Amid the growing world population, the shrinking arable land and global challenges like climate change, the need for resource-efficient farming systems is becoming absolutely vital to feed the booming population. This is possible only through innovations in plant breeding. The new plant varieties that can withstand the sudden excessive temperature, draught, flood and salinity have become essential. The new plants should also be more tolerant or resistant to pest, disease, and other biotic and abiotic stresses. Simultaneously, these plants should be more productive and the yield should be stable, irrespective of climate and various stresses. Increased productivity means the use of less resources and inputs, such as, land, water, pesticides, fertilisers or other nutrients.
By 2050, the world population is expected to increase to 9.8 billion from the present 7.3 billion (2016), while the availability of arable land will decrease to 0.15 hectare from the existing 0.20 hectare per capita. The average global temperature is expected to rise to 16.0ºC from the current average of 14.7ºC. The demand for water will rise to 5,500 km3 from present 3,500 km3. Due to the global warming, it is estimated that 20-25 per cent of crop will be lost to pests compared to the present loss of 10-15 per cent. These are no longer any assumption as these are happening in reality.
Humans are in critical juncture of history. Booming population, urbanisation, desertification, degradation of land fertility, climate change and other environmental factors like melting of the Arctic ice and mountain glaciers, rising sea level and the changing pattern of various ecosystems at various places are threatening the food security at an unprecedented scale. Bangladesh will be one of the worst affected countries. So, improved varieties of food crops are the only way to reduce the risk of economic and climatic shocks for millions of people who are resource poor and vulnerable.
Producing more foods with fewer resources by improving the agricultural productivity should, therefore, be the main focus of Bangladesh agricultural scientists, plant breeders and policymakers. The UN Convention to Combat Desertification (UNCCD) insists that there is an urgent need to boost agricultural productivity to meet the present and future demands for food. The climate change is already making food insecurity worse, while global agriculture crop yield may diminish by 30 per cent by 2050.
CROP IMPROVEMENT ? VARIOUS METHODS: There is nothing new in crop improvement, as it has been taking place in various ways for thousands of years, but it gained the momentum in 1866 with the introduction of Mendel's Law of Genetics. It even accentuated further from crossbreeding in the 1900s and introduction of mutation breeding from the 1930s. Furthermore, with the new technologies like genome sequencing and elucidation of gene functions, it is now possible to introduce new breeding methods that helps improve the selection process. By using genetic markers, breeders now can select specific genetic traits more efficiently and select useful traits that can be best combined in crossbreeding to develop not only hybrid, but crops to resist biotic and abiotic stresses.
TIMELINE: Plant breeding has a long history of innovation. Originally, crop was improved through a selection process. By 10,000 BC, human started improving crops like wheat. The timeline from history shows that by 5,000 BC human improved linseed, flak wheat, Barley; by 4000 BC Maize and Millets; by 3000 BC potatoes, by 2000 BC rapeseeds (oil seeds) and water melon; by 1000 BC rye; and by 1950 AD they improved sugar beet. In 1866, Mendel established his "law of genetics". Following the same principle, crossbreeding started in 1900, hybrid breeding in 1920, mutation breeding in 1930. Subsequently, agricultural scientists established tissue culture in 1960, gene transfer (GMO) in 1996, Marker assisted breeding in 2000, and new technologies of genome sequencing in 2010, finally introduced the gene editing in plant breeding in 2013. However, controversies surrounding the crops produced from gene editing are yet to be settled. The issue in question is whether such crops are GMO (Genetically Modified Organism) or not.
From the above timeline of innovation, one can see that humans have been vying to improve crop quality and productivity from the advent of the agricultural civilisations 12-13,000 years ago. However, since the introduction of laws of genetic by Mendel, plant breeders have developed many new breeding methods and techniques. These methods have increased genetic diversity and allowed the selection of best performing traits, and eventually the most efficient plants. The major goal of plant breeding is to continuously make the use of plant genetic diversity, and simultaneously increase plant diversity.
Radiation was first used in the 1930s to induce random mutations in plant's genome, followed by intense selection process to identify the valuable traits. Besides radiations, chemicals are also used for various crops to induce mutations and selection of most desirable traits. Recently, a draught-tolerant wheat has been developed in Kenya using gamma radiation which increases yield significantly. These plants produce predominantly female flowers and set fruits without pollination.
