**Abstract**

Citrus production is affected globally by several environmental stresses. Some citrus-producing regions suffer from severe ecological abiotic stresses, including cold, soil salinity and sodicity, extreme temperature, and drought. These abiotic stresses can alleviate the growth, fruit yield, and quality of citrus. Strategies that attempt to sustain and increase tolerance of citrus against the negative effect of abiotic stresses are the use of antiperspirant compounds, phytohormones, synthetic and natural growth regulators, soil and plant moisture retaining tools and structures, nutrition management, application of organic fertilizers, rootstocks breeding in citriculture, and others. These strategies increase the yield and growth of the plant along with the relative improvement of the fruit quality during the growth and fruiting period, increasing the absorption of water and nutrients, the extensive accumulation of osmolytes and the increase of antioxidant enzymes, changes in the amount of signaling substances, and the expression of genes under stress, increase tolerance to abiotic stresses in citrus fruits. In this review, we tried to provide a summary of the abiotic stress management in citrus by literature.

**Keywords:** citrus, climate change, soil salinity and sodicity, drought, extreme temperature, cold

## **1. Introduction**

Citrus species are momentous commercial fruit crops globally and are grown in more than 140 countries around the world. Citrus consists of more than 162 species belonging to the order Geraniales, family Rutaceae, and subfamily Aurantoideae. Oranges (*Citrus sinensis* (L.) Osb.), grapefruits (*Citrus paradisi* Macf.), lemons (*Citrus limon* Burm. F.), limes (*Citrus latifolia* Tan. and *Citrus aurantifolia Swingle)*, mandarins (*Citrus reticulata* Blanco), and pummelos (*Citrus maxima* (Burm.) Merr.), are the most common types of citrus fruits that are used as fresh fruit, fruit juice, and concentrate [1, 2]. Citrus is one of the fruit culture parts with the highest production on a global scale (**Figure 1**), and China is the world's largest citrus producer with 44,063,061 tons of production per year. Brazil comes second with 19,652,788 tons of yearly production. With 14,013,000 tons of production per year, India is the

**Figure 2.**

*Global citrus production and export quantity in 2021 [3].*

third-largest producer of total citrus. Mexico with 8,756,488 tons, and the United States of America, with 7,230,854 tons of production per year are ranked 4 and 5, respectively [1].

Oranges account for half of the production and represent over 40% of world citrus exports, followed by tangerines/mandarins, lemons/limes, and grapefruit. Global exports are estimated at 11 million tons with oranges representing over 40% and tangerines/mandarins nearly 30%. Exports are propelled by tangerines/mandarins from China, South Africa, and Turkey, and to a lesser extent, higher lemon exports from Mexico, South Africa, and Turkey. South Africa is the largest exporter followed by Turkey and Egypt. U.S. citrus exports are dropping primarily due to lower orange exports. They have not been able to participate in the rising global tangerine or lemon trade due to reduced exportable supplies (**Figure 2**) [3].

Traditional citrus production methods have been successfully used over the years, and global citrus production and export have grown continuously over the past three decades. However, these methods are limited by environmental stresses, and citrus

#### *Abiotic Stresses Management in Citrus DOI: http://dx.doi.org/10.5772/intechopen.108337*

species struggle with many abiotic stresses, including cold, soil salinity and sodicity, extreme temperature, drought, and others [4].

One of the factors that cause extreme temperature, droughts, and cold, caused by severe rains and others, is climate change [5]. Global warming and climate change event have exacerbated the destructive effects of drought stress with various impacts on temperature and rainfall patterns in different areas of the world [6]. In such circumstances, water scarcity and precipitation are considered limiting factors for agriculture and crop productivity in some countries. The minus effects of abiotic stresses generally reduce tree growth, fruit yield, quality, and limit crop productivity. Under normal conditions, citrus trees mostly confront numerous stresses simultaneously, so there is a direct and indirect interplay between approximately all physical abiotic stresses. The morphological, physiological, and biochemical responses of citrus trees exposed to two or more abiotic stress factors can change, depending on stress duration or intensity. Intricate genetic responses to abiotic stresses are polygenic, making them more challenging to detect, control, and manipulate [7].

Soil salinity and drought stress are one of the main factors of yield losses in the world that can reduce the relative water content and leaf water potential. It also prevents cell enlargement more than cell proliferation. As a result, drought and salt stresses reduce plant growth and leaf area, ultimately affecting plants' photosynthesis, respiration, secondary metabolites, and carbohydrate production [4, 8]. As mentioned, climate change causes extreme temperature fluctuations, namely increase or decrease in temperature, and can cause adverse effects on plants in terms of physiology, biochemistry, and gene regulation pathways. Increased temperature causes heat stress in plants, depending on the light intensity, duration, and quality. Also, decreased temperature results in the loss of membrane integrity, leaf damage, electrolyte leakage, impaired photosynthesis, chlorophyll pigments, and protein assembly [9].

As high-temperature stress causes soil dryness and drought stress, soil waterlogging will also be stressful for the plant. Plants grow well by absorbing water through the roots and transpiration through the leaves. If the soil becomes saturated or supersaturated, waterlogging stress occurs. In this case, the leaf pores are closed, chlorophyll is lost, chlorosis is created in the leaves, and as a result, photosynthesis is reduced [10]. Stresses, such as nutrient deficiency and excessiveness, metal toxicity, and ultraviolet irradiance may occur less often, but these stresses decrease the quality and quantity of the products. Reducing the application of organic fertilizers and the imbalanced use of chemical fertilizers are the leading causes of nutritional deficiencies in plants, and we do not explain these stresses here [11]. Therefore, new production programs are essential to obtain crops more tolerant to abiotic stresses. Plant breeding programs, phytohormones, metabolic inhibitors, anti-transpiration and anti-evaporations, and plant nutrition management are critical against abiotic stress. Consequently, in this updated review, we will introduce types of abiotic stresses in citrus fruits and manage the stress tolerance of citrus by providing solutions to deal with these stresses. Hoping to provide readers with good ideas on increasing citrus fruit tolerance under abiotic stress conditions.
