Seeds are the cornerstone of food security for a growing global population. An ample supply of healthy, high-quality seeds of improved crop varieties is crucial to human nutrition and health. To meet this need, the global seed industry has become increasingly complex, characterized by multinational operations speeding the development of new varieties and efficiently providing adequate seed supplies. With accelerating international seed movement, the potential risks associated with seedborne pathogens are receiving increasing scrutiny, and phytosanitary regulations are frequently changing. At the same time, technological advances are driving the development of progressively more sensitive seed health testing methods, which are often required by national plant protection organizations to allow seed lots to be imported. Emerging seedborne plant pathogens, such as viral diseases of tomato, maize, and cucurbits, and changing import requirements have caused major disruptions in seed industry operations in recent years. A variety of innovative public-private sector collaborations has emerged in response to the challenges of international seed movement.

Plant diseases significantly impact food security and food safety. It was estimated that food production needs to increase by 50% to feed the projected 9.3 billion people by 2050. Yet, plant pathogens and pests are documented to cause up to 40% yield losses in major crops, including maize, rice, and wheat, resulting in annual worldwide economic losses of approximately US$220 billion. Yield losses due to plant diseases and pests are estimated to be 21.5% (10.1 to 28.1%) in wheat, 30.3% (24.6 to 40.9%) in rice, and 22.6% (19.5 to 41.4%) in maize. In March 2023, The American Phytopathological Society (APS) conducted a survey to identify and rank key challenges in plant pathology in the next decade. Phytopathology subsequently invited papers that address those key challenges in plant pathology, and these were published as a special issue. The key challenges identified include climate change effect on the disease triangle and outbreaks, plant disease resistance mechanisms and its applications, and specific diseases including those caused by Candidatus Liberibacter spp. and Xylella fastidiosa. Additionally, disease detection, natural and man-made disasters, and plant disease control strategies were explored in issue articles. Finally, aspects of open access and how to publish articles to maximize the Findability, Accessibility, Interoperability, and Reuse of digital assets in plant pathology were described. Only by identifying the challenges and tracking progress in developing solutions for them will we be able to resolve the issues in plant pathology and ultimately ensure plant health, food security, and food safety.

Transgenic insect -resistant maize has been assessed thoroughly in the field but not in storage. The effects of several transgenic Bacillus thuringiensis (Bt) maize hybrids on the interactions between stored -grain insects (Indianmeal moth, Plodia interpunctella, or maize weevil, Sitophilus zeamais) and the storage fungus Aspergillus flavus were evaluated in this study under laboratory conditions. Grain of Bt and non -Bt maize hybrids, with or without the conidia of A. flavus, were infested with P. interpunctella larvae or S. zeamais adults separately and stored at 32 degrees C and 80-85 % relative humidity. In Bt maize hybrids with lepidopteran resistance genes expressing Cry1Ab, Cry1Ab x Cry1F, and Cry1Ab x Cry1F x Vip3Aa proteins, the mortality of P. interpunctella was 100 % at the end of the 28 -day storage period. In Bt hybrids with coleopteran resistance genes expressing mCry3A and mCry3A x Cry34A/35Ab1 proteins, mortality of S. zeamais was 100 %. In the non -Bt grain, aflatoxin levels at the end of the storage period increased by almost two -fold in the presence of either P. interpunctella or S. zeamais (p <= 0.01). Insect infestation did not enhance A. flavus or aflatoxin contamination on transgenic hybrids because of deterred insect activity. In the non -Bt hybrid, A. flavus caused increased mortality, reduced survivorship, and lower growth indices of both insects, limiting their feeding in the A. flavus coated conventional grain. As a result, insect damage and grain weight loss were significantly higher in the absence of A. flavus. Insect infestation only enhanced aflatoxin contamination in the absence of transgenic insect resistance genes. This study demonstrated that Bt proteins were effective against the stored -grain insects P. interpunctella and S. zeamais and suggests that the use of transgenic hybrids can mitigate the risk of insect infestation, and A. flavus and aflatoxin contamination in stored grain.

