Understanding and effectively leveraging the genetic diversity present in breeding programs is decisive for increasing genetic gain and rapidly responding to changes in breeding objectives. In this work, a set of 472 representative lines from the Argentine National Institute of Agricultural Technology (INTA) temperate maize (Zea mays L.) breeding program was genotyped with a mid-density DArTag panel to assess genetic diversity, degree of linkage disequilibrium (LD) and population structure. In addition, a breeding core set that captured the program’s genetic diversity was selected to facilitate future functional studies. After curation of the genotypic matrix, 461 lines and 2,199 single nucleotide polymorphisms (SNPs) remained in the analysis. SNPs were highly informative, with an average polymorphic information content of 0.32. Inbred lines exhibited low heterozygosity (1.6

Many plants respond to fungal infections by producing and/or emitting a specific blend of oxylipins, some of them through the lipoxygenase (LOX) pathway. In vitro bioassays revealed that volatiles from silks and grains of a set of six maize genotypes with variable resistance to Fusarium verticillioides affected fungal growth in different ways. Analyses by solid phase microextraction and GC‐MS showed different volatile profiles in silks and grains of each genotype. Susceptible genotypes with higher concentrations of precursor polyunsaturated fatty acids produced more volatiles, mainly C9 compounds, in comparison to moderately resistant ones. Real‐time PCR from several lipoxygenase transcripts revealed that levels of gene expression depended on the genotype and the inoculation level and suggested that F. verticillioides could use compounds from the 9‐LOX pathway to promote infection in grains. On the other hand, volatiles produced by the 13‐LOX pathway were more important in moderately resistant genotypes and could be associated to field resistance. Results from this set of genotypes indicate that LOX‐regulated volatile compounds might be important in F. verticillioides infection and should be targeted in further research to understand disease resistance.

Fusarium verticillioides and F. graminearum cause ear rots in maize (Zea mays L.) that reduce yield and contaminate the grain with mycotoxins produced by the fungi. To map QTLs for resistance to these ear rots, a F5 mapping population, consisting of 298 recombinant inbreds obtained by randomly selfing of the cross between LP4637 (moderately resistant) and L4674 (susceptible), was genotyped with 250 single nucleotide polymorphism markers and phenotyped 2 years for disease severity after silk inoculation with conidial suspensions of F. verticillioides and F. graminearum. Four QTLs were mapped in chromosomes 2, 3 and 5, bins 2.03, 3.05, 3.07 and 5.07, explaining ranges of 11.2–11.8, 3.4–5.1, 6.2–7.6 and 3.8–5.0 of phenotypic variances (%), respectively, depending on year and fungus. Additive effects of each QTL ranged from 5.0 to 11.9 % of ear area covered by mold and no epistatic interactions were observed. The four QTLs were effective for both Fusarium species and environments indicating that LP4637 is a source of broad resistance to Fusarium stable across environments. These results are consistent with previous research reporting QTLs for ear rot resistance in the same chromosome regions from sources of resistance growing in North America, Africa, Europe and China.

The glyoxalase system is ubiquitous among all forms of life owing to its central role in relieving the cell from the accumulation of methylglyoxal, a toxic metabolic byproduct. In higher plants, this system is upregulated under diverse metabolic stress conditions, such as in the defence response to infection by pathogenic microorganisms. Despite their proven fundamental role in metabolic stresses, plant glyoxalases have been poorly studied. In this work, glyoxalase I from Zea mays has been characterized both biochemically and structurally, thus reporting the first atomic model of a glyoxalase I available from plants. The results indicate that this enzyme comprises a single polypeptide with two structurally similar domains, giving rise to two lateral concavities, one of which harbours a functional nickel(II)-binding active site. The putative function of the remaining cryptic active site remains to be determined.

