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Rhizoctonia solani Kühn and Sclerotium rolfsii Sacc. are the primary soil-borne plant diseases responsible for significant reductions in global crop yields. The primary goal of this study was to investigate the antifungal potentials of clove essential oil (CEO), nanoemulsion form (CEONE) and chitosan/nanoemulsion nanocomposite (CS/CEONE) against R. solani and S. rolfsii through in vitro and in vivo trials. Both CEONE and CS/CEONE were prepared and investigated for their physical chemical and morphological characterization. The poisoned medium method was utilized to evaluate the inhibitory effects of CEO, CEONE and CS/CEONE on the mycelial growth and enzymatic activity of R. solani and S. rolfsii. The changes of hyphae of R. solani and S. rolfsii in response to treating with CEONE and CS/CEONE were observed with scanning electron microscope (SEM). The results revealed that CEONE have larger size 86 ± 3 nm and a broader range of PDI 0.121 ± 0.011 on the average. While, CS/CEONE has smaller size of 49 ± 4 nm and narrower PDI of 0.099 ± 0.009. Both nanoemulsions had uniform spherical nanodroplets form and exhibited acidic nature. Fourier Transform Infrared Spectroscopy (FTIR) and UV-Visible Spectroscopy (UV-Vis) verified the successful incorporation of both CS and CEO within the nanoemulsion system. The results demonstrated a sustained and prolonged release profile from CS/CEONE for up to 4 days. The inhibitory effect of CEONE and CS/CEONE showed dose-dependent activity against mycelial growth of both fungi. CEONE and CS/CEONE at concentration 500 µL/L exhibited the strongest inhibition with a significant (p < 0.05) variation among them with value ranging from 56.11% to 71.94% and 52.2% to 79.2%, respectively. Comparing to control, CS/CEONE revealed the highest inhibitory effect against S. rolfsii after 96 h followed by CEONE with value reached 50.6% and 44.1%, respectively. The antifungal activity of the nanoemulsion showed strain–dependent behavior, where S. rolfsii was the most affected. SEM images showed changes in the hyphal structure of S. rolfsii and R. solani resulting from the impact of CEONE and CS/CEONE. Activity of pectinase and cellulase secreted by both fungi was also negatively affected by CEO, CEONE and CS/CEONE at all tested concentrations. Greenhouse trials revealed that increasing the concentrations of CEO, CEONE, and CS/CEONE from 50 to 500 μL/L gradually increased their effectiveness in reducing the DI% and DS% of black scurf, stem canker, pre-damping off, and post-damping off diseases on potato. The results suggest that incorporation of CS to CEONE enhanced its activity and can be utilized as a secure and non-toxic nanocomposite. Supplementary Material Supplementary Material File [ABSTRACT FROM AUTHOR]

Neoscytalidium dimidiatum is an asexual, opportunistic and necrotrophic pathogen that causes the devastating stem canker disease of dragon fruit species (Selenicereus spp.). Despite this, information about its intraspecific diversity remains lacking. Examination of the morphological variations of 40 N. dimidiatum isolates hosted by S. megalanthus, S. monacanthus and S. undatus from eight allopatric regions in the Philippines detected three distinct morphotypes. Sequencing of three partial gene markers (ITS, ACT and TUB2) of representative isolates revealed low intraspecific genetic diversity of the pathogen from the three hosts. Phylogenetic analysis of internal transcribed spacer (ITS) sequences of the isolates in this study and worldwide collections of the phytopathogen in the GenBank database infers similar founding populations and the possible specificity of the dragon fruit‐infecting N. dimidiatum. Pathogenicity and aggressiveness assay of the isolates on detached stems of dragon fruit did not detect host specificity to S. monacanthus and S. undatus. However, some isolates (i.g., MBDF0802A, MBDF0808B, MBDF0339A and MBDF0007A) significantly had shorter latent period to the stems of S. undatus than S. monacanthus. A higher aggressiveness component of lesion size development on S. undatus stems by isolates from S. monacanthus was recorded suggesting a possible directional selection of highly aggressive N. dimidiatum in this host. This is the first population study on the phenotypic traits and the genetic structure of N. dimidiatum. Valuable inputs for further study of the pathogen are provided, which may help inform the design of management options for stem canker disease of dragon fruit. [ABSTRACT FROM AUTHOR]

Sweet cherry (Prunus avium) is a commercially important species in China, experiencing a rapid increase in production. In June 2022, a severe infection, affecting more than 8% of sweet cherry trees, was observed on the Tetian cultivar in a 2–3‐year‐old orchard in Dalian City, northern China. Initially, spindle‐shaped brown disease spots formed on the surfaces of the branches. These spots continued to spread and merge, and the middle portion of the cankers sunk inward and gradually dried. Small black particles were found on the surface of the stems. The disease spread was more prevalent during the rainy season, leading to the withering of numerous branches and the death of the whole plant. Seven isolates, named lncy1‐1, lncy4‐1, lncy5‐1, lncy6‐1, lncy7‐1, lncy8‐1 and lncy9‐1, were obtained from 24 disease samples. Phylogenetic analysis based on three loci (rDNA ITS, TEF1 and TUB2) coupled with morphological identification confirmed that these seven isolates belong to Diaporthe eres. A representative isolate, lncy1‐1, was inoculated onto sweet cherry branches in a controlled environment, and showed that the isolate lncy1‐1 was pathogenic. The fungus isolated from diseased tissues was identified as D. eres based on morphological and molecular criteria. To the best of our knowledge, this is the first report of stem canker in sweet cherry caused by D. eres in China, which will promote disease management and expand the known host range of D. eres. [ABSTRACT FROM AUTHOR]

Idesia polycarpa is a woody oil plant with great development and application prospects. However, stem canker disease of I. polycarpa was frequently observed in Henan and Hubei provinces of China in 2020–2022. The seriousness of the disease caused a large number of trees deaths, which affected seedling production and fruit yield, restricting the development of the I. polycarpa industry. We performed isolation, purification and pathogenicity analysis of canker samples. Pathogenicity tests reproduced typical canker disease symptoms on detached branches of I. polycarpa. Based on morphological observations, conidial morphology and phylogenetic analysis of isolates with high similarity to the rDNA internal transcribed spacer (ITS), EF‐1α and TUB2 sequences screened in GenBank by BLAST, the pathogen of canker disease on I. polycarpa was identified as Botryosphaeria dothidea. This is the first report of B. dothidea as the pathogen of stem canker of I. polycarpa. [ABSTRACT FROM AUTHOR]