The importance of seed treatments has increased rapidly in the past decade, mainly due to their high efficacy controlling early-season pests and diseases, and their limited environmental impact. Chemical seed treatments require a smaller amount of pesticide use and reduce environmental spread compared to foliar or soil applications; similarly, selection pressure for the development of resistance in the pest population is reduced. However, the rapid dissipation of seed treatment active ingredients after planting is associated with unpredictable duration of control, limiting the performance of seed treatment technology. Polyanhydrides are synthetic biodegradable polymers that can be used to deliver active ingredients or pharmaceuticals in pathological systems. They can provide a steady and sustained release of active compounds, enhancing the treatment of diseases caused by pathogens. Our study consists of experiments using polyanhydride nanoparticle-encapsulated fludioxonil and thiabendazole (two fungicides commonly used against Fusarium graminearum) at different rates on maize and soybean. We employed both rolled-towel assays (simulating a seedborne infection) and delayed emergence assays (simulating a soilborne infection). In the rolled-towel assay, nanoparticle-encapsulated fungicides performed similarly to standard formulations. However, when emergence was delayed for one week by low temperature, nanoparticle-encapsulated fungicides showed superior control over standard formulations. For longer emergence delay treatments, nanoparticle and conventional fungicide formulations showed similar levels of control. Polyanhydride encapsulated seed treatments showed the potential to prolong effectiveness of active ingredients when emergence is delayed due to cold temperatures, a very common situation in temperate maize production areas, such as the American Midwest.

Gummy stem blight (GSB) is a major disease of cucurbits worldwide. It is caused by three fungal species that are morphologically identical and have overlapping geographic and host ranges. Controlling GSB is challenging due to the lack of resistant cultivars and the pathogens' significant ability to develop resistance to systemic fungicides. The causal agent of GSB is recognized as a complex of three phylogenetically distinct species belonging to domain Eukaryota, kingdom Fungi, phylum Ascomycota, subphylum Pezizomycotina, class Dothideomycetes, subclass Pleosporomycetida, order Pleosporales, family Didymellaceae, genus Stagonosporopsis, species cucurbitacearum, citrulli, and caricae. Pycnidia are tan with dark rings of cells around the ostiole measuring 120-180 mu m in diameter. Conidia are 6-13 mu m long, hyaline, cylindrical with round ends, and non- or monoseptate. Pseudothecia are black and globose in shape and have a diameter of 125-213 mu m. Ascospores are 14-18 x 4-6 mu m long, hyaline, ellipsoidal with round ends, and monoseptate with a distinct constriction at the septum. Eight ascospores are found per ascus. The upper end of the apical cell is pointed, whereas the lower end of the bottom cell is blunt. Species-specific PCR primers that can be used in a multiplex conventional PCR assay are available. The GSB species complex is pathogenic to 37 species of cucurbits from 21 different genera. S. cucurbitacearum and S. citrulli are specific to cucurbits, while S. caricae is also pathogenic to papaya and babaco-mirim (Vasconcellea monoica), a related fruit. Under favourable environmental conditions, symptoms can appear 3-12 days after spore germination. Leaf spots often start at the leaf margin or extend to the margins. Spots expand and coalesce, resulting in leaf blighting. Active lesions are typically water-soaked. Cankers are observed on crowns, main stems, and vines. Red to amber gummy exudates are often seen on the stems after cankers develop on cortical tissue.

Gummy stem blight is a destructive fungal disease that affects all commonly cultivated cucurbit crops. One cultivar each of the five cucurbit species susceptible to gummy stem blight were inoculated with two isolates of Stagonosporopsis caricae, three isolates of Stagonosporopsis citrulli, and one isolate of Stagonosporopsis cucurbitacearum to explore the host range and relative aggressiveness of each isolate. In a series of greenhouse experiments, all isolates were pathogenic to the crops tested, but disease severity differed significantly among isolates and cucurbit cultivars. There were also significant interactions between isolate and cultivar. S. citrulli isolates caused the most severe symptoms across all five cultivars, and S. citrulli isolates C-68 and DbHD-10 were consistently among the most aggressive isolates on each cultivar. S. caricae isolates generally caused less severe symptoms, but W-1028 ( S. caricae) was among the most aggressive isolates on Tyria cucumber. These results add to the understanding of the relationships of the three Stagonosporopsis species with various cucurbit hosts, reinforcing knowledge about the pathogenicity of the three species across cucurbit crops and the potentially high aggressiveness of S. citrulli. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Plant pathogens cause significant reductions in yield and crop quality and cause enormous economic losses worldwide. Reducing these losses provides an obvious strategy to increase food production without further degrading natural ecosystems; however, this requires knowledge of the biology and evolution of the pathogens in agroecosystems.

