Gibberella Ear Rot Research Articles

Aggressiveness and Mycotoxin Production by Fusarium meridionale Compared with F. graminearum on Maize Ears and Stalks in the Field.

Fusarium meridionale and F. graminearum both cause Gibberella ear rot (GER) and Gibberella stalk rot (GSR) of maize in Brazil, but the former is much more common. Recent work with two isolates of each from maize suggested this dominance could be caused by greater aggressiveness and competitiveness of F. meridionale on maize. We evaluated pathogenicity and toxigenicity of 16 isolates of F. graminearum and 24 isolates of F. meridionale recovered from both wheat and maize. Strains were individually inoculated into ears of four maize hybrids in field trials. GER severity varied significantly between isolates within each species. Although ranges overlapped, the average GER severity induced by F. meridionale (25.2%) was two times as high overall as that induced by F. graminearum (12.8%) for isolates obtained from maize but was similar for those isolated from wheat (19.9 and 21.4%, respectively). In contrast, severity of GSR was slightly higher for F. graminearum (22.2%) than for F. meridionale (19.8%), with no effect of the host of origin. Deoxynivalenol and its acetylated form 15ADON were the main mycotoxins produced by F. graminearum (7/16 strains), and nivalenol toxin was produced by F. meridionale (17/24 strains). Six isolates of F. graminearum and three of F. meridionale also produced zearalenone. Results confirmed that F. meridionale from maize is, on average, more aggressive on maize but also suggested greater complexity related to diversity among the isolates within each species and their interactions with different hybrids. Further studies involving other components of the disease cycle are needed to more fully explain observed patterns of host dominance.

Assessment of deoxynivalenol and deoxynivalenol derivatives in Fusarium graminearum-inoculated Canadian maize inbreds

The prevalence of maize, wheat and other cereal crops in Ontario, Canada, has led to frequent epidemics of ear rot and head blight disease caused by the broad host pathogen Fusarium graminearum. This fungus produces the trichothecene deoxynivalenol (DON) which is one of the most common mycotoxins contaminating food and feed globally and poses a risk to human and animal health. DON is commonly glycosylated by plant hosts into deoxynivalenol-3-glucoside (DON-3G) as part of a defence mechanism to detoxify and sequester mycotoxins. However, it has been documented that DON-3G can be hydrolyzed in the digestive system of animals, increasing the bioavailability of DON. There is a need for additional documentation of the incidence and ratio of DON-3G to DON in Canadian cereal crops. We investigated the occurrence and relative proportion of DON and modified DON compounds in Canadian-adapted maize germplasm with a wide range of ear rot tolerance. Forty-nine maize inbreds were manually challenged (kernel inoculation) with F. graminearum (15-ADON chemotype) as well as phenotyped for tolerance to Gibberella ear rot (GER) under field conditions. LC/MS was used to analyse 581 maize samples for DON, DON-3G, 15-ADON, and 15-ADON-3G. The DON-3G to DON mean molar ratio ranged from 3.1 to 19.7%. DON content was positively correlated with GER disease severity (r = 0.66, p < 0.01), while the DON-3G:DON molar ratio and disease severity were negatively correlated (r = -0.64, p < 0.001). Thus, GER-tolerant maize genotypes had relatively lower total DON content and higher DON-3G:DON ratios.

First Report of Fusarium graminearum Causing Flower Blight On Hemp (Cannabis sativa) in Kentucky.

