Susceptibility of Maize to Stalk Rot Caused by Fusarium graminearum Deoxynivalenol and Zearalenone Mutants

A Comprehensive Review of Hypotheses About the Biological Function of Zearalenone, and a New Hypothesis for the Function of Resorcylic and Dihydroxyphenylacetic Macrolactones in Fungi

The special metabolite of Fusarium spp. zearalenone (ZEN) exerts estrogenic effects on mammals, stimulates plant growth, stimulates sexual development in fungi, and inhibits fungal growth. These activities inspired hypotheses about the biological function of ZEN. We briefly review the discovery of ZEN and its implications. The main subject of this review is a critical assessment of the hypotheses that ZEN is a fungal hormone, a plant hormone, a virulence factor, or a fungal defense metabolite. Conceptual and technical issues related to testing these hypotheses, such as inadequate analytical methods, confusion of incidental effects with biological functions, and lack of normalization, are illuminated. Based on these considerations, gene knockout experiments, and on the effects of biotic interactions on ZEN synthesis, we argue that ZEN is a defense metabolite protecting Fusarium spp. against mycoparasites and competitors. Similar reasoning and published data suggest that the Fusarium metabolite fusaristatin A fulfils the same function. Fungi produce many macrolactones of resorcylic acid (RALs) and dihydroxyphenylacetic acid (DHPLs) with properties similar to ZEN. Their widespread occurrence, antifungal activity, and further considerations prompt us to hypothesize that the fundamental function of fungal RALs and DHPLs lies in defense and interference competition.

Genetic and Genomic Tools in Breeding for Resistance to Fusarium Stalk Rot in Maize (Zea mays L.)

Maize (Zea mays L.) is the world's most productive cereal crop, yet it is threatened by several diseases. Among them, Fusarium stalk rot (FSR) causes an average global yield loss of 4.5%. The mycotoxins deoxynivalenol, zearalenone, fumonisins, and moniliformin persist in grain and silage after harvest and pose a risk to human and animal health. This review describes the lifestyle of the fungal pathogens that cause FSR, studies how to optimize resistance evaluation, identifies quantitative trait loci (QTLs) and candidate genes (CGs), and, finally, considers the methods for selecting FSR resistance, especially through genomic selection. To screen maize genotypes for FSR resistance, several artificial inoculation methods have been employed in most studies, including toothpick insertion, ball-bearing pellets, root infection, and the oat kernel method. However, these methods have several limitations in effectively inducing FSR disease infection. Needle injection of inoculum into the stem is recommended, especially when combined with a quantitative or percentage scale because it effectively phenotypes maize populations for FSR resistance. Nine studies with larger populations (≥150 progenies) investigated the genetic architecture of FSR resistance. The inheritance is clearly quantitative. Four major QTLs and several minor QTLs are reported to confer resistance to FSR pathogens, and a few CGs have been identified. Genomic selection is recommended as an effective method for developing routinely FSR-resistant maize, but only two studies have explored this area. An omics analysis (proteomics, transcriptomics, and metabolomics) of the expression of candidate genes should validate their role in FSR resistance, and their use might accelerate selection.

Root-associated microbial diversity and metabolomics in maize resistance to stalk rot

As one of the three major food crops in the world, maize plays a significant role in alleviating the food crisis. Maize stalk rot can reduce maize yield and mechanical harvesting efficiency. In addition, mycotoxins such as Deoxynivalenol (DON) and Zearalenone (ZEN) produced by maize stalk rot pathogens can also harm livestock and human health. Maize stalk rot is an infection of the whole growth period, and there are no effective control measures at present. Therefore, it is of great significant to study the pathogenesis and control mechanism of stalk rot from multiple perspectives. In the present study, root and rhizosphere soil of disease-resistant inbred line Y853 and disease-susceptible inbred line Q478 were collected at the dough stage (R4) and maturity stage (R6) of maize, respectively. The effects of resistant/susceptible inbred line on soil microorganisms were analyzed by amplicon sequences and metabolomics. The results showed that there was different microbial community composition from different inbred lines in different growth stages. Specifically, the abundance of Arthrobacter, Streptomyces and Bacillus in R4 rhizosphere soil was higher than that of R6, while the rhizosphere fungal composition of LR853 was significantly different from that of the other three compartments. Co-occurrence network analysis showed that the pathogen Fusarium had the highest degree centrality and closeness centrality in the DR478. Moreover, metabolomics analysis showed that four main metabolic pathways were significantly enriched, and 15 metabolites were upgrade in resistant inbred line. Furthermore, microbes, especially fungi, also were related to these 15 metabolites. Our results revealed that maize resistance to stalk rot is closely related to root-associated microbiota and rhizospheric metabolites, which would be a new perspective of phytopathogenic biocontrol.

