The Indian Journal of Genetics and Plant Breeding

QTLs associated with growth of rice seedling were mapped using a doubled-haploid (DH) population derived from a cross between lowland indica variety, IR64 and upland japonica variety, Azucena. Age-specific measures on seedling growth parameters such as seedling height, root depth, seedling weight, recorded at seven days interval, starting from 16^th day of sowing, were used to detect the QTLs. A QTL mapping technique termed as ‘conditional mapping’ has been described and the utility of the technique has been illustrated. Altogether 11 QTLs each for seedling height and root depth and 10 QTLs for seedling weight were detected.The number of QTLs varied according to stages of growth indicating age-specific action of QTLs. The number of QTLs detected by conventional mapping at different stages of observation varied between 4 to 7 for seedling height and 2 to 4 for root depth and seedling weight with few QTLs for all the traits appearing consistently over the stages of observation. The conditional mapping technique allowed detection of three QTLs for seedling height and four QTLs each for root depth and seedling weight which remained undetected by the conventional mapping technique.