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Low temperatures are a key condition for various phytopathogenic bacteria, by favouring their pathogenic potential and the development of plant diseases. So far, the signal transduction pathways related to low temperatures in phytopathogenic bacteria are little understood. The occurrence of intracellular oxidative stress under this condition has been suggested as a molecular event belonging to this signalling pathway. In this study, using the Pseudomonas savastanoi pv. phaseolicola model bacteria, we evaluated intracellular redox state under low‐temperature (18°C) conditions. Generation of an oxidative‐stress biosensor (pKL1) and fluorometry analyses with the P. savastanoi pv. phaseolicola‐roGFP2 bioreporter strain were performed. At low temperatures (18°C) the response capacity or roGFP2 oxidation diminished in relation to 28°C. Likewise, changes in the intracellular redox potential of P. savastanoi pv. phaseolicola during its growth at 28°C and 18°C were observed, with greater oxidation degree in cells grown at 18°C. These results demonstrated that low temperatures induce intracellular oxidative stress in P. savastanoi pv. phaseolicola. From this study, the oxidative stress is established as part of the cellular response to low‐temperature conditions in this bacteria. This is the first report of the relation of oxidative stress with low‐temperature conditions in phytopathogens bacteria. [ABSTRACT FROM AUTHOR]

Anthracnose, caused by species in the Colletotrichum orbiculare complex, is a major foliar disease in open‐field cucumber farming worldwide. This study aimed to develop and validate a standard area diagram (SAD) set to estimate the severity of anthracnose on cucumber leaves. For this purpose, a SAD set with nine levels of severity (1; 3; 5; 10; 20; 30; 40; 50 and 60%) is proposed. The SAD set was validated by 16 raters with no experience in evaluating plant diseases. Both accuracy and precision improved when the proposed SAD set was employed. The statistical parameters were bias coefficient factor‐Cb (no SAD set = 0.891, with SAD set = 0.982); correlation coefficient‐r (no SAD set = 0.851, with SAD set = 0.941); and Lin's concordance correlation coefficient‐ρc (no SAD set = 0.755, with SAD set = 0.924). In addition, estimates were more reliable: intra‐class correlation coefficient‐ρ (no SAD set = 0.646, with SAD set = 0.887). The SAD set proposed here is a useful tool for improving visual assessments of anthracnose severity on cucumber leaves. [ABSTRACT FROM AUTHOR]

Plant diseases pose a significant threat to global agricultural productivity and food safety. Early detection and accurate identification of these diseases are essential for effective disease management strategies. Traditional plant disease identification mainly relies on manual observation and experienced expert judgement, which has the disadvantages of being time‐consuming, labour‐intensive and low efficiency. Given the above problems, this study proposes a method for identifying apple leaf diseases based on a convolutional neural network combining hybrid attention and bidirectional long short‐term memory (BiLSTM). Appropriate apple leaf disease samples were selected from multiple public data sets to form an experimental data set. Then, the data set is imported into the improved convolutional neural network for training. Based on the original ResNet18 model, a new convolutional neural network, AppleNet, is constructed by adding a hybrid attention module and modifying the classifier structure. The experimental results show that the average recognition accuracy of AppleNet is 94.66%, which is 2.47% higher than that of the ResNet18 network. In addition, the training time of the model is only slightly increased. The ablation experiment further verified the effectiveness of the model modification. Compared with other advanced models in recognition accuracy and model training time, the superiority of AppleNet is confirmed. This study verifies that deep learning has great potential and application prospects in plant disease identification and provides a new technical solution for intelligent and convenient plant disease identification. [ABSTRACT FROM AUTHOR]

