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Marker-assisted selection IS a method recently developed to improve genetic gain in plant breeding. It is based on identification of tight linkages between markers and QTLs, and also on mapping QTLs involved. To map loci controlling heading date and cold resistance in wheat, QTL- analysis was carried out using 96 doubled-haploid lines (DH), derived from a cross between chinese spring (CS) and SQl, with 345 Molecular markers in a partially linkage map, two experiments conducted. In the first expriment DH-Lines were planted in greenhouse using a completely randomized design with 3 replications. Heading date was recorded when three plant had its spike emerged, in each replication. Heading date was considered as days from an arbitary date to the time of heading. In the second experiment each DH-line was
planted in 4 small pots as four replicates (10 plants / pot). seven days
. .
after emergence plants were transfered to cold room under 3-4 c for
five weeks to practise hardening. The pots were then transfered to
freeze chamber to determaine plant survival at four freezing points:
0 0 0 0
-6 c, -8 c, -11 c and -13 c and to find their L T50 as well as electrolyte
leakage (memberane stability) . Electrolyte leakage was measured at
0
-11 c, using a randomized complete block design with 3 replications.
The results indicated that SQl was earlier and more resistant to cold than CS. QTL-Scan analysis revealed the existance. of two QTLs for heading date, one with large effect on chromosome 5A and one with
small effect on chromosome 5B, which all-together explained 51% of
total phenotypic variation in the DH-population. One QTL was also found for cold resistance on chromosome 7 A, which explained 22% and 12% pf the electrolete leakage and LT50 phenotypic variations in the DH-line population respectively.
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