Artificial Inoculation Research Articles

Comparison of Two Shiga Toxin-producing Escherichia coli (STEC) Isolation Protocols in Raw Cow’s Milk Cheese Enrichment Broths: Direct STEC Isolation Versus Techniques Based on Immuno-concentration

The presence of Shiga toxin-producing Escherichia coli (STEC) in dairy products made with raw milk is a major concern for food safety authorities and industries. Two approaches have been proposed to isolate STEC from food. In the IC-Protocol (immuno-concentration protocol), specific serogroups are identified in the enrichment broth after the detection of the stx and eae genes. An immuno-concentration of the targeted serogroups is performed before isolating them on specific media. In the DI-Protocol (direct isolation protocol), a direct isolation of all STEC present in the enrichment broth is carried out after the detection of stx genes. We compared the ability of these two methods to isolate STEC O26:H11, O103:H2, O111:H8, O145:H28, and O157:H7 after artificial inoculation in four different raw milk cheeses. Across all serogroups and cheese types, STEC were isolated in 83.3% of samples when using the IC-Protocol but only 53.3% of samples with the DI-Protocol. For two cheese types, the DI-Protocol failed to isolate STEC O157:H7 strains altogether. Our results suggest that IC-Protocol is a robust methodology to effectively isolate STEC across a range of cheese types.

Pathogens identification and resistance evaluation on bacterial canker in Actinidia arguta germplasm

Pathogen isolation and identification were performed on Actinidia arguta ‘Longcheng No. 2’ occurring bacterial canker from Liaoning Province, China. The pathogenic bacteria were identified as Pseudomonas syringae pv. actinidiae (Psa) by the analysis of morphology,16S rRNA and gyrB sequence, which were identified as Psa biovar 2 by Psa-specific primer sequence analysis. The pathogenicity tests were carried out with the isolate ‘R12’ and type strain ‘M228’ (biovar 3) as a control; the results showed that the phloem of green stems in A. arguta ‘Kuilv’ could be infect rapidly by R12, and milky mucus flowed from wounds, then the phloem turned black-brown, but it had strong resistance to Psa M228. In order to evaluate the resistance on Psa R12, 54 A. arguta germplasm resources were infected by artificial inoculation of stems, with A. deliciosa cv. ‘Hongyang’ and A. chinensis cv. ‘Xuxiang’, as control plant material, and their resistance levels were classified according to the disease index. The 54 tested materials exhibited differences in resistance to Psa R12, but no immune materials were found. In general, the germplasms were divided into five disease resistance categories, including 2 accessions with high resistance ‘Jianfengkuilv’ and ‘TL20013’, accounted for 3.70% of all the inoculated accessions; there were 11 resistant accessions, 15 tolerant accessions, 21 susceptible accessions, 5 highly susceptible accessions among them, accounted for 20.37%, 27.78%, 38.89% and 9.26%, respectively. In this study, the screening of disease-resistant germplasms could lay a foundation for further research on gene mapping, resistance mechanisms and breeding-resistant varieties of A. arguta to Psa.

Cross-Kingdom Interactions Between Plant and Fungal Viruses.

The large genetic and structural divergences between plants and fungi may hinder the transmission of viruses between these two kingdoms to some extent. However, recent accumulating evidence from virus phylogenetic analyses and the discovery of naturally occurring virus cross-infection suggest the occurrence of past and current transmissions of viruses between plants and plant-associated fungi. Moreover, artificial virus inoculation experiments showed that diverse plant viruses can multiply in fungi and vice versa. Thus, virus cross-infection between plants and fungi may play an important role in the spread, emergence, and evolution of both plant and fungal viruses and facilitate the interaction between them. In this review, we summarize current knowledge related to cross-kingdom virus infection in plants and fungi and further discuss the relevance of this new virological topic in the context of understanding virus spread and transmission in nature as well as developing control strategies for crop plant diseases.

