ABSTRACT Modern crop varieties may exert reduced influence on their microbiome compared to their progenitors, as plant-microbe interactions were not targeted during breeding. Moreover, formerly beneficial microbiome functions might no longer be relevant in modern agricultural ecosystems. We hypothesised that such patterns could become particularly evident under drought, since drought-tolerance has not been a primary breeding target. To test this, we grew six maize landraces (released before 1945) and six modern varieties (released from 2010 onwards) in a field under ambient and 60% reduced precipitation. The experiment was repeated over two years, differing in amounts and temporal distributions of precipitation. We assessed the composition of root-associated prokaryotic communities during grain filling by 16S rRNA gene metabarcoding. Intra-variety dispersion in microbiome composition relative to plant biomass-based dispersion was higher in modern varieties, suggesting breeding may have affected plant control over microbiomes. Besides that, shifts in microbiome composition between landraces and modern varieties were driven mainly by the plants' impact on soil water potentials. Consequently, the taxa that increased in relative abundance during soil drying, mainly Actinomycetota, were similar between landraces and modern varieties. Exploring microbiome-mediated alleviation of drought effects, therefore, appears promising also for applications in modern agricultural ecosystems. Specifically, filamentous Streptomyces spp. potentially contributed to soil aggregate stability, which should be further investigated in the context of drought mitigation. The reduced plant control over microbiome composition of modern varieties suggested by dispersion analysis likely has functional implications beyond microbiome adaptation to drought and should be considered in future assessments of breeding.

The role of traditional Indigenous agriculture in preserving native maize in Mexico has been widely researched, as well as its cultural and environmental benefits. Nevertheless, the extensive and interdisciplinary literature on landrace maize production has paid less attention to the role of women’s knowledge in transforming maize into handmade tortillas, work that contributes directly to the conservation of maize agrobiodiversity, food culture, and identity. In rural Mexico, maize provides the basis of local food systems, and the transformation of this grain into handmade tortillas is intricately related to fuelwood use as the primary source of cooking energy. The notion of food sovereignty in rural Mexico must consider energetic needs and address the health and environmental implications of women’s work in maize processing. This review examines the intersection of energy use and women’s role in native maize processing activities and conservation. We explore fuelwood use in handmade tortilla making and draw a parallel between the conservation of landrace maize agro-food systems and energetic justice. Drawing on the experiences of Indigenous women dedicated to making and selling tortillas in Purepecha, Zapotec, and Mixtec communities, we illustrate their role as key articulators of native maize conservation while discussing the environmental and health implications of this livelihood. Ultimately, we argue for the need to seriously consider the tensions between native maize conservation and energy justice as essential for constructing sustainable and sovereign livelihoods in Mexico’s rural communities. Please refer to Supplementary Materials for a full text Spanish version of this article.

ABSTRACTClimate change is the greatest challenge to modern agriculture. It significantly impacts agricultural systems through an increased frequency and intensity of extreme environmental events. Maize, a vital crop for global food security, is particularly vulnerable to these changes, highlighting the urgent need to develop resilient varieties. This study aims to identify significant genes for adaptation to environmental conditions in 140 individuals derived from 28 Italian maize landraces using a landscape genomics approach to support the development of resilient maize genotypes. Landraces were genotyped using genotyping‐by‐sequencing, and the resulting genetic matrix was used to characterize the collection's diversity. Population genetic studies were conducted to investigate the genetic diversity and structure of the collection. Partial redundancy analysis (pRDA) was subsequently employed to analyze the relationship between climate variables and genetic variation of the materials. Among the 12 ancestral populations identified, both well‐defined populations and highly admixed groups were observed. This degree of admixture was reflected in the clustering analysis and principal component analysis (PCA), although clear differentiation of individual populations was still apparent. pRDA revealed that 30% of the genetic variance in the collection was explained together by climate (45%), geography (11%), and genetic structure (31%). Three potential genomic signals of adaptation were identified in relation to the environmental variability across the sampling sites. The results highlight significant intra‐landrace variability within the examined germplasm and reveal unique landraces tied to ancestral lineages. Notably, we identify distinct genetic markers strongly correlated with environmental factors. This discovery opens new avenues for potential genetic improvement in maize cultivation. Landraces preserve vital traits for the adaptation of maize to environmental stresses, thereby serving as key sources for breeding programs aimed at improving stress tolerance and yield stability under climate change.

