Differences in Yields Between Transgenic and Conventionally Bred Crops
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This document summarizes findings from a survey of yield differences between transgenic and non-transgenic crops. The survey found no clear evidence that GM crops yield more than conventionally bred crops due to a lack of valid comparative trials. GM crops are derived from a single parent and carry one or few transferred genes, whereas conventional crops benefit from hybrid vigor through crossing varieties. The document goes on to describe methods of plant breeding, including traditional, Mendelian, and Isolection breeding, and compares these proven methods to GM technology which aims to transfer genes via cell bombardment.
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Differences in Yields Between Transgenic and Conventionally Bred Crops
- 1. A SURVEY OF YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS ERTRAGSDIFFERENZEN ZWISCHEN GENETISCH MODIFIZIERTEN UND KONVENTIONELL GEZU¨ CHTETEN KULTURPFLANZEN P.M. GUERINa and T.F. GUERINb, * a 1ALockyerSt.,Lithgow,NSW2790,Australia;b 3/32WolliCreekRd,Banksia,NSW2216,Australia (Received 11 April 2003) In the current survey, there was no clear evidence that GM (genetically modified) crops are higher yielding than those conventionally bred1 . Furthermore, there were no trials to support valid comparisons of yield per se. This article investigates GM crop yields, introducing the importance of hybrid vigour and a non-stress environment for higher percentage heritability selection and therefore more productive conventional plant breeding and improved crops. GM technology and crops are compared with proven plant breeding methods, with respect to hybrid vigour and the economic viability of both systems. These proven methods of plant breeding are (1) traditional landrace cropping, (2) conventional Mendelian breeding and (3) Isolection Mendelian breeding, and are also considered historically. INTRODUCTION Yield data from GM (genetically modified) crops compared to conventionally bred1 crops are not supported by valid comparisons of yield per se. Such valid comparisons are now needed to compare yield differences in the two plant production systems. GM crops have one parent only, to which is transferred only one, or a limited number, of genes from an organism in another genus (hence the term ‘transgenic’). Currently this gene (or genes) gives the plant resistance to chemical spraying for control of either weeds or pests. Conventional crops, on the other hand, derive from crossing intraspecific varieties to unite a multitude of ‘matching genes’ from two parents, conferring hybrid vigour. This hybrid vigour applies to all conventionally bred crops but not to GM crops. Furthermore, yield comparisons are invalid without specifying the environment and its interaction with the varieties being compared. There are proven agro-ecological factors of weed and pest control: crop rotation and length of fallow, specially suited for high-yielding conventional varieties, depending on regional soils and climates (Fettell, 1980), which should not be overlooked with the *Corresponding author: E-mail: turlough.guerin@bigpond.com 1 Crops have been bred on sound genetical lines since discovery of Mendel’s laws in 1900. Archives of Agronomy and Soil Science, June 2003, Vol. 49, pp. 333 – 345 ISSN 0365-0340 print; ISSN 1476-3567 online # 2003 Taylor & Francis Ltd DOI: 10.1080/0365034031000151080
- 2. advent of GM technology. This article compares GM and conventionally bred crops, introducing the importance of hybrid vigour and a non-stress environment for higher percentage heritability selection and therefore more productive conventional plant breeding and improved crops. SCOPE AND PURPOSE In this article, GM technology and crops are compared with proven plant breeding methods, with respect to hybrid vigour and the economic viability of both systems. These proven methods of plant breeding are also considered historically. These methods are (1) traditional landrace cropping, (2) conventional Mendelian breeding and (3) Isolection Mendelian breeding. Background Information on comparative crop trials in Australia has been limited. Table I highlights the results of a survey conducted by the authors in 2002, which illustrates the variability of yields from trials. These findings indicate that comparative crop trials have not been widely conducted and/or communicated, and that much of the existing yield data is qualitative only. Furthermore, there was no evidence that these trials were scientifically designed to enable assessment of yield per se. Studies are, however, emerging outside Australia comparing GM crops with conventionally bred crops, though few are scientifically designed for meaningful comparison of GM crops with those that are conventionally bred. For instance, a report by the British Soil Association, on GM crops in North America, found that with