Febina Merlin Mathew

Species of Diaporthe cause soybean ( Glycine max L.) diseases in the United States, including stem canker, pod and stem blight, and seed decay. Among different species of Diaporthe , Diaporthe longicolla , the causal agent of pod and stem blight and seed decay, is associated with the production of cytochalasin compounds. In this study, untargeted metabolomic profiling was conducted on two isolates of D. longicolla (16-OP-SB-DIA-52 and 14-OP-PHO-SD-19) recovered from soybean plants affected by pod and stem blight to identify both known and previously uncharacterized metabolites. Axenic cultures were established in potato dextrose broth for metabolite characterization. Among the top 150 significantly upregulated metabolites compared with the potato dextrose broth control, nitro-phenoxy cytochalasin ( P = 0.009) and ortho-phenoxy cytochalasin ( P = 0.002) were putatively identified (Level 3 detection based on mass spectrometric parameters only). For 14-OP-PHO-SD-19, cytochalasin B ( P = 0.021) and nitro-phenoxy cytochalasin ( P = 0.002) were putatively detected (Level 3). In addition, metabolomic analysis putatively identified (Level 3) fumonisin B2 (16-OP-SB-DIA-52 [ P = 0.001]; 14-OP-PHO-SD-19 [ P = 0.009]) and zearalenone (16-OP-SB-DIA-52 [ P = 0.0002]; 14-OP-PHO-SD-19 [ P = 0.01]), which were significantly upregulated and among the top 400 metabolites in the two isolates. Interestingly, cytochalasin compounds, fumonisins, and zearalenone have been previously implicated in detrimental effects on livestock health (e.g., sheep, horses, and pigs). Although incorporating soybean meal into livestock diets underscores the potential relevance of D. longicolla -associated metabolites to feed safety, the present study was designed as a proof-of-concept metabolomics investigation. Consequently, any implications for animal health should be considered preliminary and require confirmation through metabolite quantification, feed analyses, and toxicity studies. Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Phomopsis stem canker of sunflower (Helianthus annuus L.) is a major disease in the United States. This study quantified the effect of Phomopsis stem canker severity on sunflower yield and evaluated the efficacy of fungicides under field conditions across Minnesota, North Dakota, Nebraska, and South Dakota. To determine the yield-disease severity index (DSI) relationship, non-treated control (NTC) plots from 80 field trials (2009-2025) were analyzed, and yield was found to decrease with increasing DSI, described by the equation: Yield (kg ha⁻¹) = 2552.52 - 11.64 × DSI (R² = 0.14, P < 0.001). Seventeen trials conducted from 2022 to 2025 evaluated fungicides containing Quinone outside Inhibitors (QoI), Demethylation Inhibitors (DMI), and Succinate Dehydrogenase Inhibitors (SDHI) applied at V8 (eight true leaves), R1 (miniature floral head), and/or R6 (flowering complete and the ray flowers wilting) stages. Trials were categorized into low-, moderate-, and high-yield environments using ±1 SD residuals to determine relative differences in yield within the overall DSI-yield relationship. Yield decreased with increasing DSI in low (R²=0.91, P=6.13×10 ^⁻5 ) and moderate (R²=0.19, P=0.000359) yielding environments. In low yield environments, fluopyram + tebuconazole at R1 followed by pyraclostrobin at R6 increased yield by up to 55%. In moderate yield environments, fluopyram (SDHI) + tebuconazole (DMI) at V8 or R6, combined with pyraclostrobin (QoI) at R1, increased yield by up to 15% over NTC. These findings indicate that fungicide efficacy differed among yield environments, suggesting that treatment decisions should account for the production environment to maximize sunflower yield.

Sudden death syndrome (SDS), caused by Fusarium virguliforme, is a major yield-limiting disease of soybean in the United States and Canada. Field trials in 2020 and 2021 across 13 U.S. states and Ontario, Canada, evaluated two SDS-targeted seed treatments and soybean cultivars: one susceptible (S) and one moderately resistant (MR) to SDS. Treatments included a base (prothioconazole + metalaxyl + penflufen, metalaxyl, and imidacloprid), base + fluopyram, and base + pydiflumetofen. Data collection included root rot ratings, SDS foliar symptoms, and yield. Under high SDS pressure (foliar disease index [FDX] ≥ 10), both SDS-targeted seed treatments and MR cultivars significantly reduced foliar symptoms (71 to 80%) compared with the base seed treatment and susceptible cultivars. Although 2020 and 2021 were not epidemic years for SDS, consistent reductions in SDS were observed. In the absence of disease, S cultivars produced greater yield than MR, but under high SDS and low soybean cyst nematode (SCN) pressure (3 of soil), the MR cultivars produced greater yield than the S cultivars. Only the base + pydiflumetofen treatment maintained greater yield in the absence of SDS. When SDS pressure was high (FDX ≥ 10), both SDS-targeted treatments had 7.0 to 9.0% more yield than the base. Under combined high SDS and SCN pressure (≥2,000/100 cm ³ of soil), only base + fluopyram preserved yield more than the base treatment. These results provide valuable insights for future SDS management through cultivar selection and seed treatments.

