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Abstract Background The crosslinking of maize cell wall components, particularly mediated by the formation of ferulic acid dimers or diferulates, has been associated with important crop valorization traits such as increased pest resistance, lower forage digestibility, or reduced bioethanol production. However, these relationships were based on studies performed using diverse unrelated inbred lines and/or populations, so genetic background could interfere on these associations. Results In the present research, the success of a pedigree selection program aimed to obtain inbred lines from a common antecessor with contrasting diferulate concentration was evaluated. From the 10 inbreds lines developed we could validate the success of the breeding program, obtaining 4 inbred lines with significant contrating values of total diferulate content in the pith tissues (two of each group): high (X̅= 0.69 mg/g of DW) and low (X̅= 0.35 mg/g). Ferulate changes in the same way were also observed: high (X̅= 3.09 mg/g of DW) and low (X̅= 1.62 mg/g). On the other hand, we found strong and positive correlations between DFAT and individual dimers, and moderate negative correlations between total DFAT and a main cell wall component such as cellulose. However, we did not find a significant effect of DFAT on maize valorization traits, except of a negative effect of DFAT on the concentration of sugars released after the enzimatic hydrolysis of the pith tissues. Interestingly, increasing DFAT in the pith does not seem to affect the digestibility of the forage or the saccharification of the stover residue, highlighting that changes in a specific tissue do not encompass correlated changes in other resources. Conclusions Overall, we have obtained contrasting inbred lines with diferulates concentration, which could be uselful in further studies focussing in the identification of regions/genes predominantly involved in the hydroxycinnamate biosynthesis pathway and cell wall crosslinking network.

IntroductionValidations of previously detected quantitative trait loci (QTLs) to assess their reliability are crucial before implementing breeding programs. The objective of this study was to determine the reliability and practical usefulness of previously reported QTLs for resistance to stem tunneling by the Mediterranean stem borer (MSB) and yield. These authors used approximately 600 recombinant inbred lines (RILs) from a multiparent advanced generation intercross (MAGIC) population to map QTL using a genome-wide association study (GWAS) approach.MethodsWe identified RILs situated at the extremes of resistance and yield distributions within the whole MAGIC, and those QTLs were evaluated per se and crossed to a tester (A638) using lattice designs. In each set, a significant single-nucleotide polymorphism (SNP) was considered validated if (1) the same SNP was associated with the trait with a p-value < 0.02, or (2) within a ±2-Mbp interval, an SNP associated with the trait exhibited a p-value < 0.02 and demonstrated linkage disequilibrium (r2 > 0.2) with the SNPs previously reported.Results and discussionThe novel QTL validation approach was implemented using improved experimental designs that led to higher heritability estimates for both traits compared to those estimated with the whole MAGIC population. The procedure used allowed us to jointly validate several QTL and to ascertain their possible contribution to hybrid improvement. Specifically, nearly three-quarters of the QTLs for tunnel length were confirmed. Notably, QTLs located in the genomic region 6.05–6.07 were consistently validated across different sets and have been previously linked to resistance against stalk tunneling in various mapping populations. For grain yield, approximately 10 out of 16 QTLs were validated. The validation rate for yield was lower than for tunnel length, likely due to the influence of dominance and/or epistatic effects. Overall, 9 out of 21 QTLs for tunnel length and 6 out of 17 QTLs for grain yield identified in our previous research were validated across both validation sets, indicating a moderate genetic correlation between per se and testcross performance of inbred lines. These findings offer insights into the reliability of QTL and genomic predictions, both derived from assessments conducted on the entire MAGIC population. Genomic predictions for tunnel length based on inbred line evaluations could be useful to develop more resistant hybrids; meanwhile, genomic prediction for yield could only be valid in a homozygous background.

The ECPGR European Evaluation Network (EVA) for Maize involves genebanks, research institutions, and private breeding companies from nine countries focusing on the valorization of maize genetic resources across Europe. This study describes a diverse collection of 626 local landraces and traditional varieties of maize (Zea mays L.) from nine European genebanks, including criteria for selection of the collection and its genetic and phenotypic diversity. High-throughput pool genotyping grouped the landraces into nine genetic groups with a threshold of 0.6 admixture, while 277 accessions were designated admixed and likely to have resulted from previous breeding activities. The grouping correlated well with the geographic origins of the collection, also reflecting the various pathways of introduction of maize to Europe. Phenotypic evaluations of 588 accessions for flowering time and plant architecture in multilocation trials over three years confirmed the great diversity within the collection, although phenotypic clusters only partially correlated with the genetic grouping. The EVA approach promotes conservation of genetic resources and opens an opportunity to increase genetic variability for developing improved varieties and populations for farmers, with better adaptation to specific environments and greater tolerance to various stresses. As such, the EVA maize collection provides valuable sources of diversity for facing climate change due to the varieties’ local adaptation.

