**2.6 Phenology**

Among the other abiotic stresses, salinity has a significant impact on the phenological attributes of the plant family Brassicaceae. Salt stress alters the duration of several physiological stages of plants, from seedling emergence, leaf unfolding, the appearance of first flowering, siliqua formation, grain filling to leaf color changing, and leaf senescence in the end. According to Mohamed et al. [43], 100 mM NaCl showed a significant effect on the duration of the flowering stage of two *B. napus* cultivars (Yangyoushuang2 and Xiangyouza553). Salinity delayed the first appearance date of flowering from 139 d to 143 d and from 141 d to 147 d in Yangyoushuang2 and Xiangyouza553 cultivars, respectively. Moreover, salinity increased the days to 50% flowering in both of the cultivars from 142 d to 146 d and from 144 d to 150 d. Another study by Pandey et al. [76] stated that under 50 mM salt stress, the cotyledonary leaf emergence rate of *B. juncea* was reduced by 30% to the control plants. According to several findings, extreme saline circumstances may bring delayed seed germination [77] because of decreased hydrolytic enzyme activity and seed metabolite mobilization [78]. *B. campestris* seed germination was delayed beyond 24 h under 120 mM salt stress level, as reported by Siddikee et al. [79].

Leaf senescence is another age-dependent phenological characteristic of plants that is related with a wide range of biochemical and molecular changes inside plant organs. Due to the decreased biosynthesis and enhanced breakdown of Chl molecules under salt stress, premature or early leaf senescence occurs in the plant life cycle. Alamri et al. [62] stated that the seedlings of *B. juncea* grown under 120 mM NaCl concentration experienced early leaf senescence.

### **2.7 Reproductive development**

Several additional reproductive stage characteristics, such as flower initiation, anther, and pollen grain development, fertilization, siliqua formation and development, and seed filling, are considerably influenced by the salinity in Brassicaceae plants. During the reproductive stage, *B. napus* seed production potential is indicated by pre-and post-flowering activities. It has been suggested that the reproductive stage is the most sensitive to stress [80]. Flowering and seed filling are the most vulnerable stages of the oilseed Brassicaceae family to extreme salinity stress than the earlier vegetative phases, such as seed germination and seedling growth. Salinity reduces plant fertility by affecting the development of male and female reproductive organs, which are very susceptible to stress [81]. The reproductive stage is intrinsically linked to seed production because fertilization and seed development occur during this stage. Therefore, tolerance to salt stress during this stage is crucial [82].

Arif et al. [83] experimented with BARI Sarisha-8 and BINA sharisha 5 cultivars of *B. napus* under 100 mM NaCl and observed that flowering and siliquae formation were significantly affected by salinity. Discoloration and rolling of the leaves and flowers, inhibition of new buds opening, and the death of young siliquae altogether, leaving the adult siliquae with wrinkled and immature growth. As a result, early maturity symptoms of the seed occurred. However, among two of those cultivars, BARI Sarisha-8 showed more sensitivity at the adult siliquae development stage, whereas the young leaves and siliquae were more vulnerable in BINA sharisha 5. Another experiment by Gyawali et al. [34] with 131 *B. napus* accession lines showed varied responses under different salinity levels (1.4, 5, 10, 15, 20, and 28 dS m−1 of NaCl). The number of branches and siliquae were affected more in two of the genotypes (Kuju 29 and Kuju 32). Similarly, in DH12075, there was a failure in fertile branches and siliquae production found under salt stress of more than 10 dS m−1. The number of fertile branches is also affected under salinity. A study from Chakraborty et al. [3] reported that with increasing salinity levels (1.65, 4.50, and 6.76 dS m−1 of NaCl), the number of siliquae on primary branches of seven cultivars, for example, CS 52, CS 54, Varuna, Pusa Jagannath, Pusa Agrani and T 9, Sagam of *B. juncea,* and *B. campestris*, were reduced. The reduction was almost 50% under 1.65 dS m−1, whereas, under 6.76 dS m−1, it was one-third of the control plants. Not only the reduction in fertile branch numbers and siliquae but salinity also caused wilting of the reproductive parts (mature flowers and fruits) of *B. napus* [84].

#### **2.8 Oxidative stress**

Salt stress leads to ionic toxicity due to higher accumulation of Na<sup>+</sup> and Cl<sup>−</sup> ions and depleted potassium ion pool in plants. Disruption in ion homeostasis leads to stomatal closure by hampering the functioning of guard cells, which in turn decreased carbon fixation due to insufficient CO2 supply in the leaves, and accelerates the generation of the ROS such as H2O2, <sup>1</sup> O2, O2 •−, HO2 • , RO• , and • OH [7]. Another effect of salinity is to create drought-like conditions in plants due to lower water potentiality and is also responsible for the increase of ROS generation by disrupting photosynthetic activities [56]. Though ROS is beneficial for activating the stress signaling molecules at a certain level, after that it becomes phytotoxic and disrupts metabolic activities and also accountable for the breakdown of different cellular components, namely proteins, lipids, carbohydrates, and nucleic acids [85]. Thus, accelerated activities of ROS boosted protein denaturation, lipid peroxidation, and oxidation of carbohydrates and ultimately created oxidative stress in plants [7; **Figure 1**].