Abstract In the context of over‐fertilization, especially of phosphorus (P), the debate about the usefulness of applying starter fertilization to maize ( Zea mays L.) must be revisited. One solution is to breed crops with an enhanced phosphorus use efficiency, which require less fertilizer yet are high‐yielding. This study examined a diverse panel of Flint elite lines and double haploid lines from six European landraces, which were crossed with two Dent testers. The resulting 588 testcross hybrids were evaluated under two fertilization treatments: with and without the addition of a di‐ammonium phosphate starter fertilization. The omission of the starter fertilization led to a decrease in early developmental traits, like plant height and biomass, in all four tested environments. Surprisingly, grain yield increased in three out of four environments, an effect that was especially noticeable in the landrace line testcrosses and is possibly caused by the increased ability to cope with environmental stress occurring at later developmental stages. Importantly, there is substantial genetic variation that can be exploited in breeding for the response to fertilizer levels, with some landrace testcrosses performing in the range of the Flint elite testcrosses. Furthermore, additive genetic effects were found to be the main contributor to early developmental traits and grain yield under both fertilization treatments. These results suggest that landraces may offer valuable genetic variation for breeding for reduced phosphate fertilizer input. In conclusion, breeding programs should include breeding for nutrient acquisition but combined with a tolerance to withstand seasonal climate variations.

This study aimed to assess the drought and heat stress tolerance of nine Tunisian maize populations and their potential stress tolerance mechanisms. Over two years, nine Tunisian maize populations were evaluated under five environments with varying stress levels and one optimal growth condition in Tunisia. This work formed part of a larger study that includes a total of 223 Mediterranean maize landraces. The nine Tunisian populations were specifically chosen to assess the behavior of landraces adapted to the drought and heat stress conditions prevalent in the southern Mediterranean. In all the locations, the trials followed an augmented design with five blocks and a total of five checks over the two-year study period replicated in each block.The study demonstrated that combined drought and heat stress severely reduced maize yield, with Tunisian landraces experiencing losses of 76% to 95% relative to optimal conditions. Factorial regression analyses were performed to provide a biological interpretation of the contribution of environmental and genotypic variables, as well as their interactions, to grain yield variability. The most representative genotypic covariates were plant height (PH) followed by the number of ears (NE), thousand-grain weight (1000GW), and aerial biomass, respectively, explaining 26%, 12%, 9%, and 8% of the total variability. The significant environmental covariates were cumulative hydric deficit (DHC) and the average anthesis silking interval (ASI_ENV) in each environment, representing 48% of the total environmental variation. The interaction between thousand-grain weight and cumulative hydric deficit had the highest contribution (9%) of interaction for grain yield. The factorial regression indicated that under stress conditions, maize plants appeared to adapt to maintain yield by increasing thousand-grain weight while reducing aerial biomass, number of ears, and grain number. This response likely reflects an enhanced capacity for efficient resource reallocation, supporting the plant's resilience under combined drought and heat stress conditions. The landraces BK, KAR, and MT2 consistently outperformed in most traits under stress conditions, showing significant tolerance and adaptability for across multiple stress levels with better yields and flowering synchronization. The selected best-performing populations could serve as valuable sources of drought and heat stress tolerance sources for future breeding programs.

This study aimed to assess the drought and heat stress tolerance of nine Tunisian maize populations and their potential stress tolerance mechanisms. Over two years, nine Tunisian maize populations were evaluated under five environments with varying stress levels and one optimal growth condition in Tunisia. This work formed part of a larger study that includes a total of 223 Mediterranean maize landraces. The nine Tunisian populations were specifically chosen to assess the behavior of landraces adapted to the drought and heat stress conditions prevalent in the southern Mediterranean. In all the locations, the trials followed an augmented design with five blocks and a total of five checks over the two-year study period replicated in each block.The study demonstrated that combined drought and heat stress severely reduced maize yield, with Tunisian landraces experiencing losses of 76% to 95% relative to optimal conditions. Factorial regression analyses were performed to provide a biological interpretation of the contribution of environmental and genotypic variables, as well as their interactions, to grain yield variability. The most representative genotypic covariates were plant height (PH) followed by the number of ears (NE), thousand-grain weight (1000GW), and aerial biomass, respectively, explaining 26%, 12%, 9%, and 8% of the total variability. The significant environmental covariates were cumulative hydric deficit (DHC) and the average anthesis silking interval (ASI_ENV) in each environment, representing 48% of the total environmental variation. The interaction between thousand-grain weight and cumulative hydric deficit had the highest contribution (9%) of interaction for grain yield. The factorial regression indicated that under stress conditions, maize plants appeared to adapt to maintain yield by increasing thousand-grain weight while reducing aerial biomass, number of ears, and grain number. This response likely reflects an enhanced capacity for efficient resource reallocation, supporting the plant’s resilience under combined drought and heat stress conditions. The landraces BK, KAR, and MT2 consistently outperformed in most traits under stress conditions, showing significant tolerance and adaptability for across multiple stress levels with better yields and flowering synchronization. The selected best-performing populations could serve as valuable sources of drought and heat stress tolerance sources for future breeding programs.

