Search

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]

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]

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.

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.

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]

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]

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.

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]

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]

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]

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.

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]

Blackleg disease, caused by Leptosphaeria maculans, is a serious threat to canola production in western Canada. While specific major resistance (R) genes can be effective, they can also be eroded rapidly by a shift in pathogen race composition. Quantitative resistance (QR) has the potential to provide more durable, if less complete, protection. However, the effectiveness of QR may vary widely in the field. It has long been suspected that elevated temperatures may limit the expression of QR. To test this hypothesis, the infection development of blackleg was assessed on three common Canadian canola cultivars (74‐44 BL, PV 530 G and 45H29) showing QR, with and without a heat treatment of 7 h daily exposure to 32 °C for 1 week during rosette to early flowering under controlled environment conditions. The impact of elevated temperature on the susceptibility to blackleg was compared with that of a moderate temperature with a 22 °C daytime high. A susceptible cultivar, Westar, was used as a control. When data from both temperatures were pooled, all three QR cultivars showed lower blackleg severity relative to Westar. Elevated temperatures increased blackleg severity in Westar only (in terms of the stem‐lesion length from the inoculation of the first true‐leaf petiole in trials involving Westar and 74‐44 BL) and in pooled data for disease severity index in trials involving Westar, PV 530 G and 45H29. These findings suggest that the QR traits in 74‐44 BL, PV 530 G and 45H29 are useful for blackleg management in western Canada, especially under warmer growing conditions when plants are at the rosette to early flowering stages. [ABSTRACT FROM AUTHOR]

Soil microorganisms and soil fauna may have a large impact on the tuber yield of potato crops. The interaction between root-lesion nematodes and the pathogenic fungus Rhizoctonia solani Kühn was studied on potato plants grown in pots under controlled conditions. In two similar experiments, different combinations of nematodes and fungal mycelium were added to the pots at three occasions; at planting, after 14 days, and after 28 days. The nematodes reduced root biomass and the combination of nematodes and R. solani resulted in reduced tuber yield in both experiments, but the interaction was not synergistic. In contrast, the number of stem canker lesions decreased in the presence of nematodes compared to treatments with R. solani only. The time of inoculation influenced the severity of both fungal and nematode damage. The nematode damage on tubers was less severe if the nematodes were added at 28 days, while the number of severe stem canker lesions increased if the fungus was added at 28 days. However, the time of nematode inoculation did not affect the incidence of fungal damage, hence the nematodes did not assist R. solani to infect the plant. Our results highlight the underestimated importance of root-lesion nematodes, not resulting in obvious above ground symptoms or misshaped tubers yet affecting the performance of other pathogens.

Stem canker caused by Phytophthora palmivora and Phytophthora megakarya is a serious disease of cacao (Theobroma cacao L.). Studies of the genetics of resistance to this disease is important to identify an effective procedure to use in breeding resistant varieties. The objective of this study was to determine mode of inheritance, combining ability and heritability of resistance to stem canker in cacao. A 6 x 6 full diallel mating design was used to generate 36 F1 hybrids which were evaluated for resistance to stem canker with three replications under artificial inoculation with 1 mm2 agar plug taken from actively growing colonies of 10-day old cultures of P. palmivora and P. megakarya. Twelve months later, the canker lesions on outer bark of the stem of the seedlings were measured and the canker lesions inside was also measured after scraping the bark. There were significant (p<0.05) variation for canker sizes both before and after scraping the bark of stem among the genotypes. The general combining ability (GCA) and specific combining ability effects were both significant (p<0.05) for stem canker resistance suggesting that both additive and non-additive gene effects are involved in expression of resistance to stem canker. However, the predominance (>50%) of GCA suggest that additive gene effects were more important than non-additive gene effects. The overall direction of results showed that using one of the following parents: P1 (Alpha B36), P4 (T17/524) and P5 (T65/238) as the female produced progenies with better resistance to stem canker disease than when they were used as the male parent. The majority reflected the resistance level of the female parent, suggesting that resistance to stem canker in cacao is influenced by maternal inheritance. Cacao genotypes Alpha B36, T17/524 and T65/238 showed significant negative GCA effects for resistance to stem canker suggesting that these genotypes will transmit the trait to their progenies and therefore recommended for cacao breeding. Narrow sense heritability for stem canker resistance was low indicating large component of dominance effects and influence of environment in inheritance of resistance to stem canker in cacao. However, the very high broad sense heritability (0.99) coupled with large variation within the cacao tree population indicate that progeny testing and within family selection would be appropriate in breeding against stem canker in cacao. [ABSTRACT FROM AUTHOR]