IntroductionThe study of yield and resistance/tolerance to pest are related traits fundamental for maize breeding programs. Genomic selection (GS), which uses all marker information to calculate genomic breeding values, is presented as an emerging alternative to phenotypic and marker-assisted selections for improving complex traits controlled by many genes with small effects. Therefore, although phenotypic selection (PS) has been effective for increasing resistance and yield under high infestation with maize stem borers, higher genetic gains are expected to be obtained through GS based on the complex architecture of both traits. Our objective was to test whether GS is more effective than PS for improving resistance and/or tolerance to maize stem borers and grain yield.MethodsFor this, we compared different selection programs based on phenotype and genotypic value for a single trait, resistance or yield, and for both traits together.Results and discussionWe obtained that GS achieved the highest genetic gain for yield, meanwhile phenotypic selection for yield was the program that achieved the highest reduction of tunnel length, but was ineffective for increasing yield. However, phenotypic or genomic selection for increased resistance may be more effective in improving both traits together; although the gains per cycle would be small for both traits.

Fusarium verticillioides poses a threat to worldwide maize production due to its ability to infect maize kernel and synthesize fumonisins that can be accumulated above safety levels for humans and animals. Maize breeding has been proposed as key tool to decrease kernel contamination with fumonisins, but metabolic studies complementary to genomic approaches are necessary to disclose the complexity of maize resistance. An untargeted metabolomic study was proposed using inbreds genetically related but with contrasting levels of resistance in order to uncover pathways implicated in resistance to Fusarium ear rot (FER) and fumonisin contamination in the maize kernel and to look for possible biomarkers. Metabolite determinations were performed in kernels collected at 3 and 10 days after inoculation with F. verticillioides (dat). Discriminant metabolites between resistant and susceptible RILs were rather found at 10 than 3 dat, although metabolite differences at later stages of colonization could be driven by subtle variations at earlier stages of infection. Within this context, differences for membrane lipid homeostasis, methionine metabolism, and indolacetic acid conjugation seemed highly relevant to distinguish between resistant and susceptible inbreds, confirming the polygenic nature of resistance to FER and fumonisin contamination in the maize kernels. Nevertheless, some specific metabolites such as the polyamine spermidine and/or the alkaloid isoquinoline seemed to be promising indirect selection traits to improve resistance to FER and reduce fumonisin accumulation. Therefore, in vitro and in vivo experiments will be necessary to validate the inhibitory effects of these compounds on fumonisins biosynthesis.

Abstract Maize kernel is exposed to several fungal species, most notably Fusarium verticillioides, which can contaminate maize kernels with fumonisins. In an effort to increase genetic gains and avoid the laborious tasks of conventional breeding, the use of marker-assisted selection or genomic selection programs was proposed. To this end, in the present study a Genome Wide Association Study (GWAS) was performed on 339 RILs of a Multiparental Advanced Generation InterCross (MAGIC) population that had previously been used to locate Quantitative Trait Locus (QTL) for resistance to Fusarium Ear Rot (FER). Six QTLs for fumonisin content were detected in the bins 3.08, 4.07, 4.10, 7.03-7.04, 9.04-9.05 and 10.04-10.5. Five of the six QTLs collocate in regions where QTLs for FER were also found. However, the genetic variation for fumonisin content in kernel is conditioned by many other QTLs of small effect that could show QTL x environment interaction effects. Although a genomic selection approach to directly reduce fumonisin content in the kernel could be suitable, improving resistance to fumonisin content by genomic selection for FER would be more advisable.

The bean weevil Acanthoscelides obtectus is one of the world’s main pests of stored beans. The heterogeneous inbred family (HIF) population of near-isogenic lines (NILs) could be an exceptional strategy to study the inheritance of the resistance against A. obtectus. We developed a HIF population of 148 NILs of R-bufa-80-12. The objectives of this research were as follows: (1) to study and understand the genetics of the attack resistance to A. obtectus in a HIF population and (2) to identify the best lines to provide weevil resistance. The pure lines of the HIF population showed a great variability for all the analyzed traits. The traits studied in this research have a normal distribution showing continuous variation, so they are considered to be quantitatively inherited. The heritabilities for resistance traits were low and very low, ranging from 0.09 to 0.17. The heritability for 100 seed weight was the highest, with a significant value of 0.90. The best lines of the HIF population for resistance to A. obtectus comprised Line-45, Line-129, Line-124, Line-142 and Line-47. In general, these lines presented lower preference of adults, and lower consumption in grams and in percentages. However, lines 45 and 129 are the most interesting from a commercial point of view because they combine resistance and seed weight.

