Influence of Propiconazole and Metconazole Formulations on Bacillus subtilis Vegetative Cell Growth and Disease Control of Fruit Crops.

Biological control agent Bacillus subtilis formulated as Theia is registered for control of fungal and bacterial diseases of fruit crops. Combinations of Theia and strategic concentrations of two demethylation inhibitor (DMI) fungicides were investigated to explore potential synergisms. Bacteria were cultured in nutrient broth and combined with technical grades and two formulations of propiconazole (emulsifiable concentrate [EC] and wettable powder) and metconazole (EC and water-dispersible granule) at 0, 10, 50, 100, and 150 µg/ml of active ingredient. After cocultivation, the optical density (OD600) and colony forming units (CFU/ml) were evaluated. In contrast to EC formulations, the wettable powder or water-dispersible granule formulations at 10 or 50 µg/ml of both DMIs did not affect vegetative cell growth. The mixture of Theia and each formulated DMI at 50 µg/ml of active ingredient resulted in a significant reduction of Monilinia fructicola lesion development on apple, Colletotrichum siamense lesion development on cherry, and Botrytis cinerea lesion development on cherry. The combination of Theia with EC formulations showed weaker disease reduction due to antagonism. Only Theia plus non-EC formulated propiconazole and metconazole significantly reduced brown rot disease incidence of apple compared with the respective solo treatments and anthracnose disease incidence of cherry compared with the untreated control. Our results indicated that at least some DMI fungicides possess bactericidal effects depending on the formulation and concentration. The combination of Theia with a lower-than-label-rate concentration (50 µg/ml) of the DMI fungicides propiconazole and metconazole showed potential for synergistic effects, especially when non-EC formulations were used.

Bioproducts of Pseudomonas chlororaphis Suppress DMI Fungicide-Induced CsCYP51A and CsCYP51B Gene Expression in Colletotrichum siamense and Generate Synergistic Effects with Metconazole and Propiconazole.

Mixtures of fungicides with different modes of action are commonly used as disease and resistance management tools, but little is known of mixtures of natural and synthetic products. In this study, mixtures of metabolites from the rhizobacterium Pseudomonas chlororaphis strain ASF009 formulated as Howler EVO with below-label rates (50 µg/ml) of conventional sterol demethylation inhibitor (DMI) fungicides were investigated for control of anthracnose of cherry (Prunus avium) caused by Colletotrichum siamense. Howler mixed with metconazole or propiconazole synergistically reduced disease severity through lesion growth. Real-time PCR showed that difenoconazole, flutriafol, metconazole, and propiconazole induced the expression of DMI target genes CsCYP51A and CsCYP51B in C. siamense. The addition of Howler completely suppressed the DMI fungicide-induced expression of both CYP51 genes. We hypothesize that the downregulation of DMI fungicide-induced expression of the DMI target genes may, at least in part, explain the synergism observed in detached fruit assays.

Loop-mediated isothermal amplification detection of Phytophthora kernoviae, Phytophthora ramorum, and the P. ramorum NA1 lineage on a microfluidic chip and smartphone platform.

Rapid, field-deployable assays such as loop-mediated isothermal amplification (LAMP) are critical for detecting nursery and forest pathogens like Phytophthora ramorum and P. kernoviae to prevent pathogen spread. We developed and validated four LAMP assays for genus-level detection of Phytophthora spp., species-level detection of P. kernoviae and P. ramorum and lineage-level detection of the P. ramorum NA1 lineage. Cross reactivity of the two species-specific LAMP assays was evaluated using a set of 18 Phytophthora spp. known to infect nursery crop hosts. The correct target species were detected by the species-level LAMP assays. The Phytophthora spp. LAMP assay was evaluated against 27 Phytophthora spp. and other bacterial and fungal pathogens and reacted with all the Phytophthora spp. evaluated but no other bacterial or fungal species. The limit of detection (LOD) of the P. kernoviae LAMP was 100 fg/µl and the LOD of the P. ramorum LAMP assay was 1 pg/µl of DNA. The NA1 LAMP assay was tested against the NA1, NA2, EU1, and EU2 lineages of P. ramorum and was lineage-specific but had a higher LOD (100pg/µl) than the species-specific LAMP assays. Both P. ramorum and P. kernoviae LAMP assays were highly precise (>0.94) in detecting the respective pathogens in symptomatic rhododendron leaves and co-inoculation experiments. The set of four LAMP assays were run in tandem on a microfluidic chip and smartphone platform and can be used in the field to detect and monitor spread of these regulatory Phytophthora spp. in forest and/or nursery settings.