CUCUMBER ? MONOECIOUS TO GYNOECIOUS: Cucumber; the varieties which are cultivated worldwide now-a-days are of gynoecious variety. Gynoecious means induction of female flowers and fruits at every nodes. Farmers and consumers, both prefer the gynoecious variety but Bangladesh lacks such variety. Agricultural scientists and breeders at Lal Teer Seeds (LTS) have been looking for the gynoecious trait in cucumber. Generally, out of different growth promoting hormone, auxin plays a vital role to define flower sex of cucumber. High auxin concentration tends to promote ethylene synthesis which favours the development of female flowers. So, based on this physiological information, breeders at LTS are trying to stop the ethylene signalling pathway to induce male flower, instead of female. They use silver ion chemical to induce male flower on gynoecious plant to maintain this noble trait. However, it is difficult to induce male on time for pollination and maintain pollen sterility.
To overcome this shortfall, breeders are using chemicals for mutation and TILLING to develop gynoecious line of cucumber. TILLING (Targeting induced Local Lesions in Genomes) is a method in molecular biology that allows the identification of mutation in a specific gene. In this process, seeds are treated with EMS (Ethyl Methane Sulfonate), a mutagenic chemical and a large mutant population is generated. Then DNA is extracted and subjected to mutation screening in genes controlling flower sex determination. There are five genes involved in sex determination of cucumber. Out of these five genes, if the monoecious gene CsACS2 is altered by mutation on TILLING platform, there might be a chance to transition the monoecious flowering character to gynoecious. Finally, back crossing with the base population creates a reverse sex type monoecy to gynoecy as a result of reverse genetics. Besides, mutant gene can be used in a hybridisation programme of cucumber in which the mutant gene can be incorporated into the genome of the preferred variety by cross-breeding. This is the way newly found trait is transferred to the new variety. Breeders in LTS are following the above process to achieve their target.
DEVELOPMENT HYBRID PLANTS ? PAST AND PRESENT: Major genetic mutations and modifications were made in the past by plant breeders. One such modifications that has fuelled past agricultural revolution was "turning the plants flowering signal to increase yield and developing hybrid plants, which can tolerate different climate, enhance growth and resist diseases. In early days, beneficial development like these were discovered by chance. Modern genomics has revealed that most of these are rooted in two core hormonal systems: Florigen which control flowering and Gibberellin which influences stem height. Recently available biotechnological tools like gene editing (CRISPR-Cas 9) can be applied to change the core system within the wide varieties of plants and do not have to wait to be discovered by chance.
Many of today's innovations are the results of both continuous innovations, improvement and disruptive innovations. It is the human insecurity that drive scientific advances to improve the quality of life. One such situation is knocking at the door. Thus, the immediate strategy should be to improve the agricultural productivity. Such strategy must be based on innovations of plants that enable farmers to face the challenges such as limited land, diseases and climate change. This will help farmers grow enough food to feed the growing population.
One recent example is the improvement in cotton plants by dwarfing the plants in China. Chinese scientists have transformed the normally sprawling cotton plant, usually ideal for southern China, into a more compact bush type, faster growing and early flowering. Such plants are better suited for China's northern climatic regions. This dwarfing system was also applied to Rice Plants to avoid damage to plants due to heavy wind and/or storm.
TINKERING IN THE CORE SYSTEM: The replication of the same techniques to different plants to achieve same results push us to think that the "core system of wide varieties of plants function in the same manner", even though these plants are very different in terms of their phylogeny. In another way, we can think that despite the phylogenic difference in a plant, they function in the same way-- from making leaves to making flowers. To make such changes in the plants, scientists took the advantage of a mutation that affects florigen, the process which promotes flowering, and its opposite, antiflorigen.
If in the core system of the plants, Gibberellin, Florigen or both are affected by mutation, then it may result in one or more noble traits. After planting such mutated seeds, breeders identify such new traits. Then it takes many years of breeding or one may even say that "tinkering of one trait with another" until finally it is best tuned to produce a right plant with right traits.
FUTURE IMPROVEMENT: To overcome the future challenges, breeders will have to develop improved plant varieties which are: (a) Resistant to pests and diseases or can be treated for diseases with less inputs; (b)Tolerant of biotic-aboitic stresses; (c) Increased yields despite the impact of climate change; (d) More yield with minimum resources like land, water, nutrients; (e) and products shall meet the farmers and consumers preferences.
In Bangladesh, for example, onions are usually planted in early November. In 2019, much of the land in the onion growing areas remained inundated (November end) due to rain during October. As a result, planting in many areas were delayed to December. Late planting means late harvesting- April. By that time, early rainfall sets in. Thus, farmers may have to harvest early, just like in 2018. Early harvest will reduce the yield and water contents will be high. That will reduce the time of storability. If the onion price remain high, then farmers may even harvest early to encash the profit, before even the bulbs are fully grown. Such situation has created the short supply or shortage of onion in the market during late 2020.
