Download contribution of biotechnology to higher maize productivity: a mini

Journal of Cell and Tissue Research Vol. 16(2) 5727-5732 (2016)
(Available online at www. Tcrjournals.com)
ISSN: 0973-0028; E-ISSN: 0974-0910
Review Article
CONTRIBUTION OF BIOTECHNOLOGY TO HIGHER MAIZE
PRODUCTIVITY: A MINI REVIEW
?
MIR, S. D.,1 AHMAD, M.,1 ZAFFAR. G.,2 LONE, A. A.,2 RATHER. M. A.,3
DAR, Z. A.,2 MEHRAJ, U.1 AND MIR, M. A.4
Division of Genetics and Plant Breeding, Faculty of Agriculture Wadura; 2Dryland (Karewa) Agricultural
Research Station, Budgam, Srinagar; 3Zeera Research Station, Gurez; 4Directorate of Sericulture,
Srinagar. Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir
Shalimar campus, Srinagar 191 121. E. mail: [email protected],
1
Received: April 17, 2016; Accepted: May 18, 2016
Abstract: In the context of current climate variability, as well as predicted increases in mean
temperature and annual precipitation, what do recent advances in agricultural biotechnology
offer the genetic enhancement of agricultural crops so that they are better adapted to biotic and
abiotic stresses, leading to higher crop productivity? Developing crops that are better adapted to
abiotic stresses is important for food production in many parts of the world today. Anticipated
changes in climate and its variability, particularly extreme temperatures and changes in rainfall,
are expected to make crop improvement even more crucial for food production. Biotechnology
approaches, molecular breeding and genetic engineering, and their integration with conventional
breeding to develop verities for Maize, Sorghum and Barley crops that is more tolerant of abiotic
stresses. In addition to a multidisciplinary approach, we also examine some constraints that need
to be overcome to realize the full potential of agricultural biotechnology for sustainable crop
production to meet the demands of a projected world population of nine billion in 2050.
Key words : Biotechnology, Maize improvement
INTRODUCTION
In recent years biotechnology is emerging as
one of the latest tools of agricultural research. In
concert with traditional plant breeding practices,
biotechnology is contributing towards the development of novel methods to genetically alter and control plant development, plant performance and
plant products. Great progress has been made over
the past decade with respect to the application of
biotechnology to generate nutritionally improved
food crops. Biofortified staple crops such as rice,
maize and wheat harboring essential micronutrients
to benefit the world’s poor are under development as
well as new varieties of crops which have the ability
to combat chronic disease. The accessibility of food
crops that are high in nutritional content is granted
for those who live in the industrialized world;
however, this is not always the case for the rural
poor who reside in developing countries. For such
populations, a diet that is balanced in adequate levels
of vitamins and minerals can be difficult to achieve
and maintain. All too often, a monotonous diet in
which a single crop such as rice predominates is all
that is on hand and affordable [1]. Fortunately, due to
recent developments in agricultural biotechnology,
it is now possible to generate food crops which are
nutritionally enhanced to improve the content and
bioavailability of essential nutrients, such as iron
and vitamin A [2,3]. A Similar technology has been
used to fend off chronic illnesses including heart
disease and cancer [4,5].
The term biotechnology is composed of two
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words bio (Greek bios, means life) and technology
(Greek technologia, means systematic treatment).
Biotechnology involves the systematic application
of biological processes for the beneficial use. One
of the areas of plant biotechnology involves the
delivery, integration and expression of defined
genes into plant cells, which can be grown in
artificial culture media to regenerate plants. Thus
biotechnological approaches have the potential to
complement conventional methods of breeding by
reducing the time taken to produce cultivars with
improved characteristics. Conventional breeding
utilizes domestic crop cultivars and related genera
as a source of genes for improvement of existing
cultivars, and this process involves the transfer of a set
of genes from the donor to the recipient. In contrast,
biotechnological approaches can transfer defined
genes from any organism, thereby increase the gene
pool available for improvement. The improvement
of wheat by biotechnological approaches primarily
involves introduction of exogenous genes in a
heritable manner, and secondarily, the availability
of genes that confer positive traits when genetically
transferred into considerable attention over the years
from plant breeders with the purpose of increasing
the grain yield and to minimize crop loss due to
unfavourable environmental conditions, and attack
by various pests and pathogens. In the early 60’s,
conventional breeding coupled with improved farm
management practices led to a significant increase
in world wheat production thereby ushering in the
green revolution. Subsequently, the targets of genetic
improvement shifted to reducing yield variability
caused by various biotic and abiotic stresses and
increasing the inputuse efficiency [6]. With this
change in the global food policy in the last few
decades, biotechnology offered a possible solution
firstly, by lowering the farm level production costs
by making plants resistant to various abiotic and
biotic stresses, and secondly, by enhancing the
product quality (i.e. by increasing the appearance
of end product, nutritional content or processing or
storage characteristics). The introduction of foreign
genes encoding for useful agronomic traits into
commercial cultivars has resulted in saving precious
time required for introgression of the desired trait
from the wild relatives by conventional practices
and alleviating the degradation of the environment
due to the use of hazardous biocides. In recent
years, wheat improvement efforts have therefore
focussed on raising the yield potential, quality
characteristics and resistance to biotic stresses
and tolerance to abiotic stresses depending on the
regional requirement of the crop.
