Ear Rot Research Articles

Comprehensive diallel analysis of combining ability and heterosis to Fusarium verticillioides ear rot resistance in maize

AbstractMaize (Zea mays L.) Fusarium ear rot (FER), which is caused by the fungal pathogen Fusarium verticillioides, is a major ear disease affecting maize production in China. Developing resistant maize hybrids is a cost‐effective and environmentally friendly method of reducing yield losses due to FER. Using the nail punch inoculation method, 17 highly resistant and 16 highly susceptible inbred lines were identified in this study, and a large‐scale maize hybrid consisting of 528 F1’s was produced using a half‐diallel cross model. The hybrids were inoculated with F. verticillioides in 6 year–location environment combinations during 2020–2022. Our results showed that estimates of genotypic, environmental, and genotype × environment interaction variance components were very significant (p < 0.001). All the crosses generated from highly resistant inbred lines exhibited high kernel resistance, whereas those generated from highly susceptible inbred lines mostly exhibited high susceptibility to FER. Crosses between resistant and susceptible inbred lines showed intermediate resistance to FER. The general combining ability (GCA) effect was greater than the specific combining ability effect across multiple environments, indicating that the inheritance of FER resistance was mainly influenced by additive genetic effects. The correlation coefficient between the expected GCA value and hybrid resistance was 0.789, whereas that between the mid‐parent value and hybrid resistance was only 0.644. Inbred performance per se and their corresponding hybrids across multiple environments were significantly correlated (r = 0.823). However, no relationship was observed between the FER resistance of F1’s and that of their parental heterotic groups.

Con7 is a key transcription regulator for conidiogenesis in the plant pathogenic fungus Fusarium graminearum.

The ascomycete fungus Fusarium graminearum is the primary cause of head blight disease in wheat and barley, as well as ear and stalk rot in maize. Given the importance of conidia and ascospores in the disease cycle of F. graminearum, precise spatiotemporal regulation of these biological processes is crucial. In this study, we characterized the Magnaporthe oryzae Con7p ortholog and discovered that FgCon7 significantly influences various crucial aspects of fungal development and pathogenicity. Notably, overexpression of FgABAA partially restored developmental defects in the FgCON7 deletion mutant. ChIP-qPCR analysis confirmed a direct genetic link between FgABAA and FgCON7. Furthermore, our research revealed a clear correlation between FgCon7 and chitin accumulation and the expression of chitin synthase genes. These findings offer valuable insights into the genetic mechanisms regulating conidiation and the significance of mycelial differentiation in this plant pathogenic fungus.

The chromosome level whole genome sequence and the seconary matabolism gene cluster prediction of Fusarium meridionale, the pathogen causing maize ear rot.

Fusarium meridionale is one of the pathogens causing maize ear rot, it produce bioactive secondary metabolites may threaten humans food safty, however, the production mechanism of the secondary metabolites and their interaction with maize ear remains poorly understood. To facilitate related studies, we sequenced and assembled the genome of F. meridionale strain JX18-4. The size of F. meridionale JX18-4 genome is 37.11 Mbp, include four nuclear chromosome contigs that consists of 11920 coding genes and one mitochondrial contig. 95.64% gene synteny collinearity was found between the assembly and the reference genomes F. graminearum strain PH-1. Compared to the sequences of seconary matabolism gene clusters sequences reported previously, the stain JX18-4 was predicted potential producing 8 clusters, including nivalenol, zearalenone, aurofusarin, fusarielin, fusaristatin A, fusarin, fusarubin and butenolide. This study aims to reveal the molecular mechanism of secondary metabolites producing, and the genomic information of JX18-4 will provide resources for the study of biological control mechanisms and plant-microbe interactions.

FvOshC Is a Key Global Regulatory Target in Fusarium verticillioides for Fumonisin Biosynthesis and Disease Control.

