Induced mutations for enhancing nutrition and food production

Article Induced mutations for enhancing nutrition and food production S. Mohan Jain* and P. Suprasanna** *Department of Agricultural Sciences, University of Helsinki, PL-27, Helsinki, Finland Email: [email protected] **Nuclear Agriculture & Biotechnology Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085. Email: [email protected] Received March,15 , 2011 Accepted May, 14, 2011 Geneconserve 40 : 201 – 215 (2011) Abstract Issues of enhanced food security depend primarily on increasing agricultural production. Given this challenge, existing and new, appropriate technologies need to be integrated into agricultural research, to focus on the problems related to improving nutritional security. Among the different approaches, mutagenesis and the isolation of improved or novel phenotypes in conjunction with conventional breeding programmes can result in mutant varieties endowed with desirable traits. Induced mutations play an important role enhancing nutritional quality in crop plants. Several mutant genes have been successfully introduced into commercial crop varieties that significantly enhance the nutritional value of crops. This review briefly outlines the aspects of induced mutations and nutritional quality in crop improvement. Introduction Agricultural development has always been on the move towards increasing crop productivity and exploiting natural resources. Such a developmental program necessitates coordination between agricultural activities, ecosystems, and human society. It is imperative that sustainable use of natural resources should be prudently managed in conjunction with the advancement in the knowledge gained from science and technology. Today human population is growing rapidly especially in the developing countries whereas in the developed countries the situation is just the reverse. Global food security continues to be the centre stage issue and plant breeders are under pressure to sustain the food production to meet the demand of ever-growing human population. Further to the problem, the erratic climatic change because of its direct effects on both food production and food security has mounted the pressure to develop sustainable (Jain 2010a). Several factors such as abiotic and biotic stresses, industrial pollution, deforestation, loss of genetic diversity, water shortages and so on are responsible for having a negative impact on food production. The world population is expected to reach 7 billion in the next 20 years, and 10 billion by 2050. The question is, Can we feed the world and sustain nutrition balance in the diet at the affordable price with the available technologies? The answer seems to be not so positive even though plant breeders are making all out efforts to sustain food production and nutrition to make genetic improvement of plants by using conventional and modern tools. Pundit Jawaharlal Nehru, the great former prime minister of India, remarked in the late 50s that “Everything else can wait but not agriculture” and this remark remain relevant today. There is no short-term magic formula to solve the world’s food problems. The genetic variability is highly desirable for developing new cultivars, which is induced by mutagen treatments and natural spontaneous changes. The spontaneous mutation rate is pretty low and can’t be exploited for breeding and that is why artificially mutations are induced with physical and chemical mutagen treatment. Quite many useful genetic changes have been induced by mutagen treatment including high yield, flower colour, disease resistance, and early maturation and so on in crop, vegetables, medicinal herbs, fruit and ornamental plants. So far, over 3000 mutant varieties have been officially released over 60 countries including rice, wheat, barley, sorghum, legumes, cotton, edible oil, ornamental plants and fruits (www-mvd.iaea.org). China and India are the major producers of mutant varieties to feed their ever-growing human population. Among all crops, the released highest number of mutant varieties is in rice. In 2005, The International Atomic Energy Agency (IAEA), Vienna, Austria was conferred Nobel Peace Prize for its contributions to the peaceful applications of nuclear energy in various fields including food and agriculture. This award was a shot in the arms by recognising the major contributions made with the use of nuclear energy in enhancing food production and economic benefits worldwide. The year 2008 marked the 80th anniversary of mutation induction in crop plants, when an international symposium on induced mutations in plants was organised in Vienna, Austria (Shu, 2010). The foremost objective of plant breeders and geneticists is to sustain food and nutrition security and that is why the selection of major crops has become crucial for meeting these goals under the existing arable land, and climate change. Malnutrition with respect to micronutrients like vitamin A, iron, and zinc affects more than 40% of the world’s population. Micronutrient deficiencies are common in many developing countries and are typically due to inadequate food intake, poor dietary quality and poor bioavailability (Fig. 1, Ramakrishnan 2002). For example in wheat, zinc is quite low in grain and consequently deficient in human diet among the