The role of oxalic acid in Clarireedia jacksonii virulence and development on creeping bentgrass.

Dollar spot is a destructive foliar disease of amenity turfgrass caused by the fungus Clarireedia spp., and mainly Clarireedia jacksonii on the northern US region's cool-season grass. Oxalic acid (OA) is an important pathogenicity factor in related fungal plant pathogens such as Sclerotinia sclerotiorum, however, the role of OA in the pathogenic development of C. jacksonii remains unclear due to its recalcitrance to genetic manipulation. To overcome these challenges, a CRISPR/Cas9-mediated homologous recombination approach was developed. Using this novel approach, the oxaloacetate acetylhydrolase (Oah) gene that is required for the biosynthesis of OA was deleted from C. jacksonii wild-type stain. Two independent knockout mutants, ΔCjoah-1 and ΔCjoah-2, were generated and inoculated on potted creeping bentgrass along with a wild-type isolate (WT) and a genome sequenced isolate LWC-10. After 12 days, bentgrass inoculated with the mutants ΔCjoah-1 and ΔCjoah-2 exhibited 59.41% lower dollar spot severity compared to the WT and LWC-10 isolates. Oxalic acid production and environmental acidification were significantly reduced in both mutants when compared to the WT and LWC-10. Surprisingly, stromal formation was also severely undermined in the mutants in vitro, suggesting a critical developmental role of OA independent of plant infection. These results demonstrate that OA plays a significant role in C. jacksonii virulence and provide novel directions for future management of dollar spot.

The Microbial Metabolite Wuyiencin Potential Targets Threonine dehydratase in Didymella segeticola to Achieve Control of Tea Leaf Spot.

Tea leaf spot caused by Didymella segeticola is a disease that has recently been discovered in the tea plantations of Southwest China, and which has a significant negative impact on the yield and quality of tea leaves. Wuyiencin is a nucleotide antimicrobial that is effective against a range of fungal diseases. However, its mode of action is still unclear. The current study found that wuyiencin inhibited the mycelial growth of D. segeticola in vitro. Meanwhile, in vivo experiments confirmed that wuyiencin had a significant curative effect on tea leaf spot. Microscopic observation represented it damaged the organelles and nucleus in fungal cells. Reverse transcription quantitative PCR assays revealed that mycelium treated with wuyiencin at the half-maximal effective concentration (EC50) dosage for 1 hour exhibited 3.23 times lower expression of Threonine dehydratase (Td) gene, which is responsible for producing pyruvate. The wild type (WT) strain had a 1.77-fold higher pyruvate concentration than that in the td mutant (P < 0.05). The td mutant was more sensitive than the WT to wuyiencin treatment, with the EC50 value in the td mutant being 30.01 µg/ml, compared with 82.34 µg/ml in the WT. Molecular docking demonstrated that wuyiencin bound to Td, with a binding energy of -10.47 kcal/mol. Compared with the WT strain, wuyiencin significantly reduced ATP concentration of the td mutant strain at dosages of 80.0 and 160.0 µg/ml. In total, wuyiencin reduced Td activity, inhibited pyruvate production, and decreased ATP content in the phytopathogenic fungus, ultimately disturbing the growth of the mycelium.

The Nuances of Plant Disease Severity Estimation Using Quantitative Ordinal Scales-Lessons Learned over Four Decades.