Fusarium verticillioides has a substantial impact on maize production, commonly leading to maize ear rot and the production of fumonisin, a mycotoxin that poses health risks to both humans and animals. Currently, there is a lack of molecular targets for preventing the disease and controlling the toxin. The biological functions of oxysterol-binding proteins (OSBP) in filamentous fungi remain unclear. In this research, 7 oxysterol-binding protein-related proteins were identified in F. verticillioides, and these proteins were obtained through prokaryotic expression and purification. FvOshC was identified as the specific protein that binds to ergosterol through fluorescence titration. Gene knockout complementation techniques confirmed that FvOSHC plays a positive role, establishing it as a novel global regulatory protein involved in the pathogenicity and FB1 biosynthesis in F. verticillioides. Additionally, the interaction between FvOshC and FvSec14 was identified using yeast two-hybrid techniques. Moreover, computer-aided drug design technology was utilized to identify the receptor molecule Xanthatin based on FvOshC. The inhibitory effect of Xanthatin on the growth of F. verticillioides and the synthesis of FB1 was significantly demonstrated. These findings provide valuable insights that can aid in the management of mycotoxin pollution.

Maize Kernel-Associated Metagenomes Reveal Potential Microbe–Microbe Interactions that Underlie Fusarium Ear Rot Disease

As an alternative to host resistance, transgenic expression of entomocidal and antimicrobial proteins from Bacillus thuringiensis ( Bt) in maize can mitigate Fusarium ear rot (FER). This study evaluated FER in Bt and conventional maize and the role of microbes in the kernel-associated metagenome using quantitative reduced representation sequencing. Our results revealed significant differences in FER severity across environments and varieties and between inoculation treatments. The lower FER scores of conventional maize Spectrum 6416 relative to other varieties highlighted resistant alleles in maize germplasm, whereas strong correlations indicated FER-induced yield loss. Mitigation of FER by transgenes was validated by about threefold enrichment of Fusarium verticillioides ( Fv) postinoculation compared with nonsignificant Fv enrichment in conventional maize. Although the major causal pathogen of FER, Fv, was the most abundant species in the metagenomes ( r = 0.41 to 0.49), a similar degree of correlation was observed between FER and several Fusarium spp. ( r = 0.2 to 0.56). The potential FER-suppressing properties of Talaromyces stipitatus and Ustilago maydis were indicated by negative correlations with FER ( r = –0.22 to –0.42), Fv, and some Fusarium spp. The more FER-resistant varieties consistently enriched for potential FER-suppressing Burkholderia cenocepacia (negatively correlated with Fv). This suggests host genetic background-dependent recruitment of beneficial microbes that suppress pathogens and that microbe–microbe interactions play a role in FER severity. Quantitative and species/strain-level metagenomic profiles hold promise for identifying robust disease-suppressing microbes and microbes that act in synergy with pathogens and for developing holobiont-aware breeding strategies that account for host–microbiome coevolution and host genotype, microbiome/metagenome, and environment interactions. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Identification and genomic insights into a strain of Bacillus velezensis with phytopathogen-inhibiting and plant growth-promoting properties

The use of biological agents offers a sustainable alternative to chemical control in managing plant diseases. In this study, Bacillus velezensis IFST-221 was isolated from the rhizosphere of a healthy maize plant amidst a population showing severe disease symptoms. The investigation demonstrated a broad-spectrum antagonistic activity of IFST-221 against eight species of pathogenic ascomycetes and oomycetes, suggesting its potential utility in combating plant diseases like maize ear rot and cotton Verticillium wilt. Additionally, our study unveiled that IFST-221 has demonstrated significant plant growth-promoting properties, particularly in maize, cotton, tomato, and broccoli seedlings. This growth promotion was linked to its ability to produce indole-3-acetic acid, nitrogen fixation, phosphate and potassium solubilization, and biofilm formation in laboratory conditions. A complete genome sequencing of IFST-221 yielded a genome size of 3.858 M bp and a GC content of 46.71%. The genome analysis identified 3659 protein-coding genes, among which were nine secondary metabolite clusters with known antimicrobial properties. Additionally, three unknown compounds with potentially novel properties were also predicted from the genomic data. Genome mining also identified several key genes associated with plant growth regulation, colonization, and biofilm formation. These findings provide a compelling case for the application of B. velezensis IFST-221 in agricultural practices. The isolate’s combined capabilities of plant growth promotion and antagonistic activity against common plant pathogens suggest its promise as an integrated biological agent in disease management and plant productivity enhancement.

