Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/4/2002
Publication Date: 10/1/2002
Citation: Interpretive Summary: Two different selection methods were practiced on the same maize backcross population to improve resistance to leaf feeding by southwestern corn borer. The methods were marker assisted and conventional backcrossing. For the marker-assisted selection, lines were selected using molecular markers to track regions of chromosomes associated with resistance. Molecular markers were used to select the chromosomal segments associated with resistance as the resistant parent type while the rest of the chromosomal regions were selected for the elite susceptible parent type. Conventional breeding methods were used on the same population. Plants were self pollinated to form families that were artificially infested with southwestern corn borer larvae in replicated trials. Three cycles of selection by both methods were practiced to produce conventional and marker-selected lines at the same stage of backcrossing and inbreeding. These lines were compared in an infested trial in three locations. The marker-selected and conventionally selected backcross lines did not differ in their levels of resistance to southwestern corn borer but both methods produced lines which were significantly more resistant than the susceptible parent.
Technical Abstract: Two maize lines, susceptible and resistant to first-generation southwestern corn borer (SWCB), Diatraea grandiosella, Dyar, were hybridized then backcrossed to the susceptible parent to form a population, which was selected over three backcross generations using either marker-assisted or conventional selection. QTL mapping was done using BC1F1 genotyping and BC1F2 infestation with SWCB. Three QTL regions were identified on chromosomes 7, 9, and 10 accounting for 28% of the phenotypic variation. Marker-assisted selection proceeded by selecting the heterozygous genotype in QTL regions and homozygous recurrent genotype outside the QTL regions in the BC1F1 and BC2F1 generations. The BC2F2 generation was selected for homozygous donor (resistant) genotype in the QTL regions. Conventional selection was initiated from the best 30 BC1F2 lines. Conventional trials of BC2F2, and BC2F3 families were infested with SWCB and based on leaf damage ratings, selected selfed progeny of the former generation formed the subsequent trial entries. A comparative trial of BC2F3 lines selected using the two methods was evaluated under SWCB infestation in three locations. No significant differences for leaf damage ratings or larvae weight were found between lines selected by the two methods. Both methods produced lines significantly improved over the susceptible parent for SWCB leaf feeding damage. In post facto analysis of lines included in the combined trial, only the QTL on chromosome 9 was found to have contributed to SWCB resistance across locations.