Dear Gholamreza Asadollahfardi straightest way is read the publications on Norman Borlaug about topic

Initially the yield increases as fertilizer application rate increases , thereafter yield reaches a maximum . From this point on, any addition of extra fertilizer does not increase the yield .

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he genes of the Green Revolution

Author links open overlay panelPeter Hedden

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https://doi.org/10.1016/S0168-9525(02)00009-4Get rights and content

Abstract

The spectacular increases in wheat and rice yields during the ‘Green Revolution’, were enabled by the introduction of dwarfing traits into the plants. Now, identification of the genes responsible for these traits shows that they interfere with the action or production of the gibberellin (GA) plant hormones. We knew that the wheat Rht genes encode growth repressors that are normally suppressed by GA, and recent work shows that the rice sd1 gene encodes a defective enzyme in the GA-biosynthetic pathway.

Section snippets

The origins of the dwarfing genes The wheat dwarfing genes of the Green Revolution originated in Japan (reviewed in [7]). Early in the 20th century, the Japanese crossed a semi-dwarf wheat variety called Daruma with American high-yielding varieties to produce Norin 10. Although it was of little importance in Japan, Norin 10 was used in breeding programmes in the USA after 1945 to produce a number of high-yielding semi-dwarf cultivars. One cross, Norin 10-Brevor 14, was sent to Norman Borlaug (later to win the Nobel Peace prize

Wheat Rht and gibberellin signal transduction The Rht dwarfing alleles cause a reduced response to the GA class of plant hormones [7]. These growth regulators are diterpenoid carboxylic acids, which participate in many developmental processes in higher plants, including stem elongation [11]. The Rht gene was identified by Peng et al. [3] and shown to be an orthologue of the Arabidopsis GAI and maize dwarf8 genes, for which mutations that result in GA-insensitive dwarfs were also known. Rht-1a/d8/GAI (these symbols refer to the wild-type

Rice sd1 and gibberellin biosynthesis In contrast to Rht, the sd1 mutation of rice is recessive, and normal height can be restored in mutants by application of GA [22], indicating that they are defective in GA production. Three research groups have isolated the sd1 gene independently and shown that it encodes a GA 20-oxidase (GA20ox), an enzyme involved in GA biosynthesis 4, 5, 6. Two of these groups used positional cloning to detect a GA20ox open reading frame that was closely linked to the sd1 locus on the long arm of chromosome

Conclusions It has been shown for many species that GA concentration limits growth and that GA20ox activity is a major determinant of GA production (e.g. [25]). Therefore, it is probably no coincidence that mutations in a GA20ox gene have been selected in screens for semi-dwarfism in rice. In hexaploid wheat loss-of-function mutations are unlikely to be effective (unless present in all three genomes) so that dwarfs were detected from dominant (gain-of-function) mutations. Both cases highlight the important

Acknowledgements I thank Drs Matsuoka and Ashikari for the photographs used in Fig. 1 and colleagues at Long Ashton Research Station for helpful comments on the manuscript.

Glossary Glossary Assimilate partitioning:Distribution between plant tissues of the products of assimilation, the process whereby simple inorganic molecules are incorporated into complex organic compounds, principally by photosynthesis.Cultivar:A plant variety that is found only in cultivation.Homoeologous genes:Equivalent genes that are present on the different sets of chromosomes in polyploid species.Indica and japonica rice:Subspecies of rice (Oryza sativa). Indica is grown mostly in tropical and subtropical

References (26)

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• M. OgawaRice gibberellin-insensitive gene homolog, OsGAI, encodes a nuclear-localized protein capable of gene activation at transcriptional level Gene (2000)
• M.D. Gale et al.Dwarfing genes in wheat
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• J.R. PengGreen revolution genes encode mutant gibberellin response modulators Nature (1999)
• L. MonnaPositional cloning of rice semidwarfing gene. sd-1: rice ‘green revolution gene’ encodes a mutant enzyme involved in gibberellin synthesis DNA Res. (2002)
• A. SasakiGreen revolution: a mutant gibberellin-synthesis gene in rice – new insight into the rice variant that helped to avert famine over thirty years ago Nature (2002)
• W. SpielmeyerSemidwarf (sd-1), green revolution rice, contains a defective gibberellin 20-oxidase gene Proc. Natl Acad. Sci. USA (2002)
• L.T. EvansFeeding the Ten Billion. Plant and population growth (1998)