Rhizoctonia stem canker and black scurf are among the most important diseases associated with potato (Solanum tuberosum L.) cultivation worldwide. Pathogenicity test of 19 isolates of Rhizoctonia solani Kühn obtained from four governorates in Syria revealed that isolates varied in their ability to cause disease with the isolate Rh15 being the most virulent in the development of the disease on potato plant under artificial infection. The relative susceptibility of seven commercial and local potato cultivars against R. solani was tested. The evaluation was based on black scurf severity and the negative impact of the disease on plant growth and expected effect on yield. The tested cultivars showed variable degrees of black scurf severity and consequent plant growth, but no completely immune cultivars were observed. Based on disease index (DI), potato varieties 'Agria', 'Ultra' and 'Labella' were highly susceptible to the disease; 'Spunta' was moderately resistant whereas 'Everest' was the most tolerant. Infection of the most susceptible cultivar "Afamia" resulted in the death of a large number of seedlings, large and deep canker on stems, with no formation of new tubers. Although 'Synergy' was moderately susceptible, and the black scurf incidence was higher than that of 'Everest' and 'Spunta', the loss of tubers weight was not significant compared to the previous two cultivars. The results suggested that use of tolerant and moderately resistant cultivars in Syria may help in reducing the development of black scurf on potatoes. [ABSTRACT FROM AUTHOR]

Apoharknessia eucalyptorum is associated with leaf spots on Eucalyptus dunnii in Southern Brazil; however, no data about its symptoms and severity are currently available. In this study, inoculation, symptomatology, and severity on leaves and stems of E. dunnii and leaves of Corymbia citriodora are analyzed and discussed. Detached and intact seedling leaves and seedling stems, with and without wounds, were inoculated with A. eucalyptorum. The severity of leaves was assessed based on the lesion area, whereas the severity on stems was considered by the size of the lesions. After inoculation, the following symptoms were observed on leaves with and without lesions: brown, circular or irregular lesions, occurring along the leaf margins, sparsely distributed, or coalescing throughout the leaf blade. The severity on detached leaves ranged from 13 to 63 % on E. dunnii and from 30 to 38 % on C. citriodora, whereas on intact seedling leaves the severity was observed only on wounded tissues, with 11.90 % on E. dunnii and 19.63 % on C. citriodora. Only inoculated stems of E. dunnii with wounds showed signs of the pathogen. This study confirms the pathogenicity of A. eucalyptorum on both E. dunnii and C. citriodora, a new host for the disease, and concludes that although the pathogen can be considered a primary pathogen based on detached leaf inoculations, the infection on non-wounded tissues is limited. Thus, the distribution of A. eucalyptorum and the possible impacts of the pathogen on Eucalyptus spp. plantations should be monitored. [ABSTRACT FROM AUTHOR]

Black scurf and stem canker caused by Rhizoctonia solani is a significant disease problem of potatoes. Currently, chemical methods are the primary means of controlling this pathogen. This study sought to explore an alternative approach by harnessing the biocontrol potential of a bacterial mix of Bacillus subtilis and Bacillus amyloliquefaciens against black scurf, and to determine their effect on rhizosphere microorganisms of soil microbiota. This study showed that these bacteria demonstrate antagonistic activity against Rhizoctonia solani. Reduced damage to potato plants during the growing season in Siberia was observed. The index of disease development decreased from 40.9% to 12.0%. The treatment of tubers with this mix of bacteria also led to a change in the composition of the rhizosphere microbiota (according to CFU, 16S and ITS sequencing). This effect was accompanied by a positive change in plant physiological parameters (spectrophotometric analysis). The concentration of chlorophyll in potatoes with the bacterial mix treatment increased by 1.3 fold (p ≤ 0.001), and of carotenoids by 1.2 fold (p ≤ 0.01) compared with the control. After bacterial mix treatment, the length of the aerial parts of plants was 1.3 fold higher (p ≤ 0.001), and the number of stems 1.4 fold higher (p ≤ 0.05). The yield of potatoes was increased by 8.2 t/ha, while the large tuber fraction was increased by 16% (p ≤ 0.05). The bacteria mix of Bacillus subtilis and Bacillus amyloliquefaciens suppressed the plant pathogenic fungus Rhizoctonia solani, and simultaneously enhanced the physiological parameters of potato plants. This treatment can be used to enhance the yield/quality of potato tubers under field conditions. [ABSTRACT FROM AUTHOR]

Cankers leading to branch, stem and plant death were observed on the South African endemic Rafnia amplexicaulis (Fabaceae) in the Cederberg Wilderness Area, South Africa, during September 2021. Conidiomatal pycnidia were found developing on the cankers, and isolations consistently yielded a Microsphaeropsis species. Phylogenetic analysis based on partial nucleotide sequences of the internal transcribed spacers (ITS), the nuclear large subunit (LSU) and RNA polymerase II second largest subunit (RPB2) regions showed that the fungus represented an undescribed species. Based on the multigene phylogeny and morphological characteristics, we describe the species here as M. rafniae sp. nov. Pathogenicity tests and the fulfilment of Koch's postulates confirmed that M. rafniae sp. nov. is the cause of the cankers of R. amplexicaulis. Presently, this disease is known from a single location in South Africa, and further surveys are required to determine its distribution and relative importance. [ABSTRACT FROM AUTHOR]

During the growth period, the potato crop is exposed to a combination of biotic and abiotic stresses. Rhizoctonia solani Kuhn is the causal agent of potato stem canker disease and one of the most important soil-borne plant pathogens that reduce the yield and quality of potatoes worldwide. Antagonistic bacteria seem to be a good alternative to chemicals in controlling plant pathogens. This study evaluated the biocontrol properties (hydrolyzing enzymes, siderophore, surfactant, biofilm) of 20 Bacillus isolates against R. solani AG3. In total, 23 to 64.9 % of isolates in dual culture assay, 38.2 to 85.4% in volatile compound production, and 76.9 to 90% in antibiotic production showed inhibition against the tested fungus. The isolates were variable in terms of biocontrol properties. Based on the in vitro results, five isolates including Ba1, Ba5, Ba8, Ba11, and Ba12 were selected for identification and additional investigations under greenhouse experiments. The selected isolates inhibited the germination of fungal sclerotium and caused mycelial fragmentation and cytoplasmic coagulation. Strains Ba1, Ba5, Ba8, Ba11, and Ba12 belonged to B. mojavensis, Bacillus sp., B. pumilus, Bacillus sp., and B. velezensis, respectively. In the greenhouse trials, the disease severity index was zero in treatments Ba5 (Bacillus sp.) and Ba8 (B. pumilus), similar to Rovral -TS fungicide and completely controlled stem canker disease. Therefore, they are suggested for additional investigations and preparation of optimal formulations. [ABSTRACT FROM AUTHOR]

Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) is a global soil-borne pathogen that severely harms potato crops, leading to significant product losses. Black scurf and stem canker are two manifestations caused by this pathogen, with variable intensity based on the distinctive anastomosis group endemic to the region. During the growing season of 2017 (March and April), 57 different fungus isolates were collected from potato crops farmed in the Jordan Valley. The identity of all the isolates was confirmed by sequencing the internal transcribed spacer (ITS) of the ribosomal DNA gene, and the hyphal interactions were also performed with R. solani isolates. The sequences were deposited in GenBank, where accession numbers were obtained. 21 of the isolates were AG-3PT R. solani, with 98–99% identity to reference strains. Somatic compatibility was determined by hyphal interactions, which showed pairing compatibility among the isolates. Around 86.7% of the pairings were somatically incompatible, indicating a high level of genetic diversity among the isolates, while only 13.3% of the pairings were somatically compatible. Testing for pathogenicity revealed that AG-3PT affected the stems of solanaceous plants, including potatoes, and the roots of other plant species. Based on the findings of this study, R. solani AG-3PT was the primary pathogen associated with potato stem canker and black scurf diseases in Jordan. To our knowledge, this is the first report on this pathogen's isolation and identification in Jordan.

In 2018, a deadly stem canker outbreak on Jatropha curcas was detected in Yunnan Province, China. A fungus isolated from the diseased stems was identified as Lasiodiplodia theobromae based on the morphology and analysis of ITS, EF1α, RPB2, and TUB2 nucleotide sequences. It caused the same cankers after inoculation and was re-isolated from the tissue. This is the first report of J. curcas stem canker caused by L. theobromae in China. [ABSTRACT FROM AUTHOR]

Plantation forests are established by planting Eucalyptus tree species to provide timber and pulp for the construction industries and to meet the energy needs in Ethiopia. Besides the extensive Eucalyptus plantations in the country, fungal pathogen-related diseases are the main challenges to successful production and management. The disease survey was conducted in the Eucalyptus growing areas of Ethiopia during 2019/2020 and 2020/2021. The objective of this research was to assess the diseases associated with Eucalyptus plant species and identify the causal fungal species. Plants of E. camaldulensis were the dominant species in the survey fields and were severely associated with stem and branch canker diseases. Diseased samples were collected and fungal species were identified as Didymellaceae according to culture morphology and affirmed by internal transcribed spacer sequence analysis. In phylogeny, isolates in the study and a reference strain formed supportive monophyletic clades with strong 90% and 95% support with Didymella coffeae-arabicae and Didymella pinodella respectively. Pathogenicity tests revealed that Didymellaceae could infect E. camaldulensis. The findings are the first reports of Eucalyptus stem canker disease caused by Didymellaceae in Ethiopia.

Antagon istic bacteria can be used as a safe and nature-friendly method of disease control. Bacteria associated with canola plants from western Iranian fields were isolated and their inhibitory effect against the blackleg pathogen of canola investigated in vitro. 8 isolates were selected based on antagonistic test results (dual cultures) and in vitro study of biocontrol mechanism. Next, their inhibitory ability against blackleg disease in the greenhouse was investigated. Selected isolates showed high inhibitory ability against Leptosphaeria maculansin vitro, suggesting the susceptibility of the blackleg pathogen to antifungal compounds produced by the selected strains. The selected isolates were able to produce antifungal antibiotics. Antifungal volatile compounds were observed in six selected isolates. All eight selected isolates generated hydrolytic enzymes such as cellulase, lipase, and amylase. Moreover, six isolates were able to produce protease. Isolate 642 (confirmed as Pseudomonas sp.) significantly inhibited blackleg disease under greenhouse conditions, suggesting its suitability for further investigation in the field. [ABSTRACT FROM AUTHOR]

Diaporthe caulivora is an economically important fungal pathogen and a causal agent of soybean stem canker and seed decay. Here, the genome of a Russian Far Eastern isolate of D. caulivora was sequenced, assembled, and announced. Assembly quality was enough for advanced annotation, including prediction of potential disease-related genes encoding virulence factors and molecular determinants contributing to pathogen-host selection, interactions, and adaptation. Comparative analysis of 15 Diaporthe species was conducted regarding general genome properties, collinearity, and proteomes, and included detailed investigation of interspersed repeats. A notable feature of this analysis is a high recombinant variability of Diaporthe genomes, determined by the number and distribution of interspersed repeats, which also proved to be responsible for the diversity of GC content and genome size. This variability is assumed the main determinant of the divergence of Diaporthe genomes. A Bayesian multi-gene phylogeny was inferred for the 15 Diaporthe species on the basis of twenty thousand polymorphic sites of > 100 orthologous genes using independently adjusted evolutionary models. This allowed for the most accurate determination of evolutionary relationships and species boundaries for effective reporting about these plant pathogens. The evidence, obtained by different genome analysis techniques, implies the host-independent evolution of Diaporthe species. Key points: • The genome of a Far Eastern isolate of D. caulivora was announced. • A high degree of recombinant variability determines genomic divergence in Diaporthe genus. • The multi-gene phylogeny implies host-independent evolution of Diaporthe species. [ABSTRACT FROM AUTHOR]

Black scurf and stem canker caused by Rhizoctonia solani is a significant disease problem of potatoes. Currently, chemical methods are the primary means of controlling this pathogen. This study sought to explore an alternative approach by harnessing the biocontrol potential of a bacterial mix of Bacillus subtilis and Bacillus amyloliquefaciens against black scurf, and to determine their effect on rhizosphere microorganisms of soil microbiota. This study showed that these bacteria demonstrate antagonistic activity against Rhizoctonia solani. Reduced damage to potato plants during the growing season in Siberia was observed. The index of disease development decreased from 40.9% to 12.0%. The treatment of tubers with this mix of bacteria also led to a change in the composition of the rhizosphere microbiota (according to CFU, 16S and ITS sequencing). This effect was accompanied by a positive change in plant physiological parameters (spectrophotometric analysis). The concentration of chlorophyll in potatoes with the bacterial mix treatment increased by 1.3 fold (p ≤ 0.001), and of carotenoids by 1.2 fold (p ≤ 0.01) compared with the control. After bacterial mix treatment, the length of the aerial parts of plants was 1.3 fold higher (p ≤ 0.001), and the number of stems 1.4 fold higher (p ≤ 0.05). The yield of potatoes was increased by 8.2 t/ha, while the large tuber fraction was increased by 16% (p ≤ 0.05). The bacteria mix of Bacillus subtilis and Bacillus amyloliquefaciens suppressed the plant pathogenic fungus Rhizoctonia solani, and simultaneously enhanced the physiological parameters of potato plants. This treatment can be used to enhance the yield/quality of potato tubers under field conditions.

Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) is a global soil-borne pathogen that severely harms potato crops, leading to significant product losses. Black scurf and stem canker are two manifestations caused by this pathogen, with variable intensity based on the distinctive anastomosis group endemic to the region. During the growing season of 2017 (March and April), 57 different fungus isolates were collected from potato crops farmed in the Jordan Valley. The identity of all the isolates was confirmed by sequencing the internal transcribed spacer (ITS) of the ribosomal DNA gene, and the hyphal interactions were also performed with R. solani isolates. The sequences were deposited in GenBank, where accession numbers were obtained. 21 of the isolates were AG-3PT R. solani, with 98-99% identity to reference strains. Somatic compatibility was determined by hyphal interactions, which showed pairing compatibility among the isolates. Around 86.7% of the pairings were somatically incompatible, indicating a high level of genetic diversity among the isolates, while only 13.3% of the pairings were somatically compatible. Testing for pathogenicity revealed that AG-3PT affected the stems of solanaceous plants, including potatoes, and the roots of other plant species. Based on the findings of this study, R. solani AG-3PT was the primary pathogen associated with potato stem canker and black scurf diseases in Jordan. To our knowledge, this is the first report on this pathogen's isolation and identification in Jordan. [ABSTRACT FROM AUTHOR]

Field surveys of E. camaldulensis diseases were conducted during 2019/20 and 2020/21 in Ethiopia. This species was found the most commonly planted in the surveyed fields and were showing stem canker diseases. Sampling was done from diseased stem and branches with clear symptoms. The morphological as well as PCR assay of the ITS1 and ITS2 loci were performed to identify the fungal pathogens. Lasiodiplodia theobromae and Didymella pinodella were the identified fungi. Four nationally licensed fungicides, Vitra (copper hydroxide), Ridomil gold (Metalaxyl-M + mancozeb), Liveshow (Pyraclostrobin + Epoxiconazole), and Sabozeb (Mancozeb) were evaluated for their in vitro efficacy against these fungi at concentrations of 500, 1000, 1500 and 2000 ppm for the management trial. Vitra and Liveshow were found to be the most effective fungicides at 2000 ppm for the control and treatment of Eucalyptus camaldulensis stem canker diseases. The findings from this research will provide foundation for future studies as this is the first report for the management of this Eucalyptus tree disease in Ethiopia. [ABSTRACT FROM AUTHOR]

Cannabis (Cannabis sativa L., marijuana) plants grown at indoor and outdoor production sites in British Columbia (BC) and Ontario with stem canker symptoms were sampled and affected tissues were surface-sterilized and plated onto potato dextrose agar. Isolates were identified by colony and spore morphology as well as PCR amplification and sequencing of the ITS1-ITS2 rDNA, beta-tubulin, and actin gene regions. The most frequently isolated fungi were Alternaria alternata, Neofusicoccum parvum, and Lasiodiplodia theobromae. In addition, A. alternata was recovered from cannabis inflorescences in BC as well as surface-sterilized hemp seed. Stemphylium vesicarium was isolated from hemp seeds for the first time. The pathogenicity of all these fungi to cannabis plants was confirmed by inoculation of leaves, stems, buds, rooted cuttings and mature plants. Disease ratings varied depending on both tissue type and pathogen. Both L. theobromae and N. parvum produced extensive stem cankers on mature cannabis plants as well as extensive lesions on leaves. All pathogens showed optimal colony growth in culture at 25–30°C. A comparison of the susceptibility of five cannabis genotypes to foliar infection by N. parvum indicated there were significant differences (p < 0.05) in lesion size, with some genotypes showing high susceptibility and others showing resistance. This is the first report of L. theobromae, N. parvum, A. alternata, and S. vesicarium causing stem canker and leaf spot symptoms on cannabis in Canada. The recovery of these fungi adds to the growing list of pathogens that cause infection and loss of quality in cannabis production. [ABSTRACT FROM AUTHOR]

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Soils in which disease fails to develop despite pathogen presence are considered disease-suppressive. They offer sustainable, effective protection to plants against infection by soil-borne pathogens. Naturally disease-suppressive soils have been reported for diseases of a diverse range of agricultural crops worldwide yet the underlying mechanisms of disease suppression are still not completely understood. Two large greenhouse experiments, conducted during 2017/18 (Year 1) and 2018/19 (Year 2), determined that soils naturally suppressive to stem canker and black scurf of potato (caused by Rhizoctonia solani) are present in vegetable-arable cropping soils of the Auckland and Waikato regions of New Zealand. Soil was pre-treated with heat prior to inoculation with R. solani and compared with untreated and uninoculated controls to ascertain if stem canker and black scurf suppression was 'general', or 'specific' (i.e. transferable; possibly involving specific microorganisms). Rhizoctonia solani inoculation was also combined with transfer of one part test soil to nine parts of a known disease-conducive soil. Abiotic factors such as soil texture and organic matter content influenced black scurf incidence and severity. Soil microorganisms were also involved in disease suppression since black scurf incidence and severity markedly increased when they were eliminated or reduced by soil heat pre-treatment. Microbial profiling of the soils through sequencing revealed that taxa of geographically close soils of the same type had similar fungal and bacterial community structure and diversity even though they differed in their capacity to suppress black scurf. These results suggest that although the soil microbiome as a whole, was mainly responsible for soil disease suppressiveness, certain bacterial genera or species may play a role in black scurf suppression. [ABSTRACT FROM AUTHOR]

In many cultivated crops, sources of resistance to diseases are sparse and rely on introgression from wild relatives. Agricultural crops often are allopolyploids resulting from interspecific crosses between related species, which are sources of diversity for resistance genes. This is the case for Brassica napus (oilseed rape, canola), an interspecific hybrid between Brassica rapa (turnip) and Brassica oleracea (cabbage). B. napus has a narrow genetic basis and few effective resistance genes against stem canker (blackleg) disease, caused by the fungus Leptosphaeria maculans, are currently available. B. rapa diversity has proven to be a valuable source of resistance (Rlm, LepR) genes, while B. oleracea genotypes were mostly considered susceptible. Here we identified a new resistance source in B. oleracea genotypes from America, potentially effective against French L. maculans isolates under both controlled and field conditions. Genetic analysis of fungal avirulence and subsequent cloning and validation identified a new avirulence gene termed AvrLm14 and suggested a typical gene‐for‐gene interaction between AvrLm14 and the postulated Rlm14 gene. AvrLm14 shares all the usual characteristics of L. maculans avirulence genes: it is hosted in a genomic region enriched in transposable elements and heterochromatin marks H3K9me3, its expression is repressed during vegetative growth but shows a strong overexpression 5–9 days following cotyledon infection, and it encodes a small secreted protein enriched in cysteine residues with few matches in databases. Similar to the previously cloned AvrLm10‐A, AvrLm14 contributes to reduce lesion size on susceptible cotyledons, pointing to a complex interplay between effectors promoting or reducing lesion development. [ABSTRACT FROM AUTHOR]