We revisit the foundations of the Horsfall-Barratt (HB) scale, a widely cited and applied plant disease visual assessment tool introduced in 1945, a full 37 years prior to T. T. Hebert's 1982 critique that raised concerns regarding the scale's rationale, particularly its reliance on the Weber-Fechner law and visual perception assumptions. Although use of the HB scale and similar ordinal scales persists, comprehensive studies have revealed that direct visual estimation using percentage scales often proves more accurate and reliable. Challenges remain, such as biases due to estimator subjectivity and the potential for misclassification. The logarithmic assumptions of the HB scale have been debunked, and the importance of choosing appropriate interval sizes and numbers of classes in developing ordinal scales is emphasized. Analyzing ordinal scale data appropriately is crucial, and recent advances offer promising methods that reduce type II error rates. The closely related disease severity index is noted to have its shortcomings and potential for misuse. The letter underscores the need for continuous refinement and critical evaluation of disease assessment methodologies.

Hiding in Plain Sight: A Widespread Native Perennial Harbors Diverse Haplotypes of 'Candidatus Liberibacter solanacearum' and Its Potato Psyllid Vector.

The unculturable bacterium 'Candidatus Liberibacter solanacearum' (CLso) is responsible for a growing number of emerging crop diseases. However, we know little about the diversity and ecology of CLso and its psyllid vectors outside of agricultural systems, which limits our ability to manage crop disease and understand the impacts this pathogen may have on wild plants in natural ecosystems. In North America, CLso is transmitted to crops by the native potato psyllid (Bactericera cockerelli). However, the geographic and host plant range of the potato psyllid and CLso beyond the borders of agriculture are not well understood. A recent study of historic herbarium specimens revealed that a unique haplotype of CLso was present infecting populations of the native perennial Solanum umbelliferum in California decades before CLso was first detected in crops. We hypothesized that this haplotype and other potentially novel CLso variants are still present in S. umbelliferum populations. To test this, we surveyed populations of S. umbelliferum in Southern California for CLso and potato psyllid vectors. We found multiple haplotypes of CLso and the potato psyllid associated with these populations, with none of these genetic variants having been previously reported in California crops. These results suggest that CLso and its psyllid vectors are much more widespread and diverse in North American natural plant communities than suggested by data collected solely from crops and weeds in agricultural fields. Further characterization of these apparently asymptomatic haplotypes will facilitate comparison with disease-causing variants and provide insights into the continued emergence and spread of CLso.

Molecular characterization of Fusarium isolates from Upland cotton roots in Uzbekistan and whole-genome comparison with isolates from the USA.

Fusarium oxysporum f. sp. vasinfectum (FOV) is a significant cotton (Gossypium spp.) pathogen causing vascular wilt, browning of the vascular tissues, and plant death in the most severe cases. This global disease is responsible for sizeable crop losses annually and is found in many cotton producing regions, including the Republic of Uzbekistan and the USA. Specifically, FOV race 4 (FOV4) has been disrupting production for years. This study aimed to genetically characterize FOV4 isolates causing disease in the main cotton producing region of Uzbekistan and compare with FOV4 isolates from the USA. A field study conducted in the Bukhara region of the Republic of Uzbekistan in the spring of 2022 identified both FOV4 and new Fusarium isolates from Upland cotton exhibiting typical Fusarium wilt symptoms. Molecular markers were initially used to identify isolates of interest, and a phylogenetic analysis was performed using partial EF1-α sequences, followed by a comparative genomic analysis. We also report for the first time the isolation of F. solani and F. commune causing Fusarium wilt in Uzbekistan. Furthermore, we show that the FOV4 population within our sampling region of Uzbekistan may be dominated by a single biotype with an effector profile similar to that of FOV race 7 (FOV7). One of these effector proteins is also present in the F. commune isolate showing virulence to cotton. Whole genome comparisons between FOV races can identify unique genetic markers for FOV4 and aid in the development of tools for breeding FOV resistant cotton varieties.

What Explains Hop Growers' Fungicide Use Intensity and Management Costs in Response to Powdery Mildew?