In October of 2020, a grower in Boyle County, KY, reported mold and blight symptoms on flowers of field-grown hemp. Plants were approaching harvest, and the mold was affecting 100% of the cultivar 'White CBG' being grown for cannabinoid (CBD) extraction. Mycelium colonized the flower heads and any seeds within bracts. Affected flower bracts were necrotic, and mycelium and necrosis in the most severe cases also encompassed adjacent (sugar) leaves. Necrotic symptomatic tissue was collected, disinfested in 10% bleach for one minute, and cultured on acidified potato dextrose agar (APDA). Each isolate was single-spored, transferred to PDA, stored in 15% glycerol at -80°C and maintained at room temperature under blacklight blue and fluorescent bulbs on a 12-hour light-dark cycle. Colonies produced white-pink mycelia with a dark red pigment on the undersides. Conidia collected after 7-9 days were falcate and septate (5 to 6). No microconidia were produced. Macroconidia measured 35.4-49.7 µm x 3.4-5.8 µm (n=50). The strains produced blue-black fertile perithecia on carrot agar when induced according to the method of (Bowden and Leslie, 1999). To confirm pathogenicity, flowers of hemp cultivars 'Lifter', 'Trump Towers', 'Wife' and 'White CBG' were inoculated in the greenhouse with a representative fungal strain (20Hemp010). Plants were inoculated at two different stages: when the styles were still green or after they had become senescent. Macroconidia were collected from 7- to 9-day-old cultures grown under a 12-hour light-dark cycle. Plants were spray-inoculated with a 5 x 105 per ml conidial suspension in 0.05% Tween 20 until runoff. Flower heads were individually covered with clear plastic bags and incubated for 72 h at 95-100% humidity under greenhouse benches to avoid direct light. Bags were removed after 72 h and returned to the bench. Greenhouse conditions were 23-25°C with a 14-hour photoperiod and 50% RH. Symptoms developed 7 dai in 1% of the flowers inoculated when styles were green, and 36% of the flowers that had senescent styles. Symptoms were similar to those initially noticed in Boyle County, including necrotic flower bracts and sugar leaves, and visible fungal growth. Symptoms were more severe on plants inoculated when styles were necrotic. Recovered fungi were morphologically similar to 20Hemp010. Genomic DNA was extracted from the mycelium with the Zymo Research Quick-DNA Fungal/Bacterial Miniprep Kit. A fragment of the translation elongation factor 1-alpha 1 gene was amplified with primers EF1 and EF2 as described by (O'Donnell et al. 1998). Amplicons were sequenced and the consensus (MZ407909) was compared with the NCBI GenBank Refseq database by BLASTn. The top hit was Fusarium graminearum with 100% identity (JF270185.1). Pairwise alignments via MycoBank Fusarium MLST and Fusarium-ID also revealed a top hit of F. graminearum with 100% identity (AY452957.1). Conidial and colony morphology were also consistent with F. graminearum (Leslie and Summerell, 2006), thus we conclude that this species was the causal agent of the flower blight and mold. The same disease was subsequently confirmed on hemp in Breathitt and Franklin Counties in KY in 2020. This is the first report of this disease in KY, although F. graminearum has been reported previously causing a similar flower blight on hemp in NY and NC (Bergstrom et al., 2019, Thiessen et al. 2020). Fusarium graminearum is common in KY as a cause of Fusarium head blight on wheat and Gibberella ear rot on corn. In cereals, fungal infection is facilitated by the production of the mycotoxin deoxynivalenol (DON), which is harmful to humans and livestock (Desjardins and Hohn, 1997). As hemp production in Kentucky continues to rise for production of CBD products and edible grains, accumulation and concentration of DON in these products could become a concern.

Presence and Correlation of Fusarium graminearum and Deoxynivalenol Accumulation in Silage Corn Plant Parts.

Corn silage, made from Zea mays, is a high-energy feed that is important for feeding dairy cows. Plant diseases, such as those caused by Fusarium graminearum, can decrease silage corn yields and quality. F. graminearum (teleomorph Gibberella zeae) is an ascomycete fungus that causes Gibberella ear and stalk rot in corn. F. graminearum produces deoxynivalenol (DON), a secondary metabolite toxic to humans and animals. An understanding of the distribution of DON and F. graminearum throughout the corn plant is important for determining the quality of corn silage. A partitioned sample experiment that included two brown midrib silage hybrids and three fungicide treatments was conducted in research plots located in Arlington, WI, U.S.A., in 2018 and 2019. At harvest, stalk and ear parts were physically separated, dried, and ground for analysis. DON concentration (in parts per million) was determined using an enzyme-linked immunosorbent assay, and F. graminearum DNA concentration (in picograms per nanogram) was determined using quantitative PCR. DON and F. graminearum DNA were detected in all samples, demonstrating accumulation of the fungus in stalks and ears of the plant. In 2018, DON contamination was as high as 30 ppm and varied drastically between stalks and ears. In 2019, DON concentrations were much lower (<5 ppm), but were consistently higher in stalk samples than ear samples. Across all samples, DON concentrations and F. graminearum accumulation were highly correlated within the separated stalk (r = 0.78) and ear portions (r = 0.87) but were not correlated between ears and stalks. Depending on the weather and planting conditions in a given year, stalk infections or ear infections may occur by F. graminearum, leading to subsequent DON increases in those respective parts that are independent of each other.