Tomanage stemcanker disease on royal poinciana, actinobacterial isolateswere used as biological control agents (BCAs) based on their strong in vitro inhibitory effects against Neoscytalidium dimidiatum. Streptomyces griseorubens UAE2 and Streptomyces wuyuanensis UAE1 had the ability to produce antifungal compounds and cell-wall-degrading enzymes (CWDEs). Only S. griseorubens, however, restored the activity of 1-aminocyclopropane-1-carboxylate (ACC) deaminase (ACCD). In vivo apple fruit bioassay showed that lesion development was successfully constrained by either isolates on fruits inoculated with N. dimidiatum. In our greenhouse and container nursery experiments, S. griseorubens showed almost complete suppression of disease symptoms. This was evident when the preventive treatment of S. griseorubens significantly (p < 0.05) reduced the numbers of conidia of N. dimidiatum and defoliated leaves of royal poinciana seedlings to lesser levels than when S. wuyuanensis was applied, but comparable to control treatments (no pathogen). The disease management of stem canker was also associated with significant (p < 0.05) decreases in ACC levels in royal poinciana stems when S. griseorubens was applied compared to the non-ACCD-producing S. wuyuanensis. This study is the first to report the superiority of antagonistic actinobacteria to enhance their effectiveness as BCAs not only for producing antifungal metabolites and CWDEs but also for secreting ACCD. [ABSTRACT FROM AUTHOR]

Cultivation of apple trees in the highlands of Ethiopia began in 1955. In 2014, blistering of the bark due to cankers on the main stems mostly below the grafting points, followed by dieback and eventually death of apple trees, was observed in apple orchards in the Hadiya Zone in Ethiopia. This study aimed to identify the causal agent of canker and dieback symptoms on the apple trees. Symptomatic trunks from 20 trees (ten per cultivar) were sampled. Isolations were performed from ten trunks (five per cultivar). Fungus colonies with similar cultural features were obtained from all the samples, and the morphology of a representative isolate was characterized. Phylogenetic analyses of the concatenated internal transcribed spacers 1 and 2 and 5.8S rRNA gene, large subunit and actin gene regions confirmed the identity of two isolates as Didymosphaeria rubi-ulmifolii. Pathogenicity was confirmed for one isolate by inoculations of healthy branches of ‘Anna’ and ‘Dorsett Golden’ apple trees resulting in lesion formation, and subsequent re-isolation of the inoculated fungus. This study is the first report of D. rubi-ulmifolii associated with dieback of apple trees. This pathogen caused death of more than 26% of apple trees in one commercial orchard, and could cause severe losses for smallholder apple growers in Ethiopia. Future studies are required to assess the magnitude, distribution and management options of this economically important canker disease in Ethiopia.

The study of oomycetes associated with crops is highly important due to the economic losses they might cause. In cacao, the genus Phytophthora has been extensively studied, but little is known about other genera and species of oomycetes associated with this plant. This study aimed to determine the oomycetes' diversity present in Colombian cacao crops. A total of 146 isolates were obtained from diseased plants and soil in 11 departments. Analysis of internal transcribed spacer (ITS) and cytochrome oxidase subunit I (coxI) sequences was performed along with the assessment of morphological characteristics. Nine species were identified, distributed in four genera: Phytophthora (P. palmivora, 54%; P. nicotianae, 1%), Phytopythium (Phy. chamaehyphon, 15%; Phy. cucurbitacearum, 9%; Phy. vexans, 7%; Phy. helicoides, 1%), Globisporangium (G. splendens, 3%), and Pythium (Py. delicense, 1%; Py. inflatum,1%). Additionally, an unidentified and possibly new species of Phytophthora (5%) and three unidentified species of Phytopythium (3%) were found. This is the first report of Globisporangium, Phytopythium, and Pythium in cacao crops of Colombia and the first report of the species Phy. chamaehyphon in the country. Interestingly, some isolates of Phytopythium spp. were isolated from necrotic leaves and vascular section of stems, which may suggest a role in cacao diseases traditionally associated with Phytophthora. Also, it is proposed that the new species of Phytophthora may be contributing significantly to black pod disease in Colombian cacao crops, and we highlight that the study of P. palmivora is urgent because of its distribution all over the country. [ABSTRACT FROM AUTHOR]

Cultivation of apple trees in the highlands of Ethiopia began in 1955. In 2014, blistering of the bark due to cankers on the main stems mostly below the grafting points, followed by dieback and eventually death of apple trees, was observed in apple orchards in the Hadiya Zone in Ethiopia. This study aimed to identify the causal agent of canker and dieback symptoms on the apple trees. Symptomatic trunks from 20 trees (ten per cultivar) were sampled. Isolations were performed from ten trunks (five per cultivar). Fungus colonies with similar cultural features were obtained from all the samples, and the morphology of a representative isolate was characterized. Phylogenetic analyses of the concatenated internal transcribed spacers 1 and 2 and 5.8S rRNA gene, large subunit and actin gene regions confirmed the identity of two isolates as Didymosphaeria rubi-ulmifolii. Pathogenicity was confirmed for one isolate by inoculations of healthy branches of 'Anna' and 'Dorsett Golden' apple trees resulting in lesion formation, and subsequent re-isolation of the inoculated fungus. This study is the first report of D. rubi-ulmifolii associated with dieback of apple trees. This pathogen caused death of more than 26% of apple trees in one commercial orchard, and could cause severe losses for smallholder apple growers in Ethiopia. Future studies are required to assess the magnitude, distribution and management options of this economically important canker disease in Ethiopia. [ABSTRACT FROM AUTHOR]

Analysis of Causative Factors for Canker Disease Epidemic on Rubber Plants in South Sumatra. Lasiodiplodia theobromae is the cause of stem canker in the rubber plant (Hevea brasiliensis), this is a new disease and has never been reported in Indonesia. Currently, data on environmental factors and cultivation techniques related to the development of stem canker are not available so research needs to be done on this subject. The objective of the study was to analyze environmental factors and cultivation techniques related to stem canker on rubber trees in southern Sumatra. The study was conducted by collecting data on environmental factors and cultivation techniques and then analyzed the association with stem canker. Field observation was carried out at 21 locations in PT. Perkebunan Nusantara VII Business Unit Padang Plawi Bengkulu, Tulung Buyut Lampung, Musilandas Palembang and Experimental Garden of Sembawa Research Center, Indonesian Rubber Research Institute at Palembang to measure the severity and incidence of this disease. Besides that, the data of cultivation technique and the condition of the garden were taken from the officer at those locations. Soil sample from each location was taken in a composite way, then its physical and chemical components were analyzed. The analysis was conducted to find out the correlation between cultivation and disease severity using chi-square test. The relationship between chemical and physical factors of the soil with the disease severity was analyzed using a multivariate test of principal component analysis/PCA. Regression analysis was conducted to show the possible relation to the incidence and severity of this disease. The location, clones, weed control and the number of plants per hectare showed a correlation with the disease severity. There was a positive correlation between incidence and severity of the disease. The highest disease severity occurred at the Sembawa location on clone BPM 24, with the number of plant population per ha was ≥ 555 trees and weed control using herbicide. Content of soil nitrogen, dust, clay and water as well as cation exchange capacity (CEC)were suggested to significantly contribute to the severity of stem canker.

