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.

Identification and Analysis of Candidate Genes Associated with Maize Fusarium Cob Resistance Using Next-Generation Sequencing Technology

The pressure to reduce mineral fertilization and the amount of pesticides used has become a factor limiting production growth, as has the elimination of many crop protection chemicals from the market. A key condition for this to be an effective form of protection is the use of varieties with higher levels of resistance. The most effective and fastest way to assist in the selection and control of pathogens is the conducting of genome-wide association studies. These are useful tools for identifying candidate genes, especially when combined with QTL mapping to map and validate loci for quantitative traits. The aim of this study was to identify new markers coupled to genes that determine maize plant resistance to fusarium head blight through the use of next-generation sequencing, association and physical mapping, and to optimize diagnostic procedures to identify selected molecular markers coupled to plant resistance to this fungal disease. As a result of field experiments and molecular analyses, molecular markers coupled to potential genes for resistance to maize ear fusariosis were selected. The newly selected markers were tested against reference genotypes. As a result of the analyses, it was found that two markers (11801 and 20607) out of the ten that were tested differentiated between susceptible and resistant genotypes. Marker number 11801 proved to be the most effective, with a specious product of 237 bp appearing for genotypes 1, 3, 5, 9 and 10. These genotypes were characterized by a field resistance of 4-6 on the 9° scale (1 being susceptible, 9 being resistant) and for all genotypes except 16 and 20, which were characterized by a field resistance of 9. In the next step, this marker will be tested on a wider population of extreme genotypes in order to use it for the preliminary selection of fusarium-resistant genotypes, and the phosphoenolpyruvate carboxylase kinase 1 gene coupled to it will be subjected to expression analysis.

The Cultured Microbiome of Pollinated Maize Silks Shifts after Infection with Fusarium graminearum and Varies by Distance from the Site of Pathogen Inoculation

Styles transmit pollen-derived sperm nuclei from pollen to ovules, but also transmit environmental pathogens. The microbiomes of styles are likely important for reproduction/disease, yet few studies exist. Whether style microbiome compositions are spatially responsive to pathogens is unknown. The maize pathogen Fusarium graminearum enters developing grain through the style (silk). We hypothesized that F. graminearum treatment shifts the cultured transmitting silk microbiome (TSM) compared to healthy silks in a distance-dependent manner. Another objective of the study was to culture microbes for future application. Bacteria were cultured from husk-covered silks of 14 F. graminearum-treated diverse maize genotypes, proximal (tip) and distal (base) to the F. graminearum inoculation site. Long-read 16S sequences from 398 isolates spanned 35 genera, 71 species, and 238 OTUs. More bacteria were cultured from F. graminearum-inoculated tips (271 isolates) versus base (127 isolates); healthy silks were balanced. F. graminearum caused a collapse in diversity of ~20-25% across multiple taxonomic levels. Some species were cultured exclusively or, more often, from F. graminearum-treated silks (e.g., Delftia acidovorans, Klebsiella aerogenes, K. grimontii, Pantoea ananatis, Stenotrophomonas pavanii). Overall, the results suggest that F. graminearum alters the TSM in a distance-dependent manner. Many isolates matched taxa that were previously identified using V4-MiSeq (core and F. graminearum-induced), but long-read sequencing clarified the taxonomy and uncovered greater diversity than was initially predicted (e.g., within Pantoea). These isolates represent the first comprehensive cultured collection from pathogen-treated maize silks to facilitate biocontrol efforts and microbial marker-assisted breeding.

Field and Greenhouse Assessment of Seed Treatment Fungicides for Management of Sudden Death Syndrome and Yield Response of Soybean

Seed treatments for the management of sudden death syndrome (SDS) caused by Fusarium virguliforme are available in the United States and Canada; however, side-by-side comparisons of these seed treatments are lacking. Sixteen field experiments were established in Illinois, Indiana, Iowa, Michigan, and Wisconsin, United States, and Ontario, Canada, in 2019 and 2020 to evaluate seed treatment combinations. Treatments included a nontreated check (NTC), fungicide and insecticide base seed treatments (base), fluopyram, base + fluopyram, base + saponin extracts from Chenopodium quinoa, base + fluopyram + heat-killed Burkholderia rinojenses, base + pydiflumetofen, base + thiabendazole + heat-killed B. rinojenses, and base + thiabendazole + C. quinoa extracts + heat-killed B. rinojenses. Treatments were tested on SDS moderately resistant and susceptible soybean cultivars at each location. Overall, NTC and base had the most root rot, most foliar disease index (FDX), and lowest yield. Base + fluopyram and base + pydiflumetofen were most effective for managing SDS. Moderately resistant cultivars reduced FDX in both years but visual root rot was greater on the moderately resistant than the susceptible cultivars in 2020. Yield response to cultivar was also inconsistent between the 2 years. In 2020, the susceptible cultivar provided significantly more yield than the moderately resistant cultivar. Treatment effect for root rot and FDX was similar in field and greenhouse evaluations. These results reinforce the need to include root rot evaluations in addition to foliar disease evaluations in the breeding process for resistance to F. virguliforme and highlights the importance of an integrated SDS management plan because not a single management tactic alone provides adequate control of the disease.