Grafting for sustainable management of Fusarium wilt disease in tomato production in Ghana

Fusarium wilt disease limits tomato production, especially in Ghana. In managing the Fusarium wilt disease, two rootstocks (Solanum torvum and Solanum macrocarpon) were used in grafting experiments. Plant growth, yield, disease severity and incidence of both grafted plants, and non-grafted plants were evaluated in a pot experiment and also under a naturally infected open field condition at Berekum. During the early stage (14 days after inoculation) under artificial inoculation conditions, grafted plants exhibited higher photosynthetic rates (10.41 μmol−2s−1) compared to the non-grafted plants (8.36 μmol−2s−1). Under naturally infested field conditions, chlorophyll content and photosynthetic rate of non-grafted plants decreased. Solanum lycopersicum grafted onto S. macrocarpon and S. torvum were moderately susceptible (20%–40%) to Fusarium oxysporum. However, the non-grafted plants were highly susceptible (50%–100%). Yield from the pot experiment for S. lycopersicum grafted onto S. macrocarpon was significantly higher (453.1 g/plant), compared to S. lycopersicum grafted onto S. torvum (350.3 g/plant) and the non-grafted plant (205 g/plant). However, in naturally infected field, the grafted plants increased in fruit yield compared to the non-grafted tomato plants. Solanum macrocarpon and S. torvum as rootstocks offered resistance against F. oxysporum and showed significantly lower disease progression, than the non-grafted plants (P < 0.05). This study revealed that grafting is an effective tool for the management of Fusarium wilt disease and for tomato growth and yield improvement.

Genome-wide association study discovers novel germplasm resources and genetic loci with resistance to Gibberella ear rot caused by Fusarium graminearum.

Gibberella ear rot (GER) in maize caused by Fusarium graminearum is one of the most devastating maize diseases reducing grain yield and quality worldwide. The genetic bases of maize GER resistance remain largely unknown. Using artificial inoculation across multiple environments, GER severity of an association panel consisting of 316 diverse inbred lines was observed with wide phenotypic variation. In the association panel, a genome-wide association study (GWAS) using a general linear model (GLM) identified 69 single-nucleotide polymorphisms (SNPs) significantly associated with GER resistance at the threshold of 2.04 x 10-5, and the average phenotypic variation explained (PVE) of these SNPs was 5.09%. We also conducted a GWAS analysis using a mixed linear model (MLM) at a threshold of 1.0 x 10-4, and 16 significant association SNPs with an average PVE of 4.73% were detected. A combined GLM and MLM method obtained 10 co-localized significant association SNPs linked to GER resistance including the most significant SNP (PZE-105079915) with the greatest PVE value, 9.07%, at bin 5.05 following ten candidate genes. These findings are significant for the exploration of the complicated genetic variations in maize GER resistance. The regions and genes identified herein provide a list of candidate targets for further investigation, in addition to the elite germplasm resources that can be used for breeding GER resistance in maize.

Mechanisms and roles of the first stage of nodule formation in lepidopteran insects.

Nodule formation is a process of cellular immunity in insects and other arthropods with open circulatory systems. Based on histological observations, nodule formation occurs in 2 stages. The first stage occurs immediately after microbial inoculation and includes aggregate formation by granulocytes. The second stage occurs approximately 2-6 h later and involves the attachment of plasmatocytes to melanized aggregates produced during the first stage. The first stage response is thought to play a major role in the rapid capture of invading microorganisms. However, little is known regarding how granulocytes in the hemolymph form aggregates, or how the first stage of the immunological response protects against invading microorganisms. Since the late 1990s, our understanding of the molecules and immune pathways that contribute to nodule formation has improved. The first stage of nodule formation involves a hemocyte-induced response that is triggered by pathogen-associated molecular pattern (PAMP) recognition proteins in the hemolymph regulated by a serine proteinase cascade and cytokine (Spätzle) and Toll signaling pathways. Hemocyte agglutination proceeds through stepwise release of biogenic amine, 5-HT, and eicosanoids that act downstream of the Toll pathway. The first stage of nodule formation is closely linked to melanization and antimicrobial peptide (AMP) production, which is critical for insect humoral immunity. Nodule formation in response to artificial inoculation with millions of microorganisms has long been studied. It has recently been suggested that this system is the original natural immune system, and enables insects to respond to a single invading microorganism in the hemocoel.