Effect of Fungicide Application and Corn Hybrid Class on the Presence of Fusarium graminearum and the Concentration of Deoxynivalenol in Ear and Stalk Parts of Corn (Zea mays) Used for Silage

In Wisconsin, the use of brown midrib (BMR) corn (Zea mays) hybrids for ensiling and subsequent feeding to dairy cows is quite common. The overall milk production from cows fed silage from BMR hybrids is typically higher than those fed silage made from dual-purpose hybrids. Gibberella diseases (ear and stalk rot) caused by Gibberella zeae (anamorph; Fusarium graminearum) and the accompanying accumulation of the mycotoxin deoxynivalenol (DON) can be significant issues during the field production of BMR hybrids. The work presented here aimed to understand the role of hybrid class on the distribution of F. graminearum DNA and DON in the ear and stalk parts of corn for silage. An ear and stalk partitioned sample experiment was conducted on silage corn from field trials in Arlington, Wisconsin, in 2020 and 2021. The trials were arranged in a randomized complete block design in both years, including one BMR hybrid, one dual-purpose hybrid, and seven fungicide application regimes. Paired ear and stalk samples were physically separated, dried, and ground at harvest before determining the concentration of F. graminearum DNA and DON in each sample. Across both years, the main effects of hybrid, treatment, and plant part were not significant (P > 0.1) on DON concentration. However, the hybrid-by-plant part interaction effect was significant (P < 0.01). Ears of the BMR hybrid accumulated the most DON, whereas the dual-purpose hybrid ears had the lowest DON concentration. The concentrations of DON and F. graminearum DNA were significantly (P < 0.01) and highly correlated in the ear (r = 0.73) but not in the stalk (r = 0.09, P = 0.33). These findings suggest that DON accumulation in the corn ear is a major contributor in the difference observed in the total DON between the hybrid classes. Therefore, growers and researchers are encouraged to focus production and breeding on hybrids in both classes that accumulate less DON in ears, resulting in lower total DON in corn chopped for silage.

Evaluation of Resistance Resources and Analysis of Resistance Mechanisms of Maize to Stalk Rot Caused by Fusarium graminearum

Stalk rot is one of the most destructive and widely distributed diseases in maize plants worldwide. Research on the performance and resistance mechanisms of maize against stem rot is constantly improving. In this study, among 120 inbred maize lines infected by Fusarium graminearum using the injection method, 4 lines (3.33%) were highly resistant to stalk rot, 28 lines (23.33%) were resistant, 57 lines (47.50%) were susceptible, and 31 lines (25.84%) were highly susceptible. The inbred lines 18N10118 and 18N10370 were the most resistant and susceptible with disease indices of 7.5 and 75.6, respectively. Treatment of resistant and susceptible maize inbred seedlings with F. graminearum showed that root hair growth of the susceptible inbred lines was significantly inhibited, and a large number of hyphae attached and adsorbed multiple conidia near the root system. However, the resistant inbred lines were delayed and inconspicuous, with only a few hyphae and spores appearing near the root system. Compared with susceptible inbred lines, resistant maize inbred line seedlings treated with F. graminearum exhibited elevated activities of catalase, phenylalanine ammonia-lyase, polyphenol oxidase, and superoxide dismutase. We identified 153 genes related to disease resistance by transcriptome analysis. The mitogen-activated protein kinase signaling and peroxisome pathways mainly regulated the resistance mechanism of maize inbred lines to F. graminearum infection. These two pathways might play an important role in the disease resistance mechanism, and the function of genes in the two pathways must be further studied, which might provide a theoretical basis for further understanding the molecular resistance mechanism of stalk rot and resistance gene mining.