Fusarium verticillioides causes ear rot and grain mycotoxins in maize (Zea mays L.), which are harmful to human and animal health. Breeding and growing less susceptible plant genotypes is one alternative to reduce these detrimental effects. A better understanding of the resistance mechanisms would facilitate the implementation of strategic molecular agriculture to breeding of resistant germplasm. Our aim was to identify genes and metabolites that may be related to the Fusarium reaction in a resistant (L4637) and a susceptible (L4674) inbred. Gene expression data were obtained from microarray hybridizations in inoculated and non-inoculated kernels from both inbreds. Fungal inoculation did not produce considerable changes in gene expression and metabolites in L4637. Defense-related genes changed in L4674 kernels, responding specifically to the pathogen infection. These results indicate that L4637 resistance may be mainly due to constitutive defense mechanisms preventing fungal infection. These mechanisms seem to be poorly expressed in L4674; and despite the inoculation activate a defense response; this is not enough to prevent the disease progress in this susceptible line. Through this study, a global view of differential genes expressed and metabolites accumulated during resistance and susceptibility to F. verticillioides inoculation has been obtained, giving additional information about the mechanisms and pathways conferring resistance to this important disease in maize.

The aim of this work was to investigate the role of pericarp phenylpropanoids as resistance factors to F. verticillioides in eleven maize genotypes. Disease severity and kernel fumonisin accumulation were measured after inoculation with F. verticillioides and related to contents of pericarp phenylpropanoids in field trials conducted during 2 years. Grain fumonisin concentrations were highly dependant on disease severity of the genotypes (r = 0.88). A detailed analysis of pericarp phenylpropanoids indicated the presence of trans-ferulic acid (tFA), cis-ferulic acid (cFA), p-coumaric acid (pCA), and five diferulates (DFAs). The most prominent diferulates were 8,5′-diferulic acid benzofuram form (8,5′-DFAbz), followed by 8,5′-DFA and 8,8′-DFA. Except for cFA, the most resistant genotypes exhibited high levels of phenylpropanoids which were related to low levels of disease severity and grain fumonisin concentration (−0.61 > r > −0.90). A stepwise regression analysis revealed that total diferulates was the best explanatory parameter for variability of disease severity (r 2 = 0.71). Grain fumonisin concentration was well depicted by contents of total diferulates, 8,5′DFAbz and pCA (r 2 = 0.82). Our findings suggest that high level of phenylpropanoids in the kernel pericarp is a trait associated to less disease severity and fumonisin accumulation caused by F. verticillioides. Further research is in progress to map quantitative trait loci for these cell wall components in bi-parental populations derived by crossing resistant and susceptible genotypes included in this study.

The genetic diversity of maize (Zea mays L) is a valuable and strategic natural resource that plays a key role in the breeding progress. However, exploitation of genetic variability from landraces has not reached a significant level of utilization in breeding programs in Argentina yet. In order to establish their breeding potential, the best 15 out of a group of about 300 landraces from Argentina, were evaluated for various agronomic characters in testcrosses with five lines representing different heterotic groups. Testcrosses were evaluated in nine environments during two growing seasons. A factorial array of those landraces and tester lines was used. Differences for landraces, testers, and landrace x tester interactions were detected for ear diameter and length, ear attachment and plant height, and grain yield. Yield data were further analyzed following additive main effects (landrace and tester) and multiplicative interaction (landrace x tester) models. The first two principal components were significant and accounted for 67% of that interaction. The first axis was consistent with the Argentine flint vs. US dent (Mo17), and US dent (B73) vs. US dent (Mo17) heterotic patterns. The second axis exhibited a contrast between Argentine flint and US dent (B73 or B73 derived line) heterotic groups. The first two principal components of the landrace x tester interaction and mean performance of testcrosses were considered to identify eight landraces as parents of three composite populations.

Somatic embryogenesis, which is still the method of choice for tissue culture, regeneration and transformation of maize, is largely considered highly genotype-dependent. The Hi II, a highly embryogenic genotype, has been extensively used in transformation protocols. However, this is not an inbred line; instead, it has a proportion of the undesirable A-188 background, and the progeny segregates for phenotypic characteristics and shows poor agronomic performance. In an effort to identify genotypes that combine a high somatic embryogenic response and good agronomic performance, we evaluated 48 advanced inbred lines developed at INTA. Callus development and somatic embryogenesis capacity were measured in 200 immature embryos per line. Embryogenic capacity [EC (mature somatic embryos/callus evaluated) x 100], Regeneration Capacity (RC) and Fertile Plant Recovery in greenhouse (FPR, fertile plants/regenerated plants) were recorded. A total of 17 lines reached an EC > 50%, and 14 out of those 17 lines regenerated seedlings. The FPR ranged between 50 and 100%. Also, we selected three promising lines with high agronomic performance, as alternatives to Hi II, in order to be included in a maize transformation scheme via somatic embryogenesis. In addition, we report the usefulness of Single Sequences Repeat (SSRs) in the determination of genetic diversity among 14 divergent lines for somatic embryogenesis response. The seven lines displaying good in vitro behaviour can be crossed to obtain hybrids combining desirable alleles for somatic embryogenesis response and different genetic backgrounds.

