R1-nj expression in parental inbreds as a predictor of amenability of maize hybrids to R1-nj-based doubled haploid development

The current method of doubled haploid (DH) development in maize involves in vivo production of haploids using R1nj-based haploid inducer lines that upon use as male render a small fraction of seed in the pollinated female ears haploid. Identification of haploid seed relies on R1-nj marker expression in the endosperm and embryo, and the degree of its expression determines efficiency of DH development process. In the present study, R1-nj expression in the endosperm was characterized in crosses of CIMMYT's R1nj-based haploid inducer TAILP1 with a set comprising 18 early maturity hybrids and their 23 parental inbreds. Kernel colour inhibition was observed only in a small proportion of the hybrids and inbreds. Comparison of R1-nj expression in the hybrids and their parental inbreds revealed a distinct pattern, which may be useful in identifying source populations and/or determining parental constituents for synthesizing source populations with predicted amenability to doubled haploid development using R1-nj-based haploid inducers. However, deviation from the pattern was noted in hybrids involving inbreds with higher degree of colour inhibition, which suggests complex nature of R1-nj phenotype expression and necessitates further investigation involving larger sets of germplasm for dissecting the role of maternal and paternal genetic factors in determining R1-nj phenotype expression. The hybrids found exhibiting complete kernel anthocyanin expression in present study can be used directly as source populations for DH development using R1-nj based haploid inducers. Besides, since the inbreds used in the study have originated from and/or are accessible to CGIAR/NARS maize breeding programmes, the information on their kernel anthocyanin expression can be helpful in selection of source populations or generating new source populations amenable for DH development using R1-nj based haploid inducers.