The MAP kinase FvHog1 regulates FB1 synthesis and Ca2+ homeostasis in Fusarium verticillioides

The high osmolarity glycerol 1 mitogen-activated protein kinase (Hog1-MAPK) cascade genes are important for diverse biological processes. The activated Hog1 upon multiple environmental stress stimuli enters into the nucleus where it directly phosphorylates transcription factors to regulate various physiological processes in phytopathogenic fungi. However, their roles have not been well-characterized in Fusarium verticillioides. In this study, FvHog1 is identified and functionally analyzed. The findings reveal that the phosphorylation level and nuclear localization of FvHog1 are increased in Fumonisin B1 (FB1)-inducing condition to regulate the expression of FB1 biosynthesis FUM genes. More importantly, the deletion mutants of Hog1-MAPK pathway show increased sensitivity to Ca2+ stress and elevated intracellular Ca2+ content. The phosphorylation level and nuclear localization of FvHog1 are increased with Ca2+ treatment. Furthermore, our results show that FvHog1 can directly phosphorylate Ca2+-responsive zinc finger transcription factor 1 (FvCrz1) to regulate Ca2+ homeostasis. In conclusion, our findings indicate that FvHog1 is required for FB1 biosynthesis, pathogenicity and Ca2+ homeostasis in F. verticillioides. It provides a theoretical basis for effective prevention and control maize ear and stalk rot disease.

Evaluation of Maize Hybrids for Resistance to Ear Rot Caused by Dominant Fusarium Species in Northeast China

Evaluation of Maize Hybrids for Resistance to Ear Rot Caused by Dominant Fusarium Species in Northeast China

Mechanism Insights into the Enantioselective Bioactivity and Fumonisin Biosynthesis of Mefentrifluconazole to Fusarium verticillioides.

The occurrence of maize ear rot caused by Fusarium verticillioides (F. verticillioides) poses a threat to the yield and quality of maize. Mefentrifluconazole enantiomers appear to have strong stereoselective activity against F. verticillioides and cause differences in fumonisin production. We evaluated the stereoselective activity of mefentrifluconazole enantiomers by determining inhibition of the strain, hyphae, and conidia. Strain inhibition by R-(-)-mefentrifluconazole was 241 times higher than S-(+)-mefentrifluconazole and 376 times higher in conidia inhibition. For the mechanism of the enantioselective bioactivity, R-mefentrifluconazole had stronger binding to proteins than S-(+)-mefentrifluconazole. Under several concentration conditions, the fumonisin concentration was 1.3-24.9-fold higher in the R-(-)-mefentrifluconazole treatment than in the S-(+)-mefentrifluconazole treatment. The R-enantiomer stimulated fumonisin despite a higher bioactivity. As the incubation time increased, the stimulation of the enantiomers on fumonisin production decreased. R-(-)-Mefentrifluconazole stimulated higher fumonisin production in F. verticillioides at 25 °C compared to 30 °C. This study established a foundation for the development of high-efficiency and low-risk pesticides.

Phenotypic characterisation and evaluation of resistance to Fusarium ear rot, fumonisin contamination and agronomic traits in a collection of maize landraces

Context Maize is a major crop in Italy and is constantly affected by the fungus Fusarium verticillioides, producing ear rot and grain contamination by fumonisins. Finding new genotypes resistant to Fusarium infection is an important goal for the improvement of maize cultivation. Aims The objective of this work was to test a collection of 33 traditional landraces from the Emilia-Romagna (Italy) region for Fusarium ear rot (FER) severity, fumonisin content, and their agronomic performance. Methods Primary ears were artificially inoculated with a toxigenic strain of F. verticillioides in a 2-year experimental trial. The landrace ‘Nostrano di Storo’ and a commercial hybrid of FAO maturity class 300 were also included and used as comparisons representing a well-known and highly valued landrace and a modern flint hybrid, respectively. Key results The collection showed great phenotypic variability for all the agronomic traits assessed and responded differently to the Fusarium infection with percentages of FER ranging from 6.6% to 49.3%, and fumonisins from 4.3 mg/kg to 34.5 mg/kg. Thirteen and six landraces displayed FER percentages and fumonisin content very similar to the hybrid, respectively. Moreover, eight landraces exhibited grain yield values comparable to the hybrid. Interestingly, Va221, Va227 and EMR03 showed the best combination among these three traits. Conclusions This local material can be considered suitable for breeding purposes targeting the development of FER and fumonisin resistant germplasm. Implications The collection may represent a resource for future research aimed at evaluating the response to multiple pathogens and their associated mycotoxins.