In the case of Bangladesh, apart from the yield, three other traits are very important-- the storability, pungency and low water contents. Modern breeding tools and techniques opened the door of possibility to improve plants to tolerate such climate conditions during the sowing and harvesting season; in other words shortening the harvesting period to avoid early rains. It also has the ability to increase or decrease pungency. Such issues are not unique to onions but for many other crops. Take the example of papaya. Consumers prefer red flash and more sweetness. Present Bangladeshi varieties lack both of these traits. Modern breeding techniques can improve these two traits.
MUTATION-- EVOLUTION VERSUS INDUCEMENT: The improvement of crop variety has been taking place through evolutionary process of mutation from the beginning of agricultural age about 10,000-13,000 years ago. Darwin's theory of evolution (1806-1882) explains how the characteristics of any species changes over a period, through natural factors. His main arguments were: (a) there is a genetic variation in a species; (b) some genes aid in adaptation more than others; (c) those genes that aid their bearers in adapting to the environment will be passed on to future generations more frequently than those genes that do not. Through natural selection, the genetic make-up of a whole species can slowly change over a time span. Thus the theory of evolution is not only about genes but also the interaction between genes and environment. The change happens because they have a shared heredity evolved through natural selection.
But geneticists believe it is really the genes that control all organism. As such, characteristics of organisms are determined by genes. However, it is often said that 80 per cent of the variation among any spices is caused by variation in their genes. There is no denying fact that genes are a powerful influence on anatomies and physiologies of all species - human, animals and for plants.
However, the process is accentuated since the discovery of the Mendel's Law of Genetics, and further accelerated from early 20th century with the introduction of cross-breeding. Now the mutation breeding and tissue culture techniques combined with the new technologies of genome sequencing and elucidation of gene functions have created new tools and new opportunities for the breeders. Such new tools are helping to accelerate the selection process of new varieties further by assigning genetic markers to specific traits more efficiently. By genetical finger printing, plant breeders can select plants with best traits and then combine other noble traits through cross breeding for better hybrids, which can yield more with less resources.
As explained in earlier para, mutation is an evolutionary process. However, it can also be induced by radiation and chemicals. Mutation affects the core system- Gibberellins and florigen or both. Mutation may result some noble traits (sometime not) which are very helpful. Mutated gene of good traits can be identified by breeders in the plant. It then takes many years of experiments by plant breeders to figure out the usefulness of the new traits and determine the level of its quality. It is most likely that in future by using the new Molecular tools like gene editing, scientist may not only detect but may create more and more novel diversity in the two hormone systems of plants which will unleash the new agricultural revolutions. One of the key moments in the agricultural history is the Green Revolution, and now the world desperately needs one more agricultural revolution.
NEW PRECISION TOOLS OF BREEDING: New molecular tools of precision breeding will help plant breeders do their job in a precise manner more efficiently and quickly, compared to the past. New tools like CRISPR - Cas-9 mechanisms -- do not only randomly increase the genetic variations, as it is done by radiation or chemical mutagenesis, but also precisely introduce mutations in genes of known functions. They are now able to either impair the particular gene functions by deleting or by improving their functions. These precision breeding tools can create plants that might also have been produced by conventional breeding methods like chemical or radiation mutagenesis. However, these plants cannot be distinguished from one another with respect to breeding methods that have been used to create these plants. The only difference lies in the efficiency of the process and the efficiency of the plants, in terms of particular traits and yield.
New molecular tools, known as precision breeding, can help improve specific traits but they need to be integrated in the desirable agro-economic characters, in terms of preferences of consumers and the requirement of farmers. For example, a plant that possess the noble traits of disease or pest resistance, but having very low yield is of no value to the farmers, or an onion variety of high yield but not pungent and contains high water contents or less storability will not be a preferable variety to Bangladeshi consumers and/or farmers. As the growing population and climate change endangering the food security, scientists around the world are working to overcome such challenges that are threatening the dietary needs of not only humans but also of livestock.
TIME AND COST TO DEVELOP NEW VARIETY: The seed industry works with plant breeders to create added value by developing new varieties of crops. Each new variety takes 8 to 11 years to develop, depending on the breeding methods. The cost to develop each new variety is difficult to determine but some estimates that in the United States the cost of developing some widely cultivated high value crops variety may even exceed US$100 million, like corn or Soybean. As the cost of developing a new variety is very high, seed companies usually tend to invest in crops which are widely cultivated to recover the investment made in R&D as soon as possible. However, the new molecular tools can reduce the time and cost both, to develop new varieties.
Abdul Awal Mintoo, M.Sc in Agricultural Economics, is a former President of the FBCCI.
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