Methods for causal inference from observational data are common in human disease epidemiology and social sciences but are used relatively little in plant pathology. We draw upon an extensive data set of the incidence of hop plants with powdery mildew (caused by Podosphaera macularis) collected from yards in Oregon from 2014 to 2017 and associated metadata on grower cultural practices, cultivar susceptibility to powdery mildew, and pesticide application records to understand variation in and causes of growers' fungicide use and associated costs. An instrumental causal forest model identified growers' spring pruning thoroughness, cultivar susceptibility to two of the dominant pathogenic races of P. macularis, network centrality of yards during May-June and June-July time transitions, and the initial strain of the fungus detected as important variables determining the number of pesticide active constituents applied by growers and the associated costs they incurred in response to powdery mildew. Exposure-response function models fit after covariate weighting indicated that both the number of pesticide active constituents applied and their associated costs scaled linearly with the seasonal mean incidence of plants with powdery mildew. Although the causes of pesticide use intensity are multifaceted, biological and production factors collectively influence the incidence of powdery mildew, which has a direct exposure-response relationship with the number of pesticide active constituents that growers apply and their costs. Our analyses point to several potential strategies for reducing pesticide use and costs for management of powdery mildew on hop. We also highlight the utility of these methods for causal inference in observational studies.

A systematic approach for identifying unique genomic sequences for Fusarium oxysporum f. sp. lactucae race 1 and development of molecular diagnostic tools.

Fusarium oxysporum f. sp. lactucae (FOLac) is a soil- and seedborne fungal pathogen that causes Fusarium wilt of lettuce, an important disease threatening global lettuce production. Based on pathogenicity on differential lettuce cultivars, four races (1-4) have been identified, with race 1 the only race detected in the United States, and the closely related, emerging race 4 known only in Europe. The development of race-specific diagnostic tools is hindered by insufficient genomic data to distinguish between the two races and FOLac from other F. oxysporum formae speciales and nonpathogenic isolates. Here, we describe a systematic approach for developing diagnostic markers for FOLac race 1 that utilized a comprehensive sequence database of F. oxysporum to identify 15 unique genomic sequences. Marker specificity was validated through an exhaustive screening process against genomic data from 797 F. oxysporum isolates representing 64 formae speciales and various plants and non-plant substrates. One of the unique sequences was used to develop a TaqMan quantitative polymerase chain reaction assay and a recombinase polymerase amplification assay, both exhibiting 100% sensitivity and specificity when tested against purified DNA from 171 F. oxysporum isolates and 69 lettuce samples. The relationship between qPCR Ct values and colony forming units (CFU)/g values was also determined. This study not only introduces a new marker for FOLac race 1 diagnostics and soil quantitation, but also underscores the value of an extensive genomic database and screening software pipeline for developing molecular diagnostics for F. oxysporum formae speciales and other fungal taxa.

A new vector of Xylella fastidiosa: The role of Mesoptyelus impictifrons as a vector in Israel.

In recent years, the bacterium Xylella fastidiosa has been spreading in almond orchards (causing almond leaf scorch) and in grapevines (causing Pierce's disease) in northern Israel. Sucking insects specialized for xylem sap-feeding transmit this plant pathogen but the identity of the vector(s) in Israel has not been determined. Hence, we sought to determine the main potential vector(s) of X. fastidiosa in Israel. In our surveys in northern Israel, we collected and identified four species of spittlebugs: Neophilaenus campestris, Philaenus arslani, Cercopis intermedia, and Mesoptyelus impictifrons. The first two species were found in very low numbers. Cercopis intermedia was found only in spring and did not transmit X. fastidiosa in controlled experiments. Mesoptyelus impictifrons was the most abundant and widely distributed species in our survey and was found in and around infected vineyards in northern Israel. In controlled experiments we found that 35%-39% of M. impictifrons adults acquire X. fastidiosa from infected vines and almonds and subsequently transmit it to vines and almonds. Taken together, this study suggests that M. impictifrons is an important new vector of X. fastidiosa in almond orchards and vineyards in northern Israel. Further studies are needed on M. impictifrons' biology, ecology, and role as a vector of X. fastidiosa.

Winter Rye Cover Crops Shelter Competent Squash Phyllosphere Bacteria to Reduce Pseudomonas syringae pv. lachrymans Growth and Angular Leaf Spot Symptoms.