The local people of north-eastern Himalayan region (NEHR) cultivate the maize landraces and consume them as food. These landraces possess desirable agronomic traits but are susceptible to turcicum leaf blight (TLB) disease caused by the fungus Exserohilum turcicum. Thus, we aimed to screen maize landraces under field conditions and introgress the Ht1 gene into the susceptible landrace. Screening of four landraces against TLB was conducted under artificially inoculated field conditions during Kharif 2023, with two standard checks. Disease reaction rating on a scale of 1-9 was used to calculate the percent disease index (PDI) values of landraces. Among the four landraces, two - LMC-15 and LMC-16 - were identified as susceptible, with a disease rating of 8, while LMC-4 and LMC-7 received a rating of 6 and were categorized as moderately susceptible. The F1 generation was produced during the spring season of 2024 through a cross between the donor parent BML-6 and the susceptible recurrent parent LMC-15. The true F1 plants were evaluated using a SSR marker umc1042, which is linked to the TLB resistance gene Ht1. Genotyping of 120 F2 plants was performed using the umc1042 SSR marker. This marker exhibited a segregation ratio of 27:61:32 in the F2 population. The chi-square value for the genotype was 0.45, which is below χ2 (p ≤ 0.05) and therefore considered non-significant, indicating a good fit to the expected 1:2:1 ratio. Overall, the findings confirm that MAS is an efficient and reliable approach for introgressing Ht1 into susceptible maize lines.

Key messageRapid cycling genomic selection is a highly efficient tool for pre-breeding of maize landraces for complex traits, especially in combination with multi-trait selection and model retraining.The introduction of landrace-derived material into modern breeding programs can only succeed if it performs satisfactorily for yield and other key agronomic traits. In this study, we explored the prospects of rapid cycling genomic selection in maize (Zea mays L.) to accelerate pre-breeding of landraces in comparison with recurrent phenotypic selection. We performed three cycles of genomic selection for testcross performance. The selection criterion was based on directional selection for biomass yield and stabilizing selection for plant height and flowering time. The prediction model was trained on testcrosses of 419 doubled-haploid (DH) lines derived from two European landraces. To estimate selection response and prediction accuracies, DH lines from all cycles (N = 204, C0–C3) were evaluated together with seven commercial hybrids in seven environments. Selection narrowed the yield gap to the commercial hybrids significantly with an increase in dry matter yield of about 10% in comparison with the reference population (C0). Despite stabilizing selection for plant height and flowering time, both traits showed a correlated response with biomass yield pointing to the importance of optimizing multi-trait selection, especially in landraces. Prediction accuracies were intermediate to high in the training population and decreased in the following cycles. Retraining the prediction model increased the prediction accuracy for all traits. Our results support the hypothesis that pre-breeding can be accelerated significantly by rapid cycling genomic selection and give valuable insights into key factors determining its success.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00122-025-05107-3.

Maize landraces under water deficit favor diverse rhizosphere communities associated with improved stress response

Evaluation of the Spanish maize landrace core collection for drought tolerance

Maize (Zea mays L.) is the most recently domesticated and dispersed worldwide among major cereals. Chloroplast genomes (plastome), with their highly conserved tetrad structure, hold a significant value in phylogenetic research due to their typical maternal inheritance. In this study, a total of 286 maize plastomes, 262 newly assembled and 24 publicly available, were investigated which included worldwide landraces, nested association mapping founders, and teosinte accessions. The maize plastomes were assembled with the filtered reads of the whole genome sequences from our re-seq data and public database by mapping to the reference plastome of B73. The maize plastomes were put into the phylogenetic analyses, with Z. perennis accession as the outgroup. The maize landraces were divided into four clades, showing a closer relationship with the Z. mays ssp. parviglumis plastome than with mexicana, indicating that parviglumis was the direct donor of the plastome to maize. Landrace diversities in Europe were quite similar to those in China and the Korean Peninsula, suggesting that the dispersal of maize following European contact with America was both rapid and accompanied by the translocation of a broad spectrum of maize germplasm. The introduced landraces have less diversity than the old landraces found in South America. This study provides information for understanding the genetic diversity of maize landraces and the process of maize dispersal in the world for exploiting the maize germplasm in breeding.

