Mapping of simple sequence repeats (SSRS) and marker assisted introgression of quantitative trait loci (QTLS) for stay-green in sorghum (SorghumbicolorI (L.)
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Date
2006
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UAS Dharwad
Abstract
With the objective of increasing the marker density in the linkage map of the staygreen
mapping population, ninety four individuals from N13 x E36-1 sorghum recombinant
inbred population were genotyped with 78 EST-SSR makers and 55 markers (70%) gave
reliable and scorable amplification. The genotypic data from these markers was integrated
with the genotypic data of 164 previously mapped RFLP, AFLP, RAPD and SSR markers to
produce the genetic maps. The genetic map constructed has a total length of 2838 cM. The
number of EST-SSR markers mapped per linkage group ranged from 2 (linkage group H) to 9
(linkage group F). Some of the markers such as Xisep0841, Xisep0733, and Xisep0938
mapped in the stay-green QTL regions making them good candidate markers to be used in
fine mapping of the QTLs and marker-assisted selection of the stay-green trait.
In a marker-assisted backcrossing programme, four stable stay-green QTLs (StgB,
Stg1, Stg3 and Stg4) were selected to be transferred from the stay-green donor parent (B35) to
the senescent recurrent parent (R16). After two additional marker-assisted backcrossing and
two selfing generations, four backcross families with single (Stg1, Stg3, Sg4 and StgB) and
five backcross families with double putative QTLs (Stg1+Stg3, Stg1+Stg4, Stg3+Stg4,
Stg3+StgB and Stg4+StgB) have been selected.
Previously generated, early generation stay-green introgression lines (BC2F2/BC1F3)
were evaluated for their agronomic and stay-green related characters under well watered and
water-stress conditions both in field (in the post rainy season) and greenhouse condition for
two seasons. Among the introgression lines, RSG 04001/RSG 05001 was found to be the
most promising line both in terms of its grain yield and stay-green related characters.
Besides high % green leaf area, the stay-green genotypes had high chlorophyll content
and leaf nitrogen concentration compared with the senescent lines showing the relationships
among these traits. The correlations of relative grain yield to relative % GLA in the stress
environments was highly significant (R2 = 0.47 in 2004-05 and R2 = 0.77 in 2005-06)
indicating the contribution of stay green to grain yield.