Abstract Background Besides the use of maize grain as food and feed, maize stover can be a profitable by-product for cellulosic ethanol production, whereas the whole plant can be used for silage production. However, yield is reduced by pest damages, stem corn borers being one of the most important yield constraints. Overall, cell wall composition is key in determining the quality of maize biomass, as well as pest resistance. This study aims to evaluate the composition of the four cell wall fractions (cellulose, hemicellulose, lignin and hydroxycinnamates) in diverse maize genotypes and to understand how this composition influences the resistance to pests, ethanol capacity and digestibility. Results The following results can be highlighted: (i) pests’ resistant materials may show cell walls with low p-coumaric acid and low hemicellulose content; (ii) inbred lines showing cell walls with high cellulose content and high diferulate cross-linking may present higher performance for ethanol production; (iii) and inbreds with enhanced digestibility may have cell walls poor in neutral detergent fibre and diferulates, combined with a lignin polymer composition richer in G subunits. Conclusions Results evidence that there is no maize cell wall ideotype among the tested for optimal performance for various uses, and maize plants should be specifically bred for each particular application.

In temperate world-wide regions, maize kernels are often infected with the fumonisin-producing fungus Fusarium verticillioides which poses food and feed threats to animals and humans. As maize breeding has been revealed as one of the main tools with which to reduce kernel contamination with fumonisins, a pedigree selection program for increased resistance to Fusarium ear rot (FER), a trait highly correlated with kernel fumonisin content, was initiated in 2014 with the aim of obtaining inbred lines (named EPFUM) with resistance to kernel contamination with fumonisins and adapted to our environmental conditions. The new released EPFUM inbreds, their parental inbreds, hybrids involving crosses of one or two EPFUM inbreds, as well as commercial hybrids were evaluated in the current study. The objectives were (i) to assess if inbreds released by that breeding program were significantly more resistant than their parental inbreds and (ii) to examine if hybrids derived from EPFUM inbreds could be competitive based on grain yield and resistance to FER and fumonisin contamination. Second-cycle inbreds obtained through this pedigree selection program did not significantly improve the levels of resistance to fumonisin contamination of their parental inbreds; however, most EPFUM hybrids showed significantly better resistance to FER and fumonisin contamination than commercial hybrids did. Although European flint materials seem to be the most promising reservoirs of alleles with favorable additive and/or dominance effects for resistance to kernel contamination with fumonisins, marketable new Reid × Lancaster hybrids have been detected as they combine high resistance and yields comparable to those exhibited by commercial hybrids. Moreover, the white kernel hybrid EPFUM-4 × EP116 exploits the genetic variability within the European flint germplasm and can be an alternative to dent hybrid cultivation because white flint grain can lead to higher market prices.

The improvement of maize double cropping has become increasingly important in recent years. In order to establish breeding programs for sustainable maize production, the goals of the research were (i) to understand the correlations between grain and stover yield and saccharification efficiency, and (ii) to identify QTL and metabolic pathways to design of breeding programs in a double exploitation approach. We carried out a genome-wide association study (GWAS) and a metabolic pathway analysis using a panel of highly diverse maize inbreds. As results, we have obtained that the regulation of energetic and developmental pathways have been pointed out as key pathways related to stover quantity and utilization, while no specific pathways could be identified in relation to grain yield. However, due to the moderate high heritability of yields and their positive correlation a phenotypic selection approach would be adequate for the improvement of both yields, while for saccharification efficiency improvement upcoming genomic selection models are more advisable. Overall, breeding strategies that manage the dual use of maize are viable and will contribute to a more sustainable maize crop in the near future.

Fusarium verticillioides is a causal agent of maize ear rot and produces fumonisins, which are mycotoxins that are toxic to animals and humans. In this study, quantitative trait loci (QTLs) and bulk-segregant RNA-seq approaches were used to uncover genomic regions and pathways involved in resistance to Fusarium ear rot (FER) and to fumonisin accumulation in maize kernels. Genomic regions at bins 4.07–4.1, 6–6.01, 6.04–6.05, and 8.05–8.08 were related to FER resistance and/or reduced fumonisin levels in kernels. A comparison of transcriptomes between resistant and susceptible inbred bulks 10 days after inoculation with F. verticillioides revealed 364 differentially expressed genes (DEGs). In the resistant inbred bulks, genes involved in sink metabolic processes such as fatty acid and starch biosynthesis were downregulated, as well as those involved in phytosulfokine signaling and many other genes involved in cell division; while genes involved in secondary metabolism and compounds/processes related to resistance were upregulated, especially those related to cell wall biosynthesis/rearrangement and flavonoid biosynthesis. These trends are indicative of a growth–defense trade-off. Among the DEGs, Zm00001d053603, Zm00001d035562, Zm00001d037810, Zm00001d037921, and Zm00001d010840 were polymorphic between resistant and susceptible bulks, were located in the confidence intervals of detected QTLs, and showed large differences in transcript levels between the resistant and susceptible bulks. Thus, they were identified as candidate genes involved in resistance to FER and/or reduced fumonisin accumulation.