Effects of the quantitative trait locus qPss3 on inhibition of photoperiod sensitivity and resistance to stalk rot disease in maize

KEY MESSAGE

We identified a quantitative trait locus, qPss3, and fine-mapped the causal locus to a 120-kb interval in maize. This locus inhibits the photoperiod sensitivity caused by ZmCCT9 and ZmCCT10, resulting in earlier flowering by 2 ~ 4 days without reduction in stalk-rot resistance in certain genotypes. Photoperiod sensitivity is a key factor affecting the adaptation of maize (Zea mays L.) to high-latitude growing areas. Although many genes associated with flowering time have been identified in maize, no gene that inhibits photoperiod sensitivity has been reported. In our previous study, we detected large differences in photoperiod sensitivity among maize inbred lines with the same photoperiod-sensitive allele at the ZmCCT10 locus. Here, we used two segregating populations with the same genetic backgrounds but different ZmCCT10 alleles to perform quantitative trait locus (QTL) analysis. We identified a unique QTL, qPss3, on chromosome 3 in the population carrying the sensitive ZmCCT10 allele. After sequential fine-mapping, we eventually delimited qPss3 to an interval of ~ 120 kb. qPss3 behaved as a dominant locus and caused earlier flowering by 2-4 days via inhibiting ZmCCT10-induced photoperiod sensitivity under long-day conditions. qPss3 also inhibited the photoperiod sensitivity induced by another flowering-related gene, ZmCCT9. For application in agriculture, an F₁ hybrid heterozygous at both qPss3 and ZmCCT10 loci constitutes an optimal allele combination, showing high resistance to stalk rot without a significant delay in flowering time. Moreover, qPss3 is of great value in regulating the flowering time of tropical maize grown at high-latitude regions.

Transcriptional differences between major Fusarium pathogens of maize, Fusarium verticillioides and Fusarium graminearum with different optimum growth temperatures

Fusarium verticillioides and Fusarium graminearum are important pathogens causing disease in maize (Zea mays) worldwide. The distributions of these fungal pathogens vary greatly in different regions and in different years, and are influenced by environmental and climatic conditions. Temperature has significant effects on the growth and mycotoxin production of Fusarium species. In this study, the effects of temperature on the growth and pathogenicity of F. verticillioides and F. graminearum were investigated. F. verticillioides grew fastest and exhibited the strongest pathogenicity to maize stems and grains at 30°C, while F. graminearum grew best at 20°C. Both species produced more toxins at 20°C than at 30°C. To explain the interspecific differences in the relationship of growth and temperature, RNA-seq was used to compare F. verticillioides and F. graminearum cultivated for 4 d at the optimum temperatures of 30°C and 20°C, respectively. Samples of F. verticillioides were also cultivated for 9 d (to maximize toxin production) at 20°C and 30°C and analyzed by RNA-seq to investigate the influence of temperature for different growth stages. The differently expressed genes (DEGs) were identified by comparison of cultures grown for the same amount of time but at different temperatures. GO enrichment analysis showed high enrichment of DEGs in categories of membrane part, catalytic activity, metabolic process, and growth at warmer temperature resulted in more down-regulated DEGs enriched in membrane components in all groups. KEGG analysis revealed enrichment of DEGs related to different temperatures in carbohydrate and amino acid metabolism pathways. For both species, there was decreased expression of many DEGs related to amino acid metabolism when cultivated at warm temperature, such as genes related to beta-alanine metabolism and arginine and proline metabolism. However, changes in genes related to glyoxylate and dicarboxylate metabolism and fatty acid degradation were more related to the growth state. The results showing different responses pattern of these pathways provides a foundation for further investigation of the molecular mechanisms underlying distinct thermal ecological niches of F. verticillioides and F. graminearum.

