Identification of Quantitative Trait Loci Underlying Shrunken Kernel Phenotype in Maize Using Four Interconnected Advanced Backcross Populations Derived From Two Donor Parents.

Recurrent selection backcross (RSB) breeding scheme has been recently utilized to transfer the trait of interest to recurrent parent from wild, exotic or elite but unadapted donor parents and also to simultaneously identify QTL governing the trait.   This study was undertaken to improve an elite inbred NEL105 following RSB breeding scheme. NEL105 is an elite Dow Agro Sciences non-stiff stalk 2YD inbred that has a marginal shrunken kernel trait. Two separate backcross populations were created using the donor parents NHG249 and MTV927 to transfer the non-shrunken kernel trait to the recurrent parent.  At the BC₁S₁ and BC₂ stage, phenotypic selections were made to identify best ear families whereas at the BC_2:3 and BC_3:4 stage, two step selection process was employed: initially phenotypic selections were made to identify best ear families followed by marker based selections to recover lines with maximum recurrent parent genome.  Using composite interval mapping (CIM)-QTL analysis, two significant markers were detected in NEL105 x NHG249 BC_2:3 population whereas four were detected in its corresponding BC_3:4 population.  Likewise, one significant marker was detected in NEL105 x MTV927 BC_2:3 population whereas three were detected in its corresponding BC_3:4 population. Two unique marker-QTL associations were consistently detected, one each in both BC_2:3 and BC_3:4 stages of NEL105 x NHG249 and in NEL105 x MTV927 crosses. However, none of the CIM-detected markers were common to both the crosses.  These results support and further demonstrate that the QTL detection is dependent on the genetic background, stage of the population and environmental conditions.   Employing RSB method, several NEL105 lines with superior kernel phenotype were identified and several QTL underlying the shrunken kernel trait were simultaneously detected that could be appropriately manipulated in our future marker assisted selection projects.