the exception of crops possessing Bacillus thuringiensis (Bt) for pest resistance, the GM crops yielded lower than conventional crops (Anonymous, 2002a). Despite higher yields with Bt corn, US farmers lost $US 1.31 per acre ($A6 per hectare). The Soil Association reported widespread contamination of seed sources, crops and the human food chain, with GM crops costing the US economy $US12 billion over the past 2 years. Another report from the Canola Council of Canada seemed to favour GM crops (Anonymous, 2002b). The Council reports an average increase of $C14.33/ha in net returns to Canadian farmers growing transgenic canola, but 37% of Canadian farmers are staying with conventional lines because the cost, $C37/ha, of the Technology Use Agreement, is prohibitive. In addition, if a hybrid GM canola was being reported, it should have been compared with a hybrid non-GM canola, which would normally yield higher than its transgenic counterpart. In Arkansas, researchers found that transgenic soybeans yielded almost 10% lower than conventional soybeans (Lappe´ and Bailey, 1999). Other yield comparisons are given in Table II. We stress that the yield data presented in this table are survey data and do not represent the results of scientifcally designed trials to assess the effect of yield per se. The remainder of the article describes and compares GM crop technology and conventional plant breeding, taking into account both genetics and environment. GM crop technology Gene technology enables plants to be cloned from a single cell of the parent plant. Gene transfer technology then enables cloned genes for a desired trait to be blasted into 334 P.M. GUERIN and T.F. GUERIN
- 6. cultured plant cells with a ‘gene gun’ that forces the genes into the cell. The cells are cultured to form a tissue mass that will grow into a plant carrying the gene or genes for herbicide or pest resistance. This results in a source of inefficiency for breeding programmes and high cost, in transferring the new gene into a commercially desirable conventional variety of the crop species being modified. Out of millions of plant cells that are bombarded with metal particles coated with DNA, only very few cells take up the DNA. If the tissue piece were then cultured, the untransformed or native cells of the invaded plant (selected to take the gene) would rapidly grow and swamp the few cells that had the added gene. Therefore, selectable marker genes are used to favour the growth of the cells that carry the new gene (Anonymous, Undated). A selectable marker gene is a gene that confers resistance to a substance that is toxic to normal plant cells. This marker gene is delivered to plant cells with the introduced gene and the cells are cultured in the presence of the toxic compound, as well as plant hormones to induce the cells to divide and grow. Only cells that contain the marker genes as well as the new gene (for pest or herbicide resistance) are able to inactivate the toxic compound, in order to survive and grow into complete plants. The selectable marker genes may be antibiotic resistance genes conferring resistance to antibiotics, or herbicide resistance genes that confer resistance to herbicide. Medical and public concern about antibiotics will undoubtedly result in other methods. There are potential unintended consequences from gene technology. For instance, gene technologists claim that they are only controlling evolution. In fact they merely show that genetically modified organisms (GMOs), have a very low survival rate and that evolution, if it ever happened, was not by this process. This, however, should not be used as an argument for releasing GMOs. Cross-pollination can take place, giving rise to undesirable or weedy plants, animals or fishes, lacking in health and true hybrid vigour, or euheterosis.2 Genetic modification reduces euheterosis and depends upon backcrossing to elite, high yielding conventional varieties, before release. Outcrossing of GM with non-GM plants complicates the study of taxonomy and should be rigorously excluded from the Vavilovian3 centres of origin of specific crops and wild relatives. For example, GM mustard plants were found to be 20 times more likely to interbreed with related species than non-GM mustard plants (conventionally bred for the same herbicide resistance) (Burgelson et al., 1998). It has been reported that GM tomatoes have been grown without the consent or knowledge of regulatory authorities in Guatemala, where hundreds if not thousands of indigenous tomato varieties are grown. The same author also claimed that cross-pollination distances needed for strict isolation have been ignored, even for pharmaceutical crops, so long as potential dangers, in the 1995 joint consultation between WHO and FAO, were ‘judged to be unrelated to food safety’ (Anderson, 2000). Others claim that with regard to the process itself, the hazards of cancer to laboratory workers and farmers is confirmed by the discovery that Agrobacterium tumefaciens, the gene transfer vector for plants, can infect animal cells (Ho et al., 2000). There are also reports of GM foods and genetically engineered (GE) L-tryptophan causing sickness and death, respectively. As the GE-tryptophan had the same label as non-GE- 2 Euheterosis is hybrid vigour for sexual reproduction and seed yield. It is intra-specific. 3 Geographical centres of origin that possess plant varieties with wide genotypes and naturally occurring biodiversity. 338 P.M. GUERIN and T.F. GUERIN