Maize stalk rot caused by Fusarium graminearum alters soil microbial composition and is directly inhibited by Bacillus siamensis isolated from rhizosphere soil

Maize stalk rot caused by Fusarium graminearum can reduce the yield of maize and efficiency of mechanized harvesting. Besides, deoxynivalenol and zearalenone toxins produced by F. graminearum can also affect domestic animals and human health. As chemical fungicides are expensive and exert negative effects on the environment, the use of biological control agents has become attractive in recent years. In the present study, we collected rhizosphere soil with severe stalk rot disease (ZDD), the rhizosphere soil with disease-free near by the ZDD (ZDH), and measured rhizosphere microbial diversity and microbial taxonomic composition by amplicon sequencing targeting either bacteria or fungi. The results showed that Fusarium stalk rot caused by the Fusarium species among which F. graminearum is frequent and can reduce the abundance and alpha diversity of rhizosphere microbial community, and shift the beta diversity of microorganisms. Furthermore, a bacterial strain, Bacillus siamensis GL-02, isolated from ZDD, was found to significantly affect growth of F. graminearum. In vitro and in vivo assays demonstrated that B. siamensis GL-02 had good capability to inhibit F. graminearum. These results revealed that B. siamensis GL-02 could be a potential biocontrol agent for the control of maize stalk rot.

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.

An Agro-Climatic Approach to Developing a National Prevention Tool for Deoxynivalenol in French Maize-Growing Areas

The levels of deoxynivalenol (DON)—a mycotoxin produced by Fusarium graminearum—in maize for food and feed are subject to European Union regulations. Obtaining a compliant harvest requires the identification of agronomic and climatic risk factors related to higher fungal contamination and DON production. A national, multiyear database for maize was created, based on field survey data collected from 2004 to 2020. This database contains information about agricultural practices, climatic sequences and DON content at harvest for a total of 2032 maize fields localized in the French maize-growing regions. A linear mixed-model approach highlighted the presence of borers, late harvest and inadequate crop residue management, normal-to-cold temperatures in March, humidity in August and the absence of a hot end of the maize development cycle with a dry August as creating conditions favoring maize contamination with DON. The various possible associations between these risky climatic conditions and agricultural practices were compared, grouped and ranked as related to very low to high DON concentrations. Some combinations may even exceed the regulatory threshold. The national prevention tool, created for producers and agricultural cooperatives, is informative and easy-to-use to control the sanitary quality of their harvest.

Species Diversity and Chemotypes of Fusarium Species Associated With Maize Stalk Rot in Yunnan Province of Southwest China

Maize stalk rot caused by Fusarium species is one of the most important fungal diseases of maize throughout the world. The disease is responsible for considerable yield losses and has also been associated with mycotoxin contamination of the crop. In this study, a survey of maize stalk rot was performed in seven locations of Yunnan Province in China during the cropping season of 2015 and 2016. Based on morphological and molecular characteristics, 204 isolates belonging to 12 Fusarium spp. from symptomatic stalks of maize were identified. Among the isolated strains, 83 were identified as Fusarium meridionale (40.5%), 46 as Fusarium boothii (22.5%), 34 as Fusarium temperatum (16.5%), 12 as Fusarium equiseti (5.9%), 10 as Fusarium asiaticum (4.9%), six as Fusarium proliferatum (3.0%), four as Fusarium verticillioides (2.0%), four as Fusarium incarnatum (2.0%), two as Fusarium avenaceum (1.0%), one as Fusarium cerealis (0.5%), one as Fusarium graminearum (0.5%), and one as Fusarium cortaderiae (0.5%). Fusarium cortaderiae was the first report on the causal agent of maize stalk rot disease in China. These isolates were divided into five chemotypes: nivalenol (NIV), deoxynivalenol (DON), beauvericin (BEA), zearalenone (ZEN), and fumonisin (FUM). Phylogenetic analysis based on partial sequences of the translation elongation factor 1α (TEF1-α) showed a high degree of interspecific polymorphisms among the isolates. Pathogenicity analysis on maize stalks indicated that all the 12 species of Fusarium were able to cause the disease symptoms with different aggressiveness. This study on population, pathogenicity, and toxigenic chemotypes of Fusarium species associated with maize stalk rot in Yunnan Province of southwest China, will help design an effective integrated control strategy for this disease.

