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Archives Of Agronomy  Soil Science (49) 333 345 Archives Of Agronomy Soil Science (49) 333 345 Document Transcript

  • Archives of Agronomy and Soil Science, June 2003, Vol. 49, pp. 333 – 345 A SURVEY OF YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS ERTRAGSDIFFERENZEN ZWISCHEN GENETISCH ¨ MODIFIZIERTEN UND KONVENTIONELL GEZUCHTETEN KULTURPFLANZEN P.M. GUERINa and T.F. GUERINb,*a 1A Lockyer St., Lithgow, NSW 2790, Australia; b 3/32 Wolli Creek Rd, Banksia, NSW 2216, Australia (Received 11 April 2003)In the current survey, there was no clear evidence that GM (genetically modified) crops are higher yieldingthan those conventionally bred1. Furthermore, there were no trials to support valid comparisons of yield perse. This article investigates GM crop yields, introducing the importance of hybrid vigour and a non-stressenvironment for higher percentage heritability selection and therefore more productive conventional plantbreeding 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 plantbreeding are (1) traditional landrace cropping, (2) conventional Mendelian breeding and (3) IsolectionMendelian breeding, and are also considered historically.INTRODUCTIONYield data from GM (genetically modified) crops compared to conventionally bred1crops are not supported by valid comparisons of yield per se. Such valid comparisonsare 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 limitednumber, 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 controlof either weeds or pests. Conventional crops, on the other hand, derive from crossingintraspecific varieties to unite a multitude of ‘matching genes’ from two parents,conferring hybrid vigour. This hybrid vigour applies to all conventionally bred cropsbut not to GM crops. Furthermore, yield comparisons are invalid without specifyingthe environment and its interaction with the varieties being compared. There are proven agro-ecological factors of weed and pest control: crop rotation andlength of fallow, specially suited for high-yielding conventional varieties, depending onregional soils and climates (Fettell, 1980), which should not be overlooked with the *Corresponding author: E-mail: 1 Crops have been bred on sound genetical lines since discovery of Mendel’s laws in 1900.ISSN 0365-0340 print; ISSN 1476-3567 online # 2003 Taylor & Francis LtdDOI: 10.1080/0365034031000151080
  • 334 P.M. GUERIN and T.F. GUERINadvent of GM technology. This article compares GM and conventionally bred crops,introducing the importance of hybrid vigour and a non-stress environment for higherpercentage heritability selection and therefore more productive conventional plantbreeding and improved crops.SCOPE AND PURPOSEIn this article, GM technology and crops are compared with proven plant breedingmethods, with respect to hybrid vigour and the economic viability of both systems.These proven methods of plant breeding are also considered historically. These methodsare (1) traditional landrace cropping, (2) conventional Mendelian breeding and (3)Isolection Mendelian breeding.BackgroundInformation on comparative crop trials in Australia has been limited. Table I highlightsthe results of a survey conducted by the authors in 2002, which illustrates the variabilityof yields from trials. These findings indicate that comparative crop trials have not beenwidely conducted and/or communicated, and that much of the existing yield data isqualitative only. Furthermore, there was no evidence that these trials were scientificallydesigned to enable assessment of yield per se. Studies are, however, emerging outside Australia comparing GM crops withconventionally bred crops, though few are scientifically designed for meaningfulcomparison of GM crops with those that are conventionally bred. For instance, a reportby the British Soil Association, on GM crops in North America, found that with theexception of crops possessing Bacillus thuringiensis (Bt) for pest resistance, the GMcrops yielded lower than conventional crops (Anonymous, 2002a). Despite higher yieldswith Bt corn, US farmers lost $US 1.31 per acre ($A6 per hectare). The Soil Associationreported 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. Anotherreport 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 toCanadian farmers growing transgenic canola, but 37% of Canadian farmers are stayingwith conventional lines because the cost, $C37/ha, of the Technology Use Agreement, isprohibitive. In addition, if a hybrid GM canola was being reported, it should have beencompared with a hybrid non-GM canola, which would normally yield higher than itstransgenic counterpart. In Arkansas, researchers found that transgenic soybeans ´yielded almost 10% lower than conventional soybeans (Lappe and Bailey, 1999). Otheryield comparisons are given in Table II. We stress that the yield data presented in thistable are survey data and do not represent the results of scientifcally designed trials toassess the effect of yield per se. The remainder of the article describes and compares GM crop technology andconventional plant breeding, taking into account both genetics and environment.GM crop technologyGene technology enables plants to be cloned from a single cell of the parent plant. Genetransfer technology then enables cloned genes for a desired trait to be blasted into