Plant diseases have become a problem, as both the quality and quantity of agricultural products can be significantly reduced. The goal of the research is to detect the infection in the plant leaf so that it can be cured before spreading of disease to other plants. The aim of the research is to find out the severity of the leaf disease so that it can be cured based on the level of severity. Also, crop loss can be predicted by using the severity loss. For object localization, we utilize 10,640 tomato leaf images of various classes from the PlantVillage standard repository. As a baseline for future work, we propose a model based on the Mask R‐CNN architecture with ResNet‐50 as the backbone that effectively performs instance segmentation for these six diseases. The dataset is annotated by using the VGG annotator tool and this annotated dataset would have been used to train the 'Mask R‐CNN model' and the ResNet50 backbone, fine‐tuning the network's weights to accurately detect and segment diseased regions on leaves. The outcomes of the suggested model achieved an average accuracy of 91.3% by using multiple performance indicators like accuracy, precision and F1 score and Recall. Based on the outcome, the severity of the disease is being identified on a scale of 0, 1, 2 and 3. [ABSTRACT FROM AUTHOR]

A novel Modified Deep Fuzzy Clustering (MDFC) based classification model involves four major phases. They are preprocessing, segmentation, feature extraction and finally, detection and classification phase. To reduce noise and smooth the edges of the input image of the cotton crop, bilateral filtering is first used as a preprocessing approach. Next, a modified deep fuzzy clustering is suggested for the segmentation procedure that creates a collection of segments from the preprocessed image. The segmented image is then processed to extract relevant characteristics by using an enhanced Pyramid of Histogram Orientation Gradient (PHOG), Local Directional Ternary Pattern (LDTP), and statistical‐based features. In order to detect and classify cotton crop diseases more effectively, this paper proposes a hybrid system. Here, the features are put through a detection phase, after which the extracted features are trained in the Bidirectional Gated Recurrent Unit (Bi‐GRU) model to determine whether or not the cotton crop is infected. Once it is detected to be diseased, the type of disease is classified via an improved Recurrent Neural Network (RNN). In terms of several performance metrics, the proposed model is validated in comparison with the traditional approaches. The MDFC‐based classification model outperforms existing models with a specificity of 0.9687 at a learning rate of 90. In contrast, other models achieve lower specificities: Bi‐GRU (0.8436), RNN (0.8359), CNN (0.8654), LSTM (0.8769), SVM (0.7983), VGG16 (0.8619), DCNN (0.8725), BI‐RNN + BI‐LSTM (0.7869), and NN + CNN (0.85478). [ABSTRACT FROM AUTHOR]

Bacterial diseases cause colossal losses in vegetable crops and are considered major limiting factors for the commercial production of vegetables around the globe. Among bacterial diseases, angular leaf spot of cucumber caused by Pseudomonas syringae is one of the most economically important diseases that cause substantial economic loss to the cucumber crop. In this study, the in‐vitro and in‐vivo effects of different strains (X1–X15) of the nematode symbiotic bacterium Xenorhabdus nematophila was determined on the growth of P. syringae in different selected media (TB, SB, SOB, SOC, YT and LB) and at different pH levels (6.5, 7.5 and 8.5) and on the incidence of angular leaf spot disease on potted cucumber plants. According to the results, maximum growth inhibition of P. syringe (25 mm) was observed in the case of strain X12, followed by strains X10 (23 mm), X8 (21 mm) and X6 (20 mm), while maximum colony growth was observed in the control. Moreover, this P. syringae growth inhibition by the X12 strain of X. nematophila was significantly maximum in SB medium and at pH 7.5. Results of the in‐vivo experiment with potted plants showed a maximum incidence (90%) of angular leaf spot disease in control plants, while a minimum disease incidence (15%) was observed for the plants treated with two times dilution of X. nematophila culture, followed by ten times (23%) and fifty times (35%). The overall results of this study demonstrate the inhibitory effect of X. nematophila on the growth and incidence of P. syringae and underscore its putative role in the biological management of plant pathogenic bacteria. [ABSTRACT FROM AUTHOR]

