S. K. Guru
6.5 Biotechnology for crop adaptation
the crops and the weeds. The main purpose of the herbicide- resistant plants is to reduce the need for tillage, finally providing protection to nearby environments through reduced erosion and enhanced soil sequestration. For example, the GM herbicide- resistant Round up ReadyTM soybean accounted for up to 95%
of no-till areas in the United States of America (USA) and in Argentina, leading to the sequestration of 63,859 million tonnes of CO2 (Kleter et al., 2008). HT crops allow farmers to kill only the weeds avoiding the greenhouse gas intensive process of weed control by traditional tillage, finally leading to more soil carbon sequestration. No-till agriculture, in addition to car- bon sequestration, reduces the consumption of fuel to operate equipment, thereby reducing CO2 emissions. The gross global warming potential (GWP) for no-till agriculture is drastically lower than both traditional and conservation tillage (Figure 6.2).
Reduction of fuel usage due to the application of biotechnol- ogy amounted to savings of about 962 million kg of CO2 emit- ted in 2005, while the adoption of reduced tillage or no-tillage practices led to the reduction of 40.43 kg/ha CO2 emissions due to less fuel usage, respectively. Therefore, in terms of carbon sequestration and reduced greenhouse gas emissions, it is clear that GM HT crops are beneficial for climate change mitigation.
strategies for the effects of climate change that are already in progress. Change of climate over time has led to a decrease in crop yield due to inadequate rainfall, various abiotic stresses, potential weeds, pests and diseases caused by fungi, bacteria and viruses. Biotechnology and the application of advanced techniques in agriculture will help in creating plants that will adapt to these new climatic conditions. One of the important ways of adapting to such changes is to apply agricultural bio- technological strategies that counter the effects by improving crop productivities per unit area of land cultivars.
The increasing demand for food crops worldwide can be satisfied in two ways: first is to increase the area under pro- duction and the second is to improve productivity on existing arable land. Given the limited amount of land for cultivation and a continuously changing climate, the second option seems to be more lucrative. Some of the conventional biotechnological options that organic farming technologies using biofertilisers include good agronomical practices such as land management, crop rotation, mixed farming, intercropping with leguminous plants with nitrogen fixing abilities and application of tradi- tional and indigenous knowledge on known chemical pests and disease control methods (Bianchi et al., 2006). In this way, agri- cultural biotechnology and other advanced breeding strategies may help to further achieve higher yields and meet the needs of an expanding population with limited land and water resources.
Climate change poses an enormous intimidation in terms of the available agricultural land and fresh water use. Abiotic stress conditions such as salinity, drought, extreme tempera- tures, chemical toxicity and oxidative stress impose negative effects on agriculture and the natural environment (Bartels and Sunkar, 2005). Rising sea levels increase water salinity and force migration, resulting in greater population density with reduced viable crop land and fresh water for irrigation. About 25 million acres of arable land is lost each year due to salin- ity caused by indefensible irrigation techniques (Ruane et al., 2008). It is estimated that if the increase in salinity continues with this speed, it will lead to 30% loss of arable land within 25 years and 50% by the year 2050 (Wang et al., 2003; Valliyodan and Nguyen, 2006). Seventy percent of the available fresh water consumed is accounted by the agriculture sector (Brookes and Barfoot, 2008), which is likely to increase with the increas- ing temperature associated with climate change. Increasing harsh conditions will force the plants to use more energy and, hence, more water to grow. The problem is aggravated when the Adaptation to
abiotic stresses
rising sea levels decrease available arable land and fresh water sources. This condition requires the need for an agriculture that truly conserves both water and land, and still gives a higher yield to feed the growing population. Biotechnology can be employed to generate an agricultural system that will be more water-efficient in the large-scale production methods.
Keeping the above information in view, the solutions that facilitate the adaptation of crops to these abiotic stresses (drought, salinity, etc.) need to be developed. The conventional approaches to reduce the effects of these abiotic stresses involve selecting and growing stress-resistant crops that can tolerate harsh conditions on marginal lands. Examples of such crops include cassava, millet and sunflower (Manavalan et al., 2009).
Tissue culture and breeding are also being used to cross stress- tolerant crops with high-yielding species, generating stress-tol- erant high-yielding hybrids (Ruane et al., 2008). Although the biotechnology community generally focuses on either molecu- lar breeding or genetic engineering approaches, it is evident that there is a need to target complex problems caused by dif- ferent stresses using integrated biotechnology approaches. As the whole genome sequence of plant, physical maps, genet- ics and functional genomics tools are becoming increasingly available, integrated approaches using molecular breeding and genetic engineering offer new opportunities for improving stress resistance (Manavalan et al., 2009). Hence, an outline for breeding a plant for the abiotic stress should incorporate conventional breeding and germplasm selection, elucidation of specific molecular control mechanisms in tolerant and sensitive genotypes, biotechnology-oriented improvement of selection and breeding procedures (functional analysis, marker probes and transformation with specific genes) and improvement and adaptation of current agricultural practices (Wang et al., 2003).