Environmental factors that affect the fumonisin content in maize grain Regression logistic techniques were used to study the environmental variables associated with fumonisin content in maize grain. The dependent variable consisted of 29 values of fumonisins B(1) and B(2) (FB(1) and FB(2)) from samples of susceptible hybrid sowed in several sites of the Pampas region from 2006/07 to 2008/09. Meteorological variables were recorded in relation to the silking stage. The Np2 variable (number of periods of two days with simultaneous recording of rainfall and relative humidity >= 81 % (day 1) and relative humidity > 70 % at the second day) was the most strongly correlated with FB(1) and FB(2) (Kendall coefficient: tau: 0.63 and 0.52 respectively) and was included in simple and bivariate regression logistic models with Txm (mean maximum temperature). A trivariate model integrated for two interactive variables and Txm achieved the highest accuracy of prediction, classifying correctly 93 % of cases. The environmental variables identified in this study stimulate F. verticillioides infection and can explain the variability in fumonisin levels at harvest. These results could be useful for the rational management of both disease and mycotoxin.

Random S5 inbreds derived from three F2 maize (Zea mays L.) populations (L1934 × LP918, LP915 × LP2541 and L7310 × L7266) were selected for ear rot resistance after inoculation with a low-fumonisin producing isolate belonging to F. proliferatum. The four less susceptible and the four most susceptible inbreds from each population were crossed and F1 seeds were pooled. Resistant and susceptible pools from each population were evaluated for disease severity (percentage of the ear visibly diseased) after inoculation with the isolate used for selection, and high toxigenic isolates belonging to F. verticillioides and F. graminearum. Grain mycotoxin concentration was assessed by ELISA. Differences in disease resistance to each fungus were observed between resistant and susceptible pools in most populations and environments indicating that selection after inoculation with a single species might be effective to develop broad-based resistance to Fusarium. Resistant pools exhibited, after inoculation with F. verticillioides, low grain fumonisin concentrations in most populations and years. Positive genotypic correlations between disease severity and fumonisin concentration (0.89 < rg < 0.98, depending on fungal species and year) indicate that selection for disease severity accounted for most of the variability for field fumonisin accumulation. Selection seemed to be also effective to reduce grain deoxynivalenol and zearalenone concentrations after inoculation with F. graminearum. Ratios between grain deoxynivalenol concentration and disease severity were lower in L7310 × L7266 than those observed in the other populations suggesting that mechanisms affecting mycotoxin accumulation might exist in this population and additional responses should be feasible if including deoxynivalenol concentration as another selection parameter.

Developing resistance to species of Fusarium in maize (Zea mays L.) is important to prevent field mycotoxin contamination. Isolates representative of natural conditions need to be identified to maximize selection responses. Sixty isolates belonging to Fusarium section Liseola collected from a major maize growing region in Argentina were tested for sexual compatibility with eight standard tester strains (A-H) of the Gibberella fujikuroi complex. A twenty-nine isolate sub-sample (MAT-A: 26, MAT-E: 2 and MAT-D: 1) was tested for in vitro production of fumonisins and for aggressiveness to two maize hybrids after silk inoculation. Mating population A (E verticillioides) was the most prevalent species (90%) coexisting with some isolates belonging to MAT-D (F eratum) and MAT-E (E subglutinans). Fumonisin production varied from 0.4 to 2884 mu g(-1) for MAT-A and from 0.3 to 0.6 mu g g(-1) for MAT-E. The only isolate from MAT-D produced undetectable levels. Most isolates showed mild aggressiveness but two uncommon highly aggressive strains (MAT-A and D) were also identified. No associations between fumonisin production and disease severity were observed. Differences in disease severity between moderately resistant and susceptible hybrids varied across years and isolates suggesting that responses to selection might depend on the isolate used to produce the inoculum. The use of isolate mixtures might reduce genotype-by-isolate interaction although it would hinder identification of resistance to specific strains.