Logistic Models Derived via LASSO Methods for Quantifying the Risk of Natural Contamination of Maize Grain with Deoxynivalenol.

Models were developed to quantify the risk of deoxynivalenol (DON) contamination of maize grain based on weather, cultural practices, hybrid resistance, and Gibberella ear rot (GER) intensity. Data on natural DON contamination of 15 to 16 hybrids and weather were collected from 10 Ohio locations over 4 years. Logistic regression with 10-fold cross-validation was used to develop models to predict the risk of DON ≥1 ppm. The presence and severity of GER predicted DON risk with an accuracy of 0.81 and 0.87, respectively. Temperature, relative humidity, surface wetness, and rainfall were used to generate 37 weather-based predictor variables summarized over each of six 15-day windows relative to maize silking (R1). With these variables, least absolute shrinkage and selection operator (LASSO) followed by all-subsets variable selection and logistic regression with 10-fold cross-validation were used to build single-window weather-based models, from which 11 with one or two predictors were selected based on performance metrics and simplicity. LASSO logistic regression was also used to build more complex multiwindow models with up to 22 predictors. The performance of the best single-window models was comparable to that of the best multiwindow models, with accuracy ranging from 0.81 to 0.83 for the former and 0.83 to 0.87 for the latter group of models. These results indicated that the risk of DON ≥1 ppm can be accurately predicted with simple models built using temperature- and moisture-based predictors from a single window. These models will be the foundation for developing tools to predict the risk of DON contamination of maize grain.

The Dominance of Fusarium meridionale Over F. graminearum Causing Gibberella Ear Rot in Brazil May Be Due to Increased Aggressiveness and Competitiveness

In Brazil, Gibberella ear rot (GER) of maize is caused mainly by Fusarium meridionale (Fmer), while F. graminearum (Fgra) is a minor contributor. To test the hypothesis that Fmer is more aggressive than Fgra on maize, six experiments were conducted in the south (summer), and one in the central-south (winter), totaling seven conditions (year ✕ location ✕ hybrid). Treatments consisted of Fgra or Fmer (two isolates of each) inoculated once four days after silk; inoculated sequentially and alternately (Fgra⇾Fmer or Fmer⇾Fgra) six days apart; or (in the central-south) inoculated sequentially without alternating species (Fmer⇾Fmer or Fgra⇾Fgra). Overall, severity was two times greater in the south (37.0%) where summer temperatures were warmer (20 to 25oC) than in central-south. In the south, severity was greatest in Fmer treatments (67.8%); followed by Fmer⇾Fgra (41.1%); then Fgra⇾Fmer (19.4%); and lowest in Fgra (2.1%), suggesting an antagonistic relationship. In the central-south (15 to 20oC), severity was generally higher in the sequential non-alternating inoculation treatments (Fmer⇾Fmer or Fgra⇾Fgra) than when either species was inoculated only once. Only nivalenol (NIV) or deoxynivalenol (DON) were detected when Fmer or Fgra, respectively, were inoculated singly, or sequentially with no alternation. Both toxins were found in grains harvested from the Fmer⇾Fgra treatment, while only NIV was found in kernels from the Fgra⇾Fmer treatment, suggesting that Fmer was more competitive than Fgra in co-inoculations. The dominance of Fmer as a cause of GER in Brazil may be due in part to its higher aggressiveness and competitiveness compared with Fgra.

CO477, CO478, CO479, and CO480 inbred lines

CO477, CO478, CO479, and CO480 are mid- to late-season [75–81 d to flowering, crop heat units (CHU) = 1720–1855] corn (Zea mays L.) inbred lines with high stalk sugar levels. The level of sugar in the stalks are very high especially when grown as inbred lines. On average, the inbred lines yield three times more sugar than their testcrosses. These inbred lines are the first to be developed and released for biofuel production, from the corn breeding program of Agriculture and Agri-Food Canada. Additionally, these inbred lines can be used for sugar and (or) silage production. They have moderate to intermediate resistance to common rust, eyespot, northern corn leaf blight and fusarium stalk rot but are susceptible to gibberella ear rot.

Mapping and Validation of a Stable Quantitative Trait Locus Conferring Maize Resistance to Gibberella Ear Rot.

