**Abstract**

Rice, world's second major, staple cereal crop that feed the more than 50% of world's population. To safeguard the production and to fulfill the demand of ever the increasing population and urbanization there is need to increase the rice production. Though the rice yield has increased due to the development of modern technology and climate resilient high yielding cultivars but still it is 10–15 per cent lower than its potential yield due to various biotic and abiotic stress. Drought, extreme temperature, salinity, harmful radiation, heavy metals, gaseous pollutants are the most detrimental abiotic stresses factors that cause the morphological, physiological and biochemical changes in the rice crops and ultimate result is the reduction of rice production globally. Tolerance against these stresses through exploitation of potent biotechnological tools, molecular markers, QTL mapping omices approaches, phytohormones which could offer a more adequate and rapid solution to overcome these abiotic stresses and to enhance the ultimate grain yield of rice.

**Keywords:** Abiotic stress, QTL mapping, phytohormones, omices

## **1. Introduction**

Rice (*Oryza sativa* L.) is the world's second-most-important cereal crop. Nearly half of the world's population utilizes it as a staple food. It belongs to the genus *Oryza* and family Poaceae, has 22 known species and has great economic importance [1]. These are adapted to variety of climatic conditions and can be grown both in dry and wetland habitats at high and low elevations. Green revolution substantially boosted rice productivity across Asia through a combination of modern new high yielding varieties and enhanced inputs like irrigation, fertilizer, and biocides [2]. Climate change is the only aspect that took away the breeder's concern from productivity despite plateauing yield in most of the cereals over the past decade. To feed the burgeoning population of the world, especially in Asia where the population is predicted to climb from 4.3 to 5.2 billion by 2050, rice production needs to expand and the quality of the grains must to be improved [3, 4]. Global warming and climate change has been predicted to decline irrigated rice yields by around 4% by 2020 and ~ 7% by 2050, while rainfed rice yields are expected to decrease by 6% and marginally (2.5%) by 2050, respectively [5]. Abiotic stress like drought,

salinity, and heat is the dominant drivers restricting agricultural growth and output of crops around the planet. Rice plants are sensitive to various abiotic stresses. Drought stress disrupts not just morphological features in rice plants, but also physiological and biochemical processes. it has been linked to a significant drop in crop yields due to detrimental effects on plant growth, physiology, and reproduction. Research studies tend to show that abiotic stress in combination of abiotic stress factors is the most harmful [6]. In rice, drought stress is the major limiting factor for rice production in both rainfed lowland (46 Mha) and upland (10 Mha) rice ecosystems across Asia [7, 8]. Soil salinity is rising expotentially with increasing sea levels in coastal areas and in irrigated lands where soluble salts washed away underwater are brought to ground level. Almost 40 Mha of rainfed lowland under rice cultivation in South and South-East Asia including India, Bangladesh, Myanmar, and Thailand, have been ravaged by unforeseen flash floods [9, 10]. Salinity stress affects the growth and development of rice plants at three different stages; germination, vegetative, and reproductive [11]. A major problem for stable rice production is high temperature in a number of tropical and sub-tropical countries, such as India, Bangladesh, China, Pakistan, Thailand, Sudan and many African countries. For the production of rice, atmospheric temperature at anthesis is crucial. Even 38°C, which is as such not high in tropical and subtropical countries, might cause substantial yield reduction due to pollen sterility [12]. The rice has emerged as a model genomic crop in the 21st century with its smaller genome size, high-quality genomic reference sequence, large genetic and genomic resources compared to every other crop. In the last 25 years a wide range of abiotic stress tolerance loci (QTLs) have been identified in rice [13]. The development of genome-wide DNA markers, i.e., simple sequence repeats, single nucleotide polymorphisms, and the identification of QTLs and marker trait associations, have prompted to new technologies in génomic and genetic engineering tolerant to various abiotic stress. Advancements in molecular biology techniques have enabled the discovery of many genes involved in abiotic stress tolerance through spatio-temporal gene expression analysis. Transgenic approaches have further validated functionally the identified candidate genes from the genetic expression analysis. Omics approaches such as genomics, proteomics, metabolomics, transcriptomics, epigenomics have emerged as powerful biotechnological tools, used for deciphering the abiotic stress responses as well as for producing climate-resilient abiotic stress-tolerant plants [14].

