Prevalence of Mycotoxins in Late-Season Corn Ear Molds in North Dakota

Widespread corn ear mold development in North Dakota and in other states was associated with cool, wet weather after physiological maturity in 2009. In response to concerns about possible grain mold and mycotoxin contamination in North Dakota, a survey of corn ear diseases was conducted in 2009 prior to harvest. Corn ears were collected from 94 field locations from 24 counties and were examined macroscopically and microscopically for mold identification. Mycotoxin testing was done with a screen for 17 tricothecenes using gas chromatography/mass spectrometry techniques. Cladosporium was the most commonly identified fungus with some Fusarium contaminated samples being observed. Other fungi identified include Alternaria, Penicillium, Aureobsidium, Rhizopus, Stemphylium and an unidentified non-pigmented fungus. Five mycotoxins were identified in 25 out of the 94 samples;deoxynivalenol, T-2, HT-2, zearalenone and nivalenol. Of the mycotoxin-positive samples, 88% had less than 2 ppm of any mycotoxin. Despite the growing season’s weather being favorable for corn ear mold development late in the season, observed mycotoxin levels were surprisingly low and most grain was deemed safe for use in food and feed channels. Surveys were planned in subsequent years, but late season molds did not develop in the 2010-2015 growing seasons.

Genome-wide association study and genomic prediction of Fusarium ear rot resistance in tropical maize germplasm

Fusarium ear rot(FER)is a destructive maize fungal disease worldwide.In this study,three tropical maize populations consisting of 874 inbred lines were used to perform genomewide association study(GWAS)and genomic prediction(GP)analyses of FER resistance.Broad phenotypic variation and high heritability for FER were observed,although it was highly influenced by large genotype-by-environment interactions.In the 874 inbred lines,GWAS with general linear model(GLM)identified 3034 single-nucleotide polymorphisms(SNPs)significantly associated with FER resistance at the P-value threshold of 1×10^(-5),the average phenotypic variation explained(PVE)by these associations was 3%with a range from 2.33%to 6.92%,and 49 of these associations had PVE values greater than 5%.The GWAS analysis with mixed linear model(MLM)identified 19 significantly associated SNPs at the P-value threshold of 1×10^(-4),the average PVE of these associations was 1.60%with a range from 1.39%to 2.04%.Within each of the three populations,the number of significantly associated SNPs identified by GLM and MLM ranged from 25 to 41,and from 5 to 22,respectively.Overlapping SNP associations across populations were rare.A few stable genomic regions conferring FER resistance were identified,which located in bins 3.04/05,7.02/04,9.00/01,9.04,9.06/07,and 10.03/04.The genomic regions in bins 9.00/01 and 9.04 are new.GP produced moderate accuracies with genome-wide markers,and relatively high accuracies with SNP associations detected from GWAS.Moderate prediction accuracies were observed when the training and validation sets were closely related.These results implied that FER resistance in maize is controlled by minor QTL with small effects,and highly influenced by the genetic background of the populations studied.Genomic selection(GS)by incorporating SNP associations detected from GWAS is a promising tool for improving FER resistance in maize.

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.

Gene-Ontology Analysis on the Differentially Expressed Genes in Maize （Zea mays L.） Ear Rot

To better know FM （Fusarium moniliforme） induced genes in maize ear rot, GO （gene ontology） method was performed to analyze detail physiological functions in the defensive response after pathogen infection. This gene annotation system was widely used to investigate large numbers of genes involving in real active role or regulator in cell response. First of all, differentially expressed genes were isolated by using genechip platform at 96 h post-inoculation with FM in maize inbred Bt-1. In total, 482 differentially expressed unique genes were screened out in inbred Bt-1 when compared to mock-inoculated bract tissues. Then, each gene was annotated to define functional class by GO method. Finally, these large FM-responsive genes with significant differentially change were sorted into cellular component, molecular function and biological process with complicated network by molecular annotation system. The demonstrated information in the GO analysis could provide another view for understanding the molecular mechanism and indicate a deeply complicated network with gene function underlying disease development in the host tissue. The findings in this study provide important bases to probe the molecular processes, the alteration of metabolism and the immune mechanism upon the FM infection in maize.

