Improving Crop Growth in Saline Environments

The United Nations (2017) reported that the world’s population will increase from the current 7. 6 billion to 9. 8 billion by 2050, thus food production needs to be increased by 60%. Already, about 10. 9% of the world’s population, were reported malnourished (FAO, 2018). This figure is predicted to increase as arable lands are diminishing due to increased non-farming developments and soil salinity caused by poor soil and irrigation management, global warming, climate change, rising sea-level, and land subsidence, posing a threat to food production. About 50% of the arable lands worldwide are already affected by salinity (Waqas et al. , 2018). With mounting pressure to produce more food to feed the growing population, improving crop production, particularly salt-tolerant crops, continues to be a crucial challenge. This investigation will demonstrate how scientific knowledge and understanding of advanced genetic engineering in genome editing can enable scientists to find solutionsto develop salt-tolerant crops. Limitations of the scientific research and impacts on social, economic, and environmentalconsequences will also be discussed. (2) Related biological science - Salt toxicity and plant growthExcessive salt (NaCl) in the soil affects the growth of normal plants due to osmotic stress which reduces plants’ ability to uptake sufficient water, causing the plant cells to shrivel and slower growth (Figure 1). Additionally, the ion-excess of salinity induces Na+ and Cl- ions to accumulate in leaves, causing severe ion imbalance and stress in the cells. High Na+ concentration inhibits uptake of K+ ion, a vital element for plant growth, resulting in leaves being “burned” and even death, as shown in Figure 2 (Prince, 2016).

Modify salt-affected soils to suit the crops, and (2) Use salt-affected soils to grow naturally salt-tolerant plants (halophytes), andresearch into developing new salt-tolerant cultivars (Ashraf et al. , 2008). With the first strategy, there are various means to modify salt-affected soils including leaching, drip irrigation, subsurface drainage, and amelioration. Leaching uses water to drain excess salts out of the rootzone to the lower soil layers. Careful drip-irrigation management reduces the salt’s effects by keeping the soils moist that helps stable leaching. Adequate subsurface drainage system carries the excess water and salts out of the area. Fertilisers containing chemicals such as gypsum, nitrogen, phosphorus and potassium sulphate are used to ameliorate the soil. (PMC, 2014; Agriculture and Food, 2016).

However, the limitations of this strategy are that it is economically non-viable and potentially harmful to the environment. Fertilisers are costly, constructing an effective irrigation system in a vast agricultural area requires huge capital investment, and leaching could increase salinity in ground-water and river systems (SA Government, 2017). Researchers are focusing on the second strategy to improve growth of halophytes and generate salt-tolerant cultivars, instead of expensive soil recovery measures to modify soil. Since the 1960s,scientists have been conducting experiments aiming to discover new techniques to improve crop growth in saline environments, and to develop new salt-resistant crops by using genetic engineering technology. Conventional breeding as well as molecular biology techniques in DNA-based markers for screening genotypes have been used in the research. Genetic mapping and quantitative trait loci (QTL) analysis by selecting desirable characteristics from superior plants and cross-breeding them to create new and improved traits have shown success in improving salt-resistance in some crops in recent years (Lema-Ruminska et al. , 2004; Mlcochova et al. , 2004). Different plants respond to salinity stress differently. Scientists have been observing the development of specific genes and proteins, and the influence of metabolites in different model plants’ mechanisms of salt tolerance (Zhang & Shi, 2013,). The discovery and understanding of how editing of genes develop salt tolerance in the plants has enabled scientists to successfully apply the knowledge to culture resilient crops such as alfalfa, durum wheat, rice (Large et al. , 2006; Ashraf and Akram, 2009).

According toZhang and Wang (2015), the rstB transgenic alfalfa plants can successfully enhance calcium accumulation which acts as a mechanism to resist salt stress. It is confirmed thatrstB transene ‘can be used as a molecular crop salt tolerance breeding’. The genetically engineered salt-resistant alfalfa is a highly nutritious, perennial legume forage containing high concentrations of vitamins B, C, D, and E. It is more easily digestible and is mainly used as animal feed, particularly dairy cattle, with a small amount for commercial manufacture of vitamins. It is herbicide tolerant thus reducing insect infestation, can produce higher yields than conventional alfalfa by about 17% which may be influenced by many factors such as seed variety, weather and soil conditions and water availability (Fernandez-Cornejo et al. , 2016)

Durum Wheat: The new TmHKT1;5-A durum wheat containing salt-resistant geneproduces a protein which expels from the leaf cells the Na+ that affects the plants’ photosynthesis process (University of Adelaide, 2012). It can grow well in both standard and saline conditions. However, in saline soil environment, it increases its yield by about 25%. Its ability to withstand salt stress allows farmers to have the option of using only one type of this durum wheat for any paddock, even though the soil may contain some salty parts. Based on the finding, scientists are able to make reliable prediction that durum wheat containing the salt-tolerance gene could outperform its wheat parent under salty conditions. It also helps in further research to cross the salt-resistant gene into bread wheat, a larger crop compared to durum wheat (Vincent, 2012; University of Adelaide, 2012).