The study was conducted to evaluate the efficacy of integrated management of stem canker and black scurf disease affecting the potato plant. The integrated management options were: T1 = Poultry manure (PM) + seed trématent (ST) with Azoxystrobin (0.05%), T2 = PM + STAzoxystrobin (0.10%), T3= PM+ST-Boric acid (3.0%), T4 = PM + ST-Carboxin (0.20%), T5 = PM + ST- Carbendazim (0.10%), T6 = PM + soil drenching (SD) - Azoxystrobin (0.05%), T7 = PM + SD-Azoxystrobin (0.10%), T8 = PM + SD-Carboxin (0.20%), T9 = PM + SD-Carbendazim (0.10%) and T10 = Untreated control. The integrated management significantly influenced the disease incidence, yield attributes and yield of potato. The lowest disease incidence (11.2%) and percentage of disease index (4.58) were found in T7 (poultry manure at 5 t ha-1 before 25 days of planting, DAP + soil drenching with Azoxystrobin at 0.10% during sowing and 45 DAP) followed by T6 (PM 5 t ha-1 + soil drenching with Azoxystrobin at 0.05%). The minimum weight of russet (480 g plot-1), deformed (450 g plot-1) and Sclerotia infected (150 g plot-1) tubers were also recorded in T7. The highest healthy tuber (1900.05 g plot-1) and tuber yield (22.4 t ha-1) were found in the same treatment. Therefore, poultry manure 5 t ha-1 before 25 DAP + soils drenching with Azoxystrobin at 0.10% during sowing and 45 DAP can be recommended to produce healthy tubers and maximum tuber yield of potato. [ABSTRACT FROM AUTHOR]

Rhizoctonia disease in potato is widely distributed in Estonia. Field experiments with cv. 'Red Fantasy' were undertaken with seven pre-crop treatments at the Estonian Research Institute of Agriculture in 2009 and 2010. Monocropped potato, spring barley, spring barley underseeded with red clover, spring wheat, grain pea, spring oil seed rape and oil seed radish were involved in the study as pre-crops. Growing conditions on both years were rather optimal for potato growth but year 2010 was drier at early bulking stage. The effect of different pre-crops on Rhizoctonia solani complex was studied (i.e. incidence and severity of stem and stolon canker and black scurf) at 15, 30, 45, 60, 90 and 120 days after planting. Results indicated that pathogenfree seed tubers are of primary importance in the disease control and no pre-crop was suppressive to disease if seed tubers had sufficient amount of inoculum. However, to achieve consistent reduction in disease development, inoculum-free seed tubers and crop rotation with non-host crops should be considered. [ABSTRACT FROM AUTHOR]