Gibberella ear rot (GER), a prevalent disease caused by Fusarium graminearum, can result in significant yield loss and carcinogenic mycotoxin contamination in maize worldwide. However, only a few quantitative trait loci (QTLs) for GER resistance have been reported. In this study, we evaluated a Chinese recombinant inbred line (RIL) population comprising 204 lines, developed from a cross between a resistant parent DH4866 and a susceptible line T877, in three field trials under artificial inoculation with F. graminearum. The RIL population and their parents were genotyped with an Affymetrix microarray CGMB56K SNP Array. Based on the genetic linkage map constructed using 1,868 bins as markers, 11 QTLs, including five stable QTLs, were identified by individual environment analysis. Joint multiple environments analysis and epistatic interaction analysis revealed six additive and six epistatic (additive × additive) QTLs, respectively. None of the QTLs could explain more than 10% of phenotypic variation, suggesting that multiple minor-effect QTLs contributed to the genetic component of resistance to GER, and both additive and epistatic effects contributed to the genetic architecture of resistance to GER. A novel QTL, qGER4.09, with the largest effect, identified and validated using 588 F2 individuals, was colocalized with genomic regions for Fusarium ear rot and Aspergillus ear rot, indicating that this genetic locus likely confers resistance to multiple pathogens and can potentially be utilized in breeding maize varieties aimed at improving the resistance not only to GER but also other ear rot diseases.

Variance Components and Correlations between Doubled Haploid Lines from Two European Flint Landraces and Their Corresponding Testcrosses for Gibberella Ear Rot Resistance, Silking Time, and Plant Height in Maize

Predicting the resistance of hybrids from lines is a relevant approach for accelerating the improvement of disease resistance in hybrid breeding. In this study, genetic variation and covariation among 76 DH lines from two flint landraces, Kemater (KE) and Petkuser (PE), and their corresponding testcrosses (TC) were estimated for the first time for this material for Gibberella ear rot (GER), days to silking (DS), and plant height (PHT). Lines and TC were evaluated in four and two environments, respectively, under artificial infection with GER. TC were, on average, 42% less GER infected than their lines. TC matured 3–4 days earlier and were about 110 cm taller than the lines. GER resistance was 10% higher in KE lines and TC than PE lines and TC. Significant (p &lt; 0.001) genotypic and genotype-by-environment interaction variances were found for all traits. Genotypic variances were generally smaller among TC than lines. Broad-sense heritability estimates were moderate to high for GER severity (0.56–0.82) and high for DS (0.78–0.88) and PHT (0.86–0.94) with higher values always observed in lines. Significant, moderate correlations between TC and line per se performance were found for GER resistance in both KE and PE (r = 0.37 and 0.55, respectively). For the two agronomic traits, correlations were higher (r = 0.59–0.76) than for GER resistance. Genomic prediction accuracies were moderate to high for GER resistance (r = 0.49–0.63) and generally higher for DS and PHT. In conclusion, a pre-selection of DH lines for GER resistance should be feasible; however, TC should be additionally tested on a later selection stage to aim for GER-resistant hybrid cultivars.

Multi-parent QTL mapping reveals stable QTL conferring resistance to Gibberella ear rot in maize

Maize production is on risk by Gibberella ear rot (GER) caused by Fusarium graminearum. This is one of the most important ear rot diseases in temperate zones as it leads to yield losses and production of harmful mycotoxins. We investigated, for the first time, the potential use of Brazilian tropical maize to increase resistance levels to GER in temperate European flint germplasm by analyzing six interconnected biparental populations. We assessed GER symptoms in Brazil and in Europe in up to six environments (= location × year combinations) during the growing seasons of 2018 and 2019. We conducted multi-parent QTL and biparental QTL mapping, and identified four QTLs with additive gene action, each explaining 5.4 to 21.8% of the total genotypic variance for GER resistance. Among them, QTL q1 was stable across test environments, populations, and between inbred lines and testcrosses. The accuracies of genomic prediction ranged from 0.50 to 0.59 depending on the resistance donor and prediction model. Jointly, our study reveals the potential use of Brazilian resistance sources to increase GER resistance levels by genomics-assisted breeding.

