In vivo haploid induction in maize - performance of new inducers and significance of doubled haploid lines in hybrid breeding

In the last three to five years, doubled hap- loid (DH) lines have increasingly been used in maize (Zea mays L.) research and breeding. This became possi- ble by substantial progress in the in vivo haploid induc- tion technology. Herein, we describe the development and characteristics of a new induction line, RWS, and dis- cuss quantitative genetic and logistic aspects of the use of DH lines in hybrid maize breeding. - Induction line RWS was derived from an F 5 plant of a cross between the Russian induction synthetic KEMS and the French induc- tion line WS14. Kernels with a haploid or F 1 embryo can be distinguished by means of the expression of the domi- nant anthocyanin marker gene R1-nj. Misclassification rates based on this marker gene are generally low except for donors carrying anthocyanin inhibitor genes. Reliable estimates of the induction rate were obtained by using tester genotypes with recessive morphological markers. In tests across various induction environments, RWS consis- tently showed the highest induction rate (8.1% on aver- age) compared to other inducers evaluated herein. - Ad- vantages of using DH lines in hybrid breeding include (1) maximum genetic variance in line per se and testcross tri- als, (2) high reproducibility of early-selection results, (3) high efficiency in stacking targeted gene arrangements and (4) simplified logistics. High cost-savings are possible due to reduced expenses for the selfing program, han- dling and shipping of seed batches, and for maintenance breeding. Moreover, outstanding DH lines may be pro- tected and commercialized several seasons earlier than lines developed by inbreeding.