Maize (Zea mays L.) is one of the major crops of the world for feed, food, and industrial uses. It was originated in Central America and introduced into Europe and other continents after Columbus trips at the end of the 15th century. Due to the large adaptability of maize, farmers have originated a wide variability of genetic resources with wide diversity of adaptation, characteristics, and uses. Nowadays, in Europe, maize is mainly used for feed, but several food specialties were originated during these five centuries of maize history and became traditional food specialties. This review summarizes the state of the art of traditional foodstuffs made with maize in Southern, South-Western and South-Eastern Europe, from an historic evolution to the last research activities that focus on improving sustainability, quality and safety of food production.

Sitophilus zeamais (Motsch.) (Coleoptera: Curculionidae) has a global distribution and is one of the most important post-harvest pests of maize (Zea mays L.). Some Mexican maize races could be a novel source of resistance against S. zeamais to improve commercial maize, generating lines, varieties, and hybrids with resistance to the pest. These are original races from the center of origin of maize and have been exposed to selection pressure from S. zeamais and other pests for thousands of years, which probably resulted in some type of resistance. We studied the resistance of Mexican maize races to S. zeamais focusing on antixenosis, antibiosis, and tolerance. Antibiosis reduces the survival and reproduction of the insect or prolongs the time between generations, whereas antixenosis reduces the rate of initial and successive accumulation of the insect population. Obligate-antibiosis and free-choice bioassays were performed, and in those experiments, resistance traits and the consumption by S. zeamais were measured. The most resistant accession showed high adult mortality and fewer adults in the 1st generation, where the number of emerged adults is an ideal trait to evaluate the level of maize resistance to the pest. Net consumption (in grams) is the most economically important trait because it indicates the gross amount lost in a store, while yield losses (percentage of consumption) allow for studying tolerance. The type of endosperm did have an influence on the resistance/tolerance to S. zeamais. The flint varieties showed significantly higher mortality of adults before entering the seed, a lower quantity of emerged adults of the first generation in the obligate-antibiosis bioassay, and lower net consumption and percentage in both bioassays. In general, the varieties of the races Cristalino de Chihuahua, Apachito, and Azul showed high levels of resistance, with the Cristalino-079 (flint) and Azul (floury) accessions also being tolerant, and low levels of consumption by S. zeamais. Both could be used in breeding programs to reduce losses caused by S. zeamais.

Cold reduces maize (Zea mays L.) production and delays sowings. Cold tolerance in maize is very limited, and breeding maize for cold tolerance is still a major challenge. Our objective was to detect QTL for cold tolerance at germination and seedling stages. We evaluated, under cold and control conditions, 919 Dent and 1009 Flint inbred lines from two nested association mapping designs consisting in 24 double-haploid populations, genotyped with 56,110 SNPs. We found a large diversity of maize cold tolerance within these NAM populations. We detected one QTL for plant weight and four for fluorescence under cold conditions, as well as one for plant weight and two for chlorophyll content under control conditions in the Dent-NAM. There were fewer significant QTL under control conditions than under cold conditions, and half of the QTL were for quantum efficiency of photosystem II. Our results supported the large genetic discrepancy between optimal and low temperatures, as the quantity and the position of the QTL were very variable between control and cold conditions. Furthermore, as we have not found alleles with significant effects on these NAM designs, further studies are needed with other experimental designs to find favorable alleles with important effects for improving cold tolerance in maize.

Senescence is an important trait in maize (Zea mais L.), a key crop that provides nutrition values and a renewable source of bioenergy worldwide. Genome-wide association studies (GWAS) can be used to identify causative genetic variants that influence the major physiological measures of senescence, which is used by plants as a defense mechanism against abiotic and biotic stresses affecting its performance. We measured four physiological and two agronomic traits that affect senescence. Six hundred seventy-two recombinant inbred lines (RILs) were evaluated in two consecutive years. Thirty-six candidate genes were identified by genome-wide association study (GWAS), and 11 of them were supported by additional evidence for involvement in senescence-related processes including proteolysis, sugar transport, and sink activity. We identified a candidate gene, Zm00001d043586, significantly associated with chlorophyll, and independently studied its transcription expression in an independent panel. Our results showed that Zm00001d043586 affects chlorophyl rate degradation, a key determinant of senescence, at late plant development stages. These results contribute to better understand the genetic relationship of the important trait senescence with physiology related parameters in maize and provide new putative molecular markers that can be used in marker assisted selection for line development.