Exploiting genetic diversity in two European maize landraces for improving Gibberella ear rot resistance using genomic tools

Key messageHigh genetic variation in two European maize landraces can be harnessed to improve Gibberella ear rot resistance by integrated genomic tools.Fusarium graminearum (Fg) causes Gibberella ear rot (GER) in maize leading to yield reduction and contamination of grains with several mycotoxins. This study aimed to elucidate the molecular basis of GER resistance among 500 doubled haploid lines derived from two European maize landraces, “Kemater Landmais Gelb” (KE) and “Petkuser Ferdinand Rot” (PE). The two landraces were analyzed individually using genome-wide association studies and genomic selection (GS). The lines were genotyped with a 600-k maize array and phenotyped for GER severity, days to silking, plant height, and seed-set in four environments using artificial infection with a highly aggressive Fg isolate. High genotypic variances and broad-sense heritabilities were found for all traits. Genotype-environment interaction was important throughout. The phenotypic (r) and genotypic ({r}_{g}) correlations between GER severity and three agronomic traits were low (r = − 0.27 to 0.20; {r}_{g}hspace{0.17em}= − 0.32 to 0.22). For GER severity, eight QTLs were detected in KE jointly explaining 34% of the genetic variance. In PE, no significant QTLs for GER severity were detected. No common QTLs were found between GER severity and the three agronomic traits. The mean prediction accuracies (rho ) of weighted GS (wRR-BLUP) were higher than rho of marker-assisted selection (MAS) and unweighted GS (RR-BLUP) for GER severity. Using KE as the training set and PE as the validation set resulted in very low rho that could be improved by using fixed marker effects in the GS model.

Natural Occurrence of Maize Gibberella Ear Rot and Contamination of Grain with Mycotoxins in Association with Weather Variables.

Gibberella ear rot (GER) severity (percent area of the ear diseased) and associated grain contamination with mycotoxins were quantified in plots of 15 to 16 maize hybrids planted at 10 Ohio locations from 2015 to 2018. Deoxynivalenol (DON) was quantified in grain samples in all 4 years, whereas nivalenol, 3-acetyldeoxynivalenol, and 15-acetyldeoxynivalenol (15ADON) were quantified only in the last 2 years. Only DON and 15ADON were detected. The highest levels of GER and DON contamination were observed for 2018, followed by 2016 and 2017. No GER symptoms or DON were detected in 2015. Approximately 41% of the samples from asymptomatic ears had detectable levels of DON, and 7% of these samples from 2016 had DON > 5 ppm. Associations between DON contamination and 43 variables representing summaries of temperature (T), relative humidity (RH), rainfall (R), surface wetness, and T-RH combinations for different window lengths and positions relative to R1 growth stage were quantified with Spearman correlation coefficients (r). Fifteen-day window lengths tended to show the highest correlations. Most of the variables based on T, R, RH, and T-RH were significantly correlated with DON for the 15-day window, as well as other windows. For moisture-related variables, there generally was a negative correlation before R1, changing to a positive correlation after R1. Results showed that GER and DON can be frequently found in Ohio maize fields, with the risk of DON being associated with multiple weather variables, particularly those representing combinations of T between 15 and 30°C and RH > 80 summarized during the 3 weeks after R1.

Stability of Hybrid Maize Reaction to Gibberella Ear Rot and Deoxynivalenol Contamination of Grain.

Trials were conducted to quantify the stability (or lack of G × E interaction) of 15 maize hybrids to Gibberella ear rot (GER; caused by Fusarium graminearum) and deoxynivalenol (DON) contamination of grain across 30 Ohio environments (3 years × 10 locations). In each environment, one plot of each hybrid was planted and 10 ears per plot were inoculated via the silk channel. GER severity (proportion of ear area diseased) and DON contamination of grain (ppm) were quantified. Multiple rank-based methods, including Kendall's concordance coefficient (W) and Piepho's U, were used to quantify hybrid stability. The results found insufficient evidence to suggest crossover G × E interaction of ranks, with W greater than zero for GER (W = 0.28) and DON (W = 0.26), and U not statistically significant for either variable (P > 0.20). Linear mixed models (LMMs) were also used to quantify hybrid stability, accounting for crossover or noncrossover G × E interaction of transformed observed data. Based on information criteria and likelihood ratio tests for GER and DON response variables, the models with more complex variance-covariance structures-heterogeneous compound symmetry and factor-analytic-provided a better fit than the model with the simpler compound symmetry structure, indicating that one or more hybrids differed in stability. Overall, hybrids were stable based on rank-based methods, which indicated a lack of crossover G × E interaction, but the LMMs identified a few hybrids that were sensitive to environment. Resistant hybrids were generally more stable than susceptible hybrids.