White Rot of Korean Wild Chive Caused by Stromatinia cepivora

In May 2020, we surveyed disease occurrence on vegetables grown in Seosan area, Korea. During the disease survey, white rot symptoms were observed in Korean wild chive (&lt;i&gt;Allium monanthum&lt;/i&gt;) plants growing in fields. The symptoms occurred mainly in the seed bulb-producing fields of the crop. The above ground parts of the diseased plants displayed premature yellowing and dying of older leaves and stunting of the plants. The bulbs and roots of the diseased plants turned black and rotted. The disease occurred in a range of 1–60% in four of the eight fields surveyed. Three isolates of &lt;i&gt;Sclerotium&lt;/i&gt; sp. were obtained from the bulb lesions of diseased plants. All isolates were identified as &lt;i&gt;Stromatinia cepivora&lt;/i&gt; based on the morphological characteristics and phylogenetic analysis. Pathogenicity of the isolates on Korean wild chive was confirmed by artificial inoculation test. The lesions induced by the inoculation test were similar to those observed in the investigated fields. This is the first report of &lt;i&gt;S. cepivora&lt;/i&gt; causing white rot in Korean wild chive.

Characterization and report of Ectophoma multirostrata, causing stem canker disease in highbush blueberry in Iran

AbstractDuring a disease survey in greenhouses of blueberry seedlings in Mohammad Shahr City, Alborz Province, Iran, in the autumn 2021, severe stem canker symptoms were observed in the cv. Emerald of highbush blueberry (Vaccinium corymbosum). The disease incidence in the affected greenhouses was more than 30%–40%. Diseased branches and stems were sampled and the associated fungus was isolated on potato dextrose agar. Based on the fungal morphological features of the colony, three isolates among which the representative isolate of UT2020 were identified as Ectophoma multirostrata. Phylogenetic analysis of the concatenated ITS‐rDNA and beta‐tubulin (tub2) gene sequence data confirmed the morphological identification of the fungal isolates. E. multirostrata differs from closely related species by having several ostiolar necks, textura angularis wall in pycnidia and oblong to ellipsoidal conidia. The pathogenicity of the isolate UT2020 in the stems of highbush blueberry cv. Emerald was confirmed by our artificial wound inoculation method. After 14 days, the same stem canker symptoms were developed on the inoculated stems, and the same fungal isolate was re‐isolated from the newly developed symptoms, fulfilling the Koch's postulates. This is the first report of E. multirostrata causing a stem canker disease in highbush blueberries. Also, Vaccinium corymbosum is reported as a new host (matrix nova) for E. multirostrata worldwide.

Leaf rust resistance genes in Aegilops genus: occurrence and efficiency

Leaf rust is a common and costly wheat disease. The introduction of resistance genes derived from wheat wild relatives is one way to improve disease control. However, due to the rapid development of virulence in the casual pathogen Puccinia triticina, the long-term effectiveness of some leaf rust resistance (Lr) genes is questionable. To assess this, we examined 130 accessions of 13 wheat wild relative species from the Aegilops genus. The presence of 9 Lr genes was determined by PCR using primers complementary to Lr gene markers. The studied individuals were exposed to artificial inoculation with P. triticina under greenhouse and field conditions, respectively. Based on infection rate, the degree of resistance for each individual was estimated. The relationship between the presence of Lr genes and the degree of manifested resistance was assessed using canonical correlation analysis (CCA) and analysis of variance (ANOVA). Our results indicate the effective participation of Lr9 in seedling resistance while Lr58 is involved in adult plant resistance.

Crown gall development on cannabis (Cannabis sativa L., marijuana) plants caused by Agrobacterium tumefaciens species-complex

Crown gall, caused by Agrobacterium tumefaciens (syn. Rhizobium radiobacter), is characterized by gall formation on crowns, stems or roots on many plant species. We describe the occurrence of this disease for the first time on cannabis (Cannabis sativa L. marijuana) plants in two licenced production facilities in British Columbia. Galls were observed on crowns, stems and roots of several genotypes, including ‘White Rhino’, ‘Pink Kush’ and ‘Sour Kush’. The affected plants displayed no other visible symptoms. The incidence of crown gall was extremely low, estimated at 0.01% of total plants. Isolations made from root and stem galls on MacConkey medium (selective for Gram -ve bacteria) and on D1 medium (selective for Agrobacterium spp.) yielded a range of bacterial species, which did not include Agrobacterium sp. However, the presence of Agrobacterium in gall tissues was confirmed following PCR amplification with primers for the indole-acetic acid (iaa) H gene on the T-DNA region of Agrobacterium spp. and showed > 99% similarity to A. tumefaciens. Artificial inoculations were conducted using an A. tumefaciens strain from ATCC (Rhizobium radiobacter, strain designation TT134 [6-1-2, CIP 104 336], cat. 15955) which resulted in gall formation on five cannabis genotypes tested. These galls contained the iaaH gene as determined by PCR and the pathogen was successfully re-isolated on MacConkey agar medium at 4 and 10 weeks post-inoculation. Our findings confirm the occurrence of A. tumefaciens on naturally infected and artificially infected cannabis plants grown under greenhouse conditions and demonstrate reproducible gall symptoms on several cannabis genotypes following A. tumefaciens inoculation.