Field surveys indicate blackleg of canola has increased in western Canada since 2010. Earlier studies showed changes in the pathogen (Leptosphaeria maculans (Sowerby) P.Karst.; Lm) population between 2007 and 2010–2011. In this study, Lm isolates were collected from trap plots (591) and/or commercial fields (372) on the prairies between 2012 and 2014, and tested for the profile of avirulence (Av) genes on a set of host differentials for 10 Lm Av alleles. Up to 35 'Westar' trap plots were set up each year, and commercial fields were surveyed in the same area in 2012 and 2013. A similar trend was observed for Av profile between the two Lm populations; Av1, Av3, Av9 and AvLep2 were at low or very low levels, while Av2, Av4, Av6 and Av7 were present in >60% of the isolates. A total of 82 races were identified in these Lm populations, suggesting a greater diversity than those reported elsewhere. Margalef and Simpson indices also confirmed the greater genetic diversity in Lm. In fact, for each known R gene, there is at least one virulent race already existing in the Lm population. The races carrying Av2, Av4, Av6 or Av7 accounted for >70% of the Lm population, indicating that an R gene corresponding to any of these Av alleles may be effective against blackleg on the prairies. However, Av results alone appeared insufficient for explaining different levels of blackleg observed in canola fields; additional factors, possibly including crop rotation and local weather, may also play a role. [ABSTRACT FROM AUTHOR]

Euphrates poplar (Populus euphratica Oliv.) constitutes about 61% of the global poplar population, thriving in arid regions of western China (Wu et al. 2023). It plays a crucial role in maintaining ecological balance, securing oasis agriculture, and driving socio-economic progress in the region. During a June 2023 investigation in the P. euphratica forest within the Hotan area of Xinjiang (37°20'21″N, 79°21'15″E), over 12% of the P. euphratica trees displayed branch withering symptoms. The affected trees exhibited cracked bark, trunk decay, darkened coloration, and an eventual black coal-smoke-like appearance. Fungal spores were notably present beneath peeling bark on trunks and main branches. The deep ulcers extended longitudinally into the cambium, leading to tree mortality. In some cases, lateral spread into the sapwood caused dark discoloration of vascular tissue. Twenty diseased branches from various locations were collected and 5-10 mm2 lesions were excised from the edges. These were then surface-disinfected with 75% ethanol for 30 s and 1% sodium hypochlorite for 2 min. After three rinses with sterile distilled water, excess moisture was removed using sterile filter paper, followed by incubating the samples on Potato Dextrose Agar (PDA) medium. Cultures were subsequently grown at 25 ± 1 ℃ under a 12-h photoperiod for three days, thus resulting in the isolation of 25 fungal strains with similar morphological characteristics. All strains displayed rapid colony growth (40 mm/d). On PDA medium, the mycelium initially presented as a white colony, transitioning to an olive-green to greyish color, finally turning dark-grey to black. Colonies generated mycelia that disintegrated into 0- to 1-septate, cylindrical to round, hyaline to brown arthroconidia, occurring singly or in arthric chains, averaging 8.9 ± 2.1 μm × 4.9 ± 1.3 μm, with a length/width ratio of 1.79. Based on morphological characteristics, the isolates were identified as Neoscytalidium dimidiatum (Penz.) Crous & Slippers (Crous et al. 2006). Molecular characterization involved amplifying the partial internal transcribed spacer (ITS) region and translation elongation factor 1-α (TEF1-α) and β-tubulin (TUB2) genes using ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Carbone and Kohn 1999), and BT2a/BT2b primers (Glass and Donaldson 1995). Sequences, available in GenBank (ITS: PP033096, PP033097, PP033098; TUB2: PP032812, PP032813, PP032814; TEF1-α: PP032815, PP032816, PP032817), exhibited 99-100% identity with the epitype N. dimidiatum Arp2-D (ITS, MK813852; TUB2, MK816354; TEF1-α, MK816355). Phylogenetic analysis, employing maximum likelihood and Bayesian inference on concatenated ITS-TEF1-TUB, was constructed using IQ-Tree and MrBayes3.2.7, revealing isolates clustering within the N. dimidiatum clade. Three isolates (HY01, HY02, and HY05) from different collection points were chosen for pathogenic investigation. Pathogenicity testing on one-year-old healthy P. euphratica seedlings involved removing a 4-mm-diameter bark plug using a cork borer. A 3-day-cultured N. dimidiatum plug of the same size was inoculated, with a blank PDA as control. The wound was covered with moistened sterile absorbent cotton and finally sealed with parafilm for three days. Experiments were repeated thrice. Symptoms manifested by day 2 post-inoculation, resembling the original symptoms by day 7. In the control group, plants remained healthy. N. dimidiatum was exclusively re-isolated from lesions on inoculated stems, confirmed as N. dimidiatum through morphological characteristics and sequence analysis, aligning with Koch's hypothesis. To our knowledge, this is the first report of N. dimidiatum inducing stem canker on P. euphratica in China. This pathogen has been reported on many tree hosts including citrus (Alananbeh et al., 2020), common fig (Güney et al., 2022), dragon fruit (Salunkhe et al., 2023), and Almond (Nouri et al., 2018). Therefore our findings will serve as a warning for authorities to a potential threat in China's P. euphratica and other trees cultivation. Thus, further epidemiological studies are essential for devising effective management strategies.