Anatomical Study on Maize Filaments Infected by Fusarium proliferatum

Conidia of Fusarium proliferatum infected epidermal cells of stigma, hairs and filaments on maize when sprayed on maize filament. Hyphae of F. proliferatum extended along with the parenehyma and vascular cells in the filaments, and infected toward ovary. Both the parenchyma cells and the epidermal cells were wrinkled, and the filament was deformed. The result showed that F. proliferatum could infect filaments directly and cause maize ear rot through filament channel.

The Beneficial Effect of Trichoderma spp. in Seed Treatment of Four Maize (Zea mays L.) Genotypes

Maize is the main crop for Mexicans;however, it is affected by species of fungi causing ear rot. This research aimed to evaluate the effect of T. asperellum T11, T. harzianum T1 4 y T. longibrachiatum T1 40 on some agronomic variables of four maize genotypes. The seeds of the genotypes H-515, Zapata 7, and H-507 were treated with a suspension of Trichoderma spp. to 1 × 108 spores mL-1, using a control (untreated seed), and Benomyl as chemical control. The planting was in Morelos, in a completely random block design with a factorial arrangement. The ear rot was natural. Data were obtained at the end of the crop cycle and processed in SAS 9.4®. H-515 genotype had the greatest effect on the treatment of maize seeds with Trichoderma spp. (5.562 kg);T. asperellum T11 was the strain that stood out with a mean yield of 50 ears in an area of 16 m2 of 4.904 kg, and control of 4.448 kg. Our results are an economic option for farmers to contemplate the use of Trichoderma and obtain its benefits.

MicroRNAs Are Involved in Maize Immunity Against Fusarium verticillioides Ear Rot

Fusarium ear rot(FER)caused by Fusarium verticillioides is one of the most common diseases affecting maize production worldwide.FER results in severe yield losses and grain contamination with health-threatening mycotoxins.Although most studies to date have focused on comprehensive analysis of gene regulation in maize during defense responses against F.verticillioides infection,less is known about the role of micro RNAs(mi RNAs)in this process.We used deep sequencing to compare small RNA libraries from the maize kernels of susceptible(N6)or resistant(BT-1)inbred lines from uninfected plants and upon F.verticillioides infection.We found that pathogen exposure was accompanied by dynamic alterations in expression levels of multiple mi RNAs,including new members of previously annotated mi RNA families.A combination of transcriptomic,degradomic,and bioinformatics analyses revealed that F.verticillioides-responsive mi RNAs and their potential target genes displayed opposite expression patterns in the susceptible and resistant genotypes.Functional category analysis uncovered preferential enrichment of the pathogen-responsive mi RNAs and their targets in the phenylpropanoid metabolic processes,plant–pathogen interactions,and plant phytohormone signal transduction pathways.Furthermore,transgenic maize plants overexpressing mi R408 b exhibited reduced resistance to F.verticillioides infection in a susceptible maize line.These findings provide new insights into the regulatory roles of mi RNAs in maize immunity against FER and new resources for breeding disease resistance into maize.

A field-deployable method for single and multiplex detection of DNA or RNA from pathogens using Cas12 and Cas13

For some Cas nucleases,trans-cleavage activity triggered by CRISPR/Cas-mediated cis-cleavage upon target nucleic acid recognition has been explored for diagnostic detection.Portable single and multiplex nucleic acid-based detection is needed for crop pathogen management in agriculture.Here,we harnessed and characterized RfxCas13d as an additional CRISPR/Cas nucleic acid detection tool.We systematically characterized AsCas12a,LbCas12a,LwaCas13a,and RfxCas13d combined with isothermal amplification to develop a CRISPR/Cas nucleic acid-based tool for single or multiplex pathogen detection.Our data indicated that sufficient detection sensitivity was achieved with just a few copies of DNA/RNA targets as input.Using this tool,we successfully detected DNA from Fusarium graminearum and Fusarium verticillioides and RNA from rice black-streaked dwarf virus in crude extracts prepared in the field.Our method,from sample preparation to result readout,could be rapidly and easily deployed in the field.This system could be extended to other crop pathogens,including those that currently lack a detection method and have metabolite profiles that make detection challenging.This nucleic acid detection system could also be used for single-nucleotide polymorphism genotyping,transgene detection,and qualitative detection of gene expression in the field.