- 7. tryptophan, it took months to link it to a disabling disease, eosinophilia myalgia syndrome (Bremner, 1999). Conventional crop plant breeding This is independent of genetic modification and may be divided into three productive methods or systems developed over 8 – 10 000 years and according to the results of particular plant breeders: (1) Traditional, (2) Conventional Mendelian and (3) the Isolection Mendelian breeding systems. These mechanisms are natural, like the agents of wind, pollinating insects and honeybees, all of which are prevented from causing evolution by means of the genetic barriers between species and even ecospecies. Here, however, the breeder controls the hybridizations and selections. All three methods can benefit from the heritability of selections (see Isolection system) made in non-stress conditions (i.e., hand spacing of plants, not drill sowings). Traditional landrace cropping This is and has been a very successful period of maintaining peasant landraces of different species and ecospecies in the various so-called Vavilovian centres of origin of our cultivated crop plants. These are mixtures of homozygous plants most suitable for their particular soil and climatic conditions, e.g., small-seeded, rust-resistant varieties or eco-species in continental climates and large-seeded, early maturing types, in Mediterranean climates. These centres are also reservoirs of genes for high yield. Maize trials show that the degree of heterosis, when open-pollinated varieties are used in hybrid combinations, is considerably higher with varieties from Latin-America (rich in Vavilovian centres) than with US Corn Belt varieties (Mangelsdorf, 1952). There is ample evidence that our various crop species have had single and sudden origins. The great genetic variability present in isolated peasant farmers’ landraces suggests that they were created, not from single plants, but from a multitude of ‘first parents’ to produce their multicultural (due to companion cropping) varieties with resistance to a broad spectrum of rusts, blight and climatic variability. The companion cropping of peasants also reduces disease and increases total yields. Vavilov recorded the various large-seeded varieties of the Mediterranean centre of origin, relative to the continental centres. His critics put this down to the greater antiquity of Mediterranean agriculture but Vavilov found this to be no greater than that of Asia Minor, Afghanistan or China. Oat grazing trials at Glen Innes after 1957 vindicated Vavilov (see Conventional Mendelian Plant Breeding section). Farmers in the Vavilovian centres of origin should be encouraged to separately maintain their landrace varieties, free from introduced high yielding varieties, which soon succumb to rusts and blight. These unique centres are, or should be, universal reservoirs of germplasm in situ for all plant breeders, in preference to under-utilized gene banks (Harlan, 1992). Inbreeders and outbreeders Here we must distinguish out-breeders like maize from self-pollinated crops like wheat, oats and barley, peas and beans. The latter are designed to be resistant to inbreeding and respond well to pure-line breeding. There is enough natural crossing (4% in wheat, 0.5% in oats) to maintain their yields in the centres of origin. Darwin was probably right in stating that selection, over thousands of years, had not made our crop plants higher yielding (Darwin, 1868). Not until the twentieth century 339YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS
- 8. did hybridizations and introductions from the centres of origin combine to give significant increases in crop yields, and this is shown in the following sections. Conventional Mendelian plant breeding During Gregor Mendel’s life (1822 – 84), hybridizations between different varieties, or ecotypes within the same species, formed the basis of the Mendelian laws of inheritance. G.H. Shull later showed that the depression in yield, following inbreeding of maize, was due to homozygosity. He hypothesized that hybrid vigour must be associated with the heterozygosity arising from crossing. In 1914, he proposed the term ‘heterosis’ for this effect. His single-cross interline hybrids, however, yielded much lower than a standard maize variety on the same area. In 1917, D.F. Jones used double-cross interline hybrids to reduce the cost of seed sufficiently to justify hybrid seed production. This could