Modern Biotechnology as an Integral Supplement to Conventional Plant Breeding: The Prospects and Challenges

The art of plant breeding was developed long before the laws of genetics became known. The advent of the principles of genetics at the turn of the last century catalyzed the growth of breeding, making it a science-based technology that has been instrumental in substantial improvements in crop plants. Largely through exploitation of hybrid vigor, grain yields of several cereal crops were substantially increased. Intervarietal and interspecific hybridizations, coupled with appropriate cytogenetic manipulations, proved useful in moving genes for resistance to diseases and insect pests from suitable alien donors into crop cultivars. Plant improvement has been further accelerated by biotechnological tools of gene transfer, to engineer new traits into plants that are very difficult to introduce by traditional breeding. The successful deployment of transgenic approaches to combat insect pests and diseases of important crops like rice (Oryza sativa L.), wheat (Triticum aestivum L.), maize (Zea mays L.), barley (Hordeum vulgare L.), and cotton (Gossypium hirsutum L.) is a remarkable accomplishment. Biofortification of crops constitutes another exciting development in tackling global hunger and malnutrition. Golden Rice, genetically enriched with vitamin A and iron, has, for example, the real potential of saving millions of lives. Yet another exciting application of transgenic technology is in the production of edible vaccines against deadly diseases. How these novel approaches to gene transfer can effectively supplement the conventional breeding programs is described. The current resistance to acceptance of this novel technology should be assessed and overcome so that its full potential in crop improvement can be realized. APARAMOUNT FACTOR in the evolution of human civilizations was a steady supply of food. Food production is therefore the oldest profession of humanity. The processes of crop cultivation and selection were an integral part of human activity. Although early “plant breeding” was developed essentially as an art, its scientific basis became well established with the rediscovery of laws of genetics at the turn of the last century. And with the application of the principles of genetics to crop improvement, the period from 1930 to 1970 witnessed a phenomenal increase in crop yields, particularly of cereal grains (Khush, 1999). Largely through exploitation of hybrid vigor, maize, pearl millet [Pennisetum glaucum (L.) R. Br.], and sorghum [Sorghum bicolor (L.) Moench] registered a considerable increase in grain yields during 1965 to 1990 (Khush, 2001; Jauhar and Hanna, 1998; Jauhar et al., 2006). Improved wheat and rice varieties with reduced height developed by incorporating dwarfing genes in the 1960s and 1970s launched the famous Green Revolution in Asia (Khush, 1999; see also Jauhar, 2006). Around the same period, the advent of the tools of cytogenetics greatly facilitated wide hybridization and chromosome-mediated gene transfers from wild species into cropplants (Jianget al., 1994; Jauhar, 1993, 2003a; Friebe et al., 1996; Fedak, 1999). Chromosome engineering methodologies, based on the manipulation of pairing control mechanisms and induced translocations, were, for example, applied to transfer into wheat cultivars specific disease and pest resistance genes of alien origin (Ceoloni and Jauhar, 2006; Jauhar, 2006;Mujeeb-Kazi, 2006). Thus, cytogenetic tools were instrumental in the genetic improvement of several crop plants, particularly cereals. The development, in the last decade and a half, of novel tools of direct gene transfer, collectively termed genetic engineering, has added newdimensions tobreeding efforts. Genetic engineering is defined as any nonconventional tool aimed at mobilizing specific genetic information from onemember of the plant kingdom (or, for that matter, any organism) into another. (Any nonconventional tool of today may of course become conventional in the future.) These asexual techniques of biotechnology help engineer into plants new characters that are otherwise very difficult to introduce by conventional breeding. The molecular techniques, including the recombinant DNA methods, involve the introduction of well-characterized alien DNA into the recipient plant cells of regenerable embryogenic calli to permanently transform the plant’s genetic makeup. Genetic engineering has the potential to accelerate crop improvement and has already yielded encouraging results (e.g., Jauhar andChibbar, 1999;Muthukrishnan et al., 2001; Repellin et al., 2001; Dahleen et al., 2001; Janakiraman et al., 2002; Patnaik and Khurana, 2003; Wesseler, 2003; Sharma et al., 2004). Value-added traits engineered into crop plants include resistance to fungal and viral diseases, and biofortification of their nutritional status (Jauhar and Khush, 2002; Schubert et al., 2004; Bajaj and Mohanty, 2005). However, as with any new technology, genetic engineering is encountering resistance from some sections of the public. There are concerns about the potential adverse impact of geneticallymodified (GM) foods USDA–ARS, Northern Crop Science Laboratory, Fargo, ND 58105. Mention of tradenames or commercial products in this publication is solely to provide specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. Received 30 Jan. 2006. Invited paper. *Corresponding author (prem. [email protected]). Published in Crop Sci. 46:1841–1859 (2006). Research & Interpretation doi:10.2135/cropsci2005.07-0223 a Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: Bt, Bacillus thuringiensis; FHB, Fusarium head blight; fl-GISH, fluorescent genomic in situ hybridization; GM, genetically modified; PDR, pathogen-derived resistance; QPM, quality protein maize. R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 1841 Published online July 25, 2006