Sweetpotato Root Development Influences Susceptibility to Black Rot Caused by the Fungal Pathogen Ceratocystis fimbriata

Black rot of sweetpotato, caused by Ceratocystis fimbriata, is an important reemerging disease threatening sweetpotato production in the United States. This study assessed disease susceptibility of the storage root surface, storage root cambium, and slips (vine cuttings) of 48 sweetpotato cultivars, advanced breeding lines, and wild relative accessions. We also characterized the effect of storage root development on susceptibility to C. fimbriata. None of the cultivars examined at the storage root level were resistant, with most cultivars exhibiting similar levels of susceptibility. In storage roots, Jewel and Covington were the least susceptible and significantly different from White Bonita, the most susceptible cultivar. In the slip, significant differences in disease incidence were observed for above- and below-ground plant structures among cultivars, advanced breeding lines, and wild relative accessions. Burgundy and Ipomoea littoralis displayed less below-ground disease incidence compared with NASPOT 8, Sunnyside, and LSU-417, the most susceptible cultivars. Correlation of black rot susceptibility between storage roots and slips was not significant, suggesting that slip assays are not useful to predict resistance in storage roots. Immature, early-developing storage roots were comparatively more susceptible than older, fully developed storage roots. The high significant correlation between the storage root cross-section area and the cross-sectional lesion ratio suggests the presence of an unfavorable environment for C. fimbriata as the storage root develops. Incorporating applications of effective fungicides at transplanting and during early-storage root development when sweetpotato tissues are most susceptible to black rot infection may improve disease management efforts.

Uncovering the biofumigant capacity of allyl isothiocyanate from several Brassicaceae crops against Fusarium pathogens in maize

BACKGROUND

Driven by environmental concerns, chemical fumigants are no longer allowed in many countries. Therefore, other strategies for reducing fungal inoculum in soils and on crop debris are being explored. In the present study, several Brassicaceae crops were screened for their potential to control Fusarium gramineaum and Fusarium poae mycelial growth in an in vitro inverted Petri dish experiment. Volatile production was measured using gas chromatography-mass spectrometry headspace analysis. A selection of cultivars from each crop species was further investigated using a pot experiment with maize.

RESULTS

Ethiopian mustard (Brassica carinata) and brown mustard (Brassica juncea) released volatile allyl isothiocyanate (AITC) and a higher concentration of AITC was correlated with a better fungal growth reduction in the in vitro screening. Brown mustard cultivar Etamine completely inhibited growth of both Fusarium spp. Pure AITC in a solution with methanol resulted in a sigmoid dose-response curve for both Fusarium spp. tested. Fusarium poae appeared to be more tolerant to AITC than F. graminearum. A pot experiment revealed that the incorporation of brown mustard plant material could alleviate the clear negative effect of F. graminearum infection on maize growth.

CONCLUSION

The present study demonstrated the correlation between the fungistatic effect of biofumigation crops on Fusarium spp. and their production of volatile AITC in vitro, without the addition of exogenous enzymes, and confirmed the biofumigation potential of brown mustard in a pot experiment with maize. These results may help farmers when selecting a green manure crop suitable for biofumigation. © 2020 Society of Chemical Industry.

Evaluation of maize lodging resistance based on the critical wind speed of stalk breaking during the late growth stage

BACKGROUND

The accurate evaluation of the stalk-lodging resistance during the late stage of maize growth can provide a basis for the selection of cultivars, the evaluation of cultivation techniques, and timely mechanical grain harvesting. In this study, the critical wind speed of stalk breaking, plant morphology, stalk mechanical strength, and lodging rate were investigated in 10 maize cultivars to identify the parameters evaluate lodging resistance during the later growth stage of maize. Clarify the relationship with the stalk mechanical strength, critical wind speed of stalk breaking, and natural lodging rate in the field.