<p><strong>Background</strong>: The large amount of native maize available in Mexico can be used in different associations with other crops, such as squash. However, it is necessary to determine whether its productivity is adequate and whether maize germplasm has an influence on it. <strong>Objective</strong>: To evaluate the yield of different native maize germplasms in monoculture and in intercropping with squash and to determine the most productive system using the Land Equivalent Ratio (LER). <strong>Methodology</strong>: In 2022, three maize landraces from the Yucatan Peninsula, a commercial hybrid as a control, and a local squash species were studied in Keste, Campeche, Mexico. With the data, Pearson's correlation, analysis of variance, Tukey's multiple mean comparison test (α = 0.05), and LER were determined.<strong> Results</strong>: Maize in monoculture yielded significantly higher (2.35 t ha-1) than in the intercropping system. Nal Xoy and X'mejenal Nal maize landraces had the highest yields, although the hybrid exceeded them. The yield of squash seeds was statistically the same in monoculture and intercropping. In the association of native maize and squash, the type of maize germplasm has a direct impact on yield. The Land Equivalent Ratio (LER) confirmed the different levels of productivity in the two systems and the effects of maize germplasm. <strong>Implications</strong>: A relationship exists between the production system, maize germplasm, and yield. <strong>Conclusion</strong>: Maize yield is higher in monoculture than in the intercropping system. The LER could be a helpful coefficient to choose the right maize landrace to be planted in intercropped systems. The identified LER coefficients of 1.6–1.9 indicate that intercropping systems utilise land area more efficiently than monoculture systems.<strong></strong></p>

Maize landraces as useful donors of genetic diversity for resilience to drought

Sampling number effects on genetic variation analysis in maize landraces using seed and leaf tissues

Root phenotypes contribute to environmental adaptation. We hypothesized that root phenotypes of maize (Zea mays L. ssp. Mays) landraces reflect their adaptation to edaphic limitations in their native soil environments, and that some root phenotypes may confer broad edaphic adaptation. We phenotyped the roots of maize landraces and used the functional-structural plant/soil model OpenSimRoot_v2 to simulate landraces and their native environments to analyze how root phene states interact with each other and with environment variables to regulate edaphic adaptation. Landraces from low phosphorus regions have root phenotypes with shallow growth angles and greater nodal root numbers, allowing them to adapt to their native environments by improved topsoil foraging. We used machine learning algorithms to detect the most important phenotypes responsible for adaptation to multiple environments. The most important phene states responsible for stability across environments are large cortical cell size and reduced diameter of roots in nodes 5 and 6. When we dissected the components of root diameter, we observed that large cortical cell size improved growth by 28%, 23 % and 114%, while reduced cortical cell file number alone improved shoot growth by 137%, 66% and 216%, under drought, nitrogen and phosphorus stress, respectively. Functional-structural analysis of 96 maize landraces from the Americas, previously phenotyped in mesocosms in the greenhouse, suggested that parsimonious anatomical phenotypes, which reduce the metabolic cost of soil exploration, are the main phenotypes associated with adaptation to multiple environments, while root architectural phenotypes were related to adaptation to specific environments. These results indicate that integrated root phenotypes with anatomical phene states that reduce the metabolic cost of soil exploration increase tolerance to edaphic stress across multiple environments and therefore would improve yield stability, regardless of their root architecture.

Molecular breeding strategies such as genome-wide association studies (GWAS) and genomic prediction have revolutionized crop improvement by enhancing selection accuracy and genetic gains. Through a comprehensive evaluation of a large set of maize lines from Germplasm Enhancement of Maize (BGEM) and their testcross hybrids, we aimed to characterize the genetic basis of oil content and fatty acid composition and predict superior hybrids and breeding populations. We evaluated 241 BGEM lines and 187 testcross hybrids derived from exotic maize landraces crossed with elite lines (PHB47 and PHZ51), across multiple environments, for oil content and 10 fatty acid traits using GWAS and genomic prediction with GBLUP and simulated RILs. Our study revealed wide phenotypic variation among BGEM lines and testcrosses for tested traits, with promising genotype mean values. Leveraging GWAS, we identified significant genomic regions associated with oil content and fatty acids, unveiling useful candidate genes. Incorporating both additive and nonadditive genomic prediction models did not enhance the predictive ability. Furthermore, our predictive modeling facilitated the identification of breeding populations with increased oil-related traits compared to the original BGEM lines. These findings highlight how BGEM germplasm can be more effectively utilized through molecular breeding approaches to enhance oil-related traits in maize.

