Download Bio3460-24 Green Revolution

01/04/2015
Green Revolution: Increasing Agricultural Productivity
30 food crops that contribute 95% of human nutrition
• the world relies on very few plant species for
most of its food
• in the 1950s serious food shortages occurred in
many developing countries
• it was widely recognized that additional food supplies
would be necessary to feed growing populations
The Green Revolution
•
a response to the food shortages
•
occurred in the 1960s
“Record yields, harvests of unprecedented size and
crops now in the ground demonstrate that throughout
much of the developing world - and particularly in Asia we are on the verge of an agricultural revolution.
•
resulted in production of more food per area of
cropland by using modified agricultural methods
It is not a violent red revolution like that of the Soviets,
nor is it a white revolution like that of the Shah of Iran.
•
these new methods primarily included:
I call it the Green Revolution.”
1) use of commercial inorganic fertilizers (and pesticides)
2) development and introduction of high yielding
dwarf varieties of wheat and rice
William Gaud
United States Agency for International Development
March 1968
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Haber-Bosch Process for Ammonia Synthesis
N2 + 3 H2 + energy --> 2 NH3
Temperatures: 400°C to 650°C
Pressures:
200 atm to 400 atm
Metal Catalyst: Iron
N2 from air
H2 from extracted from natural gas
Haber was awarded the 1918 Nobel Prize (Chemistry)
- for pioneering work on the synthesis of ammonia and
its potential application in agriculture
Haber’s Original Apparatus for Ammonia Synthesis
Haber-Bosch Process for Ammonia Synthesis
before World War I in Germany the manufacture of explosives and
fertilizer depended on import of sodium nitrate from Chile
just before the start of the WWI in 1909 Fritz Haber developed a
process to make ammonia
this process was scaled up for industrial production by engineer
Carl Bosch in 1914 - government sponsored intensive research
synthesis of ammonia prolonged the WWI but Germany’s inability
to produce enough for both munitions and fertilizer helped to end
the war
after WWI - Britain and France got access to industrial plants and
replicated the Haber-Bosch process & plants were built in USA
by 1930 more ammonia was synthesized than sodium nitrate was
mined, after 1945 munitions plants were switched to make fertilizer
www.sciencemadness.org
Annual input of Nitrogen in global croplands
Fertilizers & the Problem of Lodging
Inorganic fertilizers
85 M tonnes
Availability of inorganic fertilizers allowed farmers to
supply much more nitrogen to crops
Decomposition-mineralization
30 M tonnes
Biological N2 fixation
30 M tonnes
Animal wastes
15 M tonnes
Total Inputs
175 M tonnes
Major crops (wheat, rice) produced larger, heavier seed
heads associated with higher yields that were induced
by fertilizers
A new problem appeared - with the heavy seed heads,
the crop plants fall over (lodging) which reduced the
harvested yields
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Harvest Index = grain mass/total plant mass
Rise of the Dwarfs
Dwarf plant varieties can support heavy seed heads
without lodging
-increased from 0.35 to 0.50 after widespread
introduction of dwarf varieties
Dwarf varieties do not waste energy on growing long
stalks so more energy can be diverted to seed
heads
So dwarf varieties boost crop yields in two ways:
1) They allow more fertilizer to be used
2) They convert nutrients more efficiently into useful
grain rather than useless stalks
Norman Borlaug & the Green Revolution
• an American agronomist
• first introduced dwarf wheat
varieties into Mexico
• developed new “shuttle breeding”
techniques: highland - summer
lowland desert - winter
• developed in Mexico new wheat
strains that were disease resistant
and insensitive to day-length
• took new dwarf wheat varieties to
India & Pakistan
• encouraged use of dwarf rice
varieties in Asia
• awarded Nobel Peace Prize 1970
In the 3 decades after 1970 the new dwarf wheat
varieties quickly replaced traditional crop varieties
across the developing world
In 2000 - the new dwarf varieties accounted for a large
proportion of the cultivated land area:
Wheat
Asia
Latin America
Middle East & Africa
86%
90%
66%
Asia
China
74%
100%
Rice
Uses of Herbicides
Fertilizers made stem shortening necessary
Herbicides made it possible for dwarf varieties
to be grown successfully – reduced weeds
Discovery of auxin (IAA) and related synthetic
hormones also contributed to increases in
agricultural productivity in the Green Revolution
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Dwarfing genes in Wheat
2,4-D a synthetic Auxin that kills dicot weeds
Dwarfing genes in Wheat
Wheat is hexaploid - it contains 3 diploid genomes
from hybridization events, 3 x 14 = 42 chromosomes
3 genomes termed A,B,D
Dwarf phenotype is caused by genes that prevent
gibberellin activity: reduced height (Rht) genes
Rht-B1b and Rht-D1b are the genes present in
many commercial wheat varieties
Some varieties contain both genes - additive effects
Dwarfing genes in Wheat
Rht-B1b and Rht-D1b genes contain point mutations
that introduce a ‘stop’ codon in the DELLA domain of
the DELLA protein involved in the GA signal
transduction pathway
Part of the Gibberellin Biosynthesis Pathway
GA8
GA2ox
sln
DELLA protein does not respond to gibberellin and
growth is repressed --> dwarf phenotype
Rht-B1c has more severe effects including reduced
grain yield so beneficial dwarfing effects are not
continuous
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Semi-dwarf-1 (sd-1) and wild-type rice
Dwarfing genes in Rice
Rice is diploid
Semi-dwarf phenotype is caused by a gene (sd-1) that
reduces gibberellin synthesis - plants do respond
positively to gibberellin addition
sd-1 codes for a mutant GA-20 oxidase enzyme
Plants with mutant enzymes are slightly reduced in
height with no detrimental effects on grain yield
Dwarfing genes in Wheat and Rice
Food Shortages caused by high prices in 2007-08
Differences in ploidy between wheat and rice
influenced which genes could have been selected in
breeding programs for the dwarf phenotype
Between January 2007 and April 2008:
In a diploid plant like rice - a single mutation in a gene
for ‘loss of function’ in enzyme activity in GA
biosynthesis can occur and be selected for easily
In a hexaploid plant like wheat - it would be very
unlikely that a ‘loss of function’ mutation in the GA
biosynthetic pathway would occur because the
mutation would have to occur in all three resident
genomes. A mutation in the signal transduction
pathway was much more likely.
wheat prices doubled
rice prices tripled
Price increases caused food shortages that put
100 Million people into hunger across the world
and stimulated food riots in several countries
Caused by:
- high oil prices -> transportation and fertilizer costs
- more meat-rich diets increased demands for grain use
as animal feed (China & India middle class)
- diversion of food crops into bio-fuel production
Is a second Green Revolution needed?
Increased food production to meet the world’s population
growth:
6.8 Billion in 2011
9.1 Billion in 2050
Increased production can be done easily if:
- extra land is used in agriculture
- more fertilizer & pesticide are used
- increase use (depletion) of ground water reserves
But we really need a second Green Revolution with Sustainable Intensification of Agriculture
Nature (2011) 471: 141
- to avoid pitfalls of further environmental degradation
and further loss of biodiversity
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Current plant physiology research is working on:
New research is needed for crop varieties that:
- have higher yields
- use less water
- require less fertilizer
- are more resistant to drought, heat, pests
- converting rice to C4 photosynthetic metabolism
- producing wheat varieties with deeper roots
- improving Rubisco performance
- reducing photorespiration
- adding biosynthetic pathways to increase production
of useful products (starch, oils)
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