Is Trichoderma ear rot on maize really a new dangerous plant disease?

Is Trichoderma ear rot on maize really a new dangerous plant disease?

Chemical and genetic control of Stenocarpella sp. and Fusarium sp. in maize

The complex of phytopathogenic agents that cause ear rot in maize (mainly Fusarium spp. and Stenocarpella spp.) accounts for quantitative (weight) and qualitative (mycotoxins) losses. Therefore, a management protocol for maize ear rot was established in this study, based on chemical and genetic control. To this end, the response of 23 maize hybrids to four phytosanitary managements was studied: (I) picoxystrobin + cyproconazole (0.35 L ha-1) + mineral oil (0.5 L ha-1) + carbendazim (1.0 L ha-1) at VT; (II) pyraclostrobin + epoxiconazole (0.3 L ha-1) in (V8) with picoxystrobin + cyproconazole (0.35 L ha-1) + mineral oil (0.5 L ha-1) + carbendazim (1.0 L ha-1) at VT; (III) Pyraclostrobin + epoxiconazole (0.3 L ha-1) + mineral oil (0.3 L ha-1 at V8 picoxystrobin + cyproconazole (0.35 L ha-1) + mineral oil (0.5 L ha-1) + carbendazim (1.0 L ha-1) at VT and at VT + 12 days with azoxystrobin+ cyproconazole (0.3 L ha-1) + mineral oil (0.5 L ha-1) + carbendazim (1.0 L ha-1), and (IV) a negative control. Severity and incidence of Stenocarpella sp. and Fusarium sp. were more effectively controlled by genetic management. Chemical control was ineffective for either disease agent. Further studies on new genotypes and more molecules to control these phytopathogens are recommended.

Distribution of maize ear rot in southwestern Ethiopia and its association with biophysical factors

A survey was carried out on 135 maize farms across nine districts and three zones of southwestern Ethiopia to determine the distribution of maize ear rot and its association with biophysical factors. Results revealed the prevalence of the disease across survey areas, albeit at varied intensities. Ear rot incidence and severity ranged from 41 to 54% and 31 to 40%, respectively. All maize grain samples collected from the survey area were positive for potentially toxigenic fungi genera, with Fusarium, Aspergillus, and Penicillium occurring at frequencies of 100%, 60%, and 58%, respectively. Higher ear rot incidence (>50%) had significant associations with zones, higher altitude, previous crop, lack of residue management, maize variety, and insect damage. The study indicates ear rot and kernel contamination by potentially toxigenic fungi is highly prevalent in southwestern Ethiopia and requires the use of certified seeds, residue management, shifting crops and reducing insect damage to manage the disease.

Cytotoxic effect by ear and kernel rot diseases under different storage conditions in three maize genotypes

Cytotoxic effect by ear and kernel rot diseases under different storage conditions in three maize genotypes

First Report of Panicle Wilting on Rice (Oryza sativa L.) Caused by Fusarium kyushuense in Heilongjiang Province, China.