The pathogenic fungus Rhizoctonia solani causes major economic losses for potato producers in Sweden. Producers, as well as extension officers, have reported possible increases in severity of R. solani when free-living plant-parasitic nematodes are present and active. The aim of this study was to investigate possible interactions and spatial correlations between root-lesion nematodes ( Pratylenchus spp.), stubby-root nematodes (Trichodoridae) and the severity of stem canker caused by the fungus R. solani under field conditions. Nematodes in the genus Globodera were also included after finding high numbers of these potato cyst nematode juveniles in the samples. Soil samples were taken in eight potato fields, located in the middle part of Sweden, with observed outbreaks of soil-borne stem canker caused by R. solani . Grading of stem canker and soil collections for nematode extraction were performed along transects starting from the centre of field patches with observed stem canker. There was no difference in the number of nematodes within the patches for any of the investigated nematode taxa, but the severity of stem canker was higher on plants graded in the centre of the patches compared to those graded in the margins. In addition, there was a spatial correlation between R. solani and stubby-root nematodes as well as potato cyst nematodes, but not for root-lesion nematodes. These results show that there is an interaction between plant-parasitic nematodes and R. solani in the field and this knowledge is of importance for future decisions of appropriate management methods. [ABSTRACT FROM AUTHOR]

An experiment was conducted at Tuber Crops Research Centre, BARI, Bogra during 2008-2009 to evaluate the organic amendment for controlling the stem canker and black scurf of potato. The different kinds of organic amendments were: T1 =Poultry refuse (PR) at 4 t ha-1, T2 =PR at 5 t ha-1, T3 =PR at 6 t ha-1, T4 =Mustard oil cake (MOC) at 300kg ha-1, T5 =MOC at 500kg ha-1, T6 =Neem oil cake (NOC) at 300kg ha-1, T7 =NOC at 500kg ha-1, T8 =Sawdust burning and T9 = Control. The experiment was laid out in a randomized complete block design (RCBD) with four replications. The organic amendment significantly influenced the disease incidence, yield attributes and yield of potato. The lowest disease incidence (17.5%) and per cent disease index (9.99) were found in T3 (poultry waste at 6 t ha-1). The minimum russet, deformed and Sclerotia infected tubers were also recorded in poultry waste at 6 t ha-1. The highest healthy tubers and tuber yield were found in the same treatment. Therefore, poultry manure 6 t ha-1 along with recommended dose of chemical fertilizer can be recommended to produce healthy tubers and maximum tuber yield of potato.

Stem canker of brassicas, also known as blackleg is the most damaging disease of many Brassicaceae. The disease is caused by Leptosphaeria maculans (Desm.) Ces et de Not. and L. biglobosa sp. nov., Shoemaker & Brun, which coexist in plants and resulting in disease symptoms and decreased yield, quantity and quality of cultivated vegetables and oilseed rape. The paper presents taxonomic relationships between these coexisting pathogen species, describes particular stages of their life cycles, summarizes the differences between the species, and reviews methods for their identification.

Stem canker of brassicas is a severe disease of oilseed rape in Australia, Canada and Europe, including Poland. The disease is caused by Leptosphaeria maculans and L. biglobosa - two pathogens belonging to the class Dothideomycetes. The species differ in pathogenicity, but they have identical shape and size of fruiting bodies and spores of the generative and vegetative stages. Both pathogens are often found together in infected tissues of oilseed rape plants. The main goal of the experiments was to measure the rate of pseudothecial maturation and to monitor ascospore concentration of L. maculans and L. biglobosa in air samples. The paper is the first investigation on the generative stage development of these two species in south-east Poland. The studies were done for three consecutive years (2005-2007), for six most important months in pathogen development and plant infection, including 3 months in the spring (March - May) and 3 months in the autumn (September - November). The stage of pseudothecial maturation was assessed visually, based on the development of asci and ascospores. Monitoring of spore concentration in the air was performed using a Hirst-type 7-day volumetric trap. It was proved that differences in pseudothecial maturation rate in south-east Poland, encompassing the climatic regions of the Carpathian Foothills and Cracow, do not exceed two weeks within one season. The first and the highest ascospore concentration dates depended on weather conditions in a particular season. The total number of spores during the studied seasons varied from 9 to 12 spores/m3, which was from 70 to 90 times lower than the average from five other monitoring sites around Poland. The short exposition to spore showers and very small concentrations of L. maculans and L. biglobosa ascospores in air samples were the most probable reasons for relatively small damage of oilseed rape crops by stem canker in the south-east part of Poland.