Cover crops, a soil conservation practice, can contribute to reducing disease pressure caused by Pseudomonas syringae, considered one of the most important bacterial plant pathogens. We recently demonstrated that the phyllosphere (leaf surface) bacterial community structure changed when squash (Cucurbita pepo) was grown with a rye (Secale cereale) cover crop treatment, followed by a decrease of angular leaf spot disease symptoms on squash caused by P. syringae pv. lachrymans. Application of biocontrol agents is a known agricultural practice to mitigate crop losses due to microbial disease. In this study, we tested the hypothesis that some phyllosphere bacteria promoted when squash is grown on cover crops could be isolated and used as a biocontrol agent to decrease angular leaf spot symptoms. We grew squash during a 2-year field experiment using four agricultural practices: bare soil, cover crops, chemically terminated cover crops, and plastic cover. We sampled squash leaves at three different dates each year and constructed a collection of cultivable bacterial strains isolated from squash leaves and rye cover crop material. Each isolated strain was identified by 16S rRNA gene sequencing and used in in vitro (Petri dish) pathogen growth and in vivo (greenhouse) symptom control assays. Four bacterial isolates belonging to the genera Pseudarthrobacter, Pseudomonas, Delftia, and Rhizobium were shown to inhibit P. syringae pv. lachrymans growth and angular leaf spot symptom development. Strikingly, the symptom control efficacy of all strains was stronger on older leaves. This study sheds light on the importance of bacterial isolation from cover crop sources to promote disease control. [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.

Drosophila hydei as a Potential Vector of Ceratocystis fimbriata, the Causal Agent of Sweetpotato Black Rot, in Storage Facilities.

Ceratocystis fimbriata, the causal agent of sweetpotato black rot, is a pathogen capable of developing and spreading within postharvest settings. A survey of North Carolina sweetpotato storage facilities was conducted to determine the arthropods present and identify potential vectors of C. fimbriata. Sixteen taxonomic categories were recovered, and the genus Drosophila (Diptera: Drosophilidae) accounted for 79% of individuals sampled, with Drosophila hydei being the most abundant species. Behavioral assays were conducted to determine if D. hydei is attracted to C. fimbriata-inoculated roots and if the pathogen could be recovered from external or internal surfaces of the insect. Flies were released in insect-trapping pitchers containing either C. fimbriata-inoculated or noninoculated roots or Petri dishes. No significant differences in fly number were detected in sweetpotato-baited pitchers; however, significant differences were found in the pitcher baited with a mature C. fimbriata culture. Flies were subjected to washes to determine if viable C. fimbriata was present (internally or externally); washes were plated onto carrot agar plates and observed for the presence of C. fimbriata colonies. Both external and internal washes had viable C. fimbriata inocula with no significant differences, and inoculated sweetpotatoes had a significantly higher number of flies carrying C. fimbriata. This study suggests that D. hydei can carry C. fimbriata from infected sweetpotatoes and move viable C. fimbriata inocula both externally and internally, making this the first report of any Drosophila sp. serving as a potential vector for the Ceratocystis genus.

Phenazine-1-carboxamide Regulates Pyruvate Dehydrogenase of Phytopathogenic Fungi to Control Tea Leaf Spot Caused by Didymella segeticola.

Due to a lack of understanding of the disease epidemiology and comprehensive control measures, tea leaf spot caused by Didymella segeticola has a significant negative impact on tea yield and quality in the tea plantations of Southwest China. Phenazine-1-carboxamide (PCN) is a phenazine compound derived from Pseudomonas species, which exhibits antimicrobial activity against various pathogens. However, its inhibitory mechanism is not yet clear. The current study evaluated the inhibitory activity of PCN against various phytopathogenic fungi and found that PCN has inhibitory activity against multiple pathogens, with a half-maximal effective concentration (EC50) value for D. segeticola of 16.11 µg/mL in vitro and a maximum in-vivo curative activity of 72.28% toward tea leaf spot. Morphological changes in the hyphae after exposure to PCN were observed through microstructure and ultrastructure analysis, and indicated that PCN causes abnormalities in the hyphae, such as cytoplasmic coagulation, shortened hyphal inter-septum distances, and unclear boundaries of organelles. Transcriptomic analysis revealed that PCN upregulated the expression of genes related with energy metabolism. PCN significantly reduced the ATP concentration in the hyphae and decreased mitochondrial membrane potential. Molecular docking analysis indicated that PCN binds to one of the candidate target proteins, pyruvate dehydrogenase, with lower free energy of -10.7 kcal/mol. This study indicated that PCN can interfere with energy metabolism, reducing ATP generation, ultimately affecting hyphal growth. Overall, PCN shows potential for future application in the control of tea leaf spot due to its excellent antifungal activity and unique mode of action.

