With climate change and a rapidly growing global population, what are the latest innovations and debates in biotechnology for improving crops and livestock?
Compared with wild ancestors, most modern crops are unrecognisable; even the most basic crops are the result of some form of human induced genetic manipulation. The modern banana, for example, has a long history of genetic modification. It is thought that the first banana was cultivated around 7,000 years ago in Southeast Asia. The banana’s ancient ancestor is Musa acuminate, a plant that had small okra-like pods. This was eventually crossed with M. balbisiana, which created plantains that – with further modification over thousands of years – has led to the more familiar yellow/green fruits of modern times.
Domestication and development of plants and animals to produce the foods consumed today has, until recently, been predominantly dependent on selective breeding – a time-consuming process of cross-breeding crop and livestock varieties and selecting for particular traits, e.g. productivity, disease resistance, abiotic stress tolerance, and quality. However, asexual production has also been used for centuries by farmers to perfect their crops. Domestic bananas, for instance, have long since lost the seeds that allowed their wild ancestors to reproduce – so the bananas we eat today are produced asexually, in other words by vegetative propagation, so that the new plant is genetically identical to the parent plant.
So given that all our modern crops have been genetically modified in some way, how do we define biotechnology? The traditional definition is the use of living systems and organisms to develop or make products. However, a more modern, inclusive definition, used in the Convention on Biological Diversity, encompasses any technological application that uses biological systems, living organisms or their derivatives to make useful products or processes. Modern biotechnology has been driven by a revolution in cellular and molecular biology that occurred in the second half of the 20th century, which includes a range of tools involving gene manipulation and transfer that researchers have used to understand and modify the genetic makeup of crops and livestock. Biotechnology is therefore not just genetic engineering and, whilst the response to genetically modified organisms (GMOs) is complex and continues to be hotly debated, some of the less controversial techniques are making significant advances in producing more tolerant and resistant crops and livestock breeds to biotic (pests, diseases) and abiotic stresses (drought, high temperatures, etc.).
Making a mark
For example, in recent decades, crop and livestock breeding has been revolutionised by the development of marker-assisted selection (MAS), which provides a short cut to identifying preferred traits by using a unique ‘marker’ gene (or genetic sequence) tightly linked to the gene of interest. The value of MAS lies in the potential to identify the presence of a trait in seedlings or even seeds which makes the breeding process far quicker and more cost-effective as new varieties can be brought to commercialisation in as little as four, instead of 10, generations under conventional breeding processes. In Africa, significant impact has also been achieved in breeding for resistance to maize streak virus (MSV), the most serious viral crop disease on the continent, which causes losses of more than 5 million t per year. Prior to MAS, seedlings had to be grown and subjected to virus carrying insects to identify resistance which was prohibitively expensive and time-consuming for national breeding programmes. However, with MAS techniques, MSV resistant genes can be speedily identified and durable resistance has now been back-crossed into germplasm adapted to many diverse African environments, and these varieties are still being disseminated. For example, in May 2016, three high-yielding commercial breeds with resistance to MSV, rust and Striga hermonthica were registered in Nigeria and released by Monsanto.
However, although MAS is already routinely applied by private seed companies, its wider use in the public sector, particularly in developing countries, is still facing some constraints. These include high costs, poor infrastructure, inadequate capacity and lack of breeder-friendly markers. Nevertheless, achievements across Africa include MAS used in Sudan to tackle Striga in sorghum and to develop resistance to cassava mosaic disease (CMD), which can result in yield losses of up to 90%. Furthermore, as new tools and technologies (e.g. next-generation sequencing, high-throughput genotyping and genome wide selection) are making MAS increasingly based on the whole genome, rather than small segments, the number of crop species with sequenced genomes is steadily growing and it is likely that MAS will continue to become more widely adopted. For those against transgenesis (GMOs), MAS raises less safety concerns, is accepted by the public and permitted in organic farming.
The various guises of GM
However, there are some important distinctions to be made with regard to GMOs and their application in improving crops and livestock. Genetic engineering enables the direct transfer of genes from one organism to another. This technique, known as transgenesis, is where a gene is taken from one organism and inserted in the genetic code of a particular crop to provide resistance or tolerance to biotic and abiotic stresses. For example, crop varieties can be engineered to express a bacterial gene (e.g. from Bacillus thuringiensis, a soil bacterium commonly used as a biological pesticide) that controls certain insect pests – as in the case of Bt cotton. Some of the most valuable applications have been achieved in confering resistance to bacterial and virus diseases. For example, viral resistance can be achieved by transferring certain viral genes that interfere with normal viral replication, thereby inhibiting spread of infection e.g. cassava resistant to CMD.
In Africa, Uganda has a particularly diverse transgenic programme, particularly in bananas but also for other staple crops. However, despite this well recognised research, Uganda is the only country in Africa to have confined field trials (CFT) for GM crops with no biosafety law (see p26, A rich legacy in biotechnology). Conversely, Burkina Faso is one of three African countries that has commercialised GM crops and is well known for its Bt cotton developed by Monsanto, which it has been growing and selling since 2008. However, increasing concerns over cotton quality and decreased profitability of GM compared to conventional cotton has led the country’s biggest farmers’ association to recommend abandoning the crop. But, with Bt cotton, it is yet to be seen whether farmers will be able to cope with bollworm attacks through conventional practises and maintain cotton yields (see p24, A temporary setback for GM cotton?).
