Marker-Assisted Breeding of Improved Maternal Haploid Inducers in Maize for the Tropical/Subtropical Regions

Vijay Chaikam,Albrecht E Melchinger,Leocadio Martinez,Sudha K Nair,Prasanna M Boddupalli,H Friedrich Utz,Luis Antonio Lopez

doi:10.3389/fpls.2018.01527

Abstract

For efficient production of doubled haploid (DH) lines in maize, maternal haploid inducer lines with high haploid induction rate (HIR) and good adaptation to the target environments is an important requirement. In this study, we present second-generation Tropically Adapted Inducer Lines (2GTAILs), developed using marker assisted selection (MAS) for qhir1, a QTL with a significant positive effect on HIR from the crosses between elite tropical maize inbreds and first generation Tropically Adapted Inducers Lines (TAILs). Evaluation of 2GTAILs for HIR and agronomic performance in the tropical and subtropical environments indicated superior performance of 2GTAILs over the TAILs for both HIR and agronomic performance, including plant vigor, delayed flowering, grain yield, and resistance to ear rots. One of the new inducers 2GTAIL006 showed an average HIR of 13.1% which is 48.9% higher than the average HIR of the TAILs. Several other 2GTAILs also showed higher HIR compared to the TAILs. While employing MAS for qhir1 QTL, we observed significant influence of the non-inducer parent on the positive effect of qhir1 QTL on HIR. The non-inducer parents that resulted in highest mean HIR in the early generation qhir1+ families also gave rise to highest numbers of candidate inducers, some of which showed transgressive segregation for HIR. The mean HIR of early generation qhir1+ families involving different non-inducer parents can potentially indicate recipient non-inducer parents that can result in progenies with high HIR. Our study also indicated that the HIR associated traits (endosperm abortion rate, embryo abortion rate, and proportion of haploid plants among the inducer plants) can be used to differentiate inducers vs. non-inducers but are not suitable for differentiating inducers with varying levels of haploid induction rates. We propose here an efficient methodology for developing haploid inducer lines combining MAS for qhir1 with HIR associated traits.

Highlights

Through in vivo induction of haploids and subsequent chromosomal doubling, genetically homozygous breeding lines can be produced in maize in just two crop seasons compared to the traditional inbreeding approach that requires 6–9 crop seasons
Doubled Haploid (DH) technology could play an important role in rapid development and deployment of improved maize hybrids in the tropical environments
The Second-generation Tropically Adapted Inducer Lines (TAILs) (2GTAILs) developed through this study have the potential to address an important need for haploid inducers with superior agronomic performance and high Haploid Induction Rate (HIR) especially in thetropical environments

Summary

Introduction

Through in vivo induction of haploids and subsequent chromosomal doubling, genetically homozygous breeding lines can be produced in maize in just two crop seasons compared to the traditional inbreeding approach that requires 6–9 crop seasons. Based on Stock 6 derived inducers, more effective haploid inducers with high HIR (>6%) were developed in the last 15– 20 years, which made commercial production of DH lines a possibility in maize. These inducers include RWS (Röber et al, 2005) and UH4001 in Germany, MHI in Moldavia (Chalyk, 1999), and the PHI series in Romania (Rotarenco et al, 2010). Inducers equipped with high oil trait were developed in Germany (Melchinger et al, 2013) and China (Dong et al, 2014), which aid automation of haploid identification (Melchinger et al, 2018)

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