Computer Simulation to Guide Choice of Breeding Strategies for Marker-aided Multiple Trait Integration in Maize By

With the rapid rate of adoption by farmers worldwide of crop varieties containing multiple value-added traits, mainly genetically modified traits, as many as 15 to 20 transgenic events may be offered in new maize hybrids by 2030 (Que et al. 2010; Fraley 2012). Multiple Trait Integration (MTI) is designed to integrate the specific transgenic events conferring the value-added trait phenotypes into the elite genetic package represented by the target hybrid, regaining the performance attributes of the target hybrid along with reliable expression of the value-added traits. From a breeding standpoint, MTI involves four steps: Single Event Introgression, Event Pyramiding, Trait Fixation, and Version Testing. We considered the breeding process to introgress 15 transgenic events into a target maize hybrid, incorporating 8 into the female parent and 7 into the male parent, to design a comprehensive and efficient approach to MTI overall. Focusing on the first step, Single Event Introgression which is conducted in parallel streams to convert a given recurrent parent for individual events, the primary breeding goal is to minimize residual non-recurrent parent germplasm remaining from the trait donor, especially in the chromosomal proximity to the event (i.e. linkage drag). Setting a defined lower limit of 96.66% recurrent parent (RP) germplasm recovery (i.e. ≤ 120 cM non-recurrent parent germplasm), conversion for 15 events requires the final selections in Single Event Introgression to have < 8 cM total amount of non-recurrent parent germplasm across the genome with ~ 1 cM non-recurrent parent germplasm in the 20 cM region flanking the event. Using computer simulation, we sought to identify optimal breeding strategies for Single Event Introgression in terms of selection scheme, required population size, and selection intensity.