Rice-Magnaporthe transcriptomics reveals host defense activation induced by red seaweed-biostimulant in rice plants.

Red seaweed extracts have been shown to trigger the biotic stress tolerance in several crops. However, reports on transcriptional modifications in plants treated with seaweed biostimulant are limited. To understand the specific response of rice to blast disease in seaweed-biostimulant-primed and non-primed plants, transcriptomics of a susceptible rice cultivar IR-64 was carried out at zero and 48h post inoculation with Magnaporthe oryzae (strain MG-01). A total of 3498 differentially expressed genes (DEGs) were identified; 1116 DEGs were explicitly regulated in pathogen-inoculated treatments. Functional analysis showed that most DEGs were involved in metabolism, transport, signaling, and defense. In a glass house, artificial inoculation of MG-01 on seaweed-primed plants resulted in the restricted spread of the pathogen leading to the confined blast disease lesions, primarily attributed to reactive oxygen species (ROS) accumulation. The DEGs in the primed plants were defense-related transcription factors, kinases, pathogenesis-related genes, peroxidases, and growth-related genes. The beta-D-xylosidase, a putative gene that helps in secondary cell wall reinforcement, was downregulated in non-primed plants, whereas it upregulated in the primed plants indicating its role in the host defense. Additionally, Phenylalanine ammonia-lyase, pathogenesis-related Bet-v-I family protein, chalcone synthase, chitinases, WRKY, AP2/ERF, and MYB families were upregulated in seaweed and challenge inoculated rice plants. Thus, our study shows that priming rice plants with seaweed bio-stimulants resulted in the induction of the defense in rice against blast disease. This phenomenon is contributed to early protection through ROS, protein kinase, accumulation of secondary metabolites, and cell wall strengthening.

Evaluation of organics, antagonists and carbendazim against Fusarium wilt of pigeonpea (Cajanus cajan L.)

In India, pigeonpea [Cajanus Cajan (L.) Millsp.] wilt caused by Fusarium udum is prevalent in all areas it cultivated. Among the major soil borne diseases pigeonpea, the Fusarium wilt caused by Fusarium udum is one of the most important diseases and can cause 30-100% loss in grain yield. A pot experiment was conducted to assess the efficacy of Trichoderma harzianum, Pseudomonas fluorescens, farm yard manure, spent mushroom substrate of oyster mushroom and the fungicide Carbendazim 50% WP against Fusarium wilt of pigeonpea in terms ofseed germination and disease incidence under artificial inoculation conditions during Kharif 2021. Among the treatments assessed, maximum seed germination (95.83%) was recorded in treatments in which seed were treated with Carbendazim 50% WP or soil amended with the combination of spent mushroom substrate+Trichoderma harzianum or spent mushroom substrate+(Trichoderma harzianum+ Pseudomonas fluorescens) prior to sowing. Maximum reduction in disease incidence (73.81%) of Fusarium wilt over the control was recorded in treatment in which soil was amended with combination of spent mushroom substrate+(Trichoderma harzianum+ Pseudomonas fluorescens). The results revealed that all the treatments applied as prophylactic measure, reduced the Fusarium wilt and increased the seed germination significantly over the unprotected crop.