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Oilseed rape residues are a crucial determinant of stem canker epidemiology as they support the sexual reproduction of the fungal pathogen Leptosphaeria maculans. The aim of this study was to characterize the impact of a resistance gene against L. maculans infection on residue microbial communities and to identify microorganisms interacting with this pathogen during residue degradation. We used near‐isogenic lines to obtain healthy and infected host plants. The microbiome associated with the two types of plant residues was characterized by metabarcoding. A combination of linear discriminant analysis and ecological network analysis was used to compare the microbial communities and to identify microorganisms interacting with L. maculans. Fungal community structure differed between the two lines at harvest, but not subsequently, suggesting that the presence/absence of the resistance gene influences the microbiome at the base of the stem whilst the plant is alive, but that this does not necessarily lead to differential colonization of the residues by fungi. Direct interactions with other members of the community involved many fungal and bacterial amplicon sequence variants (ASVs). L. maculans appeared to play a minor role in networks, whereas one ASV affiliated to Plenodomus biglobosus (synonym Leptosphaeria biglobosa) from the Leptosphaeria species complex may be considered a keystone taxon in the networks at harvest. This approach could be used to identify and promote microorganisms with beneficial effects against residue‐borne pathogens and, more broadly, to decipher the complex interactions between multispecies pathosystems and other microbial components in crop residues. [ABSTRACT FROM AUTHOR]

The significance of nematodes for disease development caused by other soil-borne pathogens has been demonstrated in many crops throughout the world and specifically prevalent are interactions between plant-parasitic nematodes and species of plant pathogenic fungi. Here, the interaction between the fungus Rhizoctonia solani (AG2) and the migratory endoparasitic root-lesion nematode Pratylenchus penetrans was investigated on potato. The hypotheses were that the combination of R. solani and P. penetrans would result in more severe canker lesions, reduced quality of the tubers and lower tuber yield, and we also expected higher nematode levels to render more nematode damage. To test this, potato plants were grown in pots in two replicate experiments and the presence and/or abundance of the two pathogens were controlled. The first three hypotheses were rejected as (1) the tuber yield decreased when the fungus and nematode occurred together but not more than the sum of their separate effects, i.e. additive, (2) there was no effect of presence of nematodes on the incidence of stem canker, and (3) the quality of tubers was actually partly improved as the presence of the nematodes reduced the likelihood of elephant hide on the tubers in one of the experiments. As expected, there were more visible nematode damages with addition of more nematodes, but beyond that the different nematode levels rendered in most cases similar responses. To have knowledge about interactions between pathogens, as the one showed here, is essential for disease control through appropriate management methods. [ABSTRACT FROM AUTHOR]

Blackleg, caused by Leptosphaeria maculans, is a serious disease on canola or rapeseed in Canada, Australia and Europe. Disease levels have increased in western Canada recently and additional tools are needed to improve blackleg management. Seed treatment can be a cost-effective approach against blackleg, but there is currently no registered seed-treatment product targeting aboveground blackleg infection. In this study, a range of fungicides was evaluated for control of cotyledon infection by L. maculans and blackleg of canola. Under controlled environmental conditions, fluopyram showed greater efficacy than fluquinconazole (used against blackleg in Australia) in limiting cotyledon infection, while Prosper® EverGol and Helix® Vibrance (industry standards) were ineffective. Fluopyram at a rate of 30–150 g/100 kg seed generally inhibited cotyledon infection and this efficacy was not affected by delayed soil moisture for 3 weeks after planting. This indicates that the efficacy will unlikely be affected by a slight delay in germination due to a soil moisture deficit after seeding. In addition to typical mechanisms of succinate dehydrogenase inhibitor fungicides, fluopyram also induced expression of the indicator gene coding PR-1 proteins substantially, indicating the potential for inducing disease resistance. In field trials at 75 and 150 g/100 kg seed, fluopyram reduced the infection on cotyledons resulting from pricking inoculation on both susceptible and resistant canola cultivars, potentially limiting the infection into the stem. These seed treatment rates reduced the disease severity index (DSI) substantially on the susceptible cultivar, while DSI was low on a resistant cultivar with or without fluopyram treatment. [ABSTRACT FROM AUTHOR]

Phytophthora palmivora (Butler) is an hemibiotrophic oomycete capable of infecting over 200 plant species including one of the most economically important crops, Theobroma cacao L. commonly known as cocoa. It infects many parts of the cocoa plant including the pods, causing black pod rot disease. This review will focus on P. palmivora’s ability to infect a plant host to cause disease. We highlight some current findings in other Phytophthora sp. plant model systems demonstrating how the germ tube, the appressorium and the haustorium enable the plant pathogen to penetrate a plant cell and how they contribute to the disease development in planta. This review explores the molecular exchange between the oomycete and the plant host, and the role of plant immunity during the development of such structures, to understand the infection of cocoa pods by P. palmivora isolates from Papua New Guinea. [ABSTRACT FROM AUTHOR]

To manage stem canker disease on royal poinciana, actinobacterial isolates were used as biological control agents (BCAs) based on their strong in vitro inhibitory effects against Neoscytalidiumdimidiatum. Streptomyces griseorubens UAE2 and Streptomyces wuyuanensis UAE1 had the ability to produce antifungal compounds and cell-wall-degrading enzymes (CWDEs). Only S. griseorubens, however, restored the activity of 1-aminocyclopropane-1-carboxylate (ACC) deaminase (ACCD). In vivo apple fruit bioassay showed that lesion development was successfully constrained by either isolates on fruits inoculated with N. dimidiatum. In our greenhouse and container nursery experiments, S. griseorubens showed almost complete suppression of disease symptoms. This was evident when the preventive treatment of S. griseorubens significantly (p < 0.05) reduced the numbers of conidia of N. dimidiatum and defoliated leaves of royal poinciana seedlings to lesser levels than when S. wuyuanensis was applied, but comparable to control treatments (no pathogen). The disease management of stem canker was also associated with significant (p < 0.05) decreases in ACC levels in royal poinciana stems when S. griseorubens was applied compared to the non-ACCD-producing S. wuyuanensis. This study is the first to report the superiority of antagonistic actinobacteria to enhance their effectiveness as BCAs not only for producing antifungal metabolites and CWDEs but also for secreting ACCD.

Canker and needle blight of Araucaria heterophylla (Norfolk Island pine) trees were observed during the surveys conducted in Addis Ababa and Adama cities (Ethiopia) from November to December 2016. The main objective of this study was to investigate fungal pathogens that cause diseases on Araucaria heterophylla trees. Six localities with Araucaria heterophylla plantings were purposively surveyed for disease symptoms. Samples from symptomatic parts of trees were collected, surface sterilized, cultured on PDA and morphologically identified for genus and species. A total of 36 isolates of fungi were identified. Based on macro- and microscopic morphological features of the colonies, the fungal isolates were found to be the genus Diplodia and species Lasiodiplodia theobromae (Pat.) Griffon & Maubl (syn. Botryodiplodia theobromae), the anamorph of Botryosphaeria rhodina (Berk. & M.A. Curtis) Arx. The pathogenicity test showed that the isolates of Lasiodiplodia theobromae, caused stem canker and needle blight on Araucaria heterophylla. This finding is important in the study of management options for future prevention and control of diseases in the country.

