Abstract
Lacking elite haploid inducers performing high haploid induction rate (HIR) and agronomic performance is one of fundamental factors hindering the rapid adoption of doubled haploid technology in maize hybrid breeding, especially under tropical savanna climate. Breeding haploid inducers for specific agro-ecology, thus, is indispensable yet challenging. We used temperate inducer Stock6 as genetic source for haploid induction ability and eight tropical maize genotypes as principal donors for agronomic adaptation. Three cycles of modified ear-to-row with 5% intra-family selection were applied in a population set of 78 putative haploid inducer families emphasized on agronomic performance, R1-nj anthocyanin intensity, and inducer seed set. Genetic gains, variance components, and heritability on given traits were estimated. Hierarchical clustering based on five selection criteria was performed to investigate the phenotypic diversity of putative families. Cycle effect was predominant for all observed traits. Realized genetic gain was positive for HIR (0.40% per cycle) and inducer seed set (30.10% or 47.30 seeds per ear per cycle). In this study, we reported the first haploid inducers for regions under tropical savanna climate. Three inducer families, KHI-42, KHI-54, and KHI-64, were promising as they possessed HIR about 7.8% or 14 haploid seeds per tester ear and inducer seed rate about 95.0% or 208 inducer seeds per ear. The breeding method was effective for enhancing the seed set and the expression of R1-nj anthocyanin marker of inducers, yet it showed a low effectiveness to improve haploid induction rate. Introgression of temperate inducer Stock6 into tropical gene pool followed by phenotypic selections through modified ear-to-row selection on inducer seed set and R1-nj marker did not compromise the agronomic traits of tropical inducer families. Implications and further strategies for optimizing genetic gain on HIR are discussed.
Highlights
Hybrid cultivars account for major maize acreage due to their advantages including heterosis [1], high yield, and uniformity [2]
Doubled haploid (DH) technology has significantly contributed to the improved production of maize inbred lines as it shortens the time required to achieve 100% homozygous lines from 6–8 selfings by conventional breeding to at least two generations [3]
The significance of cycle indicated that all families showed different performances on agronomic traits and haploid induction ability across three breeding cycles; genetic gains can be estimated
Summary
Hybrid cultivars account for major maize acreage due to their advantages including heterosis [1], high yield, and uniformity [2]. The first maize haploid inducer Stock had a 2.3% HIR [7], and subsequent improved inducer lines have been developed such as ZMS [8], KEMS, KMS [9], MHI [10], CAUHOI [11], RWS [12], PK6 [13], UH400 [14], PHI-3 [15], and BHI306 [16] with HIRs exceeding 10% These Stock 6-driven haploid inducer lines belong to temperate inducers, likely exhibiting poor adaptation to the tropics [17]. To the best of our knowledge, no haploid inducer is available that is adapted to this region
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