Molecular screening for Fusarium oxysporum resistance genes in chickpeas

Root rot and wilt (Fusarium oxysporum) are the most common pathogens among grain legumes, which cause yield losses of 10 to 40%. Wilt caused by Fusarium oxysporum f.sp. ciceris is a devastating disease in chickpea growing area. In this study, 50 chickpea genotypes were studied to identify genetic sources of resistance to the disease in 2021 and 2022 vegetative seasons. The studies were carried out against the natural background of the experimental field at the Saimasai Agrotechnopark site of the Kazakh National Agrarian Research University, and the studies were carried out against an artificial background at the experimental site of Agropark Ontustik LLP located in the village of Zhalpaksay, Almaty region, Karasai district. The resistance and susceptibility of the plants to F. oxysporum were determined four weeks after artificial inoculation. In field trials, 70% of the genotypes were resistant to wilt and the remaining 30% showed susceptibility to the disease with varying degrees. Molecular methods were used to identify genetic sources of resistance. In the molecular analysis, all 50 genotypes were screened using the primers CaSTMS2, TA200, TA194, TA72, TA46, TR29 and TR7, which are closely related markers to resistance genes. Marker selection can identify resistant genes when screening chickpea genotypes for this pathogen. As a result of screening, resistant chickpea genotypes have been identified that can be used in the breeding program to develop F. oxysporum resistant chickpea varieties.

Development of a Novel Real-Time Quantitative PCR Method for Detection of Ilyonectria robusta, the Predominant Species Causing Ginseng Rusty Root Rot.

Rusty root rot is the most destructive soilborne disease of ginseng caused by pathogenic Ilyonectria spp., predominantly Ilyonectria robusta, in China. However, there remains no effective strategy to control the disease. Current control of the disease requires that soil and ginseng seeds and seedlings infected with I. robusta are avoided during planting. Therefore, rapid and accurate detection of I. robusta would be indispensable in disease control programs. A one-step polymerase chain reaction (PCR) and quantitative real-time PCR (qPCR) assay was developed to detect I. robusta in ginseng seeds, roots, and soil. The species-specific primers HIS H3-F and HIS H3-R, designed based on a partial histone gene sequence of I. robusta, yielded a 268-bp product using the optimized PCR and qPCR protocol. DNA of I. robusta was detected by qPCR in all diseased soil and ginseng roots and seeds resulting from artificial inoculation and sampled from natural fields. I. robusta was detected at an abundance of 1.42 fg/μl at 12 h postinoculation and 191.31 fg/μl at 7 days postinoculation in ginseng roots that showed disease symptoms. In naturally infected soil sampled from ginseng fields, pathogen abundances ranging from 13.23 to 503.39 fg/μl were detected, which were 2.04 to 11.01 times higher than those in ginseng roots. The pathogen was first detected and was more abundant on the surface of the ginseng seed coat compared with that in the seed kernel. This study provides a high-efficiency detection technique for early diagnosis of I. robusta and real-time disease prevention and control strategies.

Molecular mapping of quantitative trait loci for resistance to early blight in tomatoes.

Early blight (EB), caused by Alternaria linariae (Neerg.) (syn. A. tomatophila) Simmons, is a disease that affects tomatoes (Solanum lycopersicum L.) throughout the world, with tremendous economic implications. The objective of the present study was to map the quantitative trait loci (QTL) associated with EB resistance in tomatoes. The F2 and F2:3 mapping populations consisting of 174 lines derived from NC 1CELBR (resistant) × Fla. 7775 (susceptible) were evaluated under natural conditions in the field in 2011 and in the greenhouse in 2015 by artificial inoculation. In all, 375 Kompetitive Allele Specific PCR (KASP) assays were used for genotyping parents and the F2 population. The broad-sense heritability estimate for phenotypic data was 28.3%, and 25.3% for 2011, and 2015 disease evaluations, respectively. QTL analysis revealed six QTLs associated with EB resistance on chromosomes 2, 8, and 11 (LOD 4.0 to 9.1), explaining phenotypic variation ranging from 3.8 to 21.0%. These results demonstrate that genetic control of EB resistance in NC 1CELBR is polygenic. This study may facilitate further fine mapping of the EB-resistant QTL and marker-assisted selection (MAS) to transfer EB resistance genes into elite tomato varieties, including broadening the genetic diversity of EB resistance in tomatoes.

