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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 1 01/04/2015 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 2 01/04/2015 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 3 01/04/2015 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 4 01/04/2015 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 5 01/04/2015 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) 6