  • TABLE I Results of qualitative survey (Spring 2002) to identify sources of comparative yield studies of GM crops and comparable conventionally bred varietiesLocation Organization (s) Response of literature and Email survey1Australia Auscott2 (on farm trials) At Auscott, Narrabri, during the 1998 – 99 season, a completely unsprayed large-scale trial involving conventional, Ingard and two Bt gene cotton using a common Siokra V15 background showed the following relativeyields of Conventional SiokraV 15, 34%;Ingard SiokraV15i,84%; and Two Bt gene Siokra V15ii, 100%, respectively.Australia GeneEthics Claims 7.5% reduction in yield of Bt Cotton varieties compared with non-Bt varieties.Australia Grains Research & Development Corporation No comparative yield data available. Because of the OGTR regulations on growing GM crops in the field (GRDC) (separation distance), there are no GM crops grown side-by-side with conventional varieties in field trials to provide comparative yield data. As a result, there are no data for such trials in GRDC supported, variety testing activities undertaken by State Departments of Agriculture.Australia Various State & Federal Government No comparative yield data available from the Department of Agriculture, Fisheries and Forestry, The Gene Departments Technology Information Service, or NSW Agriculture.Canada Agriculture & Biotechnology Strategies Inc. ‘Comparative yield data for commercial production is very difficult to come by’. (AGBIOS) ‘In small scale trials, significant variations in yield have not been the norm, largely because the novel traits introduced into commercially available GM varieties are for traits such as herbicide tolerance or insect resistance and not yield enhancement’. ‘Some yield drag was noted in very early glyphosate tolerant soybean varieties but this has been addressed by backcrossing the HT trait into better yielding commercial varieties’.United States Agronomy Journal4 High-yield, non-herbicide-resistant cultivars and five other herbicide-resistant cultivars, glyphosate resistant (GR) soybean Glycine max L. Merr. were compared. GR sister lines yielded 5% (200 kg/ha) less than the non-GR sisters (GR effect).United States Alabama Cooperative Extension System ‘There have been a huge number of trials comparing cultivars in various locations and various years. Not surprisingly, there is a wide variation in reported yield/profit differences’.United States Monsanto3 Field test data concerning yields and visual observations of agronomic properties including susceptibility to diseasesand insects indicatethat Bollgard 531 cotton is not different in agronomic performance compared to non- modifiedvarieties.No mentionof yieldeffectswithRoundupReadycotton.YieldGard cornplantsareequivalent to other corn varieties in disease susceptibility and other agronomic and morphological characteristics but no specific mention is made of comparative yield data. YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS (continued overleaf ) 335
  • 336 TABLE I (continued )Location Organization (s) Response of literature and Email survey1United States ´ Marc Lappe and Britt Bailey survey of Field surveys reported a 10% reduction in yield in Roundup Ready soybeans compared with comparable non- farmers in Arkansas GM crops5.United States National Center for Food and Agricultural The examination of 40 case studiesof biotechnologyapplied to pest management in agriculture demonstratesthat Policy, Washington, DC (2002) biotechnologyishavingand can continueto havesignificant impact onimprovedyields,reducedgrowercostsand pesticide reduction. Eight currently adopted cultivars are having a significant impact, primarily in major commodity crops. Based on variety trials conducted in eight northern states, the average difference in yield potential between Roundup Ready soybean varieties and conventional varieties decreased from 4% in 1998 to 3% in 1999.United States National Center for Food and Agricultural ‘On average, it appears that the Roundup Ready varieties yield slightly less than the conventional varieties. Based Policy, Washington, DC on 1998 and 1999 