Download Facing the challenge of climate change: the role of plant breeding

Fa c i n g t h e c h a l l e n g e o f c l i m a t e
change: the role of
plant breeding
Michael Abberton
I nt ro d u c t i o n
The genetic improvement of crops plays a major role in the
enhancement of agricultural systems. In the past, genetics
has mainly been used to enhance yield and product quality
but it can be equally applicable to furthering alternative
objectives such as contributing to climate change mitigation
and reducing the environmental impacts of farming.
Genetic improvement programmes at IBERS are leading the
way in incorporating these broader objectives, using stateof-the-art approaches directed towards successful variety
development in major temperate crops, forage grasses,
clovers and oats.
Reducing greenhouse gas emissions
Mitigation here refers to interventions designed to reduce
the impact of climate change, generally by decreasing the
levels of greenhouse gases such as carbon dioxide, nitrous
oxide and methane released to the atmosphere. Breeding
Figure 4.1: White clover mapping family genotypes growing
in horizontal sand-bed lysimeters for measurement of
components of N and P use efficiency.
approaches have the potential to contribute to reduced
emissions of nitrous oxide and methane from both grazing
animals and the soil, as well as directly from the plant, and to
boost the capture (sequestration) of carbon in the soil.
Nitrous oxide (N2O) emissions can arise directly from
nitrogen (N) applied to the soil, whether this be in the form
of fertiliser, manure, crop residues, nitrogen fixation, or
indirectly from nitrates. Developments to reduce nitrate
leaching or ammonia volatilisation are also likely to reduce
nitrous oxide emissions,, so with agriculture being recognised
as a major source of N2O, forming about 67% of UK output,
any successful measures to reduce farming emissions will be
very worthwhile.
A key area where genetic approaches can have an impact is
in improving the nitrogen use efficiency (NUE) of crops to
allow lower fertiliser application and, hence, reduce N2O
emissions throughout the soil-plant-(animal)-soil cycle. This
is a major focus of the current IBERS programme of genetic
improvement in perennial ryegrass (Lolium perenne). Oats
grown for forage require less nitrogen than other feed
cereals, which means that this crop can also play a valuable
structural role in mitigating agricultural greenhouse gas
emissions. IBERS research staff are currently investigating
whether it is possible to improve the NUE of spring and
winter oats.
For livestock agriculture, enhancing the efficiency of
digestive processes in the rumen of cattle and sheep is of
critical importance in reducing emissions and has been a
focus of combined studies in plant breeding and animal
science at IBERS. The highly successful commercial
development of the Aber high sugar grasses is a prime
example of successful development in this area. For instance,
we showed that a 9% varietal improvement in the water
soluble carbohydrate (WSC) of perennial ryegrass reduced
the proportion of dietary N excreted in the urine of grazing
dairy cows from 39 to 26%. As in other cases, increasing
efficiency allows ‘win-wins’ which benefit the farmer
financially as well as reducing pollution. Thus it has also been
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i)
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the rate of input of organic matter to the soil;
the rate of decomposition of that organic matter;
soil depth; and
the physical protection of organic aggregates and organomineral complexes within the soil.
The key plant traits likely to influence C sequestration (root
depth, structure and architecture; litter composition and
amount) are reasonably well established, and genetic variation
is beginning to be characterised for many of them. Some early
progress has been made under Defra funding at IBERS with
regard to mapping the genes in perennial ryegrass which affect
C sequestration. For example, effective return of carbon to the
soil within plant litter is now known to be associated with
genetic loci on ryegrass chromosomes 1 and 5.
Role of legumes
Figure 4. 2: Field trial of oats.
shown that grazing the higher WSC variety ‘AberDart’, rather
than the UK standard variety ‘Fennema’, in upland areas
increased income from steers by £268/ha and income from
lambs by £345/ha.
On a global scale, agriculture produces between 21 and 25% of
the total anthropogenic emissions of methane. The
predominant agricultural source of this powerful greenhouse
gas is ruminant fermentation, and therefore diet can be a major
factor influencing methane emissions. We are currently testing
the hypothesis that an enhanced quality of diet, combining high
WSC grasses and white clover, will reduce methane production.
Oats can also play a key role in this area. Preliminary evidence
using in vitro methods has shown that increasing the oil content
of a conventional oats forage crop can reduce methane
emissions by up to 25% compared with wheat. We are also
investigating the potential of developing oat varieties which
combine high oil content with low levels of lignin in the husk,
which would increase feed efficiency. The role of naturally
occurring tannin compounds, found widely in some forage
legumes, particularly birdsfoot trefoil, is being assessed as a
further contribution to methane mitigation.
