Generations of farmer selection in the central Mexican highlands have produced unique maize varieties adapted to the challenges of the local environment. In addition to possessing great agronomic and cultural value, Mexican highland maize represents a good system for the study of local adaptation and acquisition of adaptive phenotypes under cultivation. In this study we characterize a recombinant inbred line population derived from the B73 reference line and the Mexican highland maize variety Palomero Toluqueño. B73 and Palomero Toluqueño showed classic rank-changing differences in performance between lowland and highland field sites, indicative of local adaptation. Quantitative trait mapping identified genomic regions linked to effects on yield components that were conditionally expressed depending on the environment. For the principal genomic regions associated with ear weight and total kernel number, the Palomero Toluqueño allele conferred an advantage specifically in the highland site, consistent with local adaptation. We identified Palomero Toluqueño alleles associated with expression of characteristic highland traits, including reduced tassel branching, increased sheath pigmentation and the presence of sheath macrohairs. The oligogenic architecture of these three morphological traits supports their role in adaptation, suggesting they have arisen from consistent directional selection acting at distinct points across the genome. We discuss these results in the context of the origin of phenotypic novelty during selection, commenting on the role of de novo mutation and the acquisition of adaptive variation by gene flow from endemic wild relatives.

Integrated weed management (IWM) relies upon multiple chemical, physical, or biological weed management techniques to achieve an acceptable level of weed control. Agents that selectively suppress weeds but not crops and that can be manipulated in agriculture will be promising components for inclusion in IWM. We used a meta-analytic approach to investigate the potential of arbuscular mycorrhizal fungi (AMF) to contribute to IWM. We quantified the effect of crop and weed host status (strong and weak AMF hosts are divided in this study by a 10% root length colonization threshold), AMF diversity (single vs. mixed), and soil N and P fertility management on plant mycorrhizal growth responses (MGRs). Our results indicated that weak host weeds had consistently lower MGRs than strong host crops in both controlled and field conditions. Moreover, these differences in MGRs between weak host weeds and strong host crops were more pronounced under mixed AMF inoculum and low N and P nutrient availability. In contrast, MGR of strong host weeds was not different from strong host crops in general. However, we observed a wide range of MGRs among strong host weeds, some of which had much lower MGRs than strong host crops. In addition, in the presence of N and P fertilizers, strong host crops had a stronger positive response to AMF than strong host weeds. Thus, our meta-analysis indicates that AMF have potential to contribute to weed control by direct and indirect pathways: directly suppress weak host weeds, and indirectly suppress some strong host weeds mediating by competitive effects exerted by strong host crops. We suggest that management practices affecting AMF diversity and crop and weed mycorrhizal responses could be chosen to improve the contribution of AMF to IWM. Better understanding is needed of crop–weed–AMF interactions and management practices that enhance this form of weed management.

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Arbuscular mycorrhizal fungi (AMF) establish symbioses with major crop species, providing their hosts with greater access to mineral nutrients and promoting tolerance to heavy metal toxicity. There is considerable interest in AMF as biofertilizers and for their potential in breeding for greater nutrient efficiency and stress tolerance. However, it remains a challenge to estimate the nutritional benefits of AMF in the field, in part due to a lack of suitable AMF-free controls. Here we evaluated the impact of AMF on the concentration of 20 elements in the leaves and grain of field grown maize using a custom genetic mapping population in which half of the families carry the AMF-incompatibility mutation castor. By comparing AMF-compatible and AMF-incompatible families, we confirmed the benefits of AMF in increasing the concentration of essential mineral nutrients (e.g., P, Zn, and Cu) and reducing the concentration of toxic elements (e.g., Cd and As) in a medium-input subtropical field. We characterised the genetic architecture of element concentration using quantitative trait mapping and identified loci that were specific to AMF-compatible or AMF-incompatible families, consistent with their respective involvement in mycorrhizal or direct nutrient uptake. Patterns of element covariance changed depending on AMF status and could be used to predict variation in mycorrhizal colonisation. We comment on the potential of AMF to drive genotype-specific differences in the host ionome across fields and to impact the alignment of biofortification breeding targets. Our results highlight the benefits of AMF in improving plant access to micronutrients while protecting from heavy metals, and indicate the potential benefits of considering AMF in biofortification programs.