QTL-seq identifies and QTL mapping refines genomic regions conferring resistance to Fusarium oxysporum f. sp. niveum race 2 in cultivated watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai

The present experiment was conducted to map resistance to Fusarium oxysporum f. sp. niveum (Fon) race 2 in a highly resistant Citrullus lanatus accession (EC794421). For this purpose, a F2:3 population was developed by crossing a susceptible accession BIL-53 with EC794421. The F2:3 progenies were screened in two bioassays employing artificial inoculation of conidial suspension (1 × 106 conidia per ml; 5 ml per plant). Based on the F2:3 progeny performance, the five most resistant and sensitive F2 genotypes were identified and their corresponding genomic DNA was bulked to constitute the resistant and the susceptible bulks, respectively for performing QTL-seq analysis. Two statistically significant genomic regions were identified on chromosome 1 and chromosome 7; of which, the latter is novel and not reported earlier. Through target-locus refining employing QTL mapping, the QTLs on chromosomes 1 and 7 were narrowed down to two and a single microsatellite marker, respectively. These markers were also validated in two populations derived from different resistant accessions. The information generated in the current study will be of use of global breeders to incorporate the Fon race 2 resistance through marker-assisted introgression into elite commercial backgrounds of watermelon without incurring linkage drag.

Control Efficacy of Jingdusha against Corynespora cassiicola (Hyphomycetales: Dematiaceae) on Cucumber

Aims: The paper aimed to clarify the effect of cucumber target leaf spot (TLS) under the Jingdusha (JDS) treatment.&#x0D; Study Design: We applied the method of artificial inoculation in the pot, and analyzed the changes in growth indexes and physiological characteristics.&#x0D; Place and Duration of Study: In 2018, these experiments were conducted in College of Bioscience and Biotechnology of Shenyang Agricultural University (Lab 240).&#x0D; Methodology: The seedlings in the two-leaf period were induced by the best application scheme of JDS, then inoculated Corynespora cassiicola for 24 h. Cucumber seedlings of each treatment group were randomly selected for photographing and growth index determination after inoculation for 5 d. The leaves of cucumber seedlings in each treatment group were randomly collected at 1 d, 3 d, 5 d, 7 d, and 9 d after inoculation for the determination of physiological and biochemical indicators.&#x0D; Results: When C. cassiicola infects cucumber, JDS can effectively improve the growth and photosynthetic pigment content of cucumber, reduce the degradation of chlorophyll (Chl) under the stress of C. cassiicola, strengthen the variety of metabolic responses in the plant, repair the enzyme protection system of cucumber leaves, reduce the accumulation of reactive oxygen species, shorten the process of membrane lipid peroxidation in blades.&#x0D; Conclusion: Taken together, these results suggest that JDS can improve the resistance of cucumber seedlings to C. cassiicola by regulating growth indexes and physiological characteristics. This work will provide a theoretical basis for further elucidating the molecular mechanism of JDS in cucumber defense against C. cassiicola.

Phenotypic and molecular identification of some blast resistance genes and biochemical responses of rice genotypes against rice blast pathogen

The current investigation was carried out to identify some isolates of Magnaporthe oryzae (anamorph: Pryicularia oryzae), the causal fungus of blast disease, and to assess their virulence against monogenic lines and other rice genotypes. In addition, the biochemical changes after inoculation with blast pathogen were evaluated. The linked markers to blast resistance genes were identified, the potential gene(s) operating in genotypes were assessed at field conditions. Twenty-seven isolates were identified as six race groups; the ID group was highly distributed, followed by group IC. Resistance genes Pii (IRBLi-F5), Piz-5 (IRBLz5-CA (R) and Pit (IRBLt- K59) were completely resistant to test races. New promising lines i.e. GZ10686-2-1-3-4, GZ10848-1-2-2-1, GZ11190-3-13-4-1, and GZ11312-3-3-1-3 were resistant for test races under artificial inoculation, and induced the highest activity for defense-related enzymes i.e. phenylalanine ammonia-lyase (PAL), chitinase, and the test antioxidant enzyme i.e. peroxidase (POX) and ascorbate peroxidase (APX). Molecular analysis confirmed the existence of genetic variation and the similarity percentage among genotype pairs was as low as 10%. The more genes a specific genotype was carrying, the more resistance and durability are expected. There was collinearity between the superiority of promising lines GZ10848-1-2-2-1 and GZ11190-3-13-4-1 and their respective number of blast-linked genes where they have the highest number of blast-linked genes. Under field evaluation, the advanced promising lines performed well in grain yield compared to the cultivated varieties, especially GZ10848-1-2-2-1, and GZ11190-3-13-4-1, and resistance to blast disease.