Transient Expression of Nicotiana tabacum Silicon-Induced Histidine-Rich Defensins in Nicotiana benthamiana Limits Necrotic Lesion Development Caused by Phytopathogenic Fungi.

Silicon (Si) supplementation permits plants to better deter infection. Supplementing hydroponically-propagated Nicotiana tabacum with 1 mM potassium silicate (K2SiO3) reduced necrotic lesion development on detached leaves by both Botrytis cinerea and Sclerotinia sclerotiorum. Previously, a family of Si-induced genes was identified in N. tabacum. These genes were members of the Solanaceous Histidine-Rich Defensin (HRD) superfamily and were termed NtHRD1s (the first identified family of Nicotiana tabacum Histidine-Rich Defensins). Defensins were originally identified to participate in innate immunity. Thus, the NtHRD1s were tested for antimicrobial effects on plant pathogens. Transient expression of NtHRD1 genes within Nicotiana benthamiana leaves restricted the development of necrotic lesions caused by B. cinerea and S. sclerotiorum. Thus, the NtHRD1s may be an additional Si-responsive factor conferring beneficial effects on plants.

Patulin inhibition of specific apple microbiome members uncovers Hanseniaspora uvarum as a potential biocontrol agent.

Penicillium expansum is a major postharvest pathogen of apples, causing loss in fruits through tissue damage, as well as in apple products due to contamination with the mycotoxin patulin. During infections, patulin is a cultivar-dependent virulence factor that facilitates apple lesion development. Patulin also has characterized antimicrobial activity and is important for inhibiting other competitive phytopathogens, but the role of this inhibitory activity has not been investigated in the context of the apple microbiome. In our current study, we isolated 68 apple microbiota and characterized their susceptibility to P. expansum extracts. We found Gram-negative bacteria and Basidiomycete yeast to demonstrate largely patulin-specific growth inhibition compared to Gram-positive and Ascomycete isolates. From co-cultures, we identified a Hanseniaspora and Gluconobacter pairing that reduced P. expansum biomass and found that Hanseniaspora uvarum alone is sufficient to reduce apple disease progression in vivo. We investigated possible mechanisms of H. uvarum biocontrol activity and found modest inhibition on apple puree plates, as well as a trend toward lower patulin levels at the wound site. Active biocontrol activity required live yeast, which also were effective in controlling Botrytis cinerea apple infections. Lastly, we explored the breadth of H. uvarum biocontrol activity with over 30 H. uvarum isolates and found consistent inhibition of P. expansum apple disease.

Pyriofenone Interacts with the Major Facilitator Superfamily Transporter of Phytopathogenic Fungi to Potentially Control Tea Leaf Spot Caused by Lasiodiplodia theobromae.

Tea leaf spot caused by Lasiodiplodia theobromae is a newly discovered fungal disease in southwest China. Due to a lack of knowledge of its epidemiology and control strategies, the disease has a marked impact on tea yield and quality. Pyriofenone is a new fungicide belonging to the aryl phenyl ketone fungicide group, which has shown marked efficacy in controlling various fungal diseases. However, its mechanism of action is not yet understood. This study found that pyriofenone exhibits strong in vitro inhibitory activity against various phytopathogenic fungi. Specifically, it showed strong inhibitory activity against L. theobromae, with a half-maximal effective concentration (EC50) value of 0.428 µg/ml determined by measuring mycelial growth rate. Morphological observations, using optical, scanning electron, and transmission electron microscopy, revealed that pyriofenone induces morphological abnormalities in L. theobromae hyphae. At lower doses, the hyphae became swollen, the distance between septa decreased, and the hyphal growth rate slowed. At higher doses and longer exposures, the hyphae collapsed. Transcriptomic and bioinformatic analyses indicated that pyriofenone can affect the expression of genes related to membrane transporters. Homology modeling suggested that pyriofenone may bind to a candidate target protein of the major facilitator superfamily (MFS) transporter, with a free binding energy of -7.1 kcal/mol. This study suggests that pyriofenone may potentially regulate the transport of metabolites in L. theobromae, thus affecting hyphal metabolism and interfering with hyphal growth. Pyriofenone exhibits in vitro inhibitory activity against various tea foliar pathogens and holds promise for future applications to the control of tea foliar diseases.