A complex of soybean diseases is caused by species from the genus Diaporthe /Phomopsis.Diaporthe phaseolorum (anamorph Phomopsis phaseoli) and Phomopsis longicolla(teleomorph unknown) are described as soybean pathogens. The first species includesthree varieties: D. phaseolorum var. sojae, anamorph Phomopsis sojae, the causal agent ofpod and stem blight, and D. phaseolorum var. caulivora and D. phaseolorum var. meridionalis,agents of northern and southern stem canker. The species P. longicolla is the most commonand most damaging agent of soybean seed decay.The diseases caused by parasites from this genus were first observed and described onsoybean in the USA. Presently they are widespread in most soybean-growing regions aroundthe world. Soybean in Serbia is attacked by all pathogens mentioned above, except forD. phaseolorum var. meridionalis, the causal agent of the southern stem canker. D. phaseolorumvar. caulivora (northern stem canker) has the greatest economic importance becauseit causes wilt and drying of plants during pod development and grain filling. Most intensiveoutbreaks of the disease occurred in the 1980s in southern and southeastern Banat, southernBačka and Srem. Prematurely wilted plants yielded 50% to 62% (depending on variety)less than healthy plants. Such heavy losses raised the question of the profitability ofsoybean growing. P. sojae and P. longicolla are less important in Serbia at the moment. Intensiveinfections of soybean seed break out occasionally. It was found that P. longicolla isthe primary agent of seed decay and latent infections of seed in our country, although theother members of this genus may cause identical symptoms.Sexual cycle of development (teleomorph stage) of the fungi of the genus Diaporthe/Phomopsis form perithecia with asci and ascospores, while in the asexual cycle (anamorphstage) various types of conidia (α and β) are formed in pycnidia. The species P. longicollahas no teleomorph stage.Infected harvest residues and soybean seeds are main sources of the inoculum. D. phaseolorumvar. caulivora forms perithecia with ascospores on overwintered harvest residues.During growing season, ascospores infect leaf laminas, petioles, or injured plant parts. P.sojae and P. longicolla form pycnidia (P. sojae sometimes forms perithecia), and they infectplants by means of conidia. Seed infection by conidia or ascospores unfolds via pods. Infectedcrop residues are the main source of the inoculum, while infected seeds help the parasitesspread over large distances. Humidity and temperature (soil and air) are the mainsfactors that affect the dynamics of fruiting body formation, spore release, establishment ofinfection and the development of disease symptoms on soybean plants.Considerable attention is devoted to finding effective sources of resistance to the diseasecomplex caused by species from the genus Diaporthe/Phomopsis. Resistance to the agents ofseed decay was found in several introduced (PI) genotypes. This resistance is controlled by oneor two pairs of dominant genes. Some cultivars are resistant to D. phaseolorum var. meridionalis(southern stem canker). Their resistance is controlled by two or four pairs of genes (Rdc). Thereis no physiological resistance to D. phaseolorum var. caulivora, the agent of northern stem canker,but significant differences in susceptibility level exist among soybean genotypes.Molecular techniques (RAPD, PCR-RFLP) showed that significant variability was presentwithin the population of D. phaseolorum var. sojae. Other species of fungi were suspectedto exist within that population, which could not be distinguished on the basis of their morphologicalcharacteristics. This was subsequently confirmed by the sequencing of differentregions of ribosomal DNA.

Cultivars within a species are traditionally distinguished by morphological traits. In some species such assoybean however, varieties are generally obtained from very similar elite parent groups, which makes the morphologicaldifferentiation rather difficult. The aim of this study was to differentiate two soybean varieties by means of microsatellitemarkers. One variety was susceptible and the other resistant to soybean stem canker, the latter essentially derived from theformer, in five backcross generations. The DNA used in the analysis was obtained from morphologically indistinguishableseed of the two varieties studied. Forty-two microsatellite loci distributed across the integrated genetic map of soybean wereanalyzed, of which one locus, Satt115, differentiated the two varieties, indicating that even essentially derived varieties can bediscriminated by molecular markers.

