A Survey of Yield Differences Between Transgenic and Non-Transgenic Crops
A SURVEY OF YIELD DIFFERENCES BETWEEN
TRANSGENIC AND NON-TRANSGENIC CROPS
ERTRAGSDIFFERENZEN ZWISCHEN GENETISCH
MODIFIZIERTEN UND KONVENTIONELL GEZU¨ CHTETEN
and T.F. GUERINb,
(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.
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: firstname.lastname@example.org
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
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.
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
337YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS
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-
Euheterosis is hybrid vigour for sexual reproduction and seed yield. It is intra-speciﬁc.
Geographical centres of origin that possess plant varieties with wide genotypes and naturally occurring
338 P.M. GUERIN and T.F. GUERIN
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
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
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
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
This concept was later developed theoretically by Falconer, using a formula for
, to obtain the additive breeding value, V A, giving:
¼ VA=VP ðphentotypic valueÞ ðFalconer and Mackay; 1996Þ
340 P.M. GUERIN and T.F. GUERIN
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 G57Þ; the female parent; Â
½V:R:A:F Â V:R S F:ð1309 G57Þ; 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,
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
(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
(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
This beneﬁt of quality proved that high total yields could be combined with high grain
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
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
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
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
Weed infestation risk Weeds compete early with crop and reduce
More emphasis on fallow tillage increases
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
(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
(Score 0 – 10)
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
0.90 0.99 1.54 0.34
Cited in Guerin and Guerin (1992).
5P = 5 Pasture cuts in dry matter yield per hectare.
Hay = hay recovered after 5P.
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.
July P = Pasture yield during coldest month.
SD = signiﬁcant diﬀerence, obtained by biometrical analysis performed by NSW Agriculture Biometricians at Rydalmere,
NSW, Australia, during 1966 – 1967.
Temora is located in central NSW, Australia.
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
. 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
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
(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
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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345YIELD DIFFERENCES BETWEEN TRANSGENIC AND NON-TRANSGENIC CROPS