Haploid induction and its application in maize breeding

Abstract

Maize is a heterosis-utilizing crop species, and the application of maize hybrids has significantly improved total maize yields worldwide. Breeding pure lines is the most important part of heterosis utilization. The double haploid (DH) breeding technology is the approach rising recently in breeding pure lines; compared to the conventional recurrent-selfing method, it can significantly accelerate the crop breeding process. Similar to molecular breeding and transgenic techniques, maize DH breeding has been playing an increasingly important role in commercial breeding and is becoming the core technique in modern maize breeding. In this review, we summarize recent progress in maize DH breeding and put forth our opinions on the future development of double haploid techniques in modern maize breeding.

Keywords: DH lines; Haploid; Inducer lines; Maize breeding.

Fig. 1

Model of the induction mechanism of maize. Type I: The normal or slightly fragmented sperm fused with normal eggs form diploids; type II: One of the sperm that has undergone chromosome fragmentation and has fertilized an egg may form haploids and abortive kernels; type III: Severe chromosome fragmentation occurs in both sperm and abortion kernels that have formed. AP, antipodal cell; PN, polar nucleus; EC, egg cell; SY, synergid cell; TR, trophic nucleus; SN, sperm nucleus; D-em, diploid embryo; H-em, haploid embryo; D-en, diploid endosperm; T-en, triploid endosperm

Fig. 2

Model of the rapid breeding of DH lines by the use of inducer lines containing purple markers or fluorescent markers. The embryos that lack purple color or fluorescent signals are haploid. They are selected to put into N6 culture media for carrying out the subsequent doubling process with the chemical reagents. N6: short for N6 culture media