Salt induced oxidative stress due to higher accumulation of ROS observed in *Brassica* sp. However, the extent of salt-induced damage depends on the species, plant growth stage, ion strength, organ specificity, and the components of the salinizing solution [86; **Table 4**]. Sarwat et al. [95] observed that upon exposure to 100 and 200 mM NaCl, *B. juncea* plants resulted in upgraded levels of H2O2 content by 1.99 and 3.35-fold, respectively, with a maximum increase of malondialdehyde (MDA) content by 2.19-fold at 200 mM NaCl-treated plants. Salt-sensitive cultivar of *B. carinata* (cv. Adet) showed a higher accumulation of thiobarbituric acid reactive substances (TBARS) compared with the salt-tolerant one (cv. Merawi) in 150 mM NaCltreated mustard plants [41]. So, it can be stated that degree of salt-induced oxidative damages depends on the cultivar type, dose, and duration of stressed period. Sami et al. [14] found elevated production of H2O2 (by 46%) and O2 •− (by 47%) in 100 mM

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

#### **Figure 1.**

*Schematic representation of ROS-induced oxidative stress in plants and its consequences under salinity.*



#### **Table 4.**

*Salt-induced oxidative damages in oilseed Brassica sp.*

NaCl-treated *B. juncea* plants together with an augmented level of lipid peroxidation by 55% at a similar level of salinity.

#### **2.9 Yield and quality**

Plants exposed to salt stress undergo morphological, physiological, and biochemical changes. It leads to a deleterious influence on reproductive characteristics and ultimate yield reduction in plants [7]. As water is the key element for flowering and siliquae formation in oilseed *Brassica* plants, the accelerated water loss from plant cells induced by salt stress has a significant influence on the reproductive stages. Salinity shows a negative impact on the growth attributes, such as SL, RL, stem diameter, FW, DW, LN, leaf size, LA, and branch number, of oilseed *Brassica* plants. Similarly, it also affects the yield contributing attributes, such as the number of flowers, number of siliquae, seed yield, 1000-seed weight, and oil content of mustard. Moreover, salinity enforces osmotic stress on plants that adversely affect the water conductance status by altering the whole nutritional status of plants [4]. Thus, it causes growth retardation, ionic and nutritional imbalance, disrupted water relations, and photosynthetic inhibition, which subsequently affects the yield attributes in oilseed Brassicaceae family. While experimenting with seven cultivars (CS 52, CS 54, Varuna, Pusa Jagannath, Pusa Agrani, and T 9, Sagam) from *B. juncea* and *B. campestris*, Chakraborty et al. [3] found a significant reduction in seed yield (SY) and oil content in all the seven cultivars. They also reported a great extent of interspecific variation in response to salinity stress in oilseed *Brassica* plants [3, 83].

Likewise, in different studies, a wide range of oilseed *Brassica* cultivars were used to investigate their varied responses in yield attributes under salinity stress (**Table 5**). Reduction in oil content and oil quality is also a common response to salt stress in oilseed *Brassica* plants. Because of the smaller seed size and reduced cellular metabolic activities, total oil content, as well as lipid, protein, and fatty acid content in the oil, is also hampered (**Table 5**). For a balanced osmotic pressure in plant cells, soluble sugar and soluble protein contents play a very significant role. Upon exposure to 100 mM NaCl concentration, two *B. napus* cultivars, Yangyoushuang2 and Xiangyouza553, showed reduced crude oil percentage by 22% and 30%, respectively. Whereas the crude protein percentage was increased by 44% and 24% for both cultivars under the saline condition. Also, seed moisture content, saturated (palmitic and arachidic acids) and unsaturated fatty


#### **Table 5.**

*Changes in yield and quality traits of oilseed Brassica sp. upon salinity stress.*

acid concentrations, glucosinolate in both cultivars were greatly influenced under salt stress. But the oleic acid concentration in Xiangyouza553 cultivar remained unchanged under stress [43]. Six ecotypes of *B. napus* were tested under 50, 100, and 150 mM NaCl stress, which showed a similar response in yield attributing characters. The ecotypes were Super, Sandal, Faisal, CON-111, AC Excel, and Punjab, among which the number of pods per plant was reduced significantly under 150 mM NaCl in Punjab cultivar. Also, a similar trend in reduction was observed for 1000-seed weight in the same cultivar with increasing salt concentration, while the other varieties showed little to no response regarding those attributes [98].
