Doubled Haploids in Tropical Maize: Influence of Inducer, Donor, and Induction Environment On In Vivo Haploid Induction Rates.

Reliable haploid induction rates (HIR) are of utmost importance when employing inducer genotypes for maize doubled haploid (DH) line development using the in vivo haploid induction technique.This work investigates the influence of the genetic constitution of inducers and donors as well as of the environmental conditions on HIR. In a first experiment, we compared HIR of three temperate inducer genotypes in subtropical and tropical environments in Mexico using a temperate liguleless tester as female parent. Testcross progenies were grown in the greenhouse until four-leaf stage and monitored visually. Haploid plants showed the liguleless phenotype. In a second experiment, a total of 150 genetically diverse tropical donors (landraces, improved open-pollinated varieties [OPV], and elite single crosses) were employed as female parents. In this experiment haploid seeds were identified using an embryo color marker. HIR were calculated by dividing the number of haploid plants/seeds by the total number of plants/seeds. Mean HIR was 14.9% (7.9-17.8%) using the temperate liguleless donor, but was only 4.8% (0-19.7%) using the tropical donors. Inducers and donors both had a significant influence on HIR. However, no significant differences were found for HIR between the donor groups of landraces, OPV, and single crosses which indicates that all groups are equally suitable for in vivo haploid induction. Although HIR of the temperate inducers were sufficiently high for large-scale application in tropical environments, haploid seed identification remains an obstacle along with poor agronomic performance of inducers and, consequently, low seed multiplication rates, which currently prevent breeders from adoption of the DH technique in tropical maize breeding programs. Therefore, the development of inducer genotypes with good adaptation to tropical/subtropical conditions and high HIR as well as a novel haploid seed identification system are premises to promote application of the DH technique in tropical maize.