At present efforts are being made to identify several stress factors in the abiotic stress tolerance and to develop rice varieties with a tolerable stress through biotechnology, molecular breeding, genomics, transcriptomics, proteomics and metabolomics [15–18]. Abiotic stresses such as drought, salinity, and heat affect the productivity of many agriculturally important crops. Therefore, to meet the food requirements of a growing world population, it is necessary to develop sustainable high-yielding varieties that can persist under abiotic stress [19]. This chapter highlights abiotic stresses such as drought, high temperatures, salinity as well as abiotic stress tolerance techniques in rice plants with emphasis on increased rice yields.

#### **2. Major abiotic stresses affecting rice crop**

Rice is the world's most significant food crop, providing calories to more than half of the world's population of 7 billion people. In most cultivable rice habitats, it has become increasingly vulnerable to losses induced by abiotic factors such as drought, floods, salt, heat, and cold. Drought or water shortages are the most damaging abiotic challenges for rice farming in rainfed habitats. Another important limitation affecting the rainfed lowlands is the submergence of rice

*Abiotic Stress Tolerance in Rice: Insight in Climate Change Scenario DOI: http://dx.doi.org/10.5772/intechopen.98909*

plants for one to two weeks owing to flash floods. Long-duration cultivars are frequently affected by floods in the early phases of development, followed by drought during blooming, resulting in significant yield deficits [20]. Meanwhile, salinity, which is determined by a heavy concentration of soluble salts in the soil, is the second most common soil issue after drought, and it is a major constraint for rice production across the world. As a result of global climate change, heat stress is becoming a severe hazard to rice production. Heat stress hinders plant development, disrupts metabolic processes, and reduces output. Rice growing in temperate locations, as well as high-altitude conditions in tropical and subtropical zones, is hampered by low temperatures. Cold stress has a negative impact on rice crops throughout the germination, vegetative development, and reproductive phases, resulting in considerable production losses. Rice crops are sometimes subjected to numerous stressors (such as salt and drought, or drought followed by submergence), resulting in massive crop losses. Rice productivity would be significantly increased while water resources and soil quality were preserved if combined tolerance to several forms of abiotic stress was improved [21].

### **2.1 Drought stress**

Drought is a severe abiotic stress that disrupts rice Morphological, Physiological, biochemical and molecular responces (**Figure 1**), resulting in considerable crop losses [22]. Drought stress has been linked to changes in plant length, biomass, and leaf area are associated with leaf senescence in a variety of crops, [23, 24] including rice (*O. sativa*) [25]. The occurrence of both drought and heat stresses in combination are more destructive (~70%) to crop production than other stresses occurring individually [26]. Drought stress causes oxidative stress by producing a buildup of reactive oxygen species in the chloroplast and mitochondria. Drought stress enhances the competitive ability of some weeds on crop plants by allowing them to use more water than crops [27]. The synergistic and antagonistic interactions between drought stress and pathogenic infection were similarly observed [28]. According to Wang et al. [29] drought before and after heading, has detrimental effects on brown and milled rice rates by influencing its quality to a great extent. It is the primary constraint to rice production in both rainfed lowland (46 Mha) and upland (10 Mha) rice ecosystems throughout Asia [7, 8]. Drought stress can alter tillering, floret initiation, and subsequent spikelet sterility, as well as grain filling, throughout vegetative growth, blooming, and the terminal period of rice cultivation [30]. Terminal drought is the most detrimental abiotic stress factor to rice grain yield [31]. Several studies on the effects of drought stress and dehydration revealed physiological acclimation of plants by altered antioxidant responses [32, 33]. Understanding the mechanisms that cause physiological responses to drought stress and dehydration conditions is critical. Drought tends to reduce the rate of cell division and expansion, leaf size, stem elongation, and root proliferation in rice crops, as well as interrupts stomatal opening and shutting periods, and plant nutrient and water absorption and utilization performance [34]. Deficiency of water and moisture in rice crops increases the rate of abscisic acid (ABA) biosynthesis which diminishes stomatal efficiency and conductance which reduces transpirational losses [35]. The complex nature of drought stress in rice and its strong interaction with the environment has slowed the breeding programs to develop drought adapted varieties.