Blueberry (Vaccinium corymbosum) plants are popular all over the world due to their high nutritional value and health benefits. In October 2020, blueberry stems (cv. O'Neal) displaying reddish brown necrotic lesions were observed from a blueberry field in Anqing (Anhui, China), with the incidence of approximately 90%. The affected plants were somewhat stunted that had smaller fruit, and in severe cases, partial or whole plant died. We randomly selected three sampling sites to collect stems with the symptoms. Samples at the margin between diseased and healthy tissues were taken out, cut into 5 mm pieces in length，and then mixed them together. Twenty small samples were surface-sterilized, and plated onto potato dextrose agar (PDA). The plates were incubated at 25°C in the dark until fungal colonies were observed. After subculturing single hyphal tips, 9 out of 12 fungal isolates with similar morphologies were obtained. The representative isolate, LMKY12 was selected for further identification. The colonies on PDA showed white, fluffy aerial mycelia with 7.9  0.2 mm (n=5) diameter after inoculation in darkness at 25°C for one week. The colony darkens in color with age, yellowish pigmentation in reverse were observed. After 15 days of incubation, dark brown, irregular hard particles (fruiting bodies in sexual stage) accumulated on the surface of the colonies. Asci were 8-spored, sessile, club-like, hyaline, and 35-46 x 6-9 μm (n=30) in size. The ascospores were oval or spindle shaped, two-celled, constricted at division, and containing four guttulates with larger guttules at centre and smaller one at ends, measured 9-11 x 2-4 um (n=50). No sporulation observed on blueberry stems after inoculated 30 days. In order to induce the production of conidiophores, mycelial plugs were placed on blueberry leaves and cultured in darkness at 25°C. There are two types of conidia observed after 20 days of inoculation. Alpha conidia were aseptate, hyaline, smooth, ovate to ellipsoidal, often biguttulate, measured 5.33-7.26 x 1.65-2.53 μm (n=50). Beta conidia were hyaline, linear, measured 12.60-17.91 x 0.81-1.38 μm (n=30). The morphological characteristics matched the previous description of D. sojae (Udayanga et al. 2015; Guo et al. 2020). To confirm the identification, the mycelial genomic DNA of LMKY12 was extracted as a template. The rDNA internal transcribed spacer (ITS), translation elongation factor 1-α gene (TEF1-α), and calmodulin (CAL) were amplified and sequenced using primers ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R, and CAL-228F/CAL-737R (Carbone and Kohn 1999), respectively. BLAST analysis revealed that the ITS (ON545758), CAL (OP886852), and TEF1-α (OP886853) sequences were 100% (527/527 base pairs), 99.21% (504/508 base pairs), and 99.41% (336/338 base pairs) similar to the strain FAU636 of D. sojae (KJ590718, KJ612115, KJ590761), respectively. Phylogenetic analysis based on concatenated sequences of ITS, TEF1-α, and CAL using MEGA 7.0 by maximum likelihood attributed the isolate LMKY12 to the D. sojae clade. Pathogenicity tests were performed on blueberry cv. O'Neal using detached stems (n=8) in laboratory, one-year-old potted plants (n=4) in greenhouse. Inoculations were done by placing mycelial plugs (7 mm in diameter) taken from a 7-day-old PDA culture on wounded stems. Inoculations with uncolonized agar plugs served as negative controls. Reddish dark brown lesions similar to the symptoms were observed on all inoculated stems 7 days after inoculation. No symptoms developed on control stems. Reisolations were successfully made from all the inoculated stems, and the pathogen was confirmed by the presence of pycnidia, alpha conidia and beta conidia. To our knowledge, this is the first report of D. sojae causing blueberry stem canker in China.