Abstract Background Corn borers constitute an important pest of maize around the world; in particular Sesamia nonagrioides Lefèbvre, named Mediterranean corn borer (MCB), causes important losses in Southern Europe. Methods of selection can be combined with transgenic approaches to increase the efficiency and durability of the resistance to corn borers. Previous studies of the genetic factors involved in resistance to MCB have been carried out using bi-parental populations that have low resolution or using association inbred panels that have a low power to detect rare alleles. We developed a Multi-parent Advanced Generation InterCrosses (MAGIC) population to map with high resolution the genetic determinants of resistance to MCB. Results We detected multiple single nucleotide polymorphisms (SNPs) of low effect associated with resistance to stalk tunneling by MCB. We dissected a wide region related to stalk tunneling in multiple studies into three smaller regions (at ~ 150, ~ 155, and ~ 165 Mb in chromosome 6) that closely overlap with regions associated with cell wall composition. We also detected regions associated with kernel resistance and agronomic traits, although the co-localization of significant regions between traits was very low. This indicates that it is possible the concurrent improvement of resistance and agronomic traits. Conclusions We developed a mapping population which allowed a finer dissection of the genetics of maize resistance to corn borers and a solid nomination of candidate genes based on functional information. The population, given its large variability, was also adequate to map multiple traits and study the relationship between them.

Limited attention has been paid to maize (Zea mays L.) resistance induced by corn borer damage, although evidence shows that induced defenses have lower resource allocation costs than constitutive defenses. Maize responses to short- and long-term feeding by the Mediterranean corn borer (MCB, Sesamia nionagrioides) have been previously studied, but the suggested differences between responses could be due to experimental differences. Therefore, in the current study, a direct comparison between short- and long-term responses has been made. The objectives were (i) to determine changes in the level of antibiosis of the stems induced by feeding of S. nonagrioides larvae for 2days (short-term feeding) and 9days (long-term feeding), (ii) to characterize the metabolome of the stems’ short- and long-term responses to borer feeding, and (iii) to look for metabolic pathways that could modulate plant resistance to MCB. Defenses were progressively induced in the resistant inbred, and constitutive defenses were broken down in the susceptible inbred. Results suggest that the different resistance levels of the two inbreds to stem tunneling by MCB could depend on their ability to establish a systemic response. Based on these results, a high throughput look for specific metabolites implicated in systemic induced resistance to maize stem borers is recommended; the current focus on constitutive defense metabolites has not been successful in finding molecules that would be valuable tools for pest control.

Increasing drought incidence and infertile soils require the improvement of maize for nitrogen use efficiency (NUE) under drought conditions. The objectives were to assess tolerance and genetic effects of Algerian populations under no-nitrogen and water stress. We evaluated a diallel among six Algerian maize populations under no-nitrogen vs. 120 kg/ha N fertilization and drought vs. control. Variability was significant among populations and their crosses for NUE under drought. Additive genetic effects could be capitalized using the populations BAH and MST, with high grain nitrogen utilization efficiency (NUtE). The most promising crosses were SHH × AOR with no-nitrogen supply under both water regimes for NUtE, AOR × IGS, under water stress for partial factor productivity (PFP), and well-watered conditions with nitrogen supply for protein content; AOR × IZM for agronomic nitrogen use efficiency (AE) under water stress; and AOR × BAH for grain nutrient utilization efficiency (NUtE) under well-watered conditions with nitrogen. These parents could be promising for developing drought-tolerant or/and low nitrogen hybrids to improve these traits. Maximum heterosis could be exploited using those populations and crosses. Reciprocal recurrent selection could be used to take advantage of additive and non-additive gene effects found based on estimations of genetic parameters.

Abstract Background Sesamia nonagrioides Lefebvere (Mediterranean corn borer, MCB) is the main pest of maize in the Mediterranean area. QTL for MCB stalk tunneling and grain yield under high MCB infestation had been located at bin 8.03–8.05 (4–21 cM and 10–30 cM respectively) in a previous analysis of the EP42 x EP39 RILs mapping population. The objective of the present work was to study with higher resolution those QTL, and validating and estimating with higher precision their locations and effects. To achieve this objective, we developed a set of 38 heterogeneous inbred families (HIFs) which were near-homozygous in the genome, except in the region under study. The HIFs were evaluated in multiple environments under artificial infestation with MCB and genotyped with SNPs. Results The QTL for grain yield under high infestation was confirmed with higher precision and improved reliability at 112.6–116.9 Mb. On the contrary, the location of the QTL for stalk tunneling was not validated probably due to the fixation of some genomic regions during the development of the HIFs. Our study confirmed that the co-localization of the QTL for stalk tunneling and grain yield in the previous study was due to linked genes, not to pleiotropic effects. So, the QTL for grain yield can be used for improving grain yield without undesirable effect on stalk tunneling. Conclusions The HIF analysis is useful for validating QTL and for conducting deeper studies in traits related to corn borer resistance.

