4.2.4 Molecular breeding to improve salt tolerance

combination of gypsum + farmyard manure (FYM) + H2SO4, CaSO42H2O + FYM + chiseling, pyrite, and humic acid (HA), in rice, wheat, sorghum crop improved soil properties, plant biomass, and yield [118, 121]. Application of N, P, K, S, Zn, B, and Mn separately or with different combination increased rice total above ground biomass and grain production under salt-affected soils [122, 123]. Humic acid improves nutrients availability by chelating with unavailable nutrients (P, K, Ca, Fe, Zn, and Cu) and buffered pH value, and enhanced soil microbial, enzymatic and physiological activities, and plant growth under salinity [121, 124]. The combined effect of humic acid (HA) with gypsum (24 and 48 kg/ha) in rice was higher than the alone effect of HA on ECe and SAR due to its chelating effect with other nutrients subjected to salinity [125]. The use by-product of sugarcane (press-mud), green manure, poultry manure, and Sesbania as a cover crop for amendment of soil to reduce the effect of salinity which is a source of macro and micronutrients especially Zn and S in crops are also good options [126]. There are some other useful agronomic practices to reduce the effect of salt stress on the plant are periodic use of fresh water, subsoiling, deep tillage, sanding, and application of organic and inor-

The hormonal imbalance is one of the salinity effects on plants. There are many plant growth regulators being used as hormones regulator or plant growth regulators such as aminoethoxyvinylglycine (AVG), ethephon, and 1-methylcyclopropene (1-MCP) for ethylene inhibitor under salt stress and enhance the boles and spikelets development in rice and cotton respectively [4]. Similarly, exogenous applications of abscisic acid (ABA), brassinosteroids (BRs) or their analogs (D-31, D-100, etc.)

To meet the demand for food and livelihood of the increasing population on the globe, the increase in the agriculture production is indispensable. Therefore, many efforts have been made to improve salinity tolerance capacity of the crops through conventional plant breeding and biotechnology [129]. Salinity tolerance is a complex trait both at the genetic and physiological level and controlled by polygenes. It has been speculated that salinity tolerance seems to be regulated by independent genes at different growth stages [130]. Traditional breeding has been considered as a more promising and efficient approach to improve the salt tolerance. Conventional breeding involves identification of QTLs using closely linked markers along with their phenotypic evaluation. One of the best-studied QTL for salt tolerance; saltol was identified by the conventional breeding approach in rice [131]. This QTL

of new QTLs and later pyramiding of these QTLs would lead to the development of the more promising salt tolerant line. Marker-assisted backcrossing (MAB), which is one of the best traditional breeding approaches that involve the transfer of the specific allele at target locus from donor to recipient parent, can be used for this purpose. Traditional breeding mainly relied on the use of diverse germplasm resources to identify the landraces showing salt tolerance and then map the locus responsible for salt tolerance. This can be seen as an advantage as well as a disadvantage. Salt tolerance is an outcome of involvement of diverse cellular processes like ion transport and homeostasis, osmoregulation, and oxidative stress protection. Identification and characterization of key genes for salt tolerance would need the

/K<sup>+</sup> ratio at the seedling stage. So, the identification

are good option to improve plant performance under salinity [127, 128].

ganic fertilizers, and adopting crop rotation [118].

4.2.2 Application of hormones regulators

Climate Change and Agriculture

4.2.3 Traditional breeding for salt tolerance

was found to control shoot Na<sup>+</sup>

212

Many salt tolerance genes have been discovered by using traditional breeding techniques, such as subtractive hybridization, differential hybridization, and through genetic information from the model organism. Furthermore, protein crystallography, a proteomic study has enabled researchers to the exploration of the protein's structure and function for salt tolerant genes. After salt tolerance gene identification, many latest techniques for foreign gene transformation to the desired plant can help to improve field crop production. Such as CRISPR CAS9, PEGmediated gene transfer, electroporation, partial or the micro projectile bombardment, microinjection, and Agrobacterium-mediated gene transfer. These techniques are available for many crops.