#### **2.2 Salt stress**

By the end of 2050, the world's population will have risen to about nine billion people. On the other hand, due to the accumulation of high salt content in the soil,





#### **Figure 1.**

*Drought stress induces various morphological, physiological, biochemical, and molecular responses in rice.*

worldwide agricultural production would almost probably remain static, resulting in crop growth inhibition and eventual crop mortality. Salt stress is a worrisome phenomenon because it diminishes soil agricultural productivity, leading to lower crop yields [36]. Salinity is becoming a critical threat because of diminishing irrigation water quality. (Flowers [37]. Salinity and water logging afflict 23% and 37% of worldwide cultivated land, respectively, and it is estimated that about 20% of all cultivated land and nearly half of irrigated land is salt-affected, greatly reducing yield well below the genetic potential [38]. The problem of salinity is particularly intense to agriculture in South and Southeast Asia, which produces about 90% of the world's rice [39]. By the middle of the twenty-first century, it is estimated that half of the cultivable land would be salt-affected [40]. It is suspected that the rise in soil salinity is due to poor irrigation water, its quality, and the use of brackish. Rice is a salinity-sensitive crop that performs poorly in soils with electrical conductivity (EC) as low as 3 dSm-1, however salty soil is commonly defined as EC >4 dSm-1 [41]. High-salt stress affects plants in several ways, such as ion toxicity, oxidative stress, alteration of metabolic processes, nutritional disorders,

*Abiotic Stress Tolerance in Rice: Insight in Climate Change Scenario DOI: http://dx.doi.org/10.5772/intechopen.98909*

genotoxicity, membrane disorganization, reduction of cell division and expansion as well as water stress. In order to cope with the antagonistic effects of soil salinity some new strategies like remediation of salinized soils, to increase the salt tolerance of crop plants through traditional as well as molecular marker-assisted breeding techniques, and biotechnology should be adopted [37, 42, 43]. Khatun and Flowers [44] observed that salt toxicity adversely affect panicle length, spikelets per panicle, and 1000-grain weight in rice crop. Salinity also delays flowering and ripening and reduces the number of tillers, biomass, and leaf area in rice crops. According to Asch and Wopereis [45], irrespective of seasons and growth stages, salt toxicity reduces rice yield, the number of panicles, and grains and causes sterility in all rice cultivars.

#### **2.3 Temperature stress**

Heat stress, characterized by prevalence of high temperature is one of the major abiotic constraints for rice production, next only to drought and salinity [46]. Vastly increased greenhouse gases in the air are predicted to significantly affect the climate and worldwide average air temperature guesstimated to significantly raise by 1.4–5.8°C between 1990 and 2100 [47, 48]. Increasing temperature with this magnitude and severity reduced global rice production [49]. The reduction in rice yield is mainly attributable to changes in critical temperature at each specific phase of growth, namely, germination, seedling, rooting, leaf elongation, tillering, panicle initiation, primordia, panicle differentiation, anthesis and maturing [50]. One of the most sensitive phenological phases to extreme temperatures is pollination that leads to poor seed set and low grain quality [51, 52]. Rice is particularly vulnerable to heat stress during the reproductive and ripening stages, as simply a few hours of heat stress causes flowering plants to become sterile. High temperatures during ripening, on the other hand, might result in a decrease in milling quality and grain filling, resulting in reduced crop yield [53].

Increase in temperature, that leads to higher humidity, can cause spikelet sterility. Consequently, amid heat stress, the floral buds are unable to mobilize carbohydrates [53]. Low temperature stress is another similar environmental stress that can cause the plant's development and growth to be slowed. Embrane structure and function, protein synthesis, and cellular cytoskeleton structure can all be severely affected by low temperature stress. Low temperatures also impede photosynthesis in both light and dark reactions; further, electron routes are disrupted, resulting in the formation of free radical species that can be harmful to rice crops, causing membrane deterioration. Japonica genotypes are more adaptable than indicas to cold temperatures and so are prevailing in high-altitude and latitude ecologies [54]. The respiratory rate of plants increase or decrease in accordance with the temperature, short-term low temperature stress leads to high respiration rate but in the case of long-term stress the cell gets damaged and eventually dies due to the reduced respiration rate.