Role of biotechnology in maize improvement:
Biote-chnology has contributed tremendous advances
in maize production via different avenues, including
application of effective bio fertilizers, plant growth
promoter and more importantly development of
transgenic traits resistant to herbicides and/or pests [7].
QTL for BSLB resistance in maize: Banded
leaf and sheath blight (BLSB) caused by
Rhizoctoniasolani Kühn in maize (Zea mays L.) is
an important disease in China as well as South and
Southeast Asia. The identification of quantitative
trait loci (QTL) for resistance to this disease would
facilitate the development of disease resistant maize
hybrids. BLSB is an enormously destructive disease
on susceptible maize. So it is desirable to exploit
additional sources of resistance against BLSB to
improve the disease resistance of present maize
hybrids. Moreover, BLSB does not occur every
year, so general resistance genes could easily be lost
in the absence of selection pressure in conventional
breeding programs. Marker-assisted selection
(MAS) promises to be superior to conventional
phenotypic selection if the trait is severely affected
by environmental conditions or is difficult to
evaluate [8]. Localization of genes controlling
disease resistance via DNA markers could allow
introgression of these genes into elite materials,
even in areas where the disease is not common.
Significant QTL were located on 11 chromosomal
regions. Two major QTL (qBLSB-2a at Ya’an and
qBLSB-6c at Chongqing) explaining phenotypic
variation of 10.35 and 9.26% were only identified
in one environment. Four other QTL (qBLSB-2c,
qBLSB-6a, qBLSB-6b, and qBLSB-10) with genetic
distances away from the closest linkage markers of
0.01 to 10.00 cM were found in both environments.
QTL qBLSB-6b and qBLSB-10 were located to two
chromosomal regions between bnlg 1600 and umc
1818 and mmc 0501 and phi 054. The QTL detected
in this region each in two environments had same
closest linkage markers bnlg 1538 and phi 054,
respectively. They may be used for MAS [9].
QTL for DM resistance in maize: Progress has
been made in mapping agriculturally important
genes with molecular makers, which forms the
foundation for marker-aided selection (MAS). The
use of MAS can expedite such difficult screening
procedures such as the testing for disease or insect
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Mir et al.
resistance. However, when several resistance genes
are initially present in a donor parent, some of them
may be lost during the breeding programs. The
chance of losing resistance genes can be reduced if
they are detected early. This is particularly useful
when the breeding process is time consuming, e.g.
when exotic germplasm is used as the resistant
parent. QTLs for resistance to P. sorghiin maize is
based on RFLP mapping a population derived from
94 RILs. [10] identied tight linkage of the RFLP
markers umc11, umc23a, and umc113 to genes
conferring resistance to P. sorghiin maize. Twoof
the three QTLs were not always constant across
seasons. However, only one QTL was stable in
both seasons. These results suggest that one major
gene and two minor genes control SDM resistance.
These markers should bevery useful in breeding
programs in facilitating the introgression of the
resistance genes into commercial varieties. DNA
markers in genomic regions of interest enable
breeders to select on the basis of genotype rather
than phenotype, which can be especially helpful if
a target trait is time-consuming to score. Markerbased breeding will revolutionize the process of
cultivar development [11]. Another interesting
application of these results would be the use of these
linked markers as a starting point for molecular
approaches, such as chromosome walking, to clone
the resistance genes [12]. Marker-assisted selection
for these loci should be productive for
Resistance QTL clusters in maize: The distribution
of the QTL in the genome showed a high concentration of QTL in a few chromosomal regions.