Abstract Maize landraces (Zea mays subsp. mays) have evolved under the joint action of environmental factors and of the farmers who cultivated them. In this study, we aim to quantify the selection gradients exerted by farmers by proposing them a selection test consisting in choosing the ears they would select if they were to grow maize landraces the following year. The study focused on the Pyrenees region of France, where landraces were cultivated until the arrival of hybrids in the 1960s and conserved ex-situ ever since. We interviewed former Pyrenean farmers or their children who were cultivating landraces 60 years ago. The survey documented seed management practices and know-how. Our selection test showed that their selection was based solely on ears: old farmers selected healthy and productive ears by using ear length and volume as the first two selection criteria. Both were highly correlated with the kernel weight per ear. Heritabilities of ear traits at an individual plant level were estimated in one trial for four landraces and were found variable between traits and landraces (average 0.36 ranging between 0 and 0.76). We calculated the expected genetic change after one generation of mass selection, following farmer selection criteria. For ear length, genetic change was expected to reach about 3.4% (from 1 to 7.5% over the 17 selection tests). We investigated seed selection practices both east and west of the Pyrenees and compared them qualitatively with those of native American farmers.

Despite the high variability of Argentine maize (Zea mays L.) landraces, they are scarcely used by breeders due to the limited knowledge available about the genetic merit of these materials. In this study, we evaluated agro-morphological and molecular traits of 36 landraces of the ‘Cristalino Colorado’ race from Buenos Aires province, Argentina. Fifteen agro-morphological traits and five polymorphic microsatellite markers located on different chromosomes (48 alleles) were used. A principal component analysis was performed using average values of agro-morphological traits across two environments. Molecular markers were subjected to a principal coordinate analysis. A generalized procrustes analysis was used to evaluate agro-morphological and molecular traits together, showing seven groups. Distance between agro-morphological and molecular data had an average value of 0.24 and the range varied between 0.02 (ARZM01017) and 0.45 (ARZM01082). The results show that Argentine landraces of the ‘Cristalino Colorado’ race are a valuable source of new alleles for crop improvement. Studies of this type facilitate the selection of landraces for introduction in genetic breeding programmes and for the establishment of core collections.

Meiotic drive elements are regions of the genome that are transmitted to progeny at frequencies that exceed Mendelian expectations, often to the detriment of the organism. In maize there are three prevalent chromosomal drive elements known as Abnormal chromosome 10 (Ab10), K10L2, and the B chromosome. There has been much speculation about how these drivers might interact with each other and the environment in traditional maize landraces and their teosinte ancestors. Here we used genotype-by-sequencing data to score more than 10,000 maize and teosinte lines for the presence or absence of each driver. Fewer than ~0.5% of modern inbred lines carry chromosomal drivers. In contrast, among individuals from 5331 open-pollinated landraces, 6.32% carried Ab10, 5.16% carried K10L2, and 12.28% carried at least one B chromosome. These frequencies are consistent with those reported in previous studies. Using a GWAS approach we identified unlinked loci that associate with the presence or absence of the selfish genetic elements. Many significant SNPs are positively associated with the drivers, suggesting that there may have been selection for alleles that ameliorate their negative fitness consequences. We then assessed the contributions of population structure, associated loci, and the environment on the distribution of each chromosomal driver. There was no significant relationship between any chromosomal driver and altitude, contrary to conclusions based on smaller studies. Our data suggest that the distribution of the major chromosomal drivers is primarily influenced by neutral processes and the deleterious fitness consequences of the drivers themselves. While each driver has a unique relationship to genetic background and the environment, they are largely unconstrained by either.

Maize (Zea mays L.) is the most widely produced crop in the world, and conventional production requires significant amounts of synthetic nitrogen fertilizer, which has negative economic and environmental consequences. Maize landraces from Oaxaca, Mexico, can acquire nitrogen from nitrogen-fixing bacteria that live in a mucilage secreted by aerial nodal roots. The development of these nodal roots is a characteristic traditionally associated with the juvenile vegetative stage of maize plants. However, mature Oaxacan landraces develop many more nodes with aerial roots than commercial maize varieties. Our study shows that Oaxacan landraces develop aerial roots during the juvenile and adult vegetative phases and even during early flowering under greenhouse and field conditions. Surprisingly, the development of these roots was only minimally affected by soil nitrogen and ambient humidity. These findings are an essential first step in developing maize varieties to reduce fertilizer needs in maize production across different environmental conditions.