Rice after years of failed research, a new salt-tolerant rice species of better quality and higher yields than normal crops has been developed with CRISPR/Cas technology, by snipping parts of DNA, editing the codes, and modifying the genes (Wallheimer, 2018; Haskins, 2018). It can produce a much higher yield of more than 50% compared to normal non-salt-resistant crops, has better quality and taste, and is healthier to eat as the salt in the soil acts as a natural pesticide and kills off bacteria. The huge increase in yield, if it is sustainable, will be good news for both the farmers and the world as be able to produce more grains to feed a vast majority of the world’s population with rice being their staple food. However, a negative environmental impact is that once the land has been converted to saltwater planting, the soil becomes saline and only salt-resistant can be grown there. Production wise, scientists have yet to determine whether it is ready for production yet. Cost wise, it will be expensive for most people unless the price can be lowered to an affordable level.

Thus far, these GE crops have all have demonstrated higher nutritional quality, higher yield, more salt-tolerant, herbicide and pesticide resistant, with less maintenance compared to their parent crops. Genetic engineering has been proven to be an efficient approach to the development of salt-tolerant plants, and it is predicted that this approach will become more powerful as more candidate genes associated with salinity tolerance are identified and widely utilized(Zhang & Shi, 2013,). . Limitations in the research However, there are limitations as well. Though some progress has been made, very few new salt-tolerant crops have been developed (Chinnusamy, et al. ,2005).

The main challenges aretime and labour cost, together with unexpected consequencessuch as unwanted genes being transferred with the desired traits. While crops’ wild relatives can provide abundant source of salt tolerant genes for incorporating into domestic crops, the reproductive barriers are not that easy to overcome as there are more failures than successes in the research over the past decades, and the scientific technology has yet to be further improved. Besides, as the experiments have mainly been done in laboratory-controlled conditions, the results may change in the actual field conditions with varied salt levels and other environmental factors (e. g. climate and soil fertility) (Yamaguchi & Blumwald, 2005). **Collaboration between scientists is essentially required in scientific research**Perhaps, the main obstacle may be that our crops plants have lost their natural resilience against salt-affected environment as a result of many years of breeding. (Emmerich, 2017). (4) Social, economic and environmental impacts The research on improving crop growth in saline environments can have significant impacts on social, economic, and environmental considerations. Successful improvement in crop’s salt-tolerance and development of new salt-resistant crop species with high quality nutrients and yields will have enormous contribution to food varieties and food production to prevent global food crisis. Salt-resilient crops will become ever more important as the environment continues to be affected by rising salinity level in soil and water systems and more arable lands for normal crops will diminish.

Furthermore, increase in agricultural activities in salt affected areas will also stimulate job growth, thus benefiting the society in many folds both socially and economically. Scientists usually publish their researches and findings on websites such as ScienceDirect and Phys. org with open-access to communicate, keep the public updated, and share their breakthroughs to raise awareness about the current challenge of food shortage. However, economic policies often encourage only on a narrow range of traditional stable crops for export markets, but not for the research on new salt-resistant crops that requires substantial financial support, yet with uncertain outcomes. In addition, political influence could complicate advance in research for new crop species due to export pressure, again, on agriculture products (Yamaguchi & Blumwald, 2005). Environmentally, the irrigation water on saline soils will cause leaching which will wash more salt to the lower soil level and pollute groundwater and fresh water rivers thus affecting the quality of water. Drinking water may taste differently and sometimes, may even cause laxative effect to both human and animals. Against approaches of using plant growth regulators, antioxidant compounds, inorganic salts to increase salt tolerance in potential crops.

The successful breeding of salt-tolerant durum wheat offers many positive impacts to the society socially, economically and environmentally. Expansion of the durum wheat industry in different regions will provide more stability in national production as losses due to drought, flooding or late season rains are usually regional. Salt-tolerant durum wheat enables farmers to extend their areas to saline soil will benefit 20% increase in yield and increase their profit margin by 50% considering there are no restricting production. Additionally, the domestic pasta industry, where milling and pasta production can also derive additional benefits from the flow on effect of durum wheat. Durum production in Australia is expected to reach 1,000,000 tonnes in the next few years, an average yield of 3. 3t/ha from 300,000ha. If the new salt-tolerant durum wheat increases yield in these soils by 20%, then national production could increase by 50,000 tonnes. Furthermore, more of the available water will be used for the wheat. This reduces any leakage below the root zone and provides a higher yield in soils with moderate salinity.

Conclusion

After years and millions of dollars of unsuccessful attempts, progress has been made in improving growth of a limited number of crops in saline environments under controlled experimental conditions. Further studies and understanding of the genetic engineering technology, together with continuing research in developing new variety of salt-resistant crops to improve quality and quantity growth is needed before mass production in commercial scale at an affordable price to consumers and overcoming world food shortage is possible. As well, more publicity on internet should be made available to the general public on the outcome of all researches undertaken to encourage understanding and acceptance of the application of scientific knowledge and outcomes.