developing countries, and to supplement it needs zince enriched wheat grains at the farmer’s field (Hussain et al 2010). World major crops like rice, wheat, maize, barley etc., would require continuous modifications for sustainable food production, where as nutrition security would be maintained by improving legumes, vegetables, and fruits. For example banana and plantain are among the world’s major food crops, and are considered as the poor man’s fruit crop, and have potential to provide subsistence diet and nutrition to millions of people. However, the major problem with fruit breeding work is long life cycle of many fruit crops, which varies from 3-25 years or even more. The large juvenile period has hampered fruit breeding work. In fruit crops, mutagenesis has been quite useful in isolation of useful mutants such as plant size, blooming time, fruit ripening, fruit colour, and resistance to pathogens. Another major fruit crop is date palm (Phoenix dactylifera L.), a major source of human nutrition including vitamins, sugars, fat, salts and minerals, and oils; and has high potential to produce bio-ethanol (Jain 2011; Jain et al 2011). Induced mutations Mutations are induced by physical (gamma radiation, high and low energy beams) and chemical (ethyl methane sulfonate, EMS) mutagen treatment of both seed and vegetative propagated crops. The mechanism of mutation induction is that the mutagen treatment breaks the nuclear DNA and during the process of DNA repair mechanism, new mutations occur randomly and are heritable. The changes can also occur in cytoplasmic organelles and also results in chlorophyll mutations, chromosomal or genomic mutations that enable plant breeders to select useful mutants such as abiotic and biotic stresses and others. By induced mutations, mutants with multiple traits can be identified. The chances of survival varieties are much higher under the climate change. In Vietnam, eight rice mutant varieties have been developed with multiple traits like high quality, tolerance to salinity and short duration allowing three harvests per year providing farmers an extra income of 300 million US dollars. Moreover, mutant varieties are readily accepted by the consumers. Induced mutations have played a pivotal role in enhancing world food security, since new food crop varieties with various induced mutations have contributed to the significant increase of crop production at locations people could directly access (Kharkwal and Shu 2010). Among physical mutagens, gamma radiation has been widely used for mutation induction for both seed and vegetative propagated crops. Recently ion energy technology- heavy ion beam (HIB) and low energy ion beam (LIB)- is being for mutation induction in wide ranging crops. HIB is predominantly used for inducing mutations in plants (Jain, 2010a). They transfer linear energy transfer (LET) and enhances the induction of higher biological effects. Several Arabidopsis mutants have been obtained including deletions, insertions, and chromosomal translocations by HIB. Plant cell tissue culture has made tremendous progress towards plant regeneration from all major food and horticultural crops. Micropropagation via organogenesis is routinely used for clonal propagation of ornamental plants and other vegetative propagated plants, especially woody and fruits trees. Explant (shoot meristem, adventitious buds, and microspores) is directly treated with mutagen and direct shoots are regenerated followed by root formation (Suprasanna et al. 2010). Regenerated plants are maintained in the greenhouse and put under the selection pressure. Similarly somatic embryogenesis of vegetative propagated crops (banana, date palm, cassava and others) are readily induced. The advantage of mutagen treatment to embryogenic cell suspension that chimeras are either eliminated or dramatically reduced, and could get mutant somatic embryos which are regenerated into plantlets. Embryogenic cells are plated on a filter paper and put on agar solidified medium; treat cells with gamma radiation followed by transfer them on culture medium and allow them to form somatic embryos. The treated cells can also be put under the selection pressure in order to isolated mutants, e.g. disease, salt, drought tolerant mutants. The selected mutant plants are transferred in the greenhouse and finally to the field evaluation and use them for crossing with other varieties. The radiosensitive curve should be determined to calculate LD50 dose (Lethal dose) for each experimental plant to avoid either very high or very low dosage. Moreover, plants and even varieties differ in radio sensitivity. Low dose of gamma radiation has promoted growth in citrus depending of cultivar (Fig. 2), maintain embryogenic nature of date palm for 2-3 years, promote growth in orchids, enhances secondary metabolites in medicinal plants, and used for improving shelf life of post harvest products A range of several mutants in different ornamental plants, maize, rice and wheat have been isolated and used for crop breeding. Similarly LIB has been used for mutation breeding and gene transfer. This method has many advantages such as low damage rate, higher mutation rate and wider mutation spectrum. In rice, 11 new lines of rice mutants with higher yield, broader disease resistance, and shorter growing