Heilongjiang is the largest rice-producing province in China, with annual yield of 28.9 million tons cultivated on 3.8 million hectares (Liu et al. 2021). During field surveys from July to August (2021-2022), symptoms of wilting were observed on rice panicles across Baoqing county (46.32°N, 132.20°E), Shuangyashan city, Heilongjiang province, China. Disease incidence ranged from 10 to 35%, and yield losses were estimated to be 5 to 20% over 7 surveyed fields of 18.5 ha in total. Initially, infected panicles exhibited carmine to brownish spots at the flowering and early grain-filling stages, which gradually merged into large and irregular lesions and spread to the entire panicle surface. Eventually, panicles became wilting and decayed at the ripening stage. To identify the etiological agent, thirty-five symptomatic panicles were collected randomly from 35 plants at different positions in 7 fields. The fragments (approximately 3 mm2) were dissected from margins of individual lesions, surface-disinfested with 70% ethanol for 30 s followed by 2% sodium hypochlorite for 2 min, and rinsed three times in sterilized water. The pieces were then dried and placed onto half-strength potato dextrose agar (PDA) supplemented with 50 μg/mL of streptomycin sulfate. After incubation at 28°C for 4 days, nineteen cultures were obtained and purified using the single-spore isolation method. On PDA plates, the colonies produced fluffy and cottony aerial mycelia and were white to yellowish with deep-yellow to red-brown pigments. The microconidia were hyaline, elliptical or clavate, zero to one septum, measuring 6.3 to 19.2 × 2.6 to 5.1 μm in size (n = 50). On carnation leaf agar (CLA), the macroconidia were thick-walled, falcate to almost straight, three to five septa, apical cell hooked to tapering, basal cell foot-shaped, measuring 27.4 to 47.8 × 3.6 to 5.4 μm in size (n = 50). No chlamydospore was observed. The internal transcribed spacer (ITS) region of ribosomal RNA, translation elongation factor (TEF-1α) gene, and β-tubulin (β-TUB) gene were amplified and sequenced using primers ITS1/ITS4 (White et al. 1990), EF1/EF2 (O'Donnell 2000), and T1/T22 (O'Donnell and Cigelnik 1997) from three representative isolates (PJ58, PJ69 and PJ83), respectively. The obtained sequences were deposited in GenBank (accession nos. ON527509, OQ772202 and OQ777725 for ITS; ON573222, OQ784926 and OQ784927 for TEF-1α; ON573223, OQ784928 and OQ784929 for β-TUB, respectively). BLASTn analysis revealed 99.8 to 100% homology with the corresponding sequences of Fusarium kyushuense (MH892849 for ITS, AB674297 for TEF-1α, and GQ915442 for β-TUB, respectively) in GenBank. Maximum likelihood phylogeny based on the concatenated sequences of ITS, TEF-1α and β-TUB grouped three representative isolates in the F. kyushuense clade. Combined with the morphological and molecular characteristics, the fungus was identified to be F. kyushuense. Pathogenicity of the three isolates of F. kyushuense was evaluated on a susceptible rice cultivar Nanjing 46 at the booting stage. The upper part of a healthy panicle was inoculated by injecting 2 ml of a conidial suspension (1 × 106 spore/ml) obtained from a 7-day-old PDA culture of each isolate. The negative control was treated with sterile distilled water. The experiment was performed thrice with ten replicated plants for each treatment. All plants were placed in a humid chamber at 25°C with a 12-h photoperiod and 80% relative humidity. Twenty days after inoculation, it was found that the inoculated panicles showed typical reddish to brownish lesions, whereas control plants remained symptomless. Pathogens were reisolated from the artificially inoculated panicles and confirmed by morphological and molecular tests, fulfilling Koch's postulates. In recent years, this species has been associated with stalk rot and ear rot of maize (Cao et al. 2021; Wang et al. 2014) and wilt of tobacco (Wang et al. 2013). Also, it was mentioned as a producer of mycotoxins, especially trichothecenes and HT-2 toxin (Varga et al. 2016). To our knowledge, this is the first report of F. kyushuense causing panicle wilting on rice in China. The appropriate control strategies should be made to reduce the risk of disease due to food security concerns and potential threats to rice production.