Map-based cloning of avirulence genes of the AvrLm1-2-6 cluster was recently undertaken in Leptosphaeria maculans and led to the identification of AvrLm1. The ensuing chromosome walk toward AvrLm6 resulted in the delineation of a 562-kb bacterial artificial chromosome (BAC) clone contig in an avirulent isolate. Following sequencing of the contig and sequence comparison with a virulent isolate, four AvrLm6 candidate genes were identified. Complementation of the virulent isolate with the four candidates was performed and one gene was found to fully restore the avirulent phenotype on Rlm6 oilseed rape genotypes. AvrLm6 was found to be located in the same genome context as AvrLm1, because it is a solo gene surrounded by 85 and 48 kb of degenerated repeats on its 5′ and 3′ sides, respectively. AvrLm6 is an orphan gene encoding a small, potentially secreted, cysteine-rich protein. Comparison of AvrLm1 and AvrLm6 expressions by quantitative reverse-transcription polymerase chain reaction revealed that both genes are highly overexpressed during primary leaf infection. Using RNA interference, decreasing expression of AvrLm6 was shown to result in virulence toward Rlm6 genotypes whenever the expression was reduced by more than 60% compared with the wild-type isolate.

The new species Phomopsis pisi Ondřej sp. n. (Anamorphic Fungi - Coelomycetes) occurred on stems of pea (Pisum sativum L.) cv. Adept at Šumperk-Temenice (Czech Republic). The fungus caused plants to die at the green maturity stage. The new species differs from Phomopsis pisicola. It differs in the length and width of conidiophores and conidia.

Macrophomina phaseolina was isolated from the crown region and roots of mature flowering dogwood (Cornus florida L.) trees in the landscape and nursery plantings. Although this pathogen has been reported in Cornus species, its occurrence and impact on C. florida has not been reported. Pathogenicity tests were conducted on dogwood seedlings, and all inoculated seedlings developed root necrotic lesions and no small lateral roots, whereas the non-inoculated control seedlings remained disease-free and developed numerous small roots. Seedlings inoculated with M. phaseolina exhibited numerous microsclerotia, but non-inoculated seedlings did not. In greenhouse experiments, plants inoculated on the stems near the soil line developed brown canker-like lesions and swellings around the inoculated area. These were not observed on noninoculated plants. [ABSTRACT FROM AUTHOR]

Using a polymerase chain reaction-based strategy, we have isolated a cDNA sequence from Brassica nigra, denoted Lm1, which significantly improves blackleg resistance when expressed in transgenic oilseed rape, B. napus. Lm1 was shown to map to locations on linkage groups 3 and 8 in the Brassica B-genome previously linked to both cotyledon, adult leaf, and stem resistance. B. napus plants transformed with Lm1 under the control of a constitutive promoter exhibited broad spectrum resistance to all L. maculans isolates tested, but enhanced resistance to Alternaria brassicae and Verticillium longisporum was not observed. A transcript corresponding to the cDNA size was induced in B. nigra 12 h after fungal challenge from a level of weak constitutive expression previous to inoculation. The Lm1 sequence bears no resemblance to previously characterized plant resistance genes but has two predicted transmembrane motifs. Several sequences with high homology to Lm1 were found in the databases. Lm1 appears to be a member of a larger group of related genes present in a variety of plant species. Most of them have unknown functions, but homology between Lm1 and the nodule inception gene of Lotus japonicus suggests an intriguing link between defense-related and symbiotic pathways.