Maize’s (Zea mays L.) nutrient content can be modified through selection. The objective of this study was to assess the nutritive value of 13 maize hybrids from four endosperm types, and the relationship between nutrient concentration, agronomic and rheological value. The hybrids were evaluated in two locations of Northwestern Spain over two years. There was genetic diversity among endosperm types and genotypes for all nutrients, with significant environmental effects, but few genotype × environment interactions. Flint hybrids had the highest protein and lipid content. The mutant wx1 significantly increased protein and reduced lipid, and both wx1 and o2 reduced ash and starch content and increased total fiber. Variability among hybrids within the wx1 endosperm was significant for most nutrients. Correlations between nutrients were rarely significant, implying that protein and lipid can be improved independently. Protein and lipid were negatively correlated with grain yield and plant height. However, improving nutrient content could alter agronomic performance, as nutrients had significant negative effects on rheological factors, particularly protein and lipid, which had negative effects on whole meal and on bread characteristics. Therefore, nutrient content can be improved in maize, but negative effects on agronomic and quality have to be taken into account.

With a high potential to generate biomass, maize stover arises as an outstanding feedstock for biofuel production. Maize stover presents the added advantage of being a multiple exploitation of the crop as a source of food, feed, and energy. In this study, contrasting groups of recombinant inbred lines (RILs) from a maize multiparent advanced generation intercross (MAGIC) population that showed variability for saccharification efficiency were screened by FTIR-ATR spectroscopy to explore compositional differences between high and low saccharification yielders. High and low saccharification efficiency groups differed in cell wall compositional features: high saccharification RILs displayed higher proportions of S subunits, aromatic compounds, and hemicellulose as opposed to low saccharification efficiency groups in which FTIR predicted higher proportions of lignin, more precisely lignin being richer in subunits G, and greater proportions of crystalline cellulose and acetyl methyl esters. The application of FTIR-ATR spectroscopy in this material allowed us to obtain a rapid and broad vision of cell wall compositional features in contrasting groups of saccharification efficiency. These results helped us to deepen our knowledge into the relationship between cell wall composition and biorefining potential; they also allowed us to establish new targets for future research regarding lignocellulosic bioconversion.

Corn borers are the most important pest affecting maize. Resistance to corn borer attack may compromise plant fitness being detrimental for some important agronomic traits such as yield. Against the attack of this pest, cell wall-bound hydroxycinnamates have been previously described as a possible defense mechanism. In this study, agronomic characterization and cell wall-bound hydroxycinnamates quantification was performed in a subset of Recombinant Inbred Lines (RILs) from a Multiparent Advanced Generation Intercross (MAGIC) population that showed contrasting behavior against corn borer attack. Resistant lines showed greater concentration of p-coumaric acid, the only hydroxycinnamate that could have a role in the resistance in these particular materials. In addition, results indicated that resistant lines showed precocity, low grain moisture at harvest, and reduced plant height, thus, selecting for resistance may be detrimental for yield. In this way, a breeding strategy directly targeting grain yield in order to tolerate corn borer attack would be the recommended one.

Drought and low nitrogen are major stresses for maize (Zea mays L.), and maize populations from the Sahara Desert are potential sources of stress tolerance. The objectives were to assess the tolerance and varietal and heterosis effects of Algerian populations under no-nitrogen fertilization and water stress. A diallel among six Algerian maize population was evaluated under drought (300 mm irrigation) vs. control (600 mm) and no-nitrogen fertilization vs. 120 kh ha−1 N fertilization. Genotypes showed significant differences and genetic effects for water- and nitrogen-stress tolerance. We propose a reciprocal recurrent selection to take advantage of additive and non-additive effects, using AOR and IGS, since they showed good performance in optimum and stress conditions, for improving yield heterosis for AOR × IGS. Negative effects are not expected on plant height, anthesis–silking interval or early vigor. These populations and BAH could be sources of inbred lines tolerant to drought and no-nitrogen fertilization. There was no relationship between origin and genetic group and stress tolerance per se or as parents of tolerant crosses. These populations and crosses could be used as base material among Algerian populations, for breeding programs focusing on tolerance to water or nitrogen stress.

