MARKER-ASSISTED BACKCROSSING OF STAY-GREEN QTLs INTO ELITE SORGHUM LINES
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Date
2004
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Professor Jayashankar Telangana State Agricultural University
Abstract
y. This C4 grass is grown in more than 80 countries mostly in tropical and sub- tropical regions. After soil nutrient deficiencies, drought &ess is the moat important abiotic constraint to sorghum production globally. Dry spells can occur at any stage of the crop growth period. In sorghum, rapid premature leaf death generally occurs when water is limiting during the grain filling stage. Therefore drought stress during the grain filling period is referred as "post-flowering drought or terminal drought". The plant charadter associated with post flowering drought tolerance is called "stay-green". Stay- green is associated with knctional green leaf area (GLA) during and after the grain filling period. Stay-green in sorghum is associated with charcoal rot, lodging resistance and superior ruminant quality. This complex trait is difficult to score. Genetic mapping of QTLs associated with stay-green is an important step towards 'developing drought tolerant hybrids. Different sources of stay-green have been identified in sorghum. The most commonly used lines in breeding program are B35 and E36-1. . Different research grotips independently developed QTL maps for stay-green using different donor parents and marker systems. After identifying the consistent Q'Ks markers. these can be tested through introgression of QTLs from their mapped sources into sorzhum elite breeding lines. This can be accomplished by cloning the genes expressing QTLs and transferring these genes to recipient breeding lines or through marker-assisted breeding (MAB) program, where QTLs are introgressed into elite breeding lines using molecular markers. MAB is the most appropriate technique when traits are complex and difficult to score/measure like yield, abiotic stress tolerance, where the genes contributing to QTLs expression have not yet been identified, and where plant transformation systems are not well established. - With the development of molecular tools and molecular genetic linkage maps for plants, marker-assisted selection (MAS) has become much more broadly applicable. From the last decade, developing ability to transfer target genomic regions using DNA markers resulted in extensive mapping experiments aimed at development of MAS. Molecular marker based genetic linkage map of sorghum has permitted the identification of six QTLs for stay-green (post-flowering drought tolerance) in sorghum line B35. This project aimed at transferlintrogression of these QTLs fiom B35 to recurrent parents, ISIAP Dorado and R16. BC3 and BC4 generations fiom each recurrent parent were genotyped with the markers linked to stay-green QTLs for foreground selection and evenly distributed unlinked markers for background selection to speed the recovery of recurrent parent genotype in genomic regions that are not associated with the target stay-green QTLs. Genotypes with desired marker allele profiles were selected and advanced to next generations. Further studies are necessary to confirm the introgression of QTLs and expression patterns ibr stay-green by phenotypic evaluation of selected genotypes.
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D7079