trials, this gap appears to be narrowing, from 4% to 3%. As the Roundup Ready trait is introducedinto the highest yieldingvarieties,it is expected that thisdifference will disappear,oreven be overcome. However, one must be cautious in interpreting the results of variety trials as many other factors besides yield potential, such as costs and weed control efficacy, affect growers’ planting decisions and, ultimately, yields’.Notes:1 P.M. GUERIN and T.F. GUERIN Survey was conducted by authors by e-mail and by reviewing published material during September – October 2002.2 Safety Assessment of Bollgard Cotton Event 531, Safety Assessment of Roundup Ready Cotton. Event 1445, and Safety Assessment of YieldGard Insect-Protected Corn Event MON 810located at www.monsanto.com4 Refer to Elmore et al. (2001).5 ´ Reported in Lappe and Bailey (1999)
  • TABLE II Summary of Comparative Yield Studies of GM Crops and Comparable Conventionally Bred Varieties Relative Yield data (t/ha) yield ofCrop type Season Location GM Variety1 GM Conventional2 Description SourceBt Corn 1999 Southeastern Higher 13.9 13.7 Two irrigated trials, top three GM varieties Integrated Pest & Crop Management Missouri, and top three non-GM varieties Newsletter, University of Missouri- United States Columbia3Bt Corn 1999 Missouri (Boone Higher 8.2 7.7 Non-irrigated, top three GM varieties and Integrated Pest & Crop Management County), top three non-GM varieties Newsletter, University of Missouri- United States ColumbiaBt Corn 1999 Missouri (Boone Higher 11.2 11.1 Irrigated, top three GM varieties and top Integrated Pest & Crop Management County), three non-GM varieties Newsletter, University of Missouri- United States ColumbiaHerbicide- 1998 Iowa, United Lower 3.31 3.44 Random sample, cross-sectional survey of Iowa State University4 tolerant States Iowa soybean fields soybeansBt Corn 1999 Missouri, Lower 9.4 9.5 154 trials in Missouri, top three GM varieties Integrated Pest & Crop Management United States and top three non-GM varieties Newsletter, University of Missouri- ColumbiaBt Corn 1999 Missouri, Lower 12.0 12.1 Non-irrigated, top three GM varieties and Integrated Pest & Crop Management United States top three non-GM varieties Newsletter, University of Missouri- ColumbiaIngard 1999/ NSW & QLD Lower 7.98 8.05 Season average over 10 major cotton Cotton Research & DevelopmentCotton 2000 cotton growing valleys in NSW/QLD Corporation (CRDC) growing areas, AustraliaHerbicide- 2000 Iowa, United Lower 2.92 3.02 Based on 172 fields (108 were herbicide- Iowa State University4tolerant States tolerant soybeans; 64 were not herbicidesoybeans tolerant).1 The higher and lower yield designations do not necessarily reflect statistically significant results. These trials have not assessed for the effect of yield per se. They represent survey data only.2 These represent comparable conventional varieties that were reported to be tested alongside the GM varieties.3 Newsletters are located at Reported by Duffy (2001). YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS 337
  • 338 P.M. GUERIN and T.F. GUERINcultured plant cells with a ‘gene gun’ that forces the genes into the cell. The cells arecultured to form a tissue mass that will grow into a plant carrying the gene or genes forherbicide or pest resistance. This results in a source of inefficiency for breeding programmes and high cost, intransferring the new gene into a commercially desirable conventional variety of the cropspecies being modified. Out of millions of plant cells that are bombarded with metalparticles coated with DNA, only very few cells take up the DNA. If the tissue piece werethen cultured, the untransformed or native cells of the invaded plant (selected to takethe 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 carrythe new gene (Anonymous, Undated). A selectable marker gene is a gene that confers resistance to a substance that is toxicto normal plant cells. This marker gene is delivered to plant cells with the introducedgene and the cells are cultured in the presence of the toxic compound, as well as planthormones to induce the cells to divide and grow. Only cells that contain the markergenes as well as the new gene (for pest or herbicide resistance) are able to inactivate thetoxic compound, in order to survive and grow into complete plants. The selectablemarker genes may be antibiotic resistance genes conferring resistance to antibiotics, orherbicide resistance genes that confer resistance to herbicide. Medical and publicconcern 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 merelyshow that genetically modified organisms (GMOs), have a very low survival rate andthat evolution, if it ever happened, was not by this process. This, however, should