Five Cycles of Mass Selection for Earliness and Ear Appearance under Corn Borer Infestation in the Maize Synthetic BS17

Five cycles of mass selection for earliness and visual ear appearance score under infestation with Mediterranean corn borer (MCB) (Sesamia nonagrioides Lef.) eggs were performed in maize (Zea mays L.) synthetic BS17. The objective of this work was to evaluate the effect of five cycles of mass selection for earliness and corn borer tolerance in the maize synthetic BS17. Evaluations were performed at two different locations (Pontevedra and Zaragoza) in Spain and on two planting dates (early and late). Responses to selection for days to silking and days to pollen shedding were -0.39 and -0.54 d per cycle, respectively. In addition, selection significantly reduced kernel moisture at harvest and plant height, whereas visual ear score and grain yield did not change over cycles. The response to selection in Zaragoza was comparable to the response in Pontevedra, where the selection program was performed. The BS17C5 population created after five cycles of selection compares favorably with other adapted breeding populations as a good source of early inbred lines with good yield potential and tolerance or resistance to MCB. Therefore, mild selection for adaptation has been efficient with no significant detrimental effects, but continued selection for earliness is not recommended.