Such a concentration in the distribution of QTL
has already been observed in previous studies by
a number of workers. Many resistance genes and
QTL in maize have been located in 3.04 and 6.01
regions of chromosomes [13]. For example, in
3.04 region, four resistance genes for rust disease
(rp3, wsm2, mv1, and scm2) were located within
5 cM by RFLP markers UMC102 and UMC10
[14,15]. The resistance QTL for European corn
borer (Ostrinianubilalis Hübner) was located in
the 3.04 region. And in the 6.01 region, resistance
genes for Cochliobolus heterostrophus (Drechs.)
Drechs. Helminthosporiummaydis (Nisikado &
Miyake) rhm1 and scm1 [14,16] were found. These
results indicated that 3.04 and 6.01 regions were
important for disease and insect resistance in maize.
In this study, only five QTL of qBLSB-1, qBLSB-3,
qBLSB-4, qBLSB-5, and qBLSB-6c were not
mapped close to other QTL. The remaining 6 QTL
were located in three chromosomal regions 2.06
to 2.08, 6.01 to 6.02, and 10.02 to 10.03, forming
three groups of QTL. These results corroborated
previous findings and supported the concept that
resistance QTL to diseases and insects in maize
were not randomly distributed across the genome
but clustered in specific regions [17].
QTL for resistance to GRS in maize: Fusarium
graminearum Schwabe, the conidial form of
Gibberellazeae, is the causal fungal pathogen
responsible for Gibberella stalk rot of maize.
Using a BC (1) F(1) backcross mapping population
derived from a cross between ‘1145’ (donor parent,
completely resistant) and ‘Y331’ (recurrent parent,
highly susceptible), two quantitative trait loci
(QTLs), qRfg1 and qRfg2, conferring resistance
to Gibberella stalk rot have been detected. The
major QTL qRfg1 was further confirmed in the
double haploid, F(2), BC(2)F(1), and BC(3)F(1)
populations. Within a qRfg1 confidence interval,
single/low-copy bacterial artificial chromosome
sequences, anchored expressed sequence tags, and
insertion/deletion polymorphisms, were exploited
to develop 59 markers to saturate the qRfg1 region.
A step by step narrowing-down strategy was
adopted to pursue fine mapping of the qRfg1 locus.
Recombinants within the qRfg1 region, screened
from each backcross generation, were backcrossed
to ‘Y331’ to produce the next backcross progenies.
These progenies were individually genotyped
and evaluated for resistance to Gibberella stalk
rot. Significant (or no significant) difference in
resistance reactions between homozygous and
heterozygous genotypes in backcross progeny
suggested presence (or absence) of qRfg1 in ‘1145’
donor fragments. The phenotypes were compared
to sizes of donor fragments among recombinants to
delimit the qRfg1 region. Sequential fine mapping
of BC(4)F(1) to BC(6)F(1) generations enabled us
to progressively refine the qRfg1 locus to a ~500-kb
interval flanked by the markers SSR334 and SSR58.
Meanwhile, resistance of qRfg1 to Gibberella stalk
rot was also investigated in BC(3)F(1) to BC(6)
F(1) generations. Once introgressed into the ‘Y331’
genome, the qRfg1 locus could steadily enhance
the frequency of resistant plants by 32-43%. Hence,
the qRfg1 locus was capable of improving maize
resistance to Gibberella stalk rot [9].
Strategies for disease control: The smut fungi
Ustilagomaydis and Sporisoriumreilianum are
parasites that attack maize plants. Ustilagomaydis
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causes a disease known as boil smut or common
smut, which is characterized by large tumour-like
structures on the leaves, cobs and male flowers in
which the fungus proliferates and produces spores.
Sporisoriumreilianum also attacks maize plants;
however, it infects the entire plant and its symptoms
become manifested only in the male and female
flowers. For this reason, it is also referred to as
maize head smut.
Little has been known up to now as to how these
pathogens cause disease. Four years ago, a team of
scientists headed by the Marburg group succeeded in
decoding the genome sequence of Ustilagomaydis.
They demonstrated that the genes, for a large
number of completely new proteins secreted by the
fungus, are arranged in groups on the chromosomes
in so-called gene clusters. These proteins control
the colonisation of the host plant. The researchers
were initially only able to demonstrate the presence
of these proteins in Ustilagomaydis. “However,
they found it hard to imagine that these proteins,
which play such a crucial role in maize infestation,
should only be present in the genome of a single
smut fungus. For this reason, they also sequenced
the genome of Sporisoriumreilianum,” explains
RegineKahmann from the Max Planck Institute in
Marburg. Over 90 percent of the proteins secreted by
Ustilagomaydis also exist in Sporisoriumreilianum.