RESULTS

The results showed that, in the late growth stage, with increasing number of days after physiological maturity, (1) the stalk lodging rate gradually increased, (2) the stalk breaking force and rind penetration strength (RPS) of the third internode above the soil gradually decreased, and (3) the critical wind speed of stalk breaking increased first and then decreased, and was highest at about 16-24 days after physiological maturity. The position of stalk lodging mostly occurred between second and fifth internodes. The torque at the base of maize plant increased as wind speed increased, and the different of torque was excited among different maize cultivars under same wind speed. Furthermore, the stalk lodging rate was significantly negatively correlated with the critical wind speed of stalk breaking. Additionally, the critical wind speed of stalk breaking was significantly positively correlated with the stalk breaking force and the RPS.

CONCLUSION

This indicates that the critical wind speed of stalk breaking is a superior way to determine the stalk lodging resistance. These results suggest that, in the late growth stage, the decrease in the stalk mechanical strength is an important reason for the decrease in the critical wind speed of stalk breaking and the increase in the lodging rate.

Bacterial Consortium for Improved Maize (Zea mays L.) Production

The ever-increasing human population is a major concern for food security. Maize is the third largest most important food crop. The major problems of cultivation arise from urbanization and land pollution. This reduces the amount of land available for agriculture. The use of chemicals in agriculture is not environmentally friendly. Thus, plant growth-promoting bacteria (PGPB) have been proposed as alternatives. This study aims to test the growth-promoting effect of maize inoculated with six indigenous PGPB isolates. These isolates were assayed for various biochemical and plant growth-promoting activities. They were also assayed for biocontrol activities. Based on the results, six isolates viz A1, A18, A29, NWU4, NWU14, and NWU198 were used to inoculate maize seeds. The inoculated seeds were tried out on the field. A randomized block design was used. PGPB used were in single, consortia of two, and three organisms. The length of the leaves, roots, and stem, plant height, numbers of leaves, and weight of 100 seeds were taken at the fourth and eighth weeks after planting. Microbial consortia increased growth parameters compared to single inoculant treatments. Thus, they can be of advantage in the eradication of low yield. They can also serve as reliable alternatives to chemical fertilizers.

Zearalenone and ß-Zearalenol But Not Their Glucosides Inhibit Heat Shock Protein 90 ATPase Activity

The mycotoxin zearalenone (ZEN) is produced by many plant pathogenic Fusarium species. It is well known for its estrogenic activity in humans and animals, but whether ZEN has a role in plant–pathogen interaction and which process it is targeting in planta was so far unclear. We found that treatment of Arabidopsis thaliana seedlings with ZEN induced transcription of the AtHSP90.1 gene. This heat shock protein (HSP) plays an important role in plant–pathogen interaction, assisting in stability and functionality of various disease resistance gene products. Inhibition of HSP90 ATPase activity impairs functionality. Because HSP90 inhibitors are known to induce HSP90 gene expression and due to the structural similarity with the known HSP90 inhibitor radicicol (RAD), we tested whether ZEN and its phase I metabolites α- and ß-zearalenol are also HSP90 ATPase inhibitors. Indeed, AtHSP90.1 and wheat TaHSP90-2 were inhibited by ZEN and ß-zearalenol, while α-zearalenol was almost inactive. Plants can efficiently glycosylate ZEN and α/ß-zearalenol. We therefore tested whether glucosylation has an effect on the inhibitory activity of these metabolites. Expression of the A. thaliana glucosyltransferase UGT73C6 conferred RAD resistance to a sensitive yeast strain. Glucosylation of RAD, ZEN, and α/ß-zearalenol abolished the in vitro inhibitory activity with recombinant HSP90 purified from Escherichia coli. In conclusion, the mycotoxin ZEN has a very prominent target in plants, HSP90, but it can be inactivated by glycosylation. This may explain why there is little evidence for a virulence function of ZEN in host plants.