period and high grain quality were developed and now being cultivated in China. In jasmine rice from Thailand, a wide range of mutants were recorded including short stature, red/purple colour of leaf sheath, collar, auricles, ligules and dark brown stripes on leaf blade, dark brown seed coat and pericarp. Mutation induction for quality and nutrition improvement Besides increase in yield of a crop, quality and nutrition components are equally important in human diet. There is a necessity to enhance mineral elements (biofortification) and amino acids essential for human and animals, alteration of protein and fatty acids profiles for nutritional and health purposes, change of physicochemical properties of starch for different end uses, enhancement of phyto-nutrients in fruits and reduction of anti-nutrients in staple food. Induced mutations could play an important role in inducing mutations for enhancing nutritional quality in crop plants. Of the 3000 mutant varieties developed globally, 776 mutants (Fig. 3) have been induced for nutritional quality (www-mvd.iaea.org). Collaborative research programme under Food & Agriculture Organization and International Atomic Energy Agency (FAO/IAEA) has been focussed on at crop improvement by induced mutation using nuclear techniques (Jain 2000) intended to produce strains of cereals with higher concentrations of micronutrients and improvement of their bioavailability by reduction in the concentration of phytic acid. In this regard, strategies should be aimed at breeding plants that can contain high levels of minerals and vitamins in their edible parts to reduce substantially the recurrent costs associated with fortification and supplementation (Shetty 2009). Such a strategy will be successful depending on farmer’s willingness to adopt such varieties, palatability of the edible parts of these varieties and consumer acceptability, and if the incorporated micronutrients can be absorbed by the human body (Bouis 2002). Certain considerations need to be addressed before a plant breeding strategy can be put in place to combat micronutrient deficiency to function and to have universally adoptability, particularly in Developing Countries (Bouis 2002). These include, feasibility to breed micronutrient- dense staple food varieties, effects on plant yields and farmer’s adoption of such varieties, possibility of changes that micronutrient density can have a great nutritional balance on the staple diet of consumers, bioavailability of extra micronutrients in staple foods to humans, and alternate options for more easily sustainable strategies for reducing micronutrient malnutrition. Several mutant genes have been successfully introduced into commercial crop varieties that significantly enhance the nutritional value of crops like maize, barley, soybean, and sunflower. In maize, quality protein maize (QPM) varieties are grown on hundreds of hectare land. They have almost twice higher amount of lysine and tryptophan, and 30% less leucine as compared to parental lines; shown a dramatic effect on human and animal nutrition, growth and performance. In cassava, three mutants have been isolated showing different size of starch grain. They have high economic potential for industrial use of starch and influence on cooking quality. Small starch grain size seems to be highly suitable for bio-ethanol production. In sweet sorghum, a mutant variety Yuantian No.1 has been developed in China (Fig. 4), which has 20% more total carbohydrates as compared to the parental lines; well suited for Food, Feed and Bio-energy (three in one). Five rice giant embryo mutants, characterized by enlarged embryo than that of wild type were found to have increase in the contents of protein, vitamin B1, vitamin B2, vitamin E, essential amino acids such as arginine, aspartic acid, glutamic acid, lysine, methionine and mineral elements such as calcium, iron, potassium, phosphorus and zinc (Zhang et al. 2007). In banana, several mutants have been isolated for different traits, namely reduced height, tolerance to Fusarium wilt, early flowering, large fruit size, Black sigatoka tolerant types (Jain, 2010b). In date palm, several mutant lines tolerant to Bayoud disease, caused by Fusarium oxysporum f. albedinis fungus, and the plants are already in the field for the last four years and growing well in Algeria (Jain 2007). New mutant varieties of barley, wheat, rice and soybean with low phytic acid (LPA) have been released and has facilitated to reduce both phosphorous pollution and increase bioavailability of phosphorous and micronutrient minerals in cereals and legumes. Relevance of Biotechnology and biofortification Prasad (2010) identified three major micronutrient deficiencies in humans which include vitamin A deficiency, iron deficiency and iodine deficiency. Micronutrient deficiency of Zn has also received global attention (Hussain et al, 2010). In addition, improving the content of essential amino acids in important staple foods, such as rice, has gained interest (Welch and Graham 2004). Rice is also one of the priority crops for enhancement of the nutritional factors such as vitamin A, Zn and iron through international schemes such as Harvest Plus (Pfeiffer and McClafferty 2007). Increase in bioavailability of Fe in rice has been investigated by transferring a gene