increase maize crop yields by 25 to 35% and sometimes by 50%, as compared with the best selected open-pollinated varieties (Guzhov, 1989). Natural selection Regarding self-pollinated crops, it was assumed for half a century after Darwin that by selecting a certain type of plant for propagation, the species or variety would be continually transformed in the same direction. This was a result of acceptance of Darwin’s evolution theory and later of Galton’s ‘law’ of inheritance, as applied to selection. Selection work commenced by W. Johannsen in 1901 on common garden bean, Phaseolus vulgaris nana var. Princess, refuted this theory in papers he wrote from 1903 to 1913 (Babcock and Clausen, 1918). Princess was actually a blend of highly homozygous pure lines. Johannsen found that selection within a pure line was without effect. Louis de Vilmorin’s wheat plants also remained identical in all respects after 50 years during which annual selection had been continued. T.H. Morgan (1866 – 1945) also rejected the possibility of natural selection bringing about evolution and found that pleiotropy, the state in which one gene has effects on a number of different traits, could control several factors in Drosophila and even cause reduced fertility. This led to the hypothesis that genes occurred in linear order along the length of the chromosome. This concept could explain linkage, which enables a group of genes to be inherited together. This was a great help to conventional breeders. Conventional Mendelian breeding reached a high point with the Green Revolution, from 1950 to 1990, when world population doubled while food production quadrupled. Isolection Mendelian plant breeding The Isolection (Guerin and Guerin, 1992) system of breeding was conceived and executed for the first time in Australia at the New England Agricultural Research Station, Glen Innes (NSW), in the drought year of 1957. All the early generation oat plants were widely spaced, at 3.66 – 5.38 plants/sq.metre, in contrast to 13.99 – 21.53 plants/sq.metre in the Temora (NSW) Research Station drill- sown breeding plots. The object of this was to eliminate environmental variance (due to competition and stress between plants) and to make more effective prostrate genotype selections. This concept was later developed theoretically by Falconer, using a formula for heritability, h2 , to obtain the additive breeding value, V A, giving: h2 ¼ VA=VP ðphentotypic valueÞ ðFalconer and Mackay; 1996Þ 340 P.M. GUERIN and T.F. GUERIN
- 9. The total variance is the phenotypic (non-additive genetic and environmental) variance, VP, that needs to be reduced, in order to increase heritability percentage. Because of the true breeding nature of homozygotes, it is possible in the F2 (second generation after a cross), to rapidly obtain a pure race with respect to any combination of parental factors provided that a large enough F2 generation was grown and tested. This concept is illustrated in the work conducted by the senior author while breeding oats for NSW Agriculture at Glen Innes after 1956. His predecessor, James Carroll, had retired several years earlier and had already selected suitable lines from a moderately wide cross that he had made to incorporate crown and stem rust resistance from the Canadian oat Garry. A moderately wide cross, in this context, means a cross between different ecospecies like a winter oat, Avena byzantina var. Fulghum and a spring oat, A. sativa var. Garry, not a very wide cross like wheat 6 rye, which are different species. Nevertheless, a yield reduction is always involved but was easily overcome by only one cross in 1957, later referred to as the high-vigour cross (HvII 57 – 75): ½F:Ga ð1183 G57ÞŠ; the female parent; Â ½V:R:A:F Â V:R S F:ð1309 G57ÞŠ; the male parent; where F = Fulghum, Ga = Garry, V = Victoria, R = Richland, A = Algerian and S = Sunrise were in the ancestry of the two 1957 rows at Glen Innes Research Station, NSW, Australia. A number of other crosses were made to study linkage, but only this one cross, the HvII, was necessary to add many genes for yield, frost resistance, drought resistance, tolerance to Barley Yellow Dwarf virus, resistance to smut, crown rust and stem rust. In conventional (Mendelian) plant breeding, one looks for traits, not genes: a big advantage over GM crop production, which adds only one or a few genes. The key features of Isolection breeding are: (a) A high rate of success in crossing oats, achieved in 1956, before starting, in order to produce a large number of homozygous F2 plants. (b) The two parents to be phenotypically similar (as in a narrow cross) but genotypically different. (c) The F2 generation plants to be widely spaced by hand, 4.52 plants/square metre, at Glen Innes, as against 17.76 plants/square metre for the conventional drill sowing at Temora Research Station (representing the southern wheat belt). Hence the name of Isolection system, to ‘isolate’ pure breeding lines, like