Tapping the genetic diversity of landraces in allogamous crops with doubled haploid lines: a case study from European flint maize

Abstract

Using landraces for broadening the genetic base of elite maize germplasm is hampered by heterogeneity and high genetic load. Production of DH line libraries can help to overcome these problems. Landraces of maize (Zea mays L.) represent a huge reservoir of genetic diversity largely untapped by breeders. Genetic heterogeneity and a high genetic load hamper their use in hybrid breeding. Production of doubled haploid line libraries (DHL) by the in vivo haploid induction method promises to overcome these problems. To test this hypothesis, we compared the line per se performance of 389 doubled haploid (DH) lines across six DHL produced from European flint landraces with that of four flint founder lines (FFL) and 53 elite flint lines (EFL) for 16 agronomic traits evaluated in four locations. The genotypic variance ([Formula: see text]) within DHL was generally much larger than that among DHL and exceeded also [Formula: see text] of the EFL. For most traits, the means and [Formula: see text] differed considerably among the DHL, resulting in different expected selection gains. Mean grain yield of the EFL was 25 and 62% higher than for the FFL and DHL, respectively, indicating considerable breeding progress in the EFL and a remnant genetic load in the DHL. Usefulness of the best 20% lines was for individual DHL comparable to the EFL and grain yield (GY) in the top lines from both groups was similar. Our results corroborate the tremendous potential of landraces for broadening the narrow genetic base of elite germplasm. To make best use of these "gold reserves", we propose a multi-stage selection approach with optimal allocation of resources to (1) choose the most promising landraces for DHL production and (2) identify the top DH lines for further breeding.

Genomic Prediction Within and Among Doubled-Haploid Libraries from Maize Landraces

“…The landraces from which the six DHL were derived, their respective abbreviation, their country of origin, and the number (n) of DH lines in each DHL were: Campan Galade (CG, France, n = 19), Gelber Badischer (GB, Germany, n = 50), Strenzfelder (SF, Germany, n = 54), Rheintaler (RT, Switzerland, n = 34), Satu Mare (SM, Romania, n = 101), and Walliser (WA, Switzerland, n = 93). The EF and DH lines used in this study represent a subset of the full panel described in a companion paper (Böhm et al 2017), encompassing in total 460 lines, including the above-mentioned lines plus 56 further lines not considered in this study from five landraces with less than eight DH lines per landrace, as well as a set of Iodent and flint founder lines.…”

“…Field trials were carried out in 2013 across four agro-ecologically diverse locations in Germany, always using a 46 3 10 a lattice design with two replications, as detailed by Böhm et al (2017).…”

“…First, one must identify the most promising accessions, commonly based on passport data provided by seed banks and results from field trials, in which the landraces are evaluated for their per se performance and/or testcross performance with suitable testers (Salhuana and Pollak 2006;Böhm et al 2014). Selection among accessions is not sufficient because both molecular and phenotypic data from various crops suggest that more genetic variation lies within than between landraces (Greene et al 2014;Monteiro et al 2016;Böhm et al 2017;Mayer et al 2017). Therefore, the second challenge is mining the genetic diversity within landraces, preferably in the form of inbred lines.…”

“…Line development has traditionally been accomplished by recurrent selfing or full-sib matings (Poehlman 1987). When applied to landraces of allogamous species, success rates are generally extremely low, because the high genetic load revealed in advanced selfing generations is manifested in poor vigor (inbreeding depression), and a loss of inbred lines due to the fixation of detrimental or (sub)lethal alleles (Böhm et al 2017). Recently, Melchinger et al (2017) showed that large-scale production of doubled-haploid (DH) lines from landraces in maize is possible, albeit at much higher expenditures compared with elite materials.…”

“…A first priority is evaluating their line per se performance, because many of the DH lines from landraces display severe weaknesses such as lodging, tillering, susceptibility to diseases, and low pollen production. Phenotyping in multilocation trials entails high costs and requires large seed quantities, yet seed multiplication is generally a problem due to the poor seed set and reduced vigor of these materials (Strigens et al 2013;Böhm et al 2017). Subsequent evaluation for testcross performance should be restricted to lines showing acceptable per se performance (Wilde et al 2010).…”