New Approaches to Plant Pathogen Detection and Disease Diagnosis.

Detecting plant pathogens and diagnosing diseases are critical components of successful pest management. These key areas have undergone significant advancements driven by breakthroughs in molecular biology and remote sensing technologies within the realm of precision agriculture. Notably, nucleic acid amplification techniques, with recent emphasis on sequencing procedures, particularly next-generation sequencing, have enabled improved DNA or RNA amplification detection protocols that now enable previously unthinkable strategies aimed at dissecting plant microbiota, including the disease-causing components. Simultaneously, the domain of remote sensing has seen the emergence of cutting-edge imaging sensor technologies and the integration of powerful computational tools, such as machine learning. These innovations enable spectral analysis of foliar symptoms and specific pathogen-induced alterations, making imaging spectroscopy and thermal imaging fundamental tools for large-scale disease surveillance and monitoring. These technologies contribute significantly to understanding the temporal and spatial dynamics of plant diseases.

Impacts of Increasing Soil Salinity on Genetic Resistance (I-3 Gene)-Based Management of Fusarium Wilt (Fusarium oxysporum f. sp. lycopercisi Race 3) in California Processing Tomatoes.

California is the primary processing tomato (Solanum lycopersicum) producer in the United States. Fusarium oxysporum f. sp. lycopercisi race 3 (Fol3), the cause of Fusarium wilt, is a major driver of yield losses. Fol3 has recently been observed causing disease in resistant cultivars (I-3 R-gene), often reported in association with high soil salinity. This study was undertaken to better understand the role of salinity in compromising resistance-based management of Fol3. Surveys established opportunity for salinity-Fol3-tomato interactions in 44% of commercial fields examined, with harmful soil salt levels up to 3.6 dS/m (P < 0.001), high sodium (P < 0.001), and high sodicity (sodium adsorption ratio > 13; P < 0.001). In controlled field studies of Fol3 in NaCl/CaCl2-treated soil, Fol3-resistant cultivars either only developed wilt under salt or only developed wilt above the industry non-hybrid threshold (2%) under salt across two trial years. The absence of yield differences indicates low to no economic impact of disease enhancement (P > 0.05). NaCl, CaCl2, and Na2SO4 had no effect on Fol3 propagule production in liquid agar versus water agar controls (P > 0.05), although CaCl2 increased propagule loads sevenfold versus ionic controls (polyethylene glycol) (P = 0.036). NaCl/CaCl2 (2:1) reduced propagule loads up to 65% versus no salt (P = 0.029) in soil with pathogen-infested tomato tissue. These results together establish the opportunity for salinity-Fol3-tomato interactions and potential for salt to influence the efficacy of resistant cultivar-based management-this does not appear to be primarily due to salt enhancement of pathogen populations, pointing to a yet-unexplored direct influence of salt on host resistance.

Plant-Derived, Nodule-Specific Cysteine-Rich Peptides as a Novel Source of Biopesticides for Controlling Citrus Greening Disease.

Nodule-specific cysteine-rich (NCR) peptides, encoded in the genome of the Mediterranean legume Medicago truncatula (barrelclover), are known to regulate plant-microbe interactions. A subset of computationally derived 20-mer peptide fragments from 182 NCR peptides was synthesized to identify those with activity against the unculturable vascular pathogen associated with citrus greening disease, 'Candidatus Liberibacter asiaticus' (CLas). Grounded in a design of experiments framework, we evaluated the peptides in a screening pipeline involving three distinct assays: a bacterial culture assay with Liberibacter crescens, a CLas-infected excised citrus leaf assay, and an assay to evaluate effects on bacterial acquisition by the nymphal stage of hemipteran vector Diaphorina citri. A subset of the 20-mer NCR peptide fragments inhibits both CLas growth in citrus leaves and CLas acquisition by D. citri. Two peptides induced higher levels of D. citri mortality. These findings reveal 20-mer NCR peptides as a new class of plant-derived biopesticide molecules to control citrus greening disease.