However, many of these proteins differ significantly
between the two species and are therefore difficult
to detect at the gene level. “Surprisingly, however,
almost all of the genes of the two organisms
are arranged in the same order. As a result, they
were able to superimpose the two genomes like
blueprints and display the differences in this way,”
says Kahmann.
The scientists discovered 43 so-called divergence
regions, in which the differences in the two sets of
genes are particularly significant. These included all
of the gene clusters identified four years ago, whose
genes play an important role in the infection of the
host plant. In addition to this, four out of six randomly
selected divergence regions influence the strength of
Ustilago maydis infection, and surprisingly, one of
these does not contain genes for secreted proteins.
“This shows that additional, thus far undiscovered
molecules control the relationship between the
fungus and the plant,” comments Jan Schirawski.
Therefore, the genes that differ most strongly
between the two fungi are in all likelihood those that
play an important role in the infestation of the maize
plant. The different life styles of Ustilagomaydis
and Sporisoriumreilianum presumably resulted in
the development of species-specific gene variants
in these fungi over the course of evolution, e. g. to
suppress the plant’s immune response. The maize
plants, in turn, modified the target molecules of
these fungal proteins. Maize plants apparently form
at least one protein to counteract each of the proteins
released by the fungi. “What they see that the signs
of an ongoing struggle between the defending
plant and attacking parasite. The variety of the
weapons of attack and defence used is the product
of an arms race between the plant and the fungus.
Each modification on one side is countered by an
adaptation on the other,” explains Schirawski. With
the help of the molecules they discovered on the
basis of the differences between the two fungi, the
Marburg-based researchers have the long term hope
that it will be possible to develop new strategies for
disease control of these and related plant parasites.
Transgenic maize: Maize has also been biofortified
with β-carotene as well as other essential micronutrients necessary to maintain one’s health. [18]
measured the triglycerol-rich lipoprotein fraction of
blood from North American female volunteers who
consumed biofortified maize porridge. In this case,
the authors found a vitamin A equivalence value
of β-carotene in biofortified maize to be 3.1-fold
higher than in conventional white porridge maize.
A similar study using Zimbabwean men found
biofortified yellow maize porridge to provide an
equivalence of 40%–50% of the US recommended
Dietary Allowance of vitamin A. Another study
using Mongolian gerbils who were fed biofortified
maize containing β-cryptoxanthin resulted in a more
efficient bioconversion than the use of a β-carotene
supplement. The results of these studies indicate that
the biofortification of maize via biotechnology can
be a useful strategy to improve vitamin A status. A
triple-vitamin fortified maize which expresses high
amounts of β-carotene, ascorbate, and folate has
been developed in the endosperm through metabolic
engineering. The transgenic kernels contained 169fold the normal amount of β-carotene, 6-fold the
normal amount of ascorbate, and double the normal
amount of folate as conventionally-bred crops.
Crops such as these can offer far more nutritionally
complete meals for Africa’s malnourished [19,20].
Transgenic maize (corn) has been deliberately
genetically modified (GM) to have agronomically
desirable traits. Traits that have been engineered
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Mir et al.
into corn include resistance to herbicides and
resistance to insect pests, the latter being achieved
by incorporation of a gene that codes for the
Bacillus thuringiensis (Bt) toxin. Hybrids with
both herbicide and pest resistance have also been
produced. In 2009, transgenic maize was grown
commercially in 11 countries, including the United
States (where 85% of the maize crop was genetically
modified), Brazil (36% GM), Argentina (83% GM),
South Africa (57% GM), Canada (84% GM), the
Philippines (19% GM) and Spain (20% GM). Corn
varieties resistant to glyphosate herbicides have
been produced. There are also corn hybrids with
tolerance to imidazoline herbicides, but in these, the
herbicide-tolerance trait was bred without the use of
genetic engineering. Herbicide-resistant GM corn is
grown in the United States. A variation of herbicideresistant GM corn was approved for import into the
European Union in 2004, but such imports remain
highly controversial.
