Doubled Haploids in Tropical Maize: I. Effects of Inducers and Source Germplasm on in vivo Haploid Induction Rates

Abstract

The adoption of the doubled haploid (DH) technology in tropical maize {Zea mays L.) breeding programs is lagging behind that of temperate programs due to a lack of tropical haploid inducers and reliable Information on the performance of temperate inducers under nontemperate conditions. The objective of this study was to determine the in vivo haploid induction ability of three temperate inducers crossed to a diverse set of tropical maize source germplasm under tropical conditions. Three experiments were conducted employing inducers as male parents to pollinate 120 source germplasm in three environments in Mexico. Haploid induction rates (HIR) obtained under field conditions were determined with two different haploid identification systems. Highly significant genotypic differences were detected among inducers and source germplasm for HIR but no interactions were observed between the two factors. Mean HIR under tropical conditions were similar to those reported for evaluations under temperate conditions indicating that temperate inducers can be employed for initiation of DH breeding programs in the tropics. Misclassification of diploids as haploids resulted in inflated HIR, particularly in highly variable source germplasm such as landraces or when expression of the identification marker was weak. We conclude that induction of haploidy is not a limiting factor for DH line production in tropical maize, but there is a need for the development of well-adapted tropical inducers.

New Insights into the Genetics ofin VivoInduction of Maternal Haploids, the Backbone of Doubled Haploid Technology in Maize

“…UH400 was developed at the University of Hohenheim, Germany, and has a HIR of 8% averaged across several tropical (Prigge et al 2011) and temperate (W. Schipprack, personal communication) environments. It carries the dominantly inherited marker gene R1-nj conferring a purple coloration of the scutellum and the aleurone of seeds (Nanda and Chase 1966;Neuffer et al 1997), which can be used as embryo and endosperm marker, respectively, to identify putative haploid seeds.…”

“…This discrepancy can be attributed to different testers and the associated haploid identification systems employed for the different mapping populations (Kebede et al 2011;Prigge et al 2011). Further, the presence of different modifier genes (Allard 1999) acting as enhancers or suppressors of major genes in different germplasm sources as well as QTL by genetic background interactions (Pumphreys et al 2007) may be responsible.…”

“…By using haploid inducer genotypes as pollinators in crosses with source germplasm, ears obtained carry a proportion of seeds containing haploid embryos of maternal origin. Subsequent treatment of haploids with mitotic inhibitors facilitates chromosome duplication resulting in diploid and completely homozygous inbred lines (see Prigge and Melchinger 2012 for a detailed description of DH production).Modern maize inducers have haploid induction rates (HIR) of about 8% on average (e.g., Röber et al 2005;Prigge et al 2011). The genetic mechanisms underlying in vivo induction of maternal haploids in maize are not yet fully understood.…”

Generation of Maize (Zea mays) Doubled Haploids via Traditional Methods

“…For instance, induction crosses arrive at an average of only 8% haploid progeny (Prigge et al, 2011). In addition, not all haploids will arrive at a successful DH line.…”

“…Research programs created improved in-vivo maternal haploid inducers based on Stock 6, including RWS, KEMS, WS14, and MHI, among many others with higher haploid induction rates (Röber et al, 2005;Shatskaya et al, 1994;Lashermes and Beckert, 1988;Eder and Chalyk, 2002). These inducers (used as the male parent) are crossed to a donor genotype or population (used as the female parent), currently resulting on average in 8% haploid progeny (Prigge et al, 2011). A dominant anthocyanin gene, R1-navajo or R1-nj (Chase and Nanda, 1965;Nanda and Chase, 1966;Greenblatt and Block, 1967;Neuffer et al, 1997), was incorporated into inducer genotypes, which allows for visual selection of mature haploid kernels.…”