for heat resistant phytase from fungal sources that degrades phytate in plant (Bhat and Vasanthi 2005) which may also increase the Zn bioavailability in rice. An adequate concentration of micronutrients seems to be essentially required in major staple crops if these crops are addressed to provide a sustainable solution to the problem of malnutrition (Pinstrup-Anderson and Pandya- Lorch 2001). This holds true for cereals since majority of the population in the developing world depend on cereal based food intake. Rice alone contributes to 23% of the energy consumed worldwide and countries that rely on rice as the main staple often consume up to 60% of their daily energy from this cereal (Khush 2003). Conventionally, nutrient content of crops can be improved by using field fortification strategies, to enhance the micronutrient and trace element content of crops by applying enriched fertilizers to the soil. Biotechnological tools have generated new opportunities to improve the amount and availability of nutrients in plant crops. These include simple plant selection for varieties with high nutrient concentration in the seeds, cross-breeding for incorporating a desired trait within a plant, and genetic engineering to manipulate the nutrient content of the plant (King 2002). One of the successful examples in using the genetic engineering approach is the production of “Golden Rice” involving the transfer of the genes necessary for the accumulation of Carotenoids (vitamin A precursors) in the endosperm that are not available in the rice gene pool. The first generation Golden Rice with a gene from daffodil and a common soil bacterium drew considerable criticism as a technological solution to a problem associated with poverty and hunger. It was argued that Golden Rice would encourage people to rely on a single food rather than the promotion of dietary diversification. The development of Golden Rice 2 by replacing the daffodil gene with an equivalent gene from maize increased the amount of beta carotene by about 20-fold resulting in about 140 grams of the rice providing a child’s RDA for beta carotene (Raney and Pingali 2007). It has also been recently demonstrated that beta carotene from golden rice is efficiently converted to vitamin A in humans (Tang et al. 2009). Neglected/underutilized crop resources for nutrition provision Agricultural biodiversity is essential both in terms of food and nutritional security. Diversity of kingdoms, species and gene pools can increase the productivity of farming systems in a range of growing conditions, and more diverse farming systems are also generally more resilient in the face of perturbations, thus enhancing food security, better nutrition and greater health (Ochatt and Jain, 2009; Frison et al. 2011). Global food security depends mostly on a handful of cultivated species and more than 50% of the daily requirement of proteins and calories is derived from three major crops viz., wheat, maize and rice (Bharucha and Pretty 2010). More than 7000 wild plant species are known to have been used for human food at some stage in human history (Grivetti and Ogle 2000); in India, 600 plant species are known to have food value (Rathore 2009). In contrast, the availability of orphan- or understudied-crops as the major staple food crops in many developing countries has contributed significantly. Some examples include, cereals (e.g. millet, tef, fonio), legumes (cowpea, bambara groundnut, grass pea), and root crops (cassava, yam, enset). Orphan crops are in general more adapted to the extreme soil and climatic conditions prevalent in Africa than the major crops of the world. Minor millets, which are high in nutrients such as calcium and iron, are grown primarily in hilly, arid areas of India where, because of their high tolerance to drought, they are often more productive than other grains (Tadele, 2009ab; Anon. 2010). However, due to lack of genetic improvement, orphan crops produce inferior yield in terms of both quality and quantity. The majority of the world’s food is produced from only a few crops, and yet many neglected and under-utilized crops are extremely important for food production in low income food deficit countries (LIFDCs). As the human population grows at an alarming rate in LIFDCs, food availability has declined and is also affected due to environmental factors, lack of improvement of local crop species, erosion of genetic diversity and dependence on a few crop species for food supply. Neglected crops are traditionally grown by farmers in their centres of origin or centres of diversity, where they are still important for the subsistence of local communities, and maintained by sociocultural preferences and traditional uses. These crops remain inadequately characterised and, until very recently, have been largely ignored by research and conservation. Radiation-induced mutation techniques have successfully been used for the genetic improvement of “major crops” and the know-how will greatly benefit genetic enhancing of under-utilized and neglected species towards their domestication and crop improvement. Realizing such a need, the FAO/IAEA initiated a program on genetic improvement of under-utilized and neglected species through a Coordinated Research Project on “Genetic Improvement of Under-utilized and Neglected Crops