A diallel analysis of a maize donor population response to in vivo maternal haploid induction: II. Haploid male fertility

Abstract

Doubled haploid (DH) lines are used in maize (Zea mays L.) breeding to accelerate the breeding cycle and create homogenous inbred lines in as little as two seasons. These pure inbred lines allow breeders to quickly evaluate new cross combinations. There are two important steps in creating DH lines: (a) generation and selection of haploid progeny, and (b) genome doubling to create fertile, diploid inbreds. Colchicine is widely used to artificially double genomes in haploid plants, which is hazardous, expensive, and time consuming. In this study, three public inbred lines-A427, A637, and NK778-were found to have substantial haploid male fertility (HMF). A sixparent full diallel between these three HMF lines and three non-HMF lines was created and HMF was scored. Diallel analysis revealed significant general combining ability (GCA) estimates of up to 17% for HMF, as well as significant specific combining ability (SCA) effects of up to 25%. No significant reciprocal effects were found. Haploid male fertility is promising to be incorporated into elite maize breeding programs to potentially overcome the need of using colchicine treatments for genome doubling. Colchicine aided doubling success rates varying from almost 0 to 30%. Haploid male fertility has an advantage over artificial genome doubling, in terms of both increased success rates and decreased costs for DH line production.

Impact of Spontaneous Haploid Genome Doubling in Maize Breeding

“…Using the traditional genome doubling agent, colchicine, the doubling rate typically ranges from 10% to 30% [18,19]. Recently, five inbred lines exhibiting haploid male fertility (HMF) greater than 65% without the use of colchicine were identified by their pollen-shedding ability and proportion of anther emergence [20]. Furthermore, a single large-effect QTL has been identified on chromosome 5 in the inbred that had the highest level of HMF, at 94% [21,22].…”

“…Spontaneous haploid genome doubling has been reported in maize at low levels for nearly as long as haploids have been studied [3,19,20,24,[33][34][35]. Many genotypes from germplasm pools originating worldwide display SHGD, typically at levels < 5%.…”

“…Many genotypes from germplasm pools originating worldwide display SHGD, typically at levels < 5%. However, some genotypes have fertility levels > 50% [3,20,24,[33][34][35].…”

“…While 80% of genotyped haploid plants are not capable of producing offspring, this approach would focus efforts for developing DH lines on the most promising genotypes based on marker data and reduce costs in the DH nursery. This threshold should be reasonable in most genetic backgrounds, given the additive gene action of the allele, large positive general combining ability, and a rate of SHGD of up to 46% in F 1 plants derived from C 0 inbreeds [20]. Furthermore, using SHGD should produce a similar, or even greater number of fertile haploids than colchicine [19].…”

Diallelic Analysis of Tropical Maize Germplasm Response to Spontaneous Chromosomal Doubling

“…Combining-ability analyses are always performed through diallel mating methods developed by Griffing [ 23 ]. A diallel analysis of HMF involving six temperate inbreds revealed significant GCA and SCA effects [ 24 ]. Additive effects were noted to be important for the selection of HMF, while epistatic effects could also play a role [ 25 ].…”