Two members of the Araceae broadly cultivated as ornamentals, namely Epipremnum aureum (common name golden pothos or, in Brazil, jiboia) and Zantedeschia aethiopica (common name arum lily or, in Brazil, copo‐de‐leite), were observed bearing Cercospora leaf spots. The former is a very common garden plant, whereas the latter is an important crop for the flower industry. An examination of the fungus associated with the disease on each plant revealed a very similar morphology which suggested that those might be conspecific. A polyphasic taxonomic study, including phylogenetic analyses based on act, cal and his3 sequences, was conducted. Both isolates from the two aroids were found to belong to the Cercospora apii complex, but were genetically distinct. Cercospora sp. Q was identified as the etiological agent of the leaf spots on E. aureum, whereas the fungus on Z. aethiopica was found to belong to Cercospora sp. G. Inoculations confirmed the pathogenicity of both isolates to their original hosts, and cross‐pathogenicity assessments revealed that both isolates were capable of infecting both E. aureum and Z. aethiopica. The limited morphological and pathological distinction between the fungi on these two hosts reflects the continued difficulty in the taxonomic treatment and species delimitation for Cercospora sp. G, Cercospora sp. Q, as well as other provisional code‐based Cercospora spp., and other components of the broad C. apii s. lat. complex. The name Cercospora richardiicola (as C. richardiaecola) was mistakenly used for the fungus on Z. aethiopica in earlier publications and this has been corrected herein. [ABSTRACT FROM AUTHOR]

Yellow mosaic and leaf curl diseases caused by whitefly‐transmitted begomo virus genera are important problems in tomato (Solanum lycopersicon L.) production in Indonesia, particularly on Java Island. The aims of this survey are to assess the percentages of disease incidence (DI) and disease severity index (DSI), evaluate the spread and complexity of begomovirus and crinivirus infections responsible for yellow mosaic and leaf curl diseases in tomato plants, and identify the species of whitefly insect vectors and their cryptic biotypes in tomato production centers located on Java Island, Indonesia. A total of 43 locations in East, Central, and West Java were surveyed during the dry season from July 2022 to September 2022. Disease incidence and severity were determined by observing 200 samples of tomato plants from five points at each location, with 40 plants per point of land. A total of 116 whitefly samples in microtubes and 215 symptomatic leaf samples were collected. The genus begomovirus and crinivirus infecting tomato were identified by PCR and RT‐PCR using genus‐specific primers. Similarly, whitefly species and their cryptic biotypes were identified by PCR using MCoI gene‐specific primers. Results showed that DI and DSI remarkably differed between the lowlands (66%–89%) and highlands (33%–62%) in the provinces of Central Java and West Java. Furthermore, PCR analysis of 215 infected tomato showing the symptoms of yellow mosaic and curly leaf revealed that three begomoviruses, one crinivirus and their mixed combination both begomoviruses, one crinivirus has been detected in all the samples. Similarly, the whitefly insect vector Bemisia tabaci biotype Q was identified in all areas, whereas Trialeurodes vaporariorum was found only in the East Java and Java highlands, respectively. [ABSTRACT FROM AUTHOR]

Productivity in agriculture plays a major role in economic expansion. Because plant disease is a widespread occurrence, plant disease detection is an important problem in the world of agriculture. Plants do suffer a significant consequence if the required care is not taken at the beginning, which affects the amount, quality or productivity of the relevant products. Because it can detect disease symptoms at the earliest stage and reduces the labour required for large crop farm tracking, the automated plant disease detection system is more advantageous. In order to detect plant diseases, this paper proposes a novel, four‐step methodology that consists of improved deep joint image segmentation, feature extraction (which includes LGXP, MBP, colour feature and hierarchy of skeleton feature extraction) and detection via hybrid DL classifier, specifically improved RNN with the transfer learning process and GoogleNet. By averaging the classifiers' results scores, the final detection result is calculated. In terms of several performance metrics, the suggested work's effectiveness is verified in comparison to the traditional models. In contrast to the SVM (79.5597), KNN (59.2767), LSTM (78.1446), GoogleNet (79.4025), CNN (77.6729), and CAE + CNN (80.1886), the F‐measure of the IRNN‐TL is 91.1949. [ABSTRACT FROM AUTHOR]

