2. Technologies developed to enhance maize productivity
Molecular breeding approach in maize starts with identifying and validating quantitative trait loci (QTLs) linked to abiotic stress tolerance. Following the identification and validation of the markers associated with QTLs for traits of interest, the candidate QTLs or genes can be introgressed in elite lines through marker-assisted backcrossing. Over the past years, linkage mapping was used to identify QTLs . However, association genetics is currently used to enhance this work in numerous crops . Nested association mapping is also being utilized for the genome-wide dissection of complex traits in maize crop . Association mapping is highly recommended to be used for identifying traits associated with abiotic stresses . Marker-assisted backcrossing has also been utilized for complex traits such as tolerance to drought, salinity, and heat, which are the key traits targeted for improving and developing crops that are adapted to low rainfall, salinity, and high temperature conditions. Marker-assisted backcrossing may not be an effective approach for introgressing QTLs in some cases. On the other hand, two other molecular breeding approaches, marker-assisted recurrent selection and genomic selection, can overcome this issue . The genetic progress obtained using marker-assisted recurrent selection and genomic selection is greater than that can be obtained using marker-assisted backcrossing. Another technology for enhancing complex traits has been developed and is based on genome-wide selection. Although marker-assisted backcrossing and marker-assisted recurrent selection need provided QTL information for complex traits, information on marker trait associations is not necessarily needed for genome-wide selection . Furthermore, genome-wide selection relies on the information associated with the prediction of the genomic-recorded breeding values of progeny.
Most areas planted with maize currently involve transgenic varieties, and the vast majority of hybrids are now resistant to insects and herbicides. Bt maize containing the protein cry1fAb has been started to be grown in 2007 in order to control