**1. Introduction**

Soil salinity can commonly be caused by the excess amount of carbonate, bicarbonate, sulfate, and chloride salt of magnesium, calcium, potassium, and sodium. Having a high quantity of adsorbed sodium ions (Na+ ) in sodic soil, the soil structure is degraded, for which aeration and water movement are limited [1]. According to the report of FAO [1], more than 424 million hectares of topsoil (0–30 cm) and 833 million hectares of subsoil (30–100 cm) are affected by salinity. Among the salt-affected soil topsoils, 85% are saline, 10% are sodic, and 5% are saline-sodic. On the other hand, 62% are saline among subsoils, 24% are sodic, and 14% are saline-sodic. The data (data on 118 countries covering 73% of the global land area) also represent more than 4.4% of topsoil, and more than 8.7% of the subsoil of the total land area is salt-affected [1]. Saline, sodic, and salinesodic soils and any other subcategories of salt-affected soils contain too much soluble salts capable of causing an anomaly in various physiological processes in most cultivated

plants [2, 3]. Soil salinity primarily provokes osmotic stress by lowering the soil water potentiality, thus reducing water uptake in plants. Whereas another effect of salinization is the imposition of ion toxicity, particularly due to excessive deposition of Na+ and chloride ions (Cl− ) in the upper part of the plants, and also interferes with the accumulation of essential nutrients [4]. Interference of salt stress in plants is liable for the disruption of metabolic activities such as permeability, biosynthesis of photosynthetic pigments and induces photosystem (PS) inefficiency of plants [5]. Forthcoming salt stress inhibits cell division, hampers cell expansion, alters stomatal closing and opening, reduces turgor pressure, and causes an imbalance in ionic homeostasis [6].

Oxidative stress due to the overgeneration of oxygen radicals and their derivatives, which are called reactive oxygen species (ROS), is the secondary effect of salinity. These ROS could be hydrogen peroxide (H2O2), ozone (O3), singlet oxygen (1 O2), superoxide radicals (O2 •−), organic hydroperoxide (ROOH), hydroxyl radicals (• OH), perhydroxy radical (HO2 • ), and peroxyl (RO2 • ), etc. [7]. The generation of ROS is a general phenomenon of plants in a normal condition to regulate different biological processes such as growth, cell cycle, hormonal regulation, defensive responses against biotic and abiotic stresses, program cell death, and development [6]. But under stressful conditions, excessive generation of ROS leads to oxidative burst and causes damage to cellular components such as carbohydrates, lipids, proteins, and nucleic acids [8]. To combat the adverse effect of this ROS-induced oxidative stress, plants are intrinsically organized with antioxidant defense mechanisms where both non-enzymatic and enzymatic antioxidants work in a coordinated manner to detoxify the overaccumulated ROS. The non-enzymatic antioxidants include flavonoids, carotenoids, vitamins, ascorbate (AsA), and glutathione (GSH), and enzymatic antioxidants are ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione *S*-transferase (GST), etc., actively perform their role in quenching the ROS to protect the plants from the oxidative stress [7].

*Brassica* is placed third among different oilseed species after soybean and palm due to its considerable economic and nutritional value [9]. The genus *Brassica* belongs to Brassicaceae family, which has nearly 435 genera and 3675 species [10]. Having food value and economic importance, plants of *Brassica* genus are well known as edible oil, vegetables, and silage. Rapeseed (*Brassica campestris* L. and *Brassica napus* L.) and mustard (*Brassica juncea* L. [Czern. & Coss.] and *Brassica carinata* A.Br.) are the most cultivated oil-yielding plants of the genus *Brassica*. Europe, as well as North America, cultivates mostly *B. napus* and *B. rapa*. The species *B. carinata* is mostly cultivated in North Africa. *B. juncea* is popular in South Asian countries. *Brassica nigra* (L.) Koch and *B. tournefortii* Gouan are limited to very small area [11, 12]. It is clear that the oilseed *Brassica* plants are cultivated in different continents throughout the world including Europe, America, Asia, and Africa [12]. Studies also prove that salinity is a major problem in different countries of the world, and this salinity is creating difficulties in the proper growth and development of oilseed *Brassica* plants. This plant is more sensitive to salinity in germination, seedling, and reproductive stage. Salinity interrupts osmoregulation, hinders water uptake, reduces water content, causes ionic toxicity, reduces chlorophyll (Chl) content, alters stomatal conductance/movement, decreases enzymatic activity, alters transpiration and photosynthesis, disrupts the antioxidant defense system, and results in the oxidative burst [13–15]. Considering the detrimental effect of salt stress, it is crucial to understand the mechanism of saltinduced damage and tolerance in *Brassica* plants. Inter- and intraspecific differences

### *Oilseed* Brassica *Responses and Tolerance to Salt Stress DOI: http://dx.doi.org/10.5772/intechopen.109149*

evidently exist between and among species of Brassicaceae family plants for various stress tolerances including salinity. Their response to salinity and exogenous elicitors under salt stress differs [12, 16]. Understanding all of these is important for enhancing salt tolerance or developing salt-tolerant oilseed *Brassica* plant cultivars. Osmoregulation, hormonal regulation, antioxidant defense, and signaling function are some of the basic strategies that need to be understood for developing salt-tolerant cultivars. Various approaches such as agronomic practices, screening of salt tolerance traits among different *Brassica* plants, traditional breeding, biotechnological approaches, and microbe assistance are some of the approaches practiced for improving salt tolerance capacity of oilseed *Brassica* plants [17–19]. This review presents the previous findings and recent progress in some approaches for the development of salt tolerance in oilseed *Brassica* plants.