The sphinganine-analog mycotoxins (SAMs) fumonisin B1 and AAL toxins are inhibitors of eukaryotic sphinganine N-acyltransferase in vitro. Treatment of eukaryotes with SAMs generally results in an accumulation of sphingoid base precursors and a depletion of complex sphingolipids. The asc,asc genotypes of tomato (Lycopersicon esculentum) and Nicotiana umbratica are sensitive to SAMs and host of the AAL toxin-producing fungus Alternaria alternata f. sp. lycopersici. Codominant insensitivity to SAMs in tomato is mediated by the Asc-1 gene, and sensitivity is associated with a frame-shift mutation present in asc-1. We investigated the function of Asc-1 in mediating insensitivity to SAMs and resistance to the fungus by overexpression of asc-1 and Asc-1. In this study, it is shown that overexpression of these genes did not lead to visual symptoms in tomato hairy roots and N. umbratica plants. Overexpression of asc-1 did not influence the (in)sensitivity to SAMs. Overexpression of Asc-1 in SAM-sensitive hairy roots and N. umbratica plants, however, mediated a high insensitivity to SAMs and resistance to plant infection by Alternaria alternata f. sp. lycopersici.

Black scurf and stem canker disease cause by the fungal pathogen of Rhizoctonia solani and it is an economical important disease of potatoes in Bangladesh and throughout the world. This study evaluated the black scurf and stem canker disease development in potato and antagonistic activity of Trichoderma spp. against R. solani. The artificial infections were carried out using the inoculums of R. solani. The treatments (%inoculum) were: T1 (0% inoculum), T2 (5% inoculum), T3 (10% inoculum), T4 (20% inoculum), T5 (50% inoculum), and T6 (100% inoculum). The infection of stem canker and black scurf on progeny tubers increased with increase in inoculum levels. The highest disease incidence and severity was found in T6 (100% inocula). T6 showed the maximum black scurf infected tubers (russet, deformed and sclerotia). The lowest germination percentage, plant height and tuber yield were also obtained in the same treatment (100% inocula). Trichoderma spp reduced the growth of R. solani and the highest growth suppression was noted in isolate TM12. According to antagonistic activity, Trichoderma spp. reduced the growth of R. solani but was not able to stop the pathogen development. This finding showed management of this disease or R. solani invasion requires an integrated approach compared to Trichoderma single approach.

Background: Pseudomonas syringae can cause stem necrosis and canker in a wide range of woody species including cherry, plum, peach, horse chestnut and ash. The detection and quantification of lesion progression over time in woody tissues is a key trait for breeders to select upon for resistance. Results: In this study a general, rapid and reliable approach to lesion quantification using image recognition and an artificial neural network model was developed. This was applied to screen both the virulence of a range of P. syringae pathovars and the resistance of a set of cherry and plum accessions to bacterial canker. The method developed was more objective than scoring by eye and allowed the detection of putatively resistant plant material for further study. Conclusions: Automated image analysis will facilitate rapid screening of material for resistance to bacterial and other phytopathogens, allowing more efficient selection and quantification of resistance responses. [ABSTRACT FROM AUTHOR]

LAMP is an innovative, simple, rapid, specific and cost-effective nucleic acid amplification method. Due to the use of a special enzyme – GspSSD polymerase, the reaction takes a short time and can be performed at isothermal conditions. The sensitivity and specificity of LAMP technique is significantly higher, than standard PCR techniques, as two or three specific primer pairs are used. The technique is regarded as a useful tool for the detection and identification of plant pathogens. In this work, LAMP was used to study the composition of the population of fungi of the genus Leptosphaeria, causing a damaging disease of oilseed rape, called blackleg or stem canker. The detection concerned DNA present in fungal spores contained in air samples obtained using Hirst-type volumetric trap, in Pomerania (north Poland) in 2010. The results achieved using the LAMP technique were similar to these obtained with previously used, highly specific method of Real-time PCR. Conducting LAMP reaction was much easier and less time-and cost-consuming, due to a simplified method of DNA isolation of pathogens from plant tissues. Then, the LAMP technique was used to assess the composition of the population of Leptosphaeria spp. in plants of oil- seed rape collected from the field in the Opole region (south-we- stern part of Poland) in 2013. In contrast to studies conducted in 2002–2003, the analysis of leaf symptoms showed a higher pro- portion of L. maculans compared to L. biglobosa, what reflects changes in the composition of pathogen population of fungi causing blackleg on oilseed rape in this part of Poland.

