Characterizing heterosis in a set of recombinant intercrosses (RIXs) developed from a multiparental maize population

The exploitation of heterosis is one of the leading activities in maize breeding. Here, we developed an innovative recombinant intercross (RIX) population by crossing pairs of multi-parental maize recombinant inbred lines (RILs) to evaluate the heterotic response in a heterozygous multi-parental population. Field phenotyping was performed on 400 RIX genotypes considering 11 agronomic traits and the resistance to Fusarium Ear Rot (FER) in two consecutive years. Thanks to the high level of allelic diversity available in parental genomes, a broad range of phenotypic diversity was observed. The broad-sense heritability (H2) was high for all traits (H2=0.48 to 0.89) illustrating a strong genetic basis. The heterotic response was computed based on RIL values as mid and best parent heterosis showing different magnitudes for different traits suggesting effects from partial dominance to over-dominance. GWAS detected 55 significant loci associated with agronomic traits across all chromosomes, with allelic effect ranging from 0.28 to 10.90 indicating the contribution of various sized QTLs. Several pleiotropic QTLs on chromosomes 8 and 3 were detected, indicating that these loci may contain valuable genes for multiple traits. RIX collection showed a moderate heritability of FER resistance and 7 putative QTL were associated to this trait on chromosomes 8 and 5. The allelic effect estimates indicated the presence of minor effect QTL with relatively small additive effects on disease resistance. Our findings confirm the usefulness of the RIX population to decipher heterotic loci in maize and support utilizing this resource in future to accelerate crop improvement.