notbe used as an argument for releasing GMOs. Cross-pollination can take place, givingrise to undesirable or weedy plants, animals or fishes, lacking in health and true hybridvigour, or euheterosis.2 Genetic modification reduces euheterosis and depends uponbackcrossing to elite, high yielding conventional varieties, before release. Outcrossing of GM with non-GM plants complicates the study of taxonomy andshould be rigorously excluded from the Vavilovian3 centres of origin of specific cropsand wild relatives. For example, GM mustard plants were found to be 20 times morelikely to interbreed with related species than non-GM mustard plants (conventionallybred for the same herbicide resistance) (Burgelson et al., 1998). It has been reported thatGM tomatoes have been grown without the consent or knowledge of regulatoryauthorities in Guatemala, where hundreds if not thousands of indigenous tomatovarieties are grown. The same author also claimed that cross-pollination distancesneeded for strict isolation have been ignored, even for pharmaceutical crops, so long aspotential dangers, in the 1995 joint consultation between WHO and FAO, were ‘judgedto be unrelated to food safety’ (Anderson, 2000). Others claim that with regard to the process itself, the hazards of cancer to laboratoryworkers and farmers is confirmed by the discovery that Agrobacterium tumefaciens, thegene transfer vector for plants, can infect animal cells (Ho et al., 2000). There are alsoreports of GM foods and genetically engineered (GE) L-tryptophan causing sicknessand 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 occurringbiodiversity.
  • YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS 339tryptophan, it took months to link it to a disabling disease, eosinophilia myalgiasyndrome (Bremner, 1999).Conventional crop plant breedingThis is independent of genetic modification and may be divided into three productivemethods or systems developed over 8 – 10 000 years and according to the results ofparticular plant breeders: (1) Traditional, (2) Conventional Mendelian and (3) theIsolection Mendelian breeding systems. These mechanisms are natural, like the agents ofwind, pollinating insects and honeybees, all of which are prevented from causingevolution by means of the genetic barriers between species and even ecospecies. Here,however, the breeder controls the hybridizations and selections. All three methods canbenefit from the heritability of selections (see Isolection system) made in non-stressconditions (i.e., hand spacing of plants, not drill sowings).Traditional landrace croppingThis is and has been a very successful period of maintaining peasant landraces ofdifferent species and ecospecies in the various so-called Vavilovian centres of origin ofour cultivated crop plants. These are mixtures of homozygous plants most suitable fortheir particular soil and climatic conditions, e.g., small-seeded, rust-resistant varieties oreco-species in continental climates and large-seeded, early maturing types, inMediterranean climates. These centres are also reservoirs of genes for high yield.Maize trials show that the degree of heterosis, when open-pollinated varieties are usedin hybrid combinations, is considerably higher with varieties from Latin-America (richin Vavilovian centres) than with US Corn Belt varieties (Mangelsdorf, 1952). There is ample evidence that our various crop species have had single and suddenorigins. The great genetic variability present in isolated peasant farmers’ landracessuggests that they were created, not from single plants, but from a multitude of ‘firstparents’ to produce their multicultural (due to companion cropping) varieties withresistance to a broad spectrum of rusts, blight and climatic variability. The companioncropping of peasants also reduces disease and increases total yields. Vavilov recorded the various large-seeded varieties of the Mediterranean centre oforigin, relative to the continental centres. His critics put this down to the greaterantiquity of Mediterranean agriculture but Vavilov found this to be no greater than thatof Asia Minor, Afghanistan or China. Oat grazing trials at Glen Innes after 1957vindicated Vavilov (see Conventional Mendelian Plant Breeding section). Farmers in theVavilovian centres of origin should be encouraged to separately maintain their landracevarieties, free from introduced high yielding varieties, which soon succumb to rusts andblight. These unique centres are, or should be, universal reservoirs of germplasm in situfor all plant breeders, in preference to under-utilized gene banks (Harlan, 1992).Inbreeders and outbreeders Here we must distinguish out-breeders like maize fromself-pollinated crops like wheat, oats and barley, peas and beans. The latter are designedto be resistant to inbreeding and respond well to pure-line breeding. There is enoughnatural crossing (4% in wheat, 0.5% in oats) to maintain their yields in the centres oforigin. Darwin was probably right in stating that selection, over thousands of years, had notmade our crop plants higher yielding (Darwin, 1868). Not until the twentieth century