P4315, and ‘select’ them for yield testing in F3. The F2 plant of P4315 produced 600 seeds. (d) Linkage assists the rapid breeding method, by observing that a winter cereal has morphological features like prostrate habit of growth and deep root system, correlated with resistance to frost, drought and grazing damage. The senior author replaced the previous conventional trial system of only two grazings per trial with one of four to five grazings, the latter being followed by a grain recovery trial. This enabled identification of a deeper root system, resistance to more severe frost and drought, and medium size grain (see reference to Vavilov in Traditional Landrace Cropping section) with high bushel weight and low husk percentage, compared to Algerian’s large husky grains (from the Mediterranean centre of origin). 341YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS
- 10. This benefit of quality proved that high total yields could be combined with high grain quality. The Isolection system has since been proven to assist in the detection of heritability, by several other workers, including K.J. Frey, although the mechanism responsible was said to be unknown (Frey, 1964). The non-stress environment (that is, separate sowing by hand) makes it possible to select the highest possible yielding lines, while the close spacing of a drill sowing does not. A comparison of the Isolection lines with conventionally bred oat lines from Temora Research Station (NSW) and other winter rainfall areas was made in 1966 at Hawkesbury Agricultural College (Table IV). The highest yielding lines were all from the high-vigour cross and were identified as P4315, P4314, Blackbutt, 871-1 G59 and 871 G59, in that order, all significantly higher yielding than conventional lines, in five grazing yields and a hay recovery cut. All five lines produced grain of high test weight and low husk percentage, ideal for stock feeding. At Tamworth Research Station (NSW), in 1973, the early variety P4315 yielded significantly more than most varieties for two grazing cuts and recovered 19.83 tonnes of grain per hectare, 100% higher than the world oat yield record and 25% higher than the 1982 UK world wheat record (Evans, 1996). In the late-maturing class, Blackbutt has yielded significantly more than all other oats, winter wheats and triticales, for grazing and grain recovery, from 1966 to 1999, on the Tablelands, Cootamundra and eastern Australia generally. It is still recommended in 2002 (McRae, 2002). Comparing GM with conventional crops This section highlights the main differences basic to the two main systems of breeding, with respect to breeding mechanism, benefits, costs, risks and agro-ecological factors (Table III). These are summarized as follows: . Conventional breeding is a natural technology and is more rapid than GM crop development. A greater length of time is required to backcross to elite conventional lines, make selections and build up seed supplies of new GM varieties for yield testing in comparison with conventional varieties. There are no yield comparisons in Australia of crops bred by conventional vs. GM technology TABLE III Comparing features of GM crops with conventional crops Feature GM crops Conventional crops (CC) Type of breeding Cloning and backcrossing to an elite CC variety IndependentofGM:amale6femalecross. Years to breed a variety 8 – 10 years Every 2 – 3 years Number of genes added Usually one or two genes Possibly 50000 allelic pairs of genes involved Source of yield benefits Controlling weeds/pests Hybrid vigour Land preparation All tillage is replaced by herbicide spraying Some tillage is needed to kill all weeds and residues Weed infestation risk Weeds compete early with crop and reduce yield More emphasis on fallow tillage increases yield Cost to farmer High cost of patented seed Relatively low cost seed Consumer acceptance High resistance Universally accepted 342 P.M. GUERIN and T.F. GUERIN
- 11. (refer to Tables I and II) with the consequence that GM varieties have been released to farmers without any yield information. Breeders of conventional crops, on the other hand, can release a new variety every 2 or 3 years but are obliged to furnish State Departments of Agriculture with several years of biometrically analysed yield data.4 . Only a limited number of genes and no hybrid vigour are added by the GM process. This makes GM technology unsuitable for the polygenic requirements of winter cereal breeding for grazing and grain yields. . GM crops have the advantage that they can be sprayed to kill weeds that emerge with the crop but the early competition involved will reduce crop yield. The no-till fallow of GM crops does, however, have other disadvantages (1) rodent, insect and disease incidence increase due to surface residues and (2) soil temperature may decrease by as much as 68C at a depth of 2.5 cm in spring, giving poor germination (Anonymous, 1982). . To gain full benefits from conventional