Dragon fruit, also known as pitahaya, pitaya, and strawberry pear, is a group of vine-like, climbing cacti. In south Florida, production of dragon fruit has been steadily increasing since the 2000s, and growers in Florida consider dragon fruit as a potential alternative fruit crop to avocado and citrus, two economically important fruit crops largely impacted by laurel wilt and huanglongbing, respectively. This new 4-page article focuses on the symptomology and epidemiology of stem and fruit canker, a prevailing disease on dragon fruit. Suggested management strategies for the disease are also discussed based on recent studies conducted in south Florida. Written by Cheng-Fang Hong, Shouan Zhang, Romina Gazis, Jonathan H. Crane, and Jeff Wasielewski, and published by the UF/IFAS Plant Pathology Department. https://edis.ifas.ufl.edu/pp355

The Eucalyptus stem canker pathogens Teratosphaeria gauchensis and T. zuluensis (Capnodiales, Teratosphaeriaceae) are found in many tropical regions of the world where their hosts are cultivated for plantation forestry. Population genetic analyses have suggested that some populations undergo recombination, even though their sexual states have never been observed. Against this background, the aim of this study was to characterize the mating type (MAT) locus of these species and thus to better understand the basis of their diversity. Known Mycosphaerellaceae MAT genes were used to identify and investigate the MAT locus in the T. gauchensis and T. zuluensis genomes. Both species were found to be heterothallic and primers were designed to amplify the opposite MAT idiomorphs as well as conserved regions within the MAT1‐1‐1 and MAT1‐2‐1 genes. Each Teratosphaeria MAT idiomorph was defined by either the MAT1‐1‐1 or the MAT1‐2‐1 gene, and an idiomorph‐specific hypothetical protein (MAT1‐1‐10 and MAT1‐2‐12). Populations of T. zuluensis from Asia and southern Africa were dominated by a single mating type, whereas the proportions of the different idiomorphs for T. gauchensis in South America and southern Africa were similar. There was no physical evidence of sexual reproduction for either species and it is argued that although recombination may be possible, it is unlikely to form an important part of their life cycles in diseased Eucalyptus plantations. Instead, continuous human‐mediated multiple introductions of these species have probably resulted in the current genetic structure of their populations, which holds risk for future disease outbreaks and interspecific hybridization. [ABSTRACT FROM AUTHOR]

Stem canker (SC), caused by Diaporthe helianthi, is the most serious sunflower disease in Uruguay. Yield losses have been estimated up to 75%. Chemical control is one of the strategies used to manage this disease, but fungicide application should be done before symptoms are visible. Ascospores are the primary source of inoculum, they are produced in perithecia which develop in infected stubble and are dispersed by wind to infect plants. As in other monocyclic diseases, quantifying primary inoculum is essential to predict an epidemic. In this study, ascospores were trapped on microscope slides with solid petroleum jelly which were placed on top of flat open cages filled with natural infected stubble. Cages were placed outdoors, slides where replaced twice a week and stained ascospores were counted under the microscope. Our objective was to develop weather-based models to predict ascospore release levels of D. helianthi from infected stubble. Explanatory weather variables were calculated during the seven-day periods prior to each field weekly ascospore count using daily weather station data from La Estanzuela, Uruguay. Then, logistic models were fit to estimate probabilities of having severe or moderate to light levels of ascospore counts. The best models included variables associated to the precipitation and dew-induced wetness frequency, combinated with the simultaneous occurrence of high relative humidity or low thermal amplitude records. Estimating the evolution of ascospore release through the weather-based models might help to guide preventive fungicide applications to control stem canker in Uruguay. [ABSTRACT FROM AUTHOR]

Studies were conducted to determine the role of 3-methylthioproprionic acid (MTPA) in the pathogenicity of potato stem canker, Rhizoctonia solani, and the concentrations required to inhibit growth of R. solani under laboratory and plant house-based conditions. The experiments were laid out in a completely randomized design with five treatments and five replications. The treatments were 0, 1, 2, 4, and 8 mM concentrations of MTPA. The purified toxin exhibited maximal activity at pH 2.5 and 30°C. MTPA at 1, 2, 4, and 8 mM levels reduced plant height, chlorophyll content, haulm fresh weight, number of stolons, canopy development, and tuber weight of potato plants, as compared to the control. MTPA significantly affected mycelial growth with 8 mM causing the highest infection. The potato seedlings treated with MTPA concentrations of 1.0–8.0 mM induced necrosis of up to 80% of root system area. Cankers were resulted from the injection of potato seedling stems with 8.0 mM MTPA. The results showed the disappearance of cell membrane, rough mitochondrial and cell walls, change of the shape of chloroplasts, and swollen endoplasmic reticulum. Seventy-six (76) hours after toxin treatment, cell contents were completely broken, cytoplasm dissolved, and more chromatin were seen in the nucleus. The results suggested that high levels of the toxin concentration caused cell membrane and cytoplasm fracture. The integrity of cellular structure was destroyed by the phytotoxin. The concentrations of the phytotoxin were significantly correlated with pathogenicity and caused damage to the cell membrane of potato stem base tissue.

Phytophthora palmivora (Butler) is an hemibiotrophic oomycete capable of infecting over 200 plant species including one of the most economically important crops, Theobroma cacao L. commonly known as cocoa. It infects many parts of the cocoa plant including the pods, causing black pod rot disease. This review will focus on P. palmivora’s ability to infect a plant host to cause disease. We highlight some current findings in other Phytophthora sp. plant model systems demonstrating how the germ tube, the appressorium and the haustorium enable the plant pathogen to penetrate a plant cell and how they contribute to the disease development in planta. This review explores the molecular exchange between the oomycete and the plant host, and the role of plant immunity during the development of such structures, to understand the infection of cocoa pods by P. palmivora isolates from Papua New Guinea.

Summary: Background : Teratosphaeria gauchensis and T. zuluensis are closely related fungi that cause Teratosphaeria (previously Coniothyrium) stem canker disease on Eucalyptus species propagated in plantations for commercial purposes. This disease is present in many countries in which Eucalyptus trees are planted, and continues to spread with the international trade of infected plant germplasm. Taxonomy: Fungi, Ascomycota, Pezizomycotina, Dothideomycetes, Dothideomycetidae, Capnodiales, Teratosphaeriaceae, Teratosphaeria. Identification: The causal agents form dark masses of pycnidia that are visible on the surface of distinct stem cankers that typically form on young green stem tissues. Accurate diagnosis of the causal agents requires DNA sequence data. Host range: Nine species of Eucalyptus are known to be affected. Of these, E. grandis and its hybrids, which include some of the most important planting stock globally, appear to be particularly vulnerable. Disease symptoms: Small necrotic lesions develop on young green stem tissue. These lesions coalesce to form large cankers that exude gum. Epicormic shoots develop below the girdling canker and, in severe cases, trees die. Useful websites: Mycobank, https://www.mycobank.org; Publications of the Forestry and Agricultural Biotechnology Institute (FABI), https://www.fabinet.up.ac.za/index.php/journals. [ABSTRACT FROM AUTHOR]