Seed vigor is a complex trait which refers the quick and uniform germination of seeds in the field. It can be highly affected by the genetic background of the seed, the environment where the seeds are grown, and storage conditions (Yang, X. B. 1999). Besides, seeds affected by quality parameters may respond differently to seedling pathogens in the soil; these responses are likely to differ according to environmental conditions. The main objective of the study was to evaluate the relationship between soybean quality and the effects of specific soil-borne pathogens on soybean emergence and seedling growth, with a specific focus on phenotyping early-stage roots. Seed lots with different levels of seed quality, represents a range of seed vigor with the same genetic background, were created by accelerated-aging (aa) treatments. The effect of aa on seed performance was tested in growth chambers with and without infested soil at 20 °C and 25 °C. A remarkable emergence reduction (65-55%) was observed in the aged-seed. Synergistic effects between seed aging and Rhizoctonia solani infestation was observed on root biomass (root dry weight) and the numbers of root tips, forks, and crossings (p<0.05). Besides, some parameters such as plant length and fresh weight, fresh root weight, root length, volume, and surface area were significantly affected by both seed quality and fungal inoculum. The results obtained from the study is expected to contribute on determining the impact of environmental conditions and stress factors on the epidemiology of soilborne pathogens. On the other hand, we expect that the results will shed light on developing new strategies for effective disease management.

Maize chlorotic mottle virus (MCMV) causes maize lethal necrosis disease in combination with a cereal-infecting potyvirus, leading to high yield losses. There is limited information on seed infection or contamination rate by MCMV and its comparison with transmission rate to maize seedlings. This study was conducted to determine the extent of seed contamination in seed lots from MCMV-infected maize fields in Kenya and the transmission of MCMV from seeds to seedlings. To determine the contamination levels, whole seeds were ground and the extract tested for the presence of MCMV using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Seedling grow-outs were tested for seed transmission of MCMV using DAS-ELISA and real-time reverse transcription polymerase chain reaction (real-time RT-PCR) methods. The seed contamination rates of the four seed lots tested ranged from 4.9 to 15.9%. MCMV transmission frequency for 37,617 seedlings, tested in 820 pools of varying seed amounts by DAS-ELISA, was 0.17%, whereas a transmission frequency of 0.025% was obtained from 8,322 seedlings tested in 242 pools by real-time RT-PCR. Seeds from plants mechanically inoculated with MCMV had an overall seed transmission rate of 0.04% in 7,846 seedlings tested in 197 pools. The study showed that even with substantial contamination of maize seed with MCMV, the transmission of the virus from the seed to seedlings was low. Nevertheless, even low rates of transmission can be significant under field conditions where insect vectors can further spread the disease from infected seedlings, unless diseased plants are detected in time and properly managed. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Scientific communication is facilitated by a data-driven, scientifically sound taxonomy that considers the end-user's needs and established successful practice. In 2013, the Fusarium community voiced near unanimous support for a concept of Fusarium that represented a clade comprising all agriculturally and clinically important Fusarium species, including the F. solani species complex (FSSC). Subsequently, this concept was challenged in 2015 by one research group who proposed dividing the genus Fusarium into seven genera, including the FSSC described as members of the genus Neocosmospora, with subsequent justification in 2018 based on claims that the 2013 concept of Fusarium is polyphyletic. Here, we test this claim and provide a phylogeny based on exonic nucleotide sequences of 19 orthologous protein-coding genes that strongly support the monophyly of Fusarium including the FSSC. We reassert the practical and scientific argument in support of a genus Fusarium that includes the FSSC and several other basal lineages, consistent with the longstanding use of this name among plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students, and researchers with a stake in its taxonomy. In recognition of this monophyly, 40 species described as genus Neocosmospora were recombined in genus Fusarium, and nine others were renamed Fusarium. Here the global Fusarium community voices strong support for the inclusion of the FSSC in Fusarium, as it remains the best scientific, nomenclatural, and practical taxonomic option available.