  • 340 P.M. GUERIN and T.F. GUERINdid hybridizations and introductions from the centres of origin combine to givesignificant increases in crop yields, and this is shown in the following sections.Conventional Mendelian plant breedingDuring Gregor Mendel’s life (1822 – 84), hybridizations between different varieties, orecotypes 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, wasdue to homozygosity. He hypothesized that hybrid vigour must be associated with theheterozygosity arising from crossing. In 1914, he proposed the term ‘heterosis’ for thiseffect. His single-cross interline hybrids, however, yielded much lower than a standardmaize variety on the same area. In 1917, D.F. Jones used double-cross interline hybridsto reduce the cost of seed sufficiently to justify hybrid seed production. This couldincrease maize crop yields by 25 to 35% and sometimes by 50%, as compared with thebest selected open-pollinated varieties (Guzhov, 1989).Natural selection Regarding self-pollinated crops, it was assumed for half a centuryafter Darwin that by selecting a certain type of plant for propagation, the species orvariety would be continually transformed in the same direction. This was a result ofacceptance 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 oncommon garden bean, Phaseolus vulgaris nana var. Princess, refuted this theory inpapers he wrote from 1903 to 1913 (Babcock and Clausen, 1918). Princess wasactually a blend of highly homozygous pure lines. Johannsen found that selectionwithin a pure line was without effect. Louis de Vilmorin’s wheat plants alsoremained identical in all respects after 50 years during which annual selection hadbeen continued. T.H. Morgan (1866 – 1945) also rejected the possibility of natural selection bringingabout evolution and found that pleiotropy, the state in which one gene has effects on anumber of different traits, could control several factors in Drosophila and even causereduced fertility. This led to the hypothesis that genes occurred in linear order along thelength of the chromosome. This concept could explain linkage, which enables a groupof 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) systemof breeding was conceived and executed for the first time in Australia at the NewEngland 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, incontrast 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 tocompetition and stress between plants) and to make more effective prostrate genotypeselections. This concept was later developed theoretically by Falconer, using a formula forheritability, h2, to obtain the additive breeding value, V A, giving: h2 ¼ VA =VP ðphentotypic valueÞ ðFalconer and Mackay; 1996Þ
  • YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS 341The 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 (secondgeneration after a cross), to rapidly obtain a pure race with respect to any combinationof 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 breedingoats for NSW Agriculture at Glen Innes after 1956. His predecessor, James Carroll, hadretired several years earlier and had already selected suitable lines from a moderatelywide cross that he had made to incorporate crown and stem rust resistance from theCanadian oat Garry. A moderately wide cross, in this context, means a cross betweendifferent 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 onecross in 1957, later referred to as the high-vigour cross (HvII 57 – 75): ½F:Ga ð1183 G57ފ; the female parent;  ½V:R:A:F  V:R S F:ð1309 G57ފ; the male parent;where F = Fulghum, Ga = Garry, V = Victoria, R = Richland, A = Algerian andS = 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, theHvII, 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. Inconventional (Mendelian) plant breeding, one looks for traits, not genes: a bigadvantage over GM crop production, which adds only one or a few genes. The keyfeatures 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 twograzings per trial with one of four to five grazings, the latter being followed by a grainrecovery trial. This enabled identification of a deeper root system, resistance to moresevere frost and drought, and medium size grain (see reference to Vavilov in TraditionalLandrace Cropping section) with high bushel weight and low husk percentage,compared to Algerian’s large husky grains (from the Mediterranean centre of origin).