Root rot occurrence has been a growing concern among soybean farmers. In 2020, a fungal isolate was collected from a soybean root symptomatic of root rot from North Dakota. The isolate was cultured in potato dextrose agar, and the morphology was observed. The colony morphology and microscopic features closely matched descriptions of Clonostachys rhizophaga. For confirmation of fungal identity using molecular techniques, DNA was extracted from the pure fungal culture and its subcultures. Multiple genomic regions were used for polymerase chain reaction (PCR). Sequencing of the PCR products followed by BLAST analysis in the NCBI nucleotide database and alignment to the C. rhizophaga reference genome showed high similarity for all loci. Phylogenetic analysis based on β-tubulin sequences placed the isolate within the C. rhizophaga clade. Among all loci analyzed, the β-tubulin gene provided the highest species-level resolution, clearly distinguishing C. rhizophaga from other Clonostachys taxa. The molecular evidence confirmed the isolate as C. rhizophaga. Pathogenicity tests were conducted by inoculating the soybean cultivar Barnes. Infected plants showed symptoms of taproot and lateral root necrosis accompanied by root discoloration in two experiments. Fungal DNA reisolated from symptomatic roots, followed by PCR and sequencing, confirmed the isolate as C. rhizophaga. To our knowledge, this is the first report of C. rhizophaga infecting soybean in North Dakota and in the United States.

Sclerotinia sclerotiorum, the causal agent of Sclerotinia stem rot (SSR), is a major fungal pathogen of soybeans, causing an estimated 31 million bushels (0.84 million metric tons) of yield loss in 2019 alone in the northern United States and Ontario, Canada. Fungicide applications are the primary management strategy, and their effectiveness depends on correct timing during the flowering period when apothecia are present on the soil surface. Accurate prediction of apothecial development can guide precise fungicide applications and reduce ineffective applications. In 2018, the University of Wisconsin-Madison developed three weather-based logistic regression models for irrigated conditions and three for non-irrigated conditions to predict the probability of S. sclerotiorum apothecial development, each incorporating different environmental variables. This current study aimed to validate the non-irrigated models and determine an appropriate action threshold for North Dakota. Models were evaluated using disease monitoring data collected from 52 non-irrigated commercial soybean fields across North Dakota over three years. To improve predictive accuracy, probabilities from non-irrigated models were averaged to create an ensemble model. The performance of individual and ensemble models was assessed. Results showed that the ensemble model achieved the highest accuracy (68%) among all the models, in predicting end-of-season disease incidence (DI, %) across all fields using a 10% DI threshold and a 35% risk probability action threshold. The model also demonstrated balanced sensitivity (70%) and specificity (67%). These findings can improve disease risk predictions, reduce unnecessary fungicide applications, and guide soybean farmers in North Dakota on optimal fungicide application timing.

Diaporthe spp. are among the most serious pathogens of soybean. Many different Diaporthe species can infect soybean plants. The species differ in their aggressiveness or virulence and in the severity of the damage they cause. Resistance breeding in soybean has been performed for only two Diaporthe species, so far. It would be very advantageous to identify soybean cultivars with resistance against other Diaporthe species as well, both as sources of resistance for breeding and to inform farmers which cultivars should be planted when a given Diaporthe species shows high incidence. We performed greenhouse experiments to differentiate levels of resistance using the Stem Cut and Stem Wound methods for inoculation of the plants with Diaporthe. Symptom severity was rated visually, and at 5 dpi the level of lipid peroxidation (LP), activity of superoxide dismutase (SOD), total phenolics and total flavonoids were measured. Among the four Diaporthe species tested, D. caulivora was most aggressive, followed by D. longicolla. Of the cultivars evaluated, Magnolia exhibited the highest level of resistance with no significant differences observed among the other cultivars. Although biochemical responses could be observed, it was impossible to determine the specific response responsible for elevated resistance in Magnolia.