in LIFDCs through Irradiation and Related Techniques” in 1998. The overall objective was to improve food security, enhance nutritional balance, and promote sustainable agriculture in LIFDCs (IAEA-TECHDOC.1426, 2004, Jain, 2009). The species that were studied included medicinal and aromatic plants that are important for the West Asia and North Africa [e.g. argel (Solenostemma arghel), caper (Capparis spp.), oregano (Origanum syriacum), mint (Mentha piperita), liquorice (Glycyrrhiza glabra), aloe (Aloe spp.), coriander (Coriandrum sativum), cumin (Cuminum cyminum) and henna (Lawsonia inermis)], Andean grains for Latin America [e.g. quinoa (Chenopodium quinoa), canihua (C. pallidicaule) and amaranth (Amaranthus caudatus)] and nutritious millets for Asia [e.g. finger millet (Eleusine coracana), Italian millet (Setaria italica) and little millet (Panicum miliare)] (Jain, 2009). Reverse and forward genetics The new gene discovery with reverse and forward genetics will open the way for developing functional genomics plant breeding. The general strategy for reverse genetics is called TILLING (Targeting Induced Local Lesions in Genomics) or coming together with traditional mutagenesis functional genomics (Gilchrist and Haughn, 2005; Tadele et al 2010). TILLING allows the identification of single-base-pair allelic variation in a target gene in a high-throughput manner. Furthermore DNA sequence information of mutants or crop plants facilitate the isolation of cisgenes, which are genes from crop plants themselves or from crossable species (Jacobsen and Schouten 2010). The increasing numbers of these isolated genes provide an opportunity to improve plant breeding while remaining within the gene pool of the classical breeder or mutation breeder. Finally, a multiple disciplinary approach would be ideal by including conventional and mutation breeding together with the molecular tools for developing new crop varieties with high yield with improved nutritional qualities in sustaining food and nutritional security worldwide. Conclusion Nutrition security is integral to food security. Induced mutations are significant as novel mutations are being isolated for enhanced nutrition quality of crop plants, for ex. micronutrients, protein, amino acids, fatty acids and vitamins. Another source of nutrition provision is from the neglected and underutilized crops, and requires more attention together with the major crops for enhancing nutrition provision to the ever-growing human population. Perhaps change of food habits would be required gradually move away from the consumption of major crops and start using underutilized crops either singly or in combination of both. Developing genetically novel germplasm with increased content of these together with other health benefit components becomes more feasible concurrent with the enhancement of breeding techniques, genomics, molecular manipulations and genetic engineering. The cost effectiveness of applying new technologies and trained manpower would be of paramount importance for nutrition provision to the low cost nations. References Anon. 2010. Bioversity International: Unlocking the potential of minor millets. http://www.bioversityinternational.org/nc/announcements/unlocking the_potential_of_minor_millets. 18 October 2010. Bharucha, Z. and Jules Pretty 2010. The roles and values of wild foods in agricultural systems. Phil. Trans. R. Soc. B 27 September 2010 vol. 365 no. 1554 2913-2926 Bhat, R. V. and S.Vasanthi. 2005. Food safety assessment issues of transgenic rice in the Indian context. In Biosafety of Transgenic Rice (eds Chopra, V. L., Shanthanam, S. and Sharma, R. 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(modified after Tadele, 2009) Common Name African eggplant African yam bean Amaranth Bambara groundnut Barbados cherry Cassava Chickpea Dika Botanical name Important trait Solanum aethiopicum High yielding Sphenostylis stenocarpa High protein content Amaranthus spp. Vigna subterranea Fast growing Rich in protein, drought tolerant Rich in vitamin Malpighia glabra Finger millet Manihot esculentum Cicer arietinum Irvingia gabonensis, wombolu Eleusine coracana Fonio Noug Quinoa Digitaria exilis Guizotia abyssinica Chenopodium quinoa Sesame Sweet potato Sesamum indicum Ipomoea batatas Tef Eragrostis tef Vernonia Vernonia galamensis I . Drought tolerant Protein source oil-rich Rich in iron, protein; low in glycaemic index Fast maturing High oil content High in protein content oxidatively stable oil rich in riboflavin and calcium Tolerant to abiotic stresses; free of gluten High oil content Figure 1. Global prevalence of micronutrient malnutrition* (Ramakrishnan 2002) *For more details, please refer Ramakrishnan (2002) Figure 2: Differential response of citrus varieties to different doses of gamma radiation treatment. Citrus var. Losslille is more radiation tolerant when compared to two other varieties: 30 Gy dose promotes shoot growth, which is much better than the control as well as other two varieties. Radiation dose effect on citrus Figure 3. Global mutant varieties with nutritional quality and other desirable attributes (based on the data from www-mvd.iaea.org; September 2010) Figure 4: A new sweet sorghum mutant variety, which is suitable for food, feed, and bioenergy New Sweet Sorghum Mutant Variety Yuantian No.1