Fusarium is one of the most important genera of plant-pathogenic fungi in the world and arguably the world's most important mycotoxin-producing genus. Fusarium species produce a staggering array of toxic metabolites that contribute to plant disease and mycotoxicoses in humans and other animals. A thorough understanding of the mycotoxin potential of individual species is crucial for assessing the toxicological risks associated with Fusarium diseases. There are thousands of reports of mycotoxin production by various species, and there have been numerous attempts to summarize them. These efforts have been complicated by competing classification systems based on morphology, sexual compatibility, and phylogenetic relationships. The current depth of knowledge of Fusarium genomes and mycotoxin biosynthetic pathways provides insights into how mycotoxin production is distributedamong species and multispecies lineages (species complexes) in the genus as well as opportunities to clarify and predict mycotoxin risks connected with known and newly described species. Here, we summarize mycotoxin production in the genus Fusarium and how mycotoxin risk aligns with current phylogenetic species concepts.

Xanthomonas vasicola pv. vasculorum (syn. X. campestris pv. vasculorum) was initially identified as the causal agent of bacterial leaf streak of corn in South Africa. The pathovar vasculorum causes disease on sugarcane and corn, but a subset of these strains was noted for its increased disease severity in corn. This subset was reclassified as X. campestris pv. zeae in the early 1990s and was found to have slightly different biochemical and genetic properties than isolates from sugarcane. There has been an emergence of X. campestris pv. zeae-like strains of X. vasicola pv. vasculorum in both the United States and Argentina since 2010. We performed whole genome sequencing on U.S. isolates to confirm their identity. Informed by comparative genomics, we then developed specific TaqMan qPCR and loop-mediated isothermal amplification (LAMP) assays for the detection of this specific subset of X. vasicola pv. vasculorum strains. The qPCR 4909 assay was tested against 27 xanthomonads (diverse representation), 32 DNA extractions from corn leaves confirmed as positive or negative for the bacterium, 41 X. vasicola pv. vasculorum isolates from corn in the United States and Argentina, and 31 additional bacteria associated with corn, sugarcane, or sorghum. In all cases the assay was shown to be specific for the X. vasicola pv. vasculorum isolates that cause more severe disease on corn. We then tested the LAMP 166 assay against the 27 xanthomonads and 32 corn leaf DNA samples, and we found this assay was also specific for this subset of X. vasicola pv. vasculorum isolates. We also developed a live/dead cells distinction protocol using propidium monoazide prior to DNA extraction for analyzing seed washes using these assays. These two detection assays can be useful for both diagnosticians and researchers to specifically identify the X. vasicola pv. vasculorum isolates that cause more severe symptoms on corn.

This paper reports original evidence regarding the potential role of seed transmission of Xanthomonas vasicola pv. vasculorum in the epidemiology of bacterial leaf streak (BLS) in maize. We evaluated the occurrence of the pathogen on seeds from diseased fields and its subsequent transmission to seedlings. In 2016 and 2017, X. vasicola pv. vasculorum was detected by TaqMan PCR from 22 of 41 maize seed lots harvested from naturally infected fields in Colorado, Nebraska, and Iowa. However, many of the PCR-positive samples did not yield culturable X. vasicola pv. vasculorum colonies. The highest levels of seed contamination were detected in dent maize and popcorn from NE and CO. Seed transmission was evaluated in greenhouse grow-outs from eight seed lots, totaling more than 14,000 plants. Putative seed transmission events from naturally contaminated seed lots, estimated from PCR results, occurred at a frequency between 0.1 and 0.5% in 10-seedling pooled samples and at a frequency of 2.7% from individual plant assays. However, no seedling symptoms were observed during these assays and live X. vasicola pv. vasculorum colonies were not recovered from PCR-positive seedlings. In contrast, seed transmission was readily demonstrated from artificially contaminated seed lots, including typical symptoms and recovery of live bacteria. Seed transmission consistently occurred from seeds soaked in bacterial suspensions with concentrations of ≥106 CFU/ml, suggesting that a threshold population of the bacterium is necessary for the development of BLS symptoms and recovery of live bacteria. The low bacterial populations on naturally contaminated seeds apparently were not sufficient to result in diseased seedlings.