The exploitation of heterosis is key in modern maize breeding to capture
the superior performance of heterozygous genotypes. Here, we developed a
recombinant intercross (RIX) population in maize by crossing pairs of multiparental
MAGIC recombinant inbred lines (RILs) to evaluate the heterosis
across mosaics of eight maize haplotypes. Field phenotyping was performed
on 400 RIX genotypes considering 11 agronomic traits as well as the
resistance to Fusarium Ear Rot (FER), caused by Fusarium verticillioides
(Sacc.) Nirenberg, in 2018 and 2019 in Piacenza, northern Italy. Phenotypic
data showed a broad range of diversity in production and phenology traits
thanks to the high level of allelic diversity available in parental
genomes. The heterotic response of agronomic traits was computed based on
RIL values as mid parent heterosis (MPH) and best parent heterosis (BPH).
Both heterosis measures showed different magnitudes for different traits,
with higher level of heterosis in yield and lower in flowering time,
suggesting effects from partial dominance to over-dominance. No correlation
was observed between phenotypic performance and heterozygosity level of
RIXs for most of the agronomic traits. A preliminary quantitative trait
locus (QTL) mapping detected a number of significant associations with
agronomic traits across all chromosomes. The RIX collection showed a
moderate heritability of FER resistance, and QTL were associated to this
trait as well. The allelic effect estimates by our mapping model indicated
the presence of minor effect QTL with relatively small additive effects on
disease resistance in both years. 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