Sudden death syndrome (SDS), primarily caused by Fusarium virguliforme, threatens soybean (Glycine max) production across the United States and Ontario, Canada. SDS thrives in cool, wet soils, with post-planting rainfall exacerbating disease, making pre-planting management strategies like resistant cultivars and seed treatments crucial. This study evaluated biological and chemical seed treatments on resistant and susceptible soybean cultivars across 14 locations in 2022 and 15 locations in 2023. Data collection included final stand counts, root rot severity, foliar SDS severity index (FDX), and yield. Trials were categorized into high (FDX ≥ 10%) or low (FDX < 10%) disease severity locations based on the non-treated control (NTC). In high disease locations, cultivar and seed treatment significantly (P ≤ 0.01) influenced FDX, root rot, and yield. The base+fluopyram and base+fluopyram+natamycin treatment reduced FDX by 6.7% and increased yield by 288.5 kg/ha over the non-treated. The resistant cultivar reduced FDX by 9.7% and root rot by 2.1%, while increasing yield by 247.7 kg/ha relative to the susceptible cultivar. Under low disease pressure, cultivar selection remained significant, with resistance reducing FDX by 2.4% and root rot by 0.8%, and improving yield by 445.5 kg/ha. In contrast, the effects of seed treatment were not significant in the low disease severity environments. No seed treatments reduced FDX or root rot and only base+fluopyram and base+fluopyram+natamycin increased yield (+254 to 301 kg/ha) compared to the non-treated in the low disease severity environments. Cultivar resistance remains the most effective SDS management strategy, with seed treatments providing significant benefits under high disease pressure.

Damping-off of soybean caused by soilborne oomycetes of the genera Globisporangium and Pythium pose a significant threat to soybean production, reducing emergence and yield in North America. Metalaxyl and metalaxyl-M are widely used against oomycetes in soybeans and corn; however, the repeated use of these active ingredients might lead to reduced sensitivity of some populations, increasing the interest in potential alternative active ingredients. Few field studies have assessed the effect of commercially available fungicide seed treatments on damping-off caused by these pathogens. This study evaluated the efficacy of fungicide seed treatments against Globisporangium and Pythium species across North America. In 2024, eight field trials were conducted in Indiana, Iowa, Ohio, Ontario, Michigan, North Dakota, Tennessee, and Wisconsin. Trials in Ohio, Ontario, and Tennessee relied on natural inoculum, whereas others were infested at planting with different pathogen species. Five commercial fungicide seed treatments were tested at label rates: (i) imidacloprid, mefenoxam, fluoxastrobin, and prothioconazole; (ii) clothianidin, ethaboxam, ipconazole, and metalaxyl; (iii) inpyrfluxam; (iv) thiamethoxam, mefenoxam, fludioxonil, and sedaxane; and (v) thiamethoxam, picarbutrazox, mefenoxam, fludioxonil, and sedaxane. A nontreated control was included. Fungicide seed treatment significantly improved seed emergence at the growth stages VC ( P = 0.0178) and V2 ( P = 0.0056). All treatments showed a positive yield effect compared with the nontreated control, although the differences were not statistically significant ( P > 0.7081). These findings suggest that seed treatments provide protection against damping-off, but further research is needed to clarify their utility in soybean production, particularly under low seeding rates.

The impact of plant diseases on soybean ( Glycine max [L.] Merrill) yield was estimated across 29 states and Ontario, Canada, from 2020 to 2024 by university and government plant pathologists. Losses from 29 pathogens or groups of pathogens were estimated at the end of each growing season through a survey and summarized across years and locations. Diseases reduced soybean yield by an estimated 1.2 billion bushels (32.8 million metric tons) valued at 14.6 billion USD for the survey period. Per acre, this estimated mean economic loss was equal to 32.93 USD (81.37 USD per hectare) across all locations and years, excluding costs such as fungicide seed treatments and foliar applications. Soybean cyst nematode (SCN) ( Heterodera glycines Ichinohe) reduced yield by 482.4 million bushels (13.1 million metric tons), a value nearly four times greater than the next greatest cause of yield loss, which was sudden death syndrome (SDS) (caused by Fusarium virguliforme O'Donnell & T. Aoki). Following SCN and SDS, the most significant yield losses were attributed to white mold (caused by Sclerotinia sclerotiorum [Lib.] de Bary), seedling diseases (caused by various pathogens), Phytophthora root and stem rot (caused by Phytophthora sojae Kaufm. & Gerd.), and root-knot nematodes ( Meloidogyne spp.), in descending order. The most important diseases in the southern United States were generally different from those in the northern United States and Ontario. The data presented here will enable government agencies, scientists, educators, commodity groups, funding organizations, and plant breeders to enhance and prioritize policy, research, funding, and education regarding soybean disease management.