Myrtus communis in Europe threatened by the pandemic and South African strains of the myrtle rust pathogen Austropuccinia psidii (Sphaerophragmiaceae, Pucciniales)

Austropuccinia psidii, the causal agent of myrtle rust, has emerged as a significant threat to Myrtaceae in planted and natural woody ecosystems. The first detection of A. puccinia in South Africa was from severely infected ornamental Myrtus communis. This raised concern that M. communis, the sole Myrtaceae species native to Europe and an important component of vegetation in Mediterranean regions, could be threatened by the rust. In light of the potential threat to this unique species, seed was collected from 12 Italian provenances of M. communis, including mainland and island (Sardinia and Sicily) populations. We assessed the susceptibility of these provenances to both the pandemic and South African strains of A. psidii. In Colombia, where the pandemic strain of A. psidii is native, seedlings rapidly became infected by natural inoculum. In South Africa, a preliminary screening of seedlings by artificial inoculation with a single-uredinium isolate produced high levels of disease. Finally, plants of each of the 12 provenances were planted and monitored in Florence, Italy. To date, these showed no signs of disease, but will continue to be monitored. This study highlights the significant threat that both the pandemic and South African strains of A. puccinia pose to M. communis in Europe.

VIRULENCE OF PSEUDOMONAS SYRINGAE STRAINS FROM SORIZ (SORGHUM ORYSOIDUM) AND THEIR SPECIALIZATION

Objective. To study the virulence properties of Pseudomonas syringae strains isolated from soriz and various representatives of sorghum crops in Ukraine and to establish the sensitivity range of plants to these pathogens. Methods. Ten strains freshly isolated from soriz (Sorghum orysoidum) were used to study virulence properties, namely: Pseudomonas syringae 210342, 211141a, 211141, 210341, 21034, 210541b, 210541, and Pseudomonas sp. 210521, 21052, 21054, pathogenic strains of sorghum crops from the collection of the Department of Phytopathogenic Bacteria of D. K. Zabolotny Institute of Microbiology and Virology of the National Academy of Sciences of Ukraine and collection strains of phytopathogens that can be potential causative agents of bacterial diseases of soriz or are causative agents of diseases of agricultural crops that can be used in crop rotation. The virulence properties of strains isolated from sorghum were determined on plants of the genus Sorghum. To establish the range of crops sensitive to these pathogens, a number of plants belonging to other genera and families, both cultivated and weed, were tested. Artificial inoculation was carried out in the greenhouse and in the field as injection of bacterial suspension of 1×109 CFU/mL into the leaf surface and stem at all phases of the development of soriz and sorghum cultures. Accounting for artificial contamination was carried out in 7 to 14 days using a locally modified 6-point scale. Aggressiveness of bacteria was assessed by the size of necrosis that formed at the site of injection of the bacterial suspension. Aggressiveness was calculated as the arithmetic mean of the results. Results. P. syringae strains isolated from soriz were found to be virulent for soriz and sorghum crops, however, heterogeneous in aggressiveness. The most aggressive strains were P. syringae 211141a, 210341, and 21034. Some collection strains, isolated from different cultures, showed higher aggressiveness against sugar and grain sorghum than against soriz and Sudan grass. The studied strains of phytopathogens were found to affect segetal vegetation; the most sensitive to the studied strains were horsetail, field bindweed, goldenrod. They showed high aggressiveness against setaria, ragweed, and common sedge. Strains of P. syringae affecting potato, beet, sunflower and tomato plants were identified. Conclusion. Pseudomonas syringae strains isolated from contaminated sorghum plants are virulent and capable of infecting a wide range of plants, including plants of the sorghum family, other types of agricultural crops, and various types of segetal vegetation. Strains of Pectobacterium carotovorum, Xanthomonas vasicola pv. holcicola, Diskeya chryzanthemy, Pantoea agglomerans can be potential pathogens of sorghum crops. The results indicate that segetal vegetation can serve as a reservoir of bacterial infections and play a role in the transfer of bacterial pathogens.