  • 342 P.M. GUERIN and T.F. GUERINThis benefit of quality proved that high total yields could be combined with high grainquality. 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 wassaid to be unknown (Frey, 1964). The non-stress environment (that is, separate sowingby hand) makes it possible to select the highest possible yielding lines, while the closespacing of a drill sowing does not. A comparison of the Isolection lines withconventionally bred oat lines from Temora Research Station (NSW) and other winterrainfall areas was made in 1966 at Hawkesbury Agricultural College (Table IV). Thehighest 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 yieldingthan conventional lines, in five grazing yields and a hay recovery cut. All five linesproduced grain of high test weight and low husk percentage, ideal for stock feeding. At Tamworth Research Station (NSW), in 1973, the early variety P4315 yieldedsignificantly more than most varieties for two grazing cuts and recovered 19.83 tonnesof grain per hectare, 100% higher than the world oat yield record and 25% higher thanthe 1982 UK world wheat record (Evans, 1996). In the late-maturing class, Blackbutthas yielded significantly more than all other oats, winter wheats and triticales, forgrazing and grain recovery, from 1966 to 1999, on the Tablelands, Cootamundra andeastern Australia generally. It is still recommended in 2002 (McRae, 2002).Comparing GM with conventional cropsThis 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 cropsFeature GM crops Conventional crops (CC)Type of breeding Cloning and backcrossing to an elite CC Independent of GM: a male 6 female cross. varietyYears to breed a variety 8 – 10 years Every 2 – 3 yearsNumber of genes added Usually one or two genes Possibly 50 000 allelic pairs of genes involvedSource of yield benefits Controlling weeds/pests Hybrid vigourLand preparation All tillage is replaced by herbicide spraying Some tillage is needed to kill all weeds and residuesWeed infestation risk Weeds compete early with crop and reduce More emphasis on fallow tillage increases yield yieldCost to farmer High cost of patented seed Relatively low cost seedConsumer acceptance High resistance Universally accepted
  • YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS 343 TABLE IV Isolection-bred vs. conventionally-bred oat varieties1Cultivar Breeding Cultivar 5P2 Hay3 Total Frost4 July P5 Method Origin (T/ha) (T/ha) (T/ha) (Score 0 – 10) (T/ha)P4315 Isolection HvII 6.55 3.62 10.17 1 1.45P4314 Isolection HvII 6.21 3.70 9.91 17 1.23Blackbutt Isolection HvII 6.67 2.86 9.53 1 1.35871-1G59 Isolection HvII 5.66 2.97 8.64 2 0.83871G59 Isolection HvII 5.60 2.99 8.59 2 0.74Klein69B Conventional Argentine 5.01 3.37 8.38 2+ 0.72Cooba Conventional Temora7 5.18 2.21 7.39 3+ 0.95Fulghum Conventional USA 4.87 2.20 7.07 3 0.64F 6 Vic Conventional Temora 4.21 2.47 6.68 4+ 0.52Coolabah Conventional Temora 4.09 2.08 6.17 6+ 0.45F 6 Avon21 Conventional Temora 3.89 2.23 6.12 4+ 0.36Avon 6 Fk Conventional Temora 3.96 1.93 5.90 7+ 0.28Avon 6 O Conventional Temora 4.04 1.81 5.85 8 0.33FxAvon20 Conventional Temora 3.45 2.11 5.57 7 0.23Fulmark Conventional Temora 3.78 1.70 5.48 9 0.20M1305 Conventional Temora 3.36 1.48 4.85 7 0.25Algerian Conventional Algeria 3.38 0.60 3.98 8 0.19SD6 0.90 0.99 1.54 0.341 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. (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). 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.
  • 344 P.M. GUERIN and T.F. GUERIN . 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.ConclusionsFrom comparing the available information on GM crops with that of conventionalcrops, 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 breedingof superior dual-purpose oats, relative to the conventional Mendelian system, as well asin a more effective detection of heritability. This was shown up by a more rigorousassessment 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 lackversatility and economic advantage. This is because GM crops are, at present, designedfor weed and pest control, not for agro-ecological factors, like crop rotation andcontour tillage. The unintended consequences of releasing GM crops, particularly in the Vaviloviancentres of landrace varieties, for maintenance of valuable germplasm, should not beunderestimated or ignored.
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