Blueberry leaf spots and stem cankers caused by Pestalotiopsis spp. have become a serious threat for the production of blueberry in Sichuan Province. To characterize the etiology of the diseases connected with these fungi, samples showing leaf spot and stem canker symptoms were collected from the 12 main blueberry-growing areas of Sichuan Province from 2015 to 2020 and used for pathogen isolation. In total, 91 fungal isolates were obtained with preliminary morphological identification and 48 representative strains were selected for further pathogenicity test and molecular identification. Four species, including Pestalotiopsis clavispora ( Neopestalotiopsis clavispora ) (57.14%), P. trachicarpicola (28.57%), P. chamaeropis (13.19%), and P. adusta (1.10%), were identified based on conidial morphology, cultural characteristics, and phylogenetic analysis of the internal transcribed spacer region, partial sequence of the β- tubulin gene, and the translation elongation factor 1-α. Pathogenicity tests showed that four species were pathogenic to leaves and stems of blueberry. Among them, P. clavispora ( N. clavispora ) was the most aggressive as the predominant species to cause both leaf spot and stem canker. P. trachicarpicola and P. chamaeropis were mainly isolated from leaves but also pathogenic to stems. P. adusta was only isolated from stems but also pathogenic to leaves. To the best of our knowledge, this is the first report of P. chamaeropis and P. adusta as pathogens causing leaf spots and stem canker on blueberry. The results provide helpful information in disease diagnosis and management of blueberry.

A survey of the relative incidence of anastomosis groups (AGs) of Rhizoctonia spp. associated with potato disease was conducted in Idaho, the leading potato producing state in the U.S.A. In total, 169 isolates of Rhizoctonia solani and seven binucleate Rhizoctonia (BNR) isolates were recovered from diseased potato plants. The AG of each isolate was determined through real-time PCR assays for AG 3-PT and phylogenetic analysis of the internal transcribed spacer region of ribosomal DNA. AG 3-PT was the predominant AG, accounting for 85% of isolates recovered, followed by AG 2-1 (5.7%) and AG 4 HG-II (4.5%). Two different subsets of AG 2-1 isolates were recovered (subset 2 and 3). Three isolates each of AG A and AG K were recovered, as well as one isolate each of AG 5 and AG W. An experiment carried out under greenhouse conditions with representative isolates of the different AGs recovered from Idaho potatoes showed differences in aggressiveness between AGs to potato stems, with AG 3-PT being the most aggressive followed by an isolate of AG 2-1 (subset 3). The three BNR isolates representative of AG A, AG K, and AG W appeared to be less aggressive to potato stems than the R. solani isolates except for the AG 2-1 (subset 2) isolate. This is the first comprehensive study of the relative incidences of Rhizoctonia species associated with Idaho potatoes and the first study to report the presence of BNR AG W outside of China.

During the last years, the Bavarian State Institute of Forestry received increasing numbers of announcements that dealt with necrosis on stems of maple trees caused by the soilborne fungus Verticillium dahliae Kleb. In this study, five forest areas were investigated along transects up to 100 m by soil sampling and mapping of diseased trees to find out if the pathogen had been introduced by infested maple seedlings. Our results yielded no evidence for this assumption. The spatial distribution of microsclerotia concentrations in the soil did not correlate with spatial patterns of diseased trees. This indicates that Verticillium was established on the sample plots independently from healthy or infested maple trees. Counting of year rings of infested maple trees revealed that the trees had developed their necrosis immediately after the drought in the year 2003. Hence, a connection between these extreme climate conditions and disease incidence cannot be excluded.