Marker assisted selection for fiber quality improvement in mutation breeding programme of cotton

Thirty four cotton genotypes were screened for fiber quality traits. Four genotypes; FH-883, FH-631S, CIM-707 (tetraploids) and Ravi (diploid) contrasting for quality traits were selected. After surveying 520 RAPDs and 435 SSRs, a genetic linkage map was constructed using 117 F_2:3 lines derived from a cross FH-631S x FH-883. Twenty loci were mapped into four linkage groups (LG) spanning around 230.2 cM with 5% of the cotton genome coverage. The average genetic distance was 11.5 cM between two adjacent loci. Low level of polymorphism between two parents was might be due to narrow genetic base of cotton. LG1 to LG4 were assigned to chromosome 20, 10, 18, and 15, respectively. QTLs for fiber traits were identified by performing SMA, IM and CIM at LOD > 2 with WinQTLCart. Sixteen putative QTLs were identified for fiber traits including fiber length, fiber fineness, fiber strength, fiber length uniformity, short fiber index, fiber elongation, and fiber color. Nine fiber QTLs were detected on A-subgenome, while seven on D-subgenome, which suggest that fiber traits result from gene interaction of both the subgenomes of cotton. CIM-707 (above 30 mm) and Ravi (17 mm) were irradiated with gamma rays (125, 150, 200, 250 and 300Gy) and treated with EMS (1, 1.5 and 2%), which depressed significantly germination percentage of cotton seed. EMS-treated M₁ population was much better than irradiated M₁ population with respect to germination and plant growth. Moreover, ploidy level also affected the germination percentage. Staple length of selected M₃ lines of Ravi was in the range of 13-17.5 mm, while of CIM-707 M₃ lines were 22-31 mm. It indicates that EMS and gamma irradiation can successfully be used for creating variation among cotton germplasm and hence mutants are valuable tool for fiber quality improvement. (author)