QTL mapping of resistance to Gibberella ear rot in maize

Gibberella ear rot (GER), caused by the fungal pathogen Fusarium graminearum, is becoming one of the most prominent pathogens responsible for ear rot in maize. In this study three F2 populations, F2-C, F2-D, and F2-J, and their corresponding F2:3 families, were constructed by crossing three highly GER-resistant inbred lines—Cheng351, Dan598, and JiV203—with the susceptible line ZW18. We used this cross for genetic analysis and QTL mapping of resistance to GER. Analysis of variance of GER in the three F2 populations revealed the presence of significant differences among genotypes and between locations. The broad-sense heritability (H2) of GER resistance was estimated to be 0.68, 0.63, and 0.64 in the three F2 populations, indicating that genetic factors play a key role in the development of phenotypic variation. Seventeen QTLs conferring resistance to GER were detected in the three F2 populations, among which the QTL qRger7.1, originating from the resistant parent Cheng351, explained 20.16–41.84% of the phenotypic variation. The physical support interval of qRger7.1 exhibited approximately 2 Mb overlap with that of qRger7.2, which was derived from the resistant parent Dan598, supporting the identification of potential “hotspots” of the target QTLs. QTLs derived from the resistant parents Dan598 and JiV203 accounted for 59.67–61.28% and 65.82–66.90%, respectively, of the phenotypic variation. The GER-resistant QTLs identified in this study are useful candidates for improving the resistance to GER in maize using molecular marker-assisted selection.

QTL mapping for resistance to ear rot caused by Fusarium graminearum using an IBM Syn10 DH population in maize

Gibberella ear rot (GER) caused by Fusarium graminearum (teleomorph Gibberella zeae), is one of the most devastating diseases in maize that not only severely reduces grain yield but also contaminates the kernels with potent mycotoxins which is harmful to livestock and humans. Identification of stable quantitative trait loci (QTL) and candidate genes conferring resistance is a promising strategy in resistance breeding programs for the disease. Here, the ten times intermated B73 × Mo17-doubled haploid (IBM Syn10 DH) population comprising a total of 298 diverse maize inbred lines were subjected to phenotypic evaluation in a 2-year field test across two environments, and the IBM Syn10 DH population were employed to detect QTL across multiple environments using an ultra-high-density bin map. Ten QTL were detected on chromosomes 1, 2, 3, 6, 7, 8, and 9, respectively. Of them, a major QTL on chromosome 7, named qGRfg7, could explain 33.26% of the phenotypic variation. Based on fine-mapping strategy, we narrowed down the interested region into 91 kb, flanked by two developed Indel markers. A predicted gene in the mapped region, encoding a lipopolysaccharide-binding protein (LBP), is suggested to be a candidate gene conferring resistance to GER disease. These results will facilitate the breeding process for GER resistance by marker-assisted selection (MAS) in maize.

CO475 corn inbred line

CO475 is an early-medium maturity (75 d to flowering), mostly Iodent, yellow semi-dent inbred that combines well with several testers in many different locations. It has moderate resistance to gibberella ear rot (both the inbred and in hybrid combinations) and intermediate response to smut, Fusarium stalk rot, northern leaf blight, eyespot, rust, and goss’s wilt.

Fusarium graminearum populations from maize and wheat in Ontario, Canada

Ontario has suffered widespread epidemics ofFusarium Head Blight orGibberella Ear Rot roughly every five years since the late 1970s. We undertook a study of the chemotype and genotype ofFusarium graminearum isolated from 1,800 samples of wheat and maize collected across the cereal growing areas over three years. 468 isolates obtained were genotyped and 60 were selected for chemotyping. The dominant genotype has remained the native 15-acetyldeoxynivalenol (15-ADON) population. Approximately 20% of the strains tested were of the native chemotype producing only 15-ADON and one strain producing solely 7α-hydroxy,15-deacetylcalonectrin (3ANX) was observed. The majority of the 15-ADON strains were also capable of producing 3ANX. There was consistent mismatch between chemotype and genotype. This reflects the considerable plasticity in the genes associated with trichothecene biosynthesis documented in severalFusarium species. Although there is a large gradient in climate from southern to eastern Ontario, we did not detect differences in the distribution of the chemotypes. Grain from which strains were isolated for chemotyping were analysed. Approximately half of the 53 samples had &gt;2 mg/kg deoxynivalenol with a maximum of 400 mg/kg and median of 14 mg/kg. 7α-hydroxy,3,15-dideacetylcalonectrin (NX toxin) was detected in three of these samples at an average of 4.5 mg/kg. The stability of theF. graminearum genotype in Ontario can be explained by several factors. Since 1980, the area planted to maize has remained stable, however, the area given to wheat has about doubled. Minimum tillage was rare in 1980 but it is now the norm. Increased crop residue on the soil has greatly increased the biomass of ascocarps that overwinter. Overall, these data demonstrate the need to monitor the mycotoxins inFusarium populations and for the need to consider the potential toxicity of NX in the feed supply.

