Toxicity and sublethal effects of phthalides analogs to Rhyzopertha dominica

Phthalides and their precursors have demonstrated a large variety of biological activities. Eighteen phthalides were synthesized and tested on the stored grain pest Rhyzopertha dominica. In the screening bioassay, compounds rac‐(2R,2aS,4R,4aS,6aR,6bS,7R)‐7‐bromohexahydro‐2,4‐methano‐1,6‐dioxacyclopenta[cd]pentalen‐5(2H)‐one (15) and rac‐(3R,3aR,4R,7S,7aS)‐3‐(propan‐2‐yloxy)hexahydro‐4,7‐methano‐2‐benzofuran‐1(3H)‐one (17) showed mortality similar to the commercial insecticide, Bifenthrin® (≥90 %). The time (LT50) and dose (LD50) necessary to kill 50 % of the R. dominica population were determined for the most efficacious phthalides 15 and 17. Compound 15 presented the lowest LD50 (1.97 μg g−1), being four times more toxic than Bifenthrin® (LD50=9.11 μg g−1). Both compounds presented an LT50 value equal to 24 h. When applied at a sublethal dose, both phthalides (especially compound 15), reduced the emergence of the first progeny of R. dominica. These findings highlight the potential of phthalides 15 and 17 as precursors for the development of insecticides for R. dominica control

Ecology and diversity of culturable fungal species associated with soybean seedling diseases in the Midwestern United States

Aims: To isolate and characterize fungi associated with diseased soybean seedlings in Midwestern soybean production fields and to determine the influence of environmental and edaphic factors on their incidence. Methods and Results: Seedlings were collected from fields with seedling disease history in 2012 and 2013 for fungal isolation. Environmental and edaphic data associated with each field was collected. 3036 fungal isolates were obtained and assigned to 76 species. The most abundant genera recovered were Fusarium (73%) and Trichoderma (11.2%). Other genera included Mortierella, Clonostachys, Rhizoctonia, Alternaria, Mucor, Phoma, Macrophomina and Phomopsis. Most recovered species are known soybean pathogens. However, non-pathogenic organisms were also isolated. Crop history, soil density, water source, precipitation and temperature were the main factors influencing the abundance of fungal species. Conclusion: Key fungal species associated with soybean seedling diseases occurring in several US production regions were characterized. This work also identified major environment and edaphic factors affecting the abundance and occurrence of these species. Significance and Impact of the Study: The identification and characterization of the main pathogens associated with seedling diseases across major soybean-producing areas could help manage those pathogens, and devise more effective and sustainable practices to reduce the damage they cause

Reduction of Pythium Damping-off in Soybean by Biocontrol Seed Treatment

Pythium spp. is one of the major groups of pathogens that cause seedling diseases on soybean, leading to both pre- and post-emergence damping-off and root rot. More than 100 species have been identified within this genus, with P. irregulare, P. sylvaticum, P. ultimum var ultimum, and P. torulosum, being particularly important for soybean production given their aggressiveness, prevalence, and abundance in production fields. This study investigated the antagonistic activity of potential BCAs native to the US Midwest against Pythium spp. First, in vitro screening identified BCAs that inhibit P. ultimum var. ultimum growth. Scanning electron microscopy demonstrated evidence of mycoparasitism of all potential biocontrol isolates against the Pythium ultimum var. ultimum and P. torulosum, with the formation of appressorium-like structures, short-hyphal branches around host hyphae, hook-shaped structures, coiling, and parallel growth of the mycoparasite along the host hyphae. Based on these promising results, selected BCAs were tested under field conditions against six different Pythium spp. Trichoderma afroharzianum 26 used alone and a mix of Trichoderma hamatum 16 + T. afroharzianum 19 used as seed treatments protected soybean seedlings from Pythium spp. infection, as BCA-treated plots had on average 15-20% increase on plant stand and increased vigor compared with control plots. Our results also indicate that some of these potential biocontrol agents could be added with a fungicide seed treatment with minimum inhibition occurring, depending on the fungicide active ingredient. This research highlights the need for the development of tools to incorporate biological control as a facet of soybean seedling disease management programs. The harnessing of native biological control agents (BCA) is a potential tool that could be integrated with other management strategies to provide efficient control of seedling diseases.This is a manuscript of an article published as Pimentel, Mirian Filgueira, Erika Arnao, Amanda J. Warner, Leonardo F. Rocha, Arjun Subedi, Nariman Elsharif, Martin I. Chilvers et al. "Reduction of Pythium Damping-off in Soybean by Biocontrol Seed Treatment." Plant Disease (2022). doi:10.1094/PDIS-06-21-1313-RE. Posted with permission

Ecology and diversity of culturable fungal species associated with soybean seedling diseases in the Midwestern United States

Aims: To isolate and characterize fungi associated with diseased soybean seedlings in Midwestern soybean production fields and to determine the influence of environmental and edaphic factors on their incidence. Methods and Results: Seedlings were collected from fields with seedling disease history in 2012 and 2013 for fungal isolation. Environmental and edaphic data associated with each field was collected. 3036 fungal isolates were obtained and assigned to 76 species. The most abundant genera recovered were Fusarium (73%) and Trichoderma (11.2%). Other genera included Mortierella, Clonostachys, Rhizoctonia, Alternaria, Mucor, Phoma, Macrophomina and Phomopsis. Most recovered species are known soybean pathogens. However, non-pathogenic organisms were also isolated. Crop history, soil density, water source, precipitation and temperature were the main factors influencing the abundance of fungal species. Conclusion: Key fungal species associated with soybean seedling diseases occurring in several US production regions were characterized. This work also identified major environment and edaphic factors affecting the abundance and occurrence of these species. Significance and Impact of the Study: The identification and characterization of the main pathogens associated with seedling diseases across major soybean-producing areas could help manage those pathogens, and devise more effective and sustainable practices to reduce the damage they cause.This article is published as Pimentel, Mirian F., Ali Y. Srour, Amanda J. Warner, Jason P. Bond, Carl A. Bradley, John Rupe, Martin I. Chilvers et al. "Ecology and Diversity of Culturable Fungal Species Associated with Soybean Seedling Diseases in the Midwestern United States." Journal of Applied Microbiology (2022). doi:10.1111/jam.15507. Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted