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The use of temperate maize (Zea mays L.) inbreds with expired Plant Variety Protection in tropical maize breeding programs could enhance the combining ability for grain yield among tropical heterotic groups. We used DNA markers from the DArTseq genotyping‐by‐sequencing platform to investigate the genetic structure of lines with expired U.S. Plant Variety Protection (ex‐PVP) relative to the International Maize and Wheat Improvement Center's (CIMMYT's) maize heterotic groups. Neighbor‐joining cluster analysis revealed two major groups: CIMMYT and ex‐PVP. The CIMMYT lines clustered according to their pedigree relationships and adaptation, but not according to their heterotic groups. In contrast, ex‐PVP lines clustered according to the Stiff Stalk Synthetic (BSSS) and non‐Stiff Stalk Synthetic (NSSS) heterotic groups, except for a few lines that were considered to be mixed. The genetic divergence, estimated as Wright's fixation index (FST), between BSSS and NSSS (FST =.053, P <.01) was four times as large as the divergence between CIMMYT Tuxpeño and non‐Tuxpeño heterotic groups (FST =.013, P =.068). Estimates of genetic divergence marginally favored breeding with BSSS in Tuxpeño and NSSS in non‐Tuxpeño. However, CIMMYT breeders may still exploit the ex‐PVP heterotic structure fully only by ensuring that the temperate heterotic groups are placed on opposite sides of the Tuxpeño and non‐Tuxpeño heterotic pattern. We also showed how estimates of admixture from model‐based clustering could be used to avoid ex‐PVP lines of mixed heterotic background when selecting lines to maximize the genetic divergence and combining ability of CIMMYT heterotic groups. [ABSTRACT FROM AUTHOR]

Breeding for disease resistance is a central component of strategies implemented to mitigate biotic stress impacts on crop yield. Conventionally, genotypes of a plant population are evaluated through a labor-intensive process of assigning visual scores (VS) of susceptibility (or resistance) by specifically trained staff, which limits manageable volumes and repeatability of evaluation trials. Remote sensing (RS) tools have the potential to streamline phenotyping processes and to deliver more standardized results at higher through-put. Here, we use a two-year evaluation trial of three newly developed biparental populations of maize doubled haploid lines (DH) to compare the results of genomic analyses of resistance to common rust (CR) when phenotyping is either based on conventional VS or on RS-derived (vegetation) indices. As a general observation, for each population × year combination, the broad sense heritability of VS was greater than or very close to the maximum heritability across all RS indices. Moreover, results of linkage mapping as well as of genomic prediction (GP), suggest that VS data was of a higher quality, indicated by higher − log p values in the linkage studies and higher predictive abilities for genomic prediction. Nevertheless, despite the qualitative differences between the phenotyping methods, each successfully identified the same genomic region on chromosome 10 as being associated with disease resistance. This region is likely related to the known CR resistance locus Rp1. Our results indicate that RS technology can be used to streamline genetic evaluation processes for foliar disease resistance in maize. In particular, RS can potentially reduce costs of phenotypic evaluations and increase trialing capacities. • Remote sensing (RS) allows for high-throughput phenotyping in genetic evaluations. • RS and visual scores (VS) from trained staff identified the same genomic regions. • Data quality of VS was higher than that of vegetation indices obtained from RS. • An index more specific to disease symptoms may improve data quality further. [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]