**5. Management of abiotic factors**

Climate changing is a global issue now and it causing a range of abiotic stresses. The notorious characteristic of abiotic factors is that they occur simultaneously in the environment. In this regard, long term exposure to abiotic stresses resulted in reduced yield ultimately. While adaptability is a major function of living beings. To fight against abiotic stresses or to minimize the effects of different abiotic factors, many plants particularly cotton have developed some defense mechanisms to overcome the impacts of abiotic stresses. These adaptabilities by cotton plants are based on physiological or molecular mechanisms. However, still an integrated management is still needed to overcome these harsh environmental stresses.

## **5.1 Drought stress management**

Drought is among the key limitation factor to suppress sustainable cotton production all over the world. In this regard, to overcome the effects of drought meaningfully, one must know comprehensively the soil conditions by exploration deeply [117]. The growing of commercial scaled upland cotton always show positive association with adequate water supply whenever grown in dry lands [118]. Cotton growing farmers always rely on altered row configuration to minimize the effects of drought stress as basic agronomic measure [119]. While the crop rotation tactic with cereal crops improve the soil health overall by increasing its water storage capacity and accessibility to respective crop [120]. Botanists who are working on plant physiology or molecular technologists should must keep in mind these factors when they are working to develop new innovative tools for management of drought stress. However, Farooq et al. have described the comprehensive review of drought impact on plants and their physiological response [81]. It is scientifically proofed that the highly efficient approach to overcome drought effects and increase the production rate of cotton could only be attained by the appropriate or judicious use of vital natural resources water and soil [121, 122].

## **5.2 Temperature stress management**

Climate change is a global issue now. While this challenging the environment overall by causing abiotic stresses directly. The globally increasing temperature is mainly due to excess carbon dioxide contented in the atmosphere. Thus, the mean increase in degree of hotness globally per annum basis leads to water transpiration from the soil that ultimately resulted in drought and salty soils [71]. Temperature stress directly damages to reproductive and vegetative phase of cotton resulting in low yield [74]; although cotton is a tropical crop and have the ability to absorb severe radiation from the sun, and resulting in high temperature of the crop during high solar intensity. While in this regard, some of the plants show adaptable behavior and respond to temperature stress by developing waxy surfaces to imitate the strong radiations from the sun. But the cotton plants responded by absorption of solar radiation that intensifies osmatic (drought) pressure. Varieties with some appropriate and desired features including dense cuticle structure and profound hairs to lower down the temperature or heat stress could helpful in this regard (CICR 2016). Frequent watering could help to overcome water stress. Recently, some new innovative plant based irrigation systems have been developed by means of temperature sensing remotes through canopy [95]. While the other adverse behavior from cotton plants is the closing of stomata

in the night ties that does not allow the cooling effect. In this context, plant breeders and biotechnologists may focus on developing such verities or cultivars that could fight against heat stress. As the roots are vital part to supply water to whole plant, so studying their structure and role is of equal importance and the types of soils as well. Because the sandy soils have less ability to store water for long so this could also aggravate the water and heat stress.

## **5.3 Role of root morphology to combat above stresses**

To overcome the drought effects management tactics may be applied according to soil or plant type. Soil type and state is vital to play key role to help to develop deeper, denser and stronger plant roots to increase the use of available resources. This could ultimately helpful to significantly overcome the severe impacts of heat and drought stress. A comprehensive description on the impacts of different dry lands on roots in relation to development of crop was covered by Whitmore and Whalley [117]. Roots have different morphology among top layer of soil and sub layer of soil according to its thick structure, it could have strong influence on the behaviors of plant; how could they manage different stresses. The plants with roots who have ability to grow more bottomless or deep layers in the soil fight drought stress in a better way [123]. Some latest findings from Australia confirmed that the fine root structure of Bollgard Roundup Ready® genetically modified cultivar, was less than conventional cotton. The production of fine roots was much lower [124]. Bell also found that the cotton roots acquire phosphorus from subsoil instead of topsoil. It is proposed that under drought conditions plants roots could active in bottom and deeper soil layer while inactive at topsoil [125]. But this stressful situation ultimately depleting the P resources among cereal crop soils in Australia where the cotton is also grown [126].

#### **5.4 Role of soil condition to combat above stresses**

Different biotic and abiotic factors are directly or indirectly related to occurrence of different diseases, outbreak and survival of insect pests and could lead to complex situation in relation with different crops to manage those pests and pathogens. Thus, the soil type, structure and composition also could adversely affect these factors. In this regard, the altered soil texture severely affects the plant-soil-water relationship and cause the low water uptake by plant roots [86] that ultimately leads to poor growth and development of plant [87]. The adverse impacts of high temperature, dry and saline soils under field could be lessened or by adopting many technological measures. These measures are generally comprised of latest irrigations systems, soil health betterment by different management approaches, and management of crop residues and selection of particular crop cultivar. All the above approaches are usable but not limited to overcome the biotic and abiotic stress. Tillage have facility to alter the soil structure in favor to keep balance between hotness and soil humidity level. Thus, tillage have direct effect on transpiration of water from soil to air and infiltration through deep soil. So, some previous findings have supported that the soils with zero or minimum tillage have bettered structure to fight these stresses by helping undisturbed root development [127]. However, in some specific conditions due to use of heavy machinery on farmland resulted in hard or compacted subsoil layer needs deep tillage for better soil structure for farming. Summing up, the integrated management of biotic and abiotic stresses entails attentive use of available tactics and strongly demands development of stress tolerant varieties by keeping in mind the

**Figure 3.**

*Outline of strategies for improving crop performance under combined drought and pathogen stress. Source: Pandey et al. [98].*

above described factors. While as Pandey et al. suggested in detail to overcome the combined effect of these stresses (**Figure 3**) [98].
