritability in replicated experiments [39]. Crop yield becomes especially vulnerable when water deficit stress occurs during the reproductive phase of plant development. Correlated secondary traits are generally easier to measure and show a higher heritability and thus may represent a more suitable target for improving maize response to water stress [40, 41].

#### **4.1 Physiological traits of water-deficit tolerance**

Chlorophyll fluorescence is a fast and noninvasive tool used for probing the activity of photosynthesis that can be successfully used for discriminating tolerance of plants to drought stress without damaging the plants [42]. One of the most-often applied chlorophyll fluorescence parameters is Fv/Fm that gives the information about the amount of the light absorbed by photosystem II via chlorophyll [43]. A decrease in the Fv/Fm parameter under water-stress conditions indicates the possibility of inhibiting or destroying the photochemical reaction centers due to the reduction of the electron acceptance and transfer capacity from the chlorophyll complex to photosystem II [44]. This parameter is reliable as a stress indicator in crops which has been documented for photochemical processes [45]. Kalaji et al. [46] concluded that in several studies, fluorescence parameters have been considered as selection tools in plant breeding. They also emphasized the importance of measuring traits related to fluorescence that have a high correlation with yield and especially stress resistance. The previous studies with the genetic analysis of wheat [47] and maize [48, 49] indicated low additive gene effect and high broad sense heritability for FV/Fm (quantum efficiency of PS II). Contrary, with genome analysis in soybean, moderate magnitude of broad sense heritability has been documented for FV/Fm [50].

Leaf chlorophyll content as an important physiological parameter plays a major role in evaluating photosynthetic efficiency, crop stresses, and nutritional status for breeding programs [51]. Chlorophyll is an essential pigment for photosynthesis and growth of plants where it converts light energy to chemical energy. In the stress conditions, chlorophyll content of leaves decreases in plants; therefore, it is a useful indicator of plant health [52]. The previous research provided that total chlorophyll content in plants such as wheat, rice, and cotton was controlled by dominance gene effects [53–55]. It is revealed by Said [56] and Shirinpour et al. [57] who reported that generation mean analysis in wheat and maize showed dominance effects for chlorophyll content and chlorophyll index under drought stress, respectively. Whereas in the other research, genetic analysis of chlorophyll index in rapeseed was observed to be under the control of additive gene effects as the main genetic effects for this trait [58]. Meanwhile, Akbari et al. [59] observed the high amount of narrow-sense heritability in the expression of total chlorophyll content and indicated the additive effects that play an important role in the control of this trait. Therefore, selection method could be an effective method to improve the mentioned trait in breeding programs.

The relative water content (RWC) of leaves is a key indicator for the degree of plant cell and tissue wilting and has been suggested as a selection criterion of cultivars for drought stress tolerance [60, 61]. The photosynthetic activity of resistant cultivars to water-deficit stress is higher than sensitive cultivars in high RWC and low-osmotic potential [62]. The reason for this is the ability of most plants to be tolerant to drought stress to reduce water loss through the epidermis of the leaves after closing the stomata or minimizing the open stomata [63]. In addition, the positive and significant correlation of RWC with photosynthesis and grain yield and its high heritability

under water stress has made measuring this trait an important indicator in determining the water status of the plant and identifying cultivars resistant to low stress [64, 65]. The relative water content of leaves is one of the traits that lead to increase the stability of yield under drought stress [66]. Under water-deficit stress, a decrease in RWC occurs due to the lack of cell turgor pressure in the leaf and leads to stomatal closure and reduced photosynthetic rate [67]. In fact, the reduction of RWC is the usual response of plants to stress [68]. In some studies, it has been reported that the high percentage of RWC in plants that are exposed to water stress is associated with stress tolerance in plants, and it is considered as an index to determine the difference between cultivars in terms of water-deficit stress tolerance [69, 70]. Moradi et al. [71] by evaluating six lines of maize under normal and drought stress conditions reported that RWC is controlled by the over-dominance effects of genes under both the conditions. In another research by the generation mean analysis of maize, it has been stated that both gene effects of dominance and epistasis play an important role in the genetic control of RWC under control and water-deficit-stress conditions [72]. By studying the gene effect of RWC in sunflower, the main role of additive gene effects in controlling the heritability of this trait has been expressed under water-deficit stress [73, 74]. Naroui Rad et al. [75] observed the importance of both additive and nonadditive gene effects in controlling the inheritance of this trait.