The industrial manufacture of nitrogen fertiliser brings with it
significant greenhouse gas emissions from the Haber-Bosch
process for synthesising ammonia and also from nitric acid
production. Ammonia is the primary feedstock for most
nitrogenous fertilisers but its production is very energy intensive,
with natural gas providing the primary energy source in the UK.
Nitric acid is required in the manufacture of ammonium nitrate,
calcium nitrate and potassium nitrate fertilisers. The oxidation
of ammonia to nitric acid also produces tail gases of nitrous
oxide, nitric oxide and nitrogen dioxide. The environmental
value of legumes, which can naturally ‘fix’ nitrogen from the
atmosphere and subsequently convert it into forms suitable for
plant growth, is thus aptly demonstrated. Increasing the
persistency and reliability of white and red clover, the major
forage legumes of UK pastures, remains an important aspect of
Enhancing carbon sequestration
The substantial stocks of carbon (c) captured by temperate
grassland ecosystems are primarily stored underground in the
roots and soil. The principal factors which determine the degree
to which C is sequestered in grassland soils are as follows:
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Figure 4. 3: Procedure for transfer of fescue genes for drought
resistance from Italian ryegrass introgression lines into a
perennial ryegrass cultivar.
breeding programmes at IBERS. The nutritional inputs of these
crops in terms of quality meat and milk production reinforce
their benefits to both the environment and farm profitability.
Adapting to climate change
Drought is an important environmental factor limiting the
productivity of crops worldwide. Climate change models
predict greater variability in rainfall patterns, and increased
periods of summer drought will affect many regions, including
temperate grasslands. Population growth will also require more
of the available water to be used for domestic and industrial use,
rather than for irrigating crops, giving a double benefit for
productive crops exhibiting enhanced drought resistance and
water use efficiency. These factors are reflected in the increasing
IBERS emphasis on design and selection of varieties better able
to tolerate prolonged periods of water deficit.
In recent years, developments in non-GM DNA-based
technologies have been applied to understanding the genetic
control of important plant characteristics in crops. These have
provided several effective new opportunities for the study of
plant responses to the environment, including very complex
traits such as drought resistance. Many of the genes involved in
plant adaptations to drought stress have also been found to
confer improved salinity tolerance. This has been observed in
the Lolium-Festuca complex, where Festuca-derived genes
incorporated for drought resistance also conferred tolerance to
prolonged exposure to saline concentrations of 150-300 mM
NaCl. Such improved genetic traits in Lolium-Festuca
introgression lines are made effective by improved osmotic
adjustment in the plant cells leading to more efficient water
retention during periods of soil water deficit.
Whilst water deficit is one of the outcomes frequently
mentioned in climate change discussions, episodes of intense
excess rainfall leading to flooding are now starting to occur
regularly and are likely to increase in frequency, bringing major
challenges to the protection of public services and national
economies. In addition, any prolonged summer droughts
which occur will increase soil compaction and, as a
consequence, bring greater vulnerability to any subsequent
surface flooding. Genes carrying the capability for stimulating
the capacity of roots to penetrate compact soils have been
identified in rice. The close genetic similarities (synteny)
between ryegrass and rice should aid the targeting and transfer
of these rice genes into ryegrass. Pilot studies at IBERS have
already identified putative gene loci (QTL) for enhanced root
development on ryegrass chromosome 3 (= rice chromosome 1).
Figure 4.4: Fescue introgressions on ryegrass chromosome 3
for drought resistance.
An integrated approach
It is important that the improvements applied to individual crop
species are seen within the context of the whole farm system,
and more broadly at catchment level where water resources are
concerned. In terms of the balance between different outcomes
(e.g., higher production, reduced water pollution, controlled
emissions), the use of modelling approaches is likely to be
extremely valuable. Life cycle analysis (LCA) is an emerging and
increasingly important tool for the development of sustainable
solutions to the delivery of multifunctional agriculture. It can
be used to identify breeding targets and the environmental
benefits of improving specific traits. For example,LCA has helped
to identify those parts of the oat production chain (farm cropmilling-cooking) which use most energy and where plant
breeding approaches can best be applied. It is likely that the
breeding approach will prove both carbon-efficient and cost
effective, but this needs to be rigorously established and
compared with other potential approaches. Many of the
strategies based on improved farm management, more efficient
processing and better animal selection may well prove to be
complementary to the plant genetic strategies, working
together in partnership.
Michael Abberton email: [email protected]
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