#### **3. Plant responses to abiotic stress**

The signals of abiotic stress are a multi-faceted phenomenon due to a wide range of environmental abuses. Plants can produce appropriate responses that cause a particular change in conjunction with a specific stress condition, whereas there is significant overlap between abiotic signals. Typically, one sort of stress happens with or is followed by other stresses. The loss of water which is due to heat stress causes drought stress and in this way, both stresses are linked to each other. Signal

perception is the first phase in a signal transduction pathway which is tracked by the production of secondary signals. Secondary signals can trigger a protein phosphorylation cascade, which can then control the activation of specific transcription factors (TFs) or target genes. Additionally, these signals can modify the quantity of secondary signals; as a result, more signaling molecules are produced, providing an extra checkpoint for signals to flow in a given direction. Till date, many signaling pathways have been reported [55].

#### **3.1 ROS signaling**

Oxygen is a two-edged sword for plants, since it is a necessary element to be able to develop normal growth, but unavoidably promotes the formation of of ROS like hydrogen peroxide (H2O2), superoxide radical, hydroxyl radical, singlet oxygen, etc. as a result of aerobic metabolic activities, such as photosynthesis and respiration. During stress circumstances in a plant, organelles such as mitochondria, peroxisomes, and chloroplast generate enormous amounts of ROS, which become highly corrosive and reactionary to nucleic acids, proteins, and lipids, inevitably leading to apoptosis or cellular damage [56].

Catalase (CAT),monodehydroascorbate reductase (MDHAR), superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), peroxiredoxin, and glutathione S transferase are all ROS foraging enzymes in plants (GST) [57]. These antioxidants work in the plant cells where they are present in different locations in order to detoxify ROS. The ROS homeostasis in plants must also be accompanied by non-enzymatic antioxidants, including tocophherols, Carotenoids, GSH, flavonoids and AsA [56]. Many other mechanisms, such as photosynthetic apparatus rearrangement, leaf movement, and leaf curling, can balance a plant's energy absorption with CO2 supply, preventing ROS overproduction [57].

#### **3.2 Phytohormone signaling**

Phytohormones, a diverse set of signaling chemicals found in minute amounts inside cells, influence the responses. Plant growth, development, and nutrient allocation are all regulated by them. Responses to abiotic stress are triggered by a variety of stimuli, but phytohormones are responsible for the majority of them. Plants, which are sessile organisms, require phytohormones for survival [58]. They can carry out their function in their synthesis site or they can go to their action location [59]. Their family consist of cytokinin (CK), Indole acetic acid (IAA), salicylic acid (SA), ethylene, ABA, gibberellins (GAs), jasmonates, and brassinosteroids. The relatively newly discovered phytohormones are strigolactones. In regulating stress responses through interactions with some other hormones, ABA plays a major role. In order to regulate climate stress, it is the most exciting and indispensable hormone of the plant. In various phases of plant development, it plays a major role especially in opening and closing stomata, drought stress, seed germination and dormancy. PYR/PYL/RCAR-PP2C-SnRK2 is regarded as an ABA-generated signaling cascade, which effectively monitors seed dormancy even in occurrence of drought. ABA buildup amid drought stress restricts stomatal disclosure and modulates transpiration [60]. ABA signaling cascade consisted of 3 units, SnRK2/OST1 (Protein kinase), PP2C (protein phosphatases) and PYR/PYL/RCAR proteins have been investigated recently and their mechanism of operation was elucidated [61].

Ethylene is another major component of phytohormone. Ethylene is supposed to be the signaling path between plant growth and weather changes. Salinity, water logging, high temperature, frost, heavy metal interaction, nutritional inadequacy,

and drought are examples of abiotic stressors that influence ethylene production [62]. Ethylene response factors (ERFs) in plants are members of a large family of transcription factors (TFs) that are activated in response to a variety of physiological and environmental stress.