In 2015, GM crops were grown globally in 28 countries and on 179.7 million ha – that is over 10% of the world’s arable land; Argentina, Brazil and the US are the biggest producers of GM crops. In the US, over 90% of soybean and maize are GM. In Europe, only one GM crop has ever been approved and grown – a type of maize with resistance to European corn borer. In Africa, GM crops are grown in South Africa (2.3 million ha), Burkino Faso (0.4 million ha) and Sudan (0.1 million ha), with the main crop being GM Bt cotton. However CFTs for a variety of GM crops were also conducted in Ghana, Kenya, Malawi, Nigeria, Tanzania, Uganda, and Zimbabwe (see infographics).
But not all GM crops are developed through transgenic techniques. For example, Irish potato with resistance to bacterial late blight (Phytophthora infestans) has been developed through cisgenesis, which takes resistant genes from a wild relative. “We transferred genes from wild relatives of the potato – Solanum bulbocastanum and S. venturii – into farmer- preferred potatoes and have achieved excellent results,” states Dr Andrew Kiggundu, head of Uganda’s National Agricultural Biotechnology Centre, Kiggundu. The advantage of this technique is that only the desired genes are transferred, so there is no ‘gene drag’ as in conventional breeding, where several backcrossed generations are needed to eliminate the unwanted genetic material. The key purpose of cisgenesis is to transfer disease resistance genes to susceptible varieties with the aim of significantly reducing pesticide application e.g in case of late blight. In the EU, cisgenesis (and intragenesis – a similar technique that involves a new combination of a partial or complete coding sequence) is currently governed by the same GMO laws as transgenesis. However, researchers at Wageningen University in the Netherlands, who have developed the technology, and the Dutch government who has supported the research, are strongly arguing for this to be changed so that cisgenesis is regulated in the same way as conventionally bred plants.
Whilst the majority of GM technologies are used to improve/enhance crop traits, new gene editing techniques are being applied to livestock. At the University of Edinburgh’s Roslin Institute, researchers have produced pigs that are potentially resistant to African Swine Fever, a highly contagious tick-borne disease which is endemic across sub-Saharan Africa and kills up to two-thirds of infected animals. The researchers used a gene-editing technique to modify individual letters of the pigs’ genetic code. The ‘modified’ pigs carry a version of a gene that is usually found in warthogs and bush pigs, which show no disease symptoms when infected. “We have used a gene-editing technique to change individual letters in the pigs’ genetic code to speed up a process that occurs spontaneously in nature. Our goal is to improve the welfare of farmed pigs around the world, making them healthier and more productive for farmers,” says Professor Bruce Whitelaw, head of Developmental Biology at the Roslin Institute. The team plans to use the same gene-editing techniques to produce cattle, chickens and sheep that are resistant to infections, but this research is at a much earlier stage. Steve Kemp, who leads the cross-cutting LiveGene initiative at the International Livestock Research Institute agrees that, “The advent of genome editing technologies (e.g. CRISPR-CAS9) provides, for the first time, a toolbox to study the effect of a variant and then to introduce exactly the characteristics that we need into the strains that most need it,” (see p23, Biotechnology advances for livestock).
Where next for biotech?
With emerging genetic technologies blurring the distinction between GM and conventional plant breeding, a new study released in May 2016 by the American National Academies of Sciences, Engineering and Medicine (Genetically Engineered Crops: Experiences and Prospects) states that genetically engineered crops are as safe for the environment as conventionally bred crops. The evidence reviewed by the study committee also reveals that although GM crops have provided economic benefits to many small-scale farmers in the early years of adoption, enduring and widespread gains will depend on such farmers receiving institutional support, such as access to credit, affordable inputs such as fertiliser, extension services, and access to profitable local and global markets for the crops. UK’s Royal Society has also produced a new guide which makes a case for GM crops to be judged on their individual merits (GM Plants: Questions and Answers). New developments in GM crops include enhancing the nutritional value of crops including an orange GM banana with elevated levels of beta-carotene which is being tested in Iowa, beta-carotene-enriched cassava recently released in Nigeria, and iron-fortified beans in Rwanda (Note: biofortification will be covered in Spore 183).
In Africa, biosafety regulations are still being developed. After three previous attempts and years of debate, Nigeria passed the National Biosafety Agency Bill law to regulate GMOs. The National Biosafety Management Agency (NBMA) mandated to regulate GMOs is building capacity to support implementation of the law. As a result, Mosanto Nigeria recently submitted an application for release of Bt cotton and maize to the NBMA which is currently being reviewed. Nigeria’s example provides potential lessons for other African countries.
For further information see:
Handbook on Agriculture, Biotechnology and Development. Edited by S. Smyth et al. (2015) ISBN 978-1-78347-135-5