The Effect of Foliar Fungicide and Insecticide Application on the Contamination of Fumonisins, Moniliformin and Deoxynivalenol in Maize Used for Food Purposes

The fungal ear rot of maize cultivated in temperate areas is mainly due to the Fusarium species. The use of insecticides against European Corn Borer (ECB) reduces the severity of fungal ear rot as well as the fumonisin (FB) and moniliformin (MON) levels in maize kernels at harvest, which in turn results in a lowering of their effect on deoxynivalenol (DON) control. However, the direct fungicidal control of ear rot has rarely been implemented for maize, and the first studies reported conflicting results on the reduction of mycotoxins. In the present experiment, field trials were carried out in North Italy over three growing seasons to study the effect of fungicide application timings on maize to control mycotoxins, considering the interaction of the application with the insecticide treatment, according to a full factorial split plot design. The mycotoxin content was determined through LC−MS/MS analysis. The field trials showed a significant reduction in ECB severity (75%), fungal ear rot severity (68%), Fusarium Liseola section infection (46%), FBs (75%) and MON (79%) as a result of the insecticide application for all the years, while the DON content increased by 60%. On the other hand, a fungicide application alone or applied in plots protected by an insecticide was never effective for the fungal symptoms, infection or mycotoxin content. The results confirm that a correct insecticide application to control ECB damage is the most effective agrochemical solution for the control of fungal ear rot, FBs and MON.

Associative and Physical Mapping of Markers Related to Fusarium in Maize Resistance, Obtained by Next-Generation Sequencing (NGS)

On the basis of studies carried out in the last few years, it is estimated that maize diseases cause yield losses of up to 30% each year. The most dangerous diseases are currently considered to be caused by fungi of the genus Fusarium, which are the main culprits of root rot, ear rots, and stalk rot. Early plant infection causes grain diminution, as well as a significant deterioration in nutritional value and fodder quality due to the presence of harmful mycotoxins. Therefore, the aim of the research was to identify new markers of the SilicoDArT and SNP type, which could be used for the mass selection of varieties resistant to fusarium. The plant material consisted of 186 inbred maize lines. The lines came from experimental plots belonging to two Polish breeding companies: Plant Breeding Smolice Ltd., (Co., Kobylin, Poland). Plant Breeding and Acclimatization Institute-National Research Institute Group (51°41'23.16″ N, 17°4'18.241″ E), and Małopolska Plant Breeding Kobierzyce, Poland Ltd., (Co., Kobierzyce, Poland) (50°58'19.411″ N, 16°55'47.323″ E). As a result of next-generation sequencing, a total of 81,602 molecular markers were obtained, of which, as a result of the associative mapping, 2962 (321 SilicoDArT and 2641 SNP) significantly related to plant resistance to fusarium were selected. Out of 2962 markers significantly related to plant resistance in the fusarium, seven markers (SilicoDArT, SNP) were selected, which were significant at the level of 0.001. They were used for physical mapping. As a result of the analysis, it was found that two out of seven selected markers (15,097-SilicoDArT and 58,771-SNP) are located inside genes, on chromosomes 2 and 3, respectively. Marker 15,097 is anchored to the gene encoding putrescine N-hydroxycinnamoyltransferase while marker 58,771 is anchored to the gene encoding the peroxidase precursor 72. Based on the literature data, both of these genes may be associated with plant resistance to fusarium. Therefore, the markers 15,097 (SilicoDArT) and 58,771 (SNP) can be used in breeding programs to select lines resistant to fusarium.

Impact of agronomic practices on Fusarium mycotoxin accumulation in maize grain

In the Great Lakes region of North America, Gibberella ear rot (GER), caused by Fusarium graminearum, affects grain quality due to the accumulation of mycotoxins. GER severity is strongly influenced by environmental conditions; however, agronomic practices can also influence disease severity and mycotoxin accumulation. In this study, three separate small-plot experiments were conducted at Ridgetown, ON, Canada during 2019 and 2020 under an inoculated-misted system to determine Fusarium mycotoxin accumulation as affected by: (1) plant population density; (2) in-row-plant developmental variability; and (3) the effect of integrated Bt refuge genetics. In this study, DON concentrations were at least 49% higher in maize at 113,600 plants/ha compared to 79,000 plants/ha. Moreover, mycotoxin accumulation was higher in plants that were delayed developmentally in the crop row; total DON concentrations were at least 310% higher in late silked plants adjacent to early silked plants. Results of the plant population density and in-row-plant developmental variability suggest that the main driver for mycotoxin accumulation was stress induced by plant competition rather than environmental conditions; this highlights the importance of avoiding plant competitive stress as a strategy to reduce the risks of mycotoxin accumulation. In this study, there was no statistical difference in DON accumulation between the Bt component and the non-Bt component in each of the four hybrids tested; however, there was evidence that hybrids varied in susceptibility, including the Bt and non-Bt components that were paired commercially in a bag of seed maize. Reducing mycotoxins in maize requires integrated management, which includes agronomic considerations. These results indicate that mycotoxins are favoured with high plant populations and plant-to-plant variability in the row, especially in susceptible hybrids.