Fusarium species are worldwide causal agents of ear rot in cereals. Their toxigenic potential is a health risk for both humans and animals. In Argentina, most identification of these fungi has been based on morphological and cross-fertility criteria which are time consuming and require considerable expertise in Fusarium taxonomy and physiology. DNA based approaches have been reported as rapid, sensitive and specific alternatives to identify the main fumonisin and trichothecene-producing Fusarium species. In this work, we used PCR assays and the partial sequence of TEF1-α gene (Translation Elongation Factor-1α) to identify the fumonisin and trichothecene-producing species in Fusarium isolates from diverse regions of Argentina. The relative efficiency and reliability of those methods to improve mycotoxin risk prediction in this country were also assessed. Species-specific PCR assays were targeted toward multicopy IGS (Intergenic Spacer of rDNA units) and on the toxin biosynthetic genes FUM1 (fumonisins) and TRI13 and TRI7 genes (trichothecenes). PCR assays based on FUM1 gene and IGS sequences allowed detection and discrimination of the fumonisin producers Fusarium proliferatum and Fusarium verticillioides. Molecular identification of nonfumonisin producers from Gibberella fujikuroi species complex was possible after determination of TEF1-α gene sequences, which indicated the presence of Fusarium subglutinans, Fusarium andiyazi and Fusarium thapsinum. TEF-1α gene sequences also allowed discrimination of the different species of the Fusarium graminearum complex (F. graminearum sensu lato) as F. graminearum sensu stricto, Fusarium meridionale and Fusarium boothii. The last two species belonged to NIV chemotype and were detected for the first time in the subtropical region of Argentina while F. graminearum sensu stricto was DON producer only, which was also confirmed by specific PCR assays based on TRI137/TRI7 genes. Our results indicated that the PCR assays evaluated in this work are reliable diagnostic tools to detect the main toxigenic Fusarium species associated to cereal grains in Argentina. An extensive epidemiological survey based on the approach presented in this work is currently in progress to know the mycotoxigenic hazard of Fusarium species in cereal grains from the subtropical region of Argentina.

Fusarium verticillioides causes maize ear rot and contaminates kernels with fumonisin mycotoxins in Argentina. The aim of this work was to elucidate if the kernel pericarp and its surface wax layer are resistance factors to fumonisin accumulation in maize genotypes from Argentina. Fourteen maize genotypes were inoculated with F. verticillioides in laboratory assays. Intact kernels of genotypes resistant to fumonisin accumulation in the field had the lowest mycotoxin concentration in the current assays suggesting that kernel factors are involved. Intact kernels of landraces, breeding populations and L4637 inbreed were less susceptible than wounded ones, suggesting that intact kernel pericarp restricted fumonisin accumulation. Removing wax from the pericarp significantly increased fumonisin concentration and a higher wax content on kernels was associated to lower fumonisin accumulation. Our results suggest that the pericarp and its wax content are resistance factors to fumonisin accumulation in most genotypes assayed. Nevertheless, other kernel factors could not be excluded.

Fusarium verticillioides causes Fusarium ear rot in maize (Zea mays L.) and contaminates grain with fumonisins, but there is little information on how the disease affects yield. Three hybrids were evaluated in conditions of natural infection and after silk inoculation with this fungus. Disease severity (percentage of the ear covered by mold) was assessed on a visual scale. In the inoculated treatment, ears within experimental units were grouped according to their disease severity rating. Grain weight and fumonisin concentration (ELISA) were assessed in each group. Relationships of disease severity with yield and with grain fumonisin concentration were mainly explained by linear models. Slopes varied from −0.6 to −2.0 g plant−1 per unit of disease severity for yield and from 3.4 to 10.9 μg g−1 per unit of disease severity for grain fumonisin concentration, depending on the hybrid and year. Linear responses suggested that losses of yield and grain quality might be reduced by using the most resistant hybrids exhibiting low frequencies of severely diseased ears.