Drought is the main constraint to maize production in the Mediterranean area. This is the first report of breeding temperate maize populations from the Algerian desert. The objective of this study was to evaluate response to selection for reduced anthesis-silking interval (ASI) in Algerian maize under drought and control conditions. Three cycles of selection for reduced ASI were carried out in four populations under control and drought conditions, and the breeding program was evaluated under both conditions. Selection under drought was more efficient than under control conditions, particularly for the LOM and TAO populations. Selection for low ASI reduced ASI and days per cycle for BTM and IGS, respectively, under drought conditions. Selection for ASI reduced anthesis in BTM, when selected under drought and evaluated under control conditions. Significant yield increase was observed for BTM under optimal conditions. Significant genetic gain for yield was observed for the population LOM under drought. Therefore, the improved Algerian populations BTM and TAO could be a novel source for reducing ASI and for earlier flowering time as a mechanism for avoiding drought. Furthermore, we propose these populations as sources to develop tolerant inbred lines and to find quantitative trait loci for drought tolerance.

Forage feedstock is the greatest source of energy for livestock. Unfortunately, less than 50% of their fiber content is actually digested and assimilated by the ruminant animals. This recalcitrance is mainly due to the high concentration of plant cell wall material and to the limited digestion of the fiber by the microorganisms. A Genome-Wide Association Study (GWAS) was carried out in order to identify Single Nucleotide Polymorphisms (SNPs) associated with forage digestibility traits in a maize Multi-Parent Advanced Generation Intercross (MAGIC) population. We identified seven SNPs, corresponding to five Quantitative Trait Loci (QTL), associated to digestibility of the organic matter, 11 SNPs, clustered in eight QTLs, associated to Neutral Detergent Fiber (NDF) content and eight SNPs corresponding with four QTL associated with Acid Detergent Fiber (ADF). Candidate genes under the QTL for digestibility of the organic matter could be the ones involved in pectin degradation or phenylpropanoid pathway. Transcription factor genes were also proposed for the fiber QTL identified, in addition to genes induced by oxidative stress, or a gene involved in lignin modifications. Nevertheless, for the improvement of the traits under study, and based on the moderate heritability value and low percentage of the phenotypic variability explained by each QTL, a genomic selection strategy using markers evenly distributed across the whole genome is proposed.

Food contamination with mycotoxins is a worldwide concern, because these toxins produced by several fungal species have detrimental effects on animal and/or human health. In maize, fumonisins are among the toxins with the highest threatening potential because they are mainly produced by Fusarium verticillioides, which is distributed worldwide. Plant breeding has emerged as an effective and environmentally safe method to reduce fumonisin levels in maize kernels, but although phenotypic selection has proved effective for improving resistance to fumonisin contamination, further resources should be mobilized to meet farmers’ needs. Selection based on molecular markers linked to quantitative trait loci (QTL) for resistance to fumonisin contamination or/and genotype values obtained using prediction models with markers distributed across the whole genome could speed up breeding progress. Therefore, in the current paper, previously identified genomic regions, genes, and/or pathways implicated in resistance to fumonisin accumulation will be reviewed. Studies done until now have provide many markers to be used by breeders, but to get further insight on plant mechanisms to defend against fungal infection and to limit fumonisin contamination, the genes behind those QTLs should be identified.

Plants defend themselves against herbivores by activating a plethora of genetic and biochemical mechanisms aimed at reducing plant damage and insect survival. The short-term plant response to insect attack is well understood, but less is known about the maintenance of this response over time. We performed transcriptomic and metabolomics analyses in order to identify genes and metabolites involved in the long-term response of maize to attack by the corn borer Sesamina nonagrioides. To determine the role of elicitors present in caterpillar secretions, we also evaluated the response of maize stem challenged with insect regurgitates. The integrative analysis of the omics results revealed that the long-term response in maize is characterized by repression of the primary metabolism and a strong redox response, mainly mediated by germin-like proteins to produce anti-nutritive and toxic compounds that reduce insect viability, and with the glutathione–ascorbate cycle being crucial to minimize the adverse effects of reactive oxygen species (ROS) on the plant. Our results suggest that different defense mechanisms are involved in the long-term response compared to those reported during the early response. We also observed a marginal effect of the caterpillar regurgitates on the long-term defensive response.