cropping, farmers must plan for weed-free sowing conditions. Fallowing cultivations are essential for Central and Northern New South Wales and for Queensland, although no-till fallowing by herbicide spraying can replace some fallow cultivation (Percival, 1979). TABLE IV Isolection-bred vs. conventionally-bred oat varieties1 Cultivar Breeding Method Cultivar Origin 5P2 (T/ha) Hay3 (T/ha) Total (T/ha) Frost4 (Score 0 – 10) July P5 (T/ha) P4315 Isolection HvII 6.55 3.62 10.17 1 1.45 P4314 Isolection HvII 6.21 3.70 9.91 17 1.23 Blackbutt Isolection HvII 6.67 2.86 9.53 1 1.35 871-1G59 Isolection HvII 5.66 2.97 8.64 2 0.83 871G59 Isolection HvII 5.60 2.99 8.59 2 0.74 Klein69B Conventional Argentine 5.01 3.37 8.38 2 + 0.72 Cooba Conventional Temora7 5.18 2.21 7.39 3 + 0.95 Fulghum Conventional USA 4.87 2.20 7.07 3 0.64 F 6 Vic Conventional Temora 4.21 2.47 6.68 4 + 0.52 Coolabah Conventional Temora 4.09 2.08 6.17 6 + 0.45 F 6 Avon21 Conventional Temora 3.89 2.23 6.12 4 + 0.36 Avon 6 Fk Conventional Temora 3.96 1.93 5.90 7 + 0.28 Avon 6 O Conventional Temora 4.04 1.81 5.85 8 0.33 FxAvon20 Conventional Temora 3.45 2.11 5.57 7 0.23 Fulmark Conventional Temora 3.78 1.70 5.48 9 0.20 M1305 Conventional Temora 3.36 1.48 4.85 7 0.25 Algerian Conventional Algeria 3.38 0.60 3.98 8 0.19 SD6 0.90 0.99 1.54 0.34 1 Cited in Guerin and Guerin (1992). 2 5P = 5 Pasture cuts in dry matter yield per hectare. 3 Hay = hay recovered after 5P. 4 Frost scored 0 for no damage and 10 for extreme damage, during a cold, dry winter (rainfall only 50% of the 86-year mean). Date of Sowing: 25th March, 1966. 5 July P = Pasture yield during coldest month. 6 SD = significant difference, obtained by biometrical analysis performed by NSW Agriculture Biometricians at Rydalmere, NSW, Australia, during 1966 – 1967. 7 Temora is located in central NSW, Australia. 4 The senior author released three new oat varieties: Bundy in 1965, Mugga in 1966 and Blackbutt in 1974, as a result of 7 years of oat plant breeding from 1957 to 1964. 343YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS
- 12. . Conventional plant breeding in Australia has been conducted hand in hand with crop rotations, judicious fallowing (cultivation of moist soil, or sheep grazing if the soil is dry). Contour tillage and contour banks can prevent erosion and store extra moisture. Sheep grazing can prevent weed seeds from setting and increases soil organic matter. Both in Australia and America, judicious fallowing, has been recommended for the past 50 years (Guerin, 1961). Thus, a 9-month fallow can give a 100% yield increase over a 3-month fallow (Fettell, 1980). . The cost of GM seed is high relative to conventionally bred varieties because of the seed patenting process. . Growing GM crops presents a risk of contaminating conventional crops. This has resulted in litigation and the loss of premium markets in the UK, Europe, Japan, China and other countries. GM crops have to contend with consumer resistance. This is based on evidence that long-term nutritional concerns are not being monitored. There is also a strong ethical component, upholding the genetic integrity of the species. This point need not, however, lower the value of gene technology, excluded from the natural environment, for fundamental research. Conclusions From comparing the available information on GM crops with that of conventional crops, we conclude the following: (a) GM crops lack hybrid vigour. (b) The inefficiency in forcing an alien gene into a plant, and the time required for backcrossing to elite conventional lines, largely prevent this system from being more rapid than conventional breeding. (c) Yield has to be studied in relation to proven agro-ecological findings, including rotations, contour tillage and moisture storage, highlighting the importance of the environment. (d) Based on the limited survey data and our understanding of how agro-ecological factors interact with genetics to effect yield, we recommend research be conducted using scientifically designed trials to compare yield per se between GM and non-GM crops. The non-stress environment of the Isolection Mendelian system resulted in the breeding of superior dual-purpose oats, relative to the conventional Mendelian system, as well as in a more effective detection of heritability. This was shown up by a more rigorous assessment of resistance to grazing, frost and drought. Grain quality was also improved. A comparison of GM crops and conventionally bred crops show that GM crops lack versatility and economic advantage. This is because GM crops are, at present, designed for weed and pest control, not for agro-ecological factors, like crop rotation and contour tillage. The unintended consequences of releasing GM crops, particularly in the Vavilovian centres of landrace varieties, for maintenance of valuable germplasm, should not be underestimated or ignored. 344 P.M. GUERIN and T.F. GUERIN
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