#### **4.2 Biochemical traits of water-deficit tolerance**

Plants needed to evolve different mechanisms including osmotic adjustment and antioxidant defense systems, which enhance their capacity to adjust and adapt to water-stress conditions. Water-deficit stress leads to the overproduction of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2) and superoxide anion radicals (O2̄) which result in plant growth and productivity inhibition [76]. Various enzymatic antioxidants, such as superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, can be activated to balance between ROS generation and scavenging [77]. Furthermore, accumulation of soluble sugars and proline and changes in protein expression have been reported in maize to increase plant resistance under waterdeficit conditions [78]. High narrow-sense heritability (0.53–0.71) has been observed for protein, proline, and soluble sugar concentrations under severe stress conditions. These results indicated that the selection in the parents' inbred lines or early segregating generations could be useful to improve these characters in the maize [79]. Gorji et al. [80] reported that there is moderate and low value of narrow-sense heritability for antioxidant enzymes activities under drought stress and normal condition, respectively. According to Shirinpour et al. [79], the values of narrow-sense heritability for antioxidant enzymes activities of catalase, peroxidases, and polyphenol oxidase were between low to moderate and expressed the major role of dominance variance in the inheritance of these enzymes. For improvement of the antioxidant enzymes, selection in the later generation and utilization of heterosis will facilitate the breeding program.

In corn, proline accumulation due to drought has been reported in the different growth stages for the maintenance of cell turgor and protection of cell structures for improvement under limited water [81]. Under stress conditions, genotypes with high proline content are mainly considered to be tolerant to a number of abiotic stresses suggesting the use of this trait as an index for indirect selection [82, 83]. According to Rahimi [84], proline content displayed over-dominance gene effects by using Haymen's graphical approach in lines of maize. The narrow-sense heritability was 0.14, and this causes the use of heterozygosis and the production of hybrid varieties

#### *Genetic Interaction and Inheritance of Physiobiochemical Traits Can Predict Tolerance of Maize… DOI: http://dx.doi.org/10.5772/intechopen.111599*

can be used to breeding of this trait. The same result was reported by Naroui Rad et al. [75] in bread wheat and Khalil et al. [83] in sunflower who found that nonadditive gene effects were predominant for the proline concentration. This result disagrees with Pourmohammad et al. [74] who inferred the presence of additive gene effects for this trait in sunflower. They suggested that selection of proline concentration should be made in the early generations.

Sugars are known as carbon suppliers; therefore, they are considered as an energy source not only for plants but also for most other organisms. Sugar plays a decisive role in the negative osmotic potential in the cytoplasm and, as a result, control the osmotic regulation. Also, they act as osmotic protectors of membranes and proteins and detoxify oxygen-free radicals [85, 86]. They also maintain and stabilize cell membranes under stress conditions [87]. The change in the amount of soluble sugars depends on the type of plant species, and the duration and severity of the drought stress [88]. An increase in the amount of soluble sugars in corn plants has been observed with an increase in the duration and intensity of stress during the low-water period [79, 89]. Accumulation of high amount of sugars such as trehalose, mannitol, sorbitol [90], sucrose, hexose, and raffinose helps the stability of dehydrated membranes and tissues and increases plant tolerance against water stress [91, 92]. In the QTL study for the content of seed-soluble sugars in sweet corn, the importance of both additive and dominance main effects in controlling the inheritance of this trait [93] and the effective role of dominance variance in controlling soluble sugars by examining the genetic analysis of chickpea seeds [94] has been reported.

One of the major biochemical changes that occur due to the decrease in soil moisture in agricultural plants is the change in the amount of production of plant proteins in order to degrade or prevent the synthesis of some of them, as well as the production of stress-specific proteins [95, 96]. The synthesis of stress proteins is the response of the plant to water-deficit-stress conditions. These proteins are soluble in water and therefore, by hydrating the plant's cellular structures, they help to withstand the stress. The synthesis of various transcription factors and stress proteins plays a significant role in the tolerance of plants to stress [97, 98]. Water-deficit stress causes oxidation of carbohydrates, proteins, lipids, and even DNA [99, 100]. In general, water stress reduces the number of cell polysomes in tissues that have less water content, depending on different plant species, and ultimately leads to a reduction in the production of proteins. In addition, the reduction of photosynthesis under drought stress causes a reduction or even a stop of protein production [101, 102]. Enzymes are an important group of intracellular proteins whose activity is inhibited under the influence of water-deficit stress. While some enzymes are stable and their activity may even increase under drought stress [103], Shirinpour et al. [79] using generations mean analysis of hybrids maize SC704 revealed that the high narrow sense heritability and the presence of additive variance for protein content under normal irrigation and water-deficit stress conditions. The authors concluded that the additive gene effects have a major role in controlling of this trait. Then, for improving of the protein content in both normal and water stress conditions, selection in the early segregating generations will be effective. Similar results were observed in the study of Akram et al. [104] and reported the genetic control of protein content by additive and partial dominance effects using bread wheat genetic analysis. These researchers also stated the effectiveness of selection in the early generations for this trait. Meanwhile, Abid et al. [100] indicated the nonadditive gene effects and low narrow sense heritability in the genetic control of protein content in cotton under water-deficit stress.