Antioxidant activity (AA) of black maize kernels attributed mainly to polyphenols has potential effects on health and possible defense functions against pests. Our objective was to evaluate the effects of maize polyphenols and AA in survival and growth of larvae of the corn borer Sesamia nonagrioides. We carried out two bioassays with S. nonagrioides larvae grown in artificial diet with white and black maize flour and control. AA was tested spectrophotometrically on each of the diets using four methods. The different measurements of AA were strongly correlated, indicating that these measurements were highly reliable. The control diet, the white-maize-diet and black-maize-diet with vitamin C and without H2O2 had the highest antioxidant activity. The processing of the maize flour altered the AA of the polyphenols. The control treatment had the highest AA, and vitamin C had stronger AA than polyphenols. AA of vitamin C hides that of polyphenols probably due to environmental effects, dilution of polyphenols, or interactions with other substances. Larvae grew more in the control diet and the addition of H2O2 had not significant effects on weight. There was a weak rank correlation between AA and larval weight. Mortality was lowest for the control diet with or without H2O2 followed by white maize with or without H2O2 and black maize without H2O2. Effects of polyphenols depend on other substances that might interact with them. The results indicate that antioxidant activity has insecticide effects on young larvae and, as the larvae grow, antioxidants have positive effects on larvae.

Introduction: The Mediterranean corn borer (MCB), Sesamia nonagrioides, is a major pest of maize, Zea mays, in Mediterranean countries, inflicting significant kernel yield losses. For that reason, it necessary to know the genetic mechanisms that regulate the agronomic and resistance traits. A quantitative trait loci (QTL) mapping study for yield, resistance against MCB attack, and other relevant agronomic traits was performed using a recombinant inbred line (RIL) population derived from the cross A637 × A509 that is expected to segregate for yield, and ear, and stalk resistance to MCB. 171 RILs were evaluated in 2014 and 2015 at Pontevedra, Spain, along with the two parental inbreds A637 and A509 using a 13 × 14 single lattice design with two replications. A genetic map with 285 SNP markers was used for QTL analysis. Our objectives were to detect QTL for resistance to MCB and tolerance-related agronomic traits, to gain insights on the genetic relationship between resistance to MCB attack and yield, and to establish the best way for simultaneously improving yield and resistance to MCB.Results: Twelve significant QTL were detected for agronomic and resistance traits. QTL at bins 1.10 and 5.04 were especially interesting because the same allelic variant at these QTL simultaneously improved yield and insect resistance. In contrast, in the region 8.04–8.05, QTL showed opposite effects for yield and resistance. Several QTL for indexes which combine yield and resistance traits were found especially in the region 10.02–10.03.Conclusions: Selecting genotypes with the favorable allele of QTL on chromosome 5 (bin 5.01) will decrease tunnel length without affect yield, silking and plant height and QTL on the region 5.04 could be used to improve stalk resistance and yield simultaneously. An allele of QTL on bin 9.07 will increase ear resistance to MCB attack but it could produce later varieties while favorable allele in region 1.10 could improve ear and stalk resistance and yield without secondary negative effects. The region 8.03–8.05 mainly but also the region 10.02–10.03 and 5.04 may play an important role to elucidate the association between yield, other agronomic traits and MCB resistance.

In spite of multiple studies elucidating individual defense mechanisms against stalk borer feeding, little information is available about the plant response to these members of Lepidoptera. Four maize inbred lines were cultivated in a greenhouse and challenged with larvae of the corn borer Sesamia nonagrioides. Transcriptome and biochemical analyses were performed to elucidate the maize response mechanisms to this insect. General plant defense mechanisms were activated, including the jasmonic acid biosynthetic pathway, proteinase inhibitors, and four defense-related transcription factors. Interestingly, gene ontology analysis shows that maize plants undergo cell-wall reorganization after being attacked. These results were confirmed through biochemical analyses showing that the concentration of some cell-wall-related compounds significantly changed after plant infestation in a genotype-dependent way. In conclusion, maize plants respond to the attack of the corn borer S. nonagrioides through cell-wall fortification, activating genes involved in cell-wall organization, which finally is reflected in a higher concentration of some cell-wall components, especially in resistant genotypes.

In the current study, the hydroxycinnamic acids in silks of diverse maize inbred lines differing in Fusarium resistance were determined at several times after inoculation with Fusarium graminearum or sterile water as control. The main objective was to determine the possible relationship between the hydroxycinnamic acid changes in silks and ear rot resistance. Several changes in the cell-wall-bound hydroxycinnamic acid concentrations were observed after inoculation with F. graminearum, although these changes were not directly correlated with genotypic resistance to this fungus. Ester-bound ferulic acid decreased, probably due to degradation of hemicellulose by hydrolytic enzymes produced by Fusarium spp., while p-coumaric acid and diferulates showed slight increases that, in conjunction, did not result in delayed F. graminearum progression through the silks. It is important to note that the decrease of ferulic acid in the F. graminearum treatment was faster in susceptible than in resistant genotypes, suggesting a differential hemicellulose degradation in silk tissues. Therefore, the ability of the maize genotypes to slow down that process through hemicellulose structural features or xylanase inhibitors needs to be addressed in future studies.