Bt corn: The European corn borer, Ostrinianubilalis,
destroys corn crops by burrowing into the stem,
causing the plant to fall over. Bt corn is a variant
of maize, genetically altered to express the bacterial
Bt toxin, which is poisonous to insect pests. In the
case of corn, the pest is the European corn borer.
Expressing the toxin was achieved by inserting a
gene from the microorganism Bacillus thuringiensis
into the corn genome. This gene codes for a toxin
that causes the formation of pores in the Lepidoptera
larval digestive tract. These pores allow naturally
occurring enteric bacteria, such as E. coli and
Enterobacter, to enter the hemocoel, where they
multiply and cause sepsis [21]. This is contrary to
the common misconception that Bt toxin kills the
larvae by starvation.
The fertilizers impact, growth and yield of maize
grain are highly responsive to nitrogen fertilization,
where maize fields, worldwide, receive around 10
million metric tons of N fertilizer per year [22].
However, nitrogen use efficiency (NUE), i.e. ratio
of grain yield to N fertilizer supplied, of maize
globally falls between 25-50%, indicating that more
than half the N fertilizer applied to maize field is
lost to the environment. On the other hand, hybrids
developed with transgenic resistance to root feeding
by corn rootworm (Diabrotica spp.) have led to larger
and healthier root system and consequently greater
N uptake. Similarly, transgenic maize hybrids with
enhanced drought tolerance could also, indirectly,
increase N uptake and utilization [23]. Application of
bio fertilizers containing Azospirillumbrasilense and
yeast Rhodotorulaglutinis at low rate of NKP (50%)
mineral fertil¬izers, plus sulfur at recommended
dose, gave comparable results for growth parameters
of maize compared with 100% NPK [24]. Genetic
engineering also helped developed Maize cultivars
with resistance to herbicides, including genetically
modified transgenic (glyphosate and glufosinate)
and non-transgenic (sethoxydim and imidazolinone)
hybrids. One example is Maize cultivar with an
hra transgene confer 1000-fold cross-resistance to
ALS (acetolactate synthase)-inhibiting herbicides
and the adoption of transgenic herbi¬cide-resistant
maize hybrids is ever increasing [25]. Finally, the
contribution of biotechnology to maize advances is
reflected in the production of nearly 75% of the maize
in the United States containing biotech traits [26].
Furthermore, continuing to discover and develop
new technologies in the agricultural sciences will
greatly contribute to the food security. Development
of second and third generation herbicide-resistant
and insect-resistant traits that stack multiple modes
of action will insure the beneficial aspects of this
technology for years to come. Also, development of
drought-tolerant maize is becoming a reality [27].
CONCLUSIONS
Biotechnology has contributed tremendous advances
in maize production via different avenues, including
application of effective biofertilizers, plant growth
promoter and more importantly development of
transgenic traits resistant to herbicides and/or pests.
Maize is the premier monocotyledonous species
for biotech research based on its transformation
characteristics, conventional and molecular breeding
advances and monetary value in the agronomic
marketplace. However, there are major factors that
greatly limiting maize production. One of these
factors is drought stress, to which Maize is highly
sensitive, especially at critical times of the growing
season, discouraging smallholder farmers from
risking investment in best management practices
including quality hybrid seed and fertilizer. Therefore, drought tolerant hybrids are being developed
for maize through conventional breeding, markerassisted breeding, and biotechnology and will be
licensed to local seed companies producing and
selling hybrids for local farmers to help reduce
smallholder farmer’s risk from drought and provide
better food security.
In spite of opposition groups, GM crops now acco-
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J. Cell Tissue Research
unt for more than 300 million acres worldwide and
are grown by over 17 million farmers in more than
25 countries. The vast majority of the increase in
farming of GM crops is in developing countries. In
2012, the World Health Assembly (WHA) agreed on
a set of global targets to hold the world accountable
for reducing malnutrition. It is unlikely that these
targets will be met within the timeframe set and new
sustainable development goals are now being set up
with the target date of 2030. To achieve the goal of
providing crops with additional health benefits on a
global scale, much work is required and will involve
interactions between many disciplines including
plant breeders, molecular biologists, nutritionists
and even social scientists. It is not worthwhile to
spend the effort generating a biofortified crop for
a given population if they are knowledgeable,
prepared and not already willing to accept the
technology or any changes in appearance of the
biofortified crop. New crop varieties with enhanced
nutritional qualities must be evaluated by clinical
trials and select populations who can benefit most
from them must be educated so that they understand
how these advantages can make a difference in their
community’s overall health.
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