Effect of seed biopriming with Trichoderma harzianum strain INAT11 on Fusarium ear rot and Gibberella ear rot diseases

Fusarium ear rot (FER) and Gibberella ear rot (GER) are common fungal diseases of maize responsible for yield losses and reduced kernel quality due to contamination by mycotoxins. Since no chemical treatments are available to control Fusarium disease in maize, biological control could represent a promising sustainable strategy. A commercial strain of Trichoderma harzianum (INAT11) was evaluated for its ability to antagonize Fusarium verticillioides and Fusarium graminearum and to reduce disease symptoms in plants through induction of a systemic resistance response in maize. Infection trials on maize plants under controlled greenhouse conditions showed that INAT11 applied to seeds is capable of reducing both F. verticillioides and F. graminearum disease incidence (37.1% and 30.7%, respectively) and severity (32.6% and 43.4%, respectively). Field trials performed under natural infection conditions showed a reduction in deoxynivalenol contamination in kernels, while no effect on fumonisin contamination was observed. The expression patterns of some defence-related genes belonging to both the ISR (LOX10, AOS, HPL and OPR8) and SAR pathways (PAL and PR1) indicated the upregulation of some ISR and SAR markers. These upregulations occurred at different levels likely related to the lifestyle of these two fungal pathogens.

Fusarium species and mycotoxin contamination in maize in Buenos Aires province, Argentina

Maize is one of the most important crops in Argentina. This crop can be affected by the presence of different Fusarium species, causing two distinct diseases known as Fusarium ear rot and Gibberella ear rot. In this study, a total of 90 samples from commercial fields of Buenos Aires province in Argentina were collected during the 2015, 2016 and 2017 harvest seasons with the aim to evaluate Fusarium species presence, mycotoxin content and to establish a relationship between the main Fusarium mycotoxins infecting maize grains and the environmental conditions. The results showed that F. verticillioides was the most isolated species followed by F. subglutinans, species of Fusarium graminearum species complex, F. proliferatum, and F. cerealis varying their presence according to the harvest season evaluated. Regarding mycotoxins, deoxynivalenol and 3-acetyl-deoxynivalenol showed content from 281.26 ± 22.51 to 359.02 ± 42.57 μg/kg in the 3 yrs evaluated, while 15-acetyl-deoxynivalenol, nivalenol, and zearalenone were not found. With regard to B1 and B2 fumonisins, these mycotoxins were detected below the detection limit of 0.3 μg/kg in some maize samples in the 3 yrs. The selection of maize genotypes, cultural practices, and climatic conditions could be responsible for the Fusarium species found and their respective mycotoxin production. Due to worldwide concern about food security and the potential risk the global climate change could impart, it will be necessary to develop predictive models based on meteorological conditions to determine the risk of Fusarium presence and mycotoxin production in maize similar to those developed in other crops.

Transcriptomic responses in resistant and susceptible maize infected with Fusarium graminearum

Gibberella ear rot (GER) caused by Fusarium graminearum (teleomorph Gibberella zeae) is a common maize disease that not only severely reduces grain yield but also contaminates maize grain with mycotoxins. We investigated the molecular mechanism underlying the host defense responses against pathogen infection using comparative transcriptomic analysis. We injected F. graminearum spore suspensions into plants of resistant (IBM-81) and a susceptible (IBM-85) maize inbred line after pollination and performed RNA-seq 48, 72, and 96 h after inoculation. Respectively 487 and 410 differentially expressed genes (DEGs) were induced in the resistant and susceptible lines across three time points, indicating that a stronger defense response was activated in the resistant than in the susceptible line. Among them, 198 genes commonly induced in the two lines were subjected to pathway analysis, revealing that most of the DEGs were closely associated with defense and a wide range of metabolic activities. DEGs associated with pathogenesis-related protein 1 (PR1) and regulation of salicylic acid were significantly enriched during F. graminearum infection, suggesting that these DEGs play dominant roles in maize resistance to GER. Our results provide a resource for future gene discovery and facilitate elucidation of the complex defense mechanisms involved in resistance to GER.