Activation and regulation of specific stress-related genes form the basis of the control mechanisms for abiotic stress tolerance (Table 6.1). Genetically engineered plants are based on different stress mechanisms, like metabolism, regula- tory controls, ion transport, antioxidants and detoxification, late embryogenesis abundance, heat shock process and heat proteins (Wang et al., 2003). A number of high-yielding GM crops tolerant to abiotic stress have already been made avail- able, some of which include tobacco (Hong et al., 2000), Arabidopsis thaliana and Brassica napus (Jaglo et al., 2001), tomato (Hsieh et al., 2002; Zhang and Blumwald, 2002), rice (Yamanouchi et al., 2002), maize, cotton, wheat and oilseed rape (Yamaguchi and Blumwald, 2005). As drought and water
table 6.1 List of representative genes conferring stress tolerance in plants
S. no. Name of gene Full form Trait
1. DREB Dehydration responsive
element binding factor
Improved drought and salt tolerance
2. SUB Submergence
(ethylene response factor like gene)
Submergence tolerance
3. HSP Heat shock protein Improved drought and salt
tolerance
4. NAC NAM/ATAF/CUC Improved drought
tolerance 5. ERF Ethylene response factor Improved drought
tolerance
6. HARDY AP2/ERF gene Improved drought and salt
tolerance
7. HSF Heat shock factor Improved temperature
tolerance
8. MYC — Improved drought
tolerance
9. MYB — Improved drought
tolerance
10. ABF Abscisic acid responsive
factor
Improved drought tolerance 11. P5CS Pyrroline-5-carboxylate
synthase
Improved drought and salt tolerance
12. TPS Trehalose-6-phosphate
synthetase
Improved drought tolerance
13. IMT Myo-inositol-O-
methyltransferase
Improved drought and salt tolerance
14. CodA Choline oxidase Improved cold and salt
tolerance
15. ProDH Proline dehydrogenase Improved salt tolerance
16. OAT Ornithine amino
transferase
Improved NaCl or mannitol tolerance
17. BADH Betaine aldehyde
dehydrogenase
Improved salt tolerance 18. Cu/ZnSOD Superoxide dismutase Improved cold and
oxidative stress tolerance 19. ALDH Aldehyde dehydrogenase Improved drought, salt and
oxidative stress tolerance
20. CDPK Calcium-dependent
protein kinase
Improved drought and salt tolerance
21. NDPK Nucleotide diphosphate
kinase
Improved cold and salt tolerance
22. NHX Na+/H+ antiporter Improved salt tolerance
scarcity are becoming more prevalent, biotechnology will help create plants that can withstand these harsh conditions. There are examples where plants are engineered to reduce the levels of poly (ADP ribose) polymerase, an important stress-related enzyme, resulting in GM plants that are able to survive drought and showed 44% increase in yield compared to their non- GM counterparts (Brookes and Barfoot, 2008). The United Kingdom Agricultural Biotechnology Council (ABC) is work- ing on another technology, which involves the use of transcrip- tion factors and stress genes that act as genetic switches. This technology has resulted in a twofold increase in productivity for Arabidopsis and a 30% increase in yield for maize during severe water stress. Additionally, new areas of research in bio- technology are working toward creating plants that are resistant to salt by introducing a gene from salt-tolerant mangroves into food crops. With this technology, the available water sources can be used more efficiently and the lands near rising oceans that are subject to ground water salination will become fertile for these salt-tolerant seeds. Creating plants with increased yields means less land will be needed to plant and grow food.
With growing populations and climate-induced land loss, pro- ducing higher yields on less land will become an essential com- ponent of agriculture. In this context, in addition to hardier and more water-efficient plants, biotechnology is also creating more space-efficient plants.
Strains, resistant to biotic stresses such as insects, fungi, bac- teria and virus have been developed through conventional landscape-management practices and breeding initiatives, leading to crop adaptation. For example, agricultural pest con- trol strategies have been significantly benefited by the ability of the soil bacteria (Bacillus thuringiensis, Bt) gene to be trans- ferred into maize, cotton and other crops to import protection Adaptation to
biotic stresses
table 6.1 (continued) List of representative genes conferring stress tolerance in plants
S. no. Name of gene Full form Trait
23. SOS Salt overly sensitive Improved salt tolerance
24. Glyoxylase — Improved salt tolerance
25. NCED 9-cis-epoxycarotenoid
dioxygenase
Improved drought tolerance
26. Invertase — Improved salt tolerance
Source: Adapted from Bartels B and Sunkar R 2005. Crit. Rev. Plant Sci., 24: 23–58.
against insects. Bt crops proved to be highly beneficial tools for the integrated pest management program by providing farm- ers with new pest control strategies (Zhe and Mitchell, 2011).
For example, transgenic canola (oilseed rape) and soybean have been modified to be resistant to specific herbicides (Bonny, 2008). Also, GM cassava, potatoes, bananas and other crops that are resistant to fungi, bacteria and viruses are in develop- ment; some have already been commercialised while others are undergoing field trials (Van Camp, 2005). Studies carried out between 2002 and 2005 found that biotic stress-resistant GM crops account for an increase in the average yield of 11–12%
for canola and maize compared to conventional crops (Brookes and Barfoot, 2008, 2009; Gomez-Barbero et al., 2008).