The threat of emerging plant diseases has become more frequent as global warming and international trade are increasing. Blackleg and soft rot of potatoes caused by the group of bacteria in the family Pectobacteriaceae and the genera Dickeya and Pectobacterium are important diseases causing economic losses globally. In the European Union, they are regulated non‐quarantine pests. Five species are commonly known to cause blackleg symptoms on potatoes indistinguishable from each other. For decades, P. atrosepticum has been the classic seed potato bacterial pathogen in cool temperate climates of Europe and North America, causing blackleg disease. However, recently several new species, unknown in Northern Europe, have emerged as virulent pathogens. One of these species is D. solani. In Finland, D. solani was first found in 2004 and has been the cause of major outbreaks of blackleg in Finland for more than a decade. Currently, its incidence has declined significantly because of a stringent, concerted engagement strategy adopted to combat the pathogen that is described in detail in this article. This strategy implemented in Finland could serve as a model system to combat other emerging and re‐emerging species of Dickeya and Pectobacterium and serve as useful support information for the formulation of a policy framework for the management of emerging plant health risks. [ABSTRACT FROM AUTHOR]

Fungal stem cankers are common and destructive diseases in apple orchards. Cytospora cincta and Neoscytalidium dimidiatum are the apple canker causal agents in Iran. Formulated biocontrol agents of plant diseases are considered alternatives to synthetic pesticides in sustainable agriculture. The results showed that Trichoderma zelobreve T20 strongly inhibited the in vitro growth of C. cincta and N. dimidiatum. Wettable powder formulation (WPF) based on T. zelobreve T20 was developed to control apple canker caused by C. cincta and N. dimidiatum. The dual culture test showed that T20 inhibited C. cincta and N. dimidiatum growth by 55.19% and 44.07% respectively. T20 culture filtrate reduced the mycelial growth of C. cincta (72.22%) but showed no activity against N. dimidiatum. T20‐based WPF inhibited C. cincta (94.62%) and N. dimidiatum (14.71%) growth on detached branches of 2‐year‐old apple trees (golden delicious cultivar). Also, T20‐based WPF inhibited apple tree canker caused by C. cincta and N. dimidiatum by 82.8% and 60% respectively. The performance of T20‐based WPF on apple trees was significantly better than detached branches. The spore count of T20‐based WPF was about 71.54% of the original count after 4 months, marking its suitable shelf life. T20‐based WPF could be considered a promising control measure against apple canker pathogens. [ABSTRACT FROM AUTHOR]

During May and June 2021, the commercially grown coffee, variety SL34, grown commercially, developed necrotic, irregularly shaped spots on 1–5% of leaves. These plants were under greenhouse culture in the area of Goheung in South Korea (34°47′N, 127°46′E). The leaf spots, often observed at leaf margins, changed with time from reddish‐brown coloration to dark brown lesions with yellow halos. Morphological and molecular analysis confirmed the fungus from the lesions as Curvularia geniculata. The pathogenicity of the fungal isolate was verified by Koch's postulates on coffee plants grown under greenhouse conditions. These findings support that C. geniculata causes leaf spot disease in coffee plants and, to our knowledge, is the first time this disease has been reported in the world. [ABSTRACT FROM AUTHOR]

Ascochyta blight caused by Ascochyta rabiei is a globally important chickpea disease. Host resistance to Ascochyta blight is considered the most practical and effective means of control, but breeding has been hindered by a lack of effective resistance sources, and time‐consuming, labour‐intensive traditional methods to screen the resistance level of chickpea genotypes. This paper evaluated the progression of pathogen infection and the disease reaction of chickpea genotypes to Ascochyta blight by traditional and molecular methods. The resistance level of 84 chickpea genotypes was assessed by a quantitative polymerase chain reaction assay (qPCR) using a standard curve produced by various known amounts of pathogen DNA and compared with disease scores based on visual assessments 8 days after inoculation. Disease assessments revealed statistically significant differences between the resistance levels of chickpea genotypes, while the quantity of target DNA in the samples inoculated with the pathogen ranged from 0.004 to 83.37 ng. Our results showed a close relationship between the visual assessment of disease severity and the quantification of the target DNA in chickpea genotypes. The genotypes Tüb‐35, Tüb‐47, Tüb‐26, Tüb‐82, Tüb‐65 and Tüb‐69 were classified as highly resistant to Ascochyta blight based on the results of both assays used for screening chickpea genotypes. This qPCR analysis could be used to quantify disease progression in plant tissues and screen chickpea genotypes as a