Effects of Antagonists on Mycotoxins of Seedborne Fusarium spp. in Sweet Corn

Fusarium species coexist as toxigenic, systemic pathogens in sweet corn seed production in southwestern Idaho, USA. We hypothesized that fungal antagonists of seedborne Fusarium would differentially alter production of Fusarium mycotoxins directly and/or systemically. We challenged the Fusarium complex by in vitro antagonism trials and in situ silk and seed inoculations with fungal antagonists. Fungal antagonists reduced growth and sporulation of Fusarium species in vitro from 40.5% to as much as 100%. Pichia membranifaciens and Penicillium griseolum reduced fumonisin production by F. verticillioides by 73% and 49%, respectively, while P. membranifaciens and a novel Penicillium sp. (WPT) reduced fumonisins by F. proliferatum 56% and 78%, respectively. In situ, pre-planting inoculation of seeds with Penicillium WPT systemically increased fumonisins in the resulting crop. Morchella snyderi applied to silks of an F1 cross systemically reduced deoxynivalenol by 47% in mature seeds of the F2. Antagonists failed to suppress Fusarium in mature kernels following silk inoculations, although the ratio of F. verticillioides to total Fusarium double with some inoculants. Fusarium mycotoxin concentrations in sweet corn seed change systemically, as well as locally, in response to the presence of fungal antagonists, although in Fusarium presence in situ was not changed.

Synthesis and bioactivities of phenazine-1-carboxylic piperazine derivatives

Phenazine-1-carboxylic acid (PCA) as a natural product which has significant inhibition effects against many soil-borne fungal phytopathogens in agricultural application and has been registered in China as the fungicide against rice sheath blight. In order to find new higher fungicidal activities lead compounds and develop new eco-friendly agrochemicals, we introduced substructure piperazines which also have high biological activity into PCA, designed and synthesized a series of phenazine-1-carboxylic piperazine derivatives, and their structures were confirmed by ¹H NMR and HRMS. Most compounds exhibited certain in vitro fungicidal activities. In particular, Compounds 5r exhibited the activity against all the tested pathogenic fungi, such as Rhizoctonia solani, Alternaria solani, Fusarium oxysporum, Fusarium graminearum, Pyricularia oryzac Cavgra, with the EC₅₀ value of 24.6μM, 42.9μM, 73.7μM, 73.8μM, 34.2μM, respectively, more potent activities than PCA (33.2μM, 81.5μM, 186.5μM, 176.4μM, 37.3μM). This result provided a highly active lead compound for the further structure optimization design.

Roles of Genotype-Determined Mycotoxins in Maize Seedling Blight Caused by Fusarium graminearum

Fusarium graminearum is an important causal agent of maize seedling blight. The species includes several chemotypes that produce various forms of deoxynivalenol (DON) and nivalenol (NIV). To understand the effects and roles of F. graminearum mycotoxins on maize seedling blight occurring at Zhang Ye of Gansu, China, 23 isolates of F. graminearum were collected and characterized. A PCR assay showed all 23 isolates belonged to the 15-acetyldeoxynivalenol (15-ADON) genotype. This was also confirmed by production of both DON and 15-ADON in either rice culture medium or maize seedling roots, detected by high performance liquid chromatography and mass spectrometry. In maize seedling roots, 15-ADON dominated at 6 days post inoculation (dpi) and DON was the main mycotoxin at 12 dpi. The biomass of F. graminearum doubled from 6 to 12 dpi, and was positively correlated with virulence of the isolates. Both mycotoxins affected maize root vitality, but 15-ADON had a greater effect than DON. ALDH9 and MDH, two dehydrogenase synthesis genes in maize, showed a lower relative expression in 15-ADON treatments than in DON treatments. It indicated that both mycotoxins affected seed germination and root development, with 15-ADON being more destructive. Under scanning electron microscopy and transmission electron microscopy, root hair formation and development were delayed by DON, but completely inhibited by 15-ADON. 15-ADON caused cell shrinkage, loose cellular structure, and widened intercellular spaces; it also destroyed organelles and caused plasmolysis, and eventually ruptured cell membranes causing cell death. DON did not affect cell morphology and arrangement, but altered the morphology of organelles, forming concentric membranous bodies and a large amount of irregular lipid droplets. Thus, both mycotoxins contributed to symptom expression of maize seedling blight, but 15-ADON was more destructive than DON.