Near-Isogenic Lines (NILs)
A good way of validating a putative QTL is by creating a Near-Isogenic Line (NIL). This is a new line that differs from its parent in only one genomic location: where the QTL is.
Using the marker identified for that QTL, backcrosses are made to the recurrent parent (usually the cultivated variety, in a wide cross) until the entire genome of the line is exactly like the recurrent parent except in the region around the marker locus. Any phenotypic differences between these 2 lines is then most probably due to the QTL linked to the marker locus, thereby validating the QTL.