FvKex2 is required for development, virulence, and mycotoxin production in Fusarium verticillioides

Fusarium verticillioides is one of the most important fungal pathogens causing maize ear and stalk rots, thereby undermining global food security. Infected seeds are usually unhealthy for consumption due to contamination with fumonisin B1 (FB1) mycotoxin produced by the fungus as a virulence factor. Unveiling the molecular factors that determine fungal development and pathogenesis will help in the control and management of the diseases. Kex2 is a kexin-like Golgi-resident proprotein convertase that is involved in the activation of some important proproteins. Herein, we identified and functionally characterized FvKex2 in relation to F. verticillioides development and virulence by bioinformatics and functional genomics approaches. We found that FvKex2 is required for the fungal normal vegetative growth, because the growth of the ∆Fvkex2 mutant was significantly reduced on culture media compared to the wild-type and complemented strains. The mutant also produced very few conidia with morphologically abnormal shapes when compared with those from the wild type. However, the kexin-like protein was dispensable for the male role in sexual reproduction in F. verticillioides. In contrast, pathogenicity was nearly abolished on wounded maize stalks and sugarcane leaves in the absence of FvKEX2 gene, suggesting an essential role of Fvkex2 in the virulence of F. verticillioides. Furthermore, high-performance liquid chromatography analysis revealed that the ∆Fvkex2 mutant produced a significantly lower level of FB1 mycotoxin compared to the wild-type and complemented strains, consistent with the loss of virulence observed in the mutant. Taken together, our results indicate that FvKex2 is critical for vegetative growth, FB1 biosynthesis, and virulence, but dispensable for sexual reproduction in F. verticillioides. The study presents the kexin-like protein as a potential drug target for the management of the devastating maize ear and stalk rot diseases. Further studies should aim at uncovering the link between FvKex2 activity and FB1 biosynthesis genes.Key points•The kexin-like protein FvKex2 contributes significantly to the vegetative growth of Fusarium verticillioides.•The conserved protein is required for fungal conidiation and conidial morphology, but dispensable for sexual reproduction.•Deletion of FvKEX2 greatly attenuates the virulence and mycotoxin production potential of F. verticillioides.

Fungal Species and Mycotoxins Associated with Maize Ear Rots Collected from the Eastern Cape in South Africa.

Maize production in South Africa is concentrated in its central provinces. The Eastern Cape contributes less than 1% of total production, but is steadily increasing its production and has been identified as a priority region for future growth. In this study, we surveyed ear rots at maize farms in the Eastern Cape, and mycotoxins were determined to be present in collected samples. Fungal isolations were made from mouldy ears and species identified using morphology and DNA sequences. Cladosporium, Diplodia, Fusarium and Gibberella ear rots were observed during field work, and of these, we collected 78 samples and isolated 83 fungal strains. Fusarium was identified from Fusarium ear rot (FER) and Gibberella ear rot (GER) and Stenocarpella from Diplodia ear rot (DER) samples, respectively. Using LC-MS/MS multi-mycotoxin analysis, it was revealed that 83% of the collected samples contained mycotoxins, and 17% contained no mycotoxins. Fifty percent of samples contained multiple mycotoxins (deoxynivalenol, 15-acetyl-deoxynivalenol, diplodiatoxin and zearalenone) and 33% contained a single mycotoxin. Fusarium verticillioides was not isolated and fumonisins not detected during this survey. This study revealed that ear rots in the Eastern Cape are caused by a wide range of species that may produce various mycotoxins.

Effect of in‐canopy foliar fungicide applications in corn on spray coverage

AbstractFoliar fungicides are available to suppress Diplodia ear rot (DER), caused by Stenocarpella maydis (Berk.) Sutton and Stenocarpella macrospora (Earle) Sutton) in corn (Zea mays L.), but previous research has indicated these fungicides have limited efficacy against the disease using traditional over‐canopy application methods. In an effort to improve coverage within the canopy and potentially improve disease control of DER, experiments were conducted in 2020, 2021, and 2022 to examine the effect of ground‐driven, in‐canopy fungicide nozzle technology on DER severity and spray coverage on the ear leaf and ear of corn plants. Application methods included over‐canopy nozzles, over‐canopy + drop nozzles, and over‐canopy + 360 Undercover nozzles. Within each application method, treatments consisted of a non‐inoculated control, or were inoculated with a conidial suspension of S. maydis. The fungicides benzovindiflupyr + azoxystrobin + propiconazole and pydiflumetofen + azoxystrobin + propiconazole were applied within each application method to measure efficacy against DER. In all years, neither fungicide product nor application method reduced DER severity. No fungicide applications increased yield compared to the non‐treated control. The addition of drop nozzles or 360 Undercover nozzles to traditional over‐canopy nozzles increased spray coverage on the ear (P < 0.0001) compared to over‐canopy nozzles alone.

Insect ear‐feeding impacts Gibberella ear rot and deoxynivalenol accumulation in corn grain

AbstractHigh deoxynivalenol (DON) levels in corn (Zea mays L.) is a grain quality issue for many growers in the US Great Lakes region. High DON levels can be attributed to the interaction of environment, pathogen (Fusarium spp. causing ear rot), and hybrid susceptibility. However, ear‐feeding insects can provide easy access for fungal infection and increase DON accumulation, hence the evaluation of insect protection strategies such as hybrid insecticidal proteins is crucial. Field trials were conducted at four locations in Michigan to study the impact of hybrids insect protection trait on ear injury, ear rot infection, and DON levels. Fungicide application (prothioconazole at silking stage) was conducted at two locations and included non‐treated control. Insect feeding incidence (IFI) and ear rot incidence (ERI) were correlated at three locations but were stronger at locations with environments not conducive to fungal growth soon after silking. Correlation between IFI and DON was observed only at locations with highest insect pressure. Hybrid with Vip3A protein reduced IFI by >70% at all locations but lowered DON concentration at one out of three tested locations compared to non‐Vip3A hybrids. Fungicide application reduced ear rot severity at one of two locations but did not impact ERI or DON levels. Overall, results showed that ear‐feeding by insects can lead to an increase in ear rot and DON levels, and use of hybrids with Vip3A protein can reduce DON levels especially under high insect pressure.

Maize pollen carry bacteria that suppress a fungal pathogen that enters through the male gamete fertilization route.

In flowering plants, after being released from pollen grains, the male gametes use the style channel to migrate towards the ovary where they fertilize awaiting eggs. Environmental pathogens exploit the style passage, resulting in diseased progeny seed. The belief is that pollen also transmits pathogens into the style. By contrast, we hypothesized that pollen carries beneficial microbes that suppress environmental pathogens on the style passage. No prior studies have reported pollen-associated bacterial functions in any plant species. Here, bacteria were cultured from maize (corn) pollen encompassing wild ancestors and farmer-selected landraces from across the Americas, grown in a common field in Canada for one season. In total, 298 bacterial isolates were cultured, spanning 45 genera, 103 species, and 88 OTUs, dominated by Pantoea, Bacillus, Pseudomonas, Erwinia, and Microbacterium. Full-length 16S DNA-based taxonomic profiling showed that 78% of bacterial taxa from the major wild ancestor of maize (Parviglumis teosinte) were present in at least one cultivated landrace. The species names of the bacterial isolates were used to search the pathogen literature systematically; this preliminary evidence predicted that the vast majority of the pollen-associated bacteria analyzed are not maize pathogens. The pollen-associated bacteria were tested in vitro against a style-invading Fusarium pathogen shown to cause Gibberella ear rot (GER): 14 isolates inhibited this pathogen. Genome mining showed that all the anti-Fusarium bacterial species encode phzF, associated with biosynthesis of the natural fungicide, phenazine. To mimic the male gamete migration route, three pollen-associated bacterial strains were sprayed onto styles (silks), followed by Fusarium inoculation; these bacteria reduced GER symptoms and mycotoxin accumulation in progeny seed. Confocal microscopy was used to search for direct evidence that pollen-associated bacteria can defend living silks against Fusarium graminearum (Fg); bacterial strain AS541 (Kluyvera intermedia), isolated from pollen of ancestral Parviglumis, was observed to colonize the susceptible style/silk entry points of Fg (silk epidermis, trichomes, wounds). Furthermore, on style/silk tissue, AS541 colonized/aggregated on Fg hyphae, and was associated with Fg hyphal breaks. These results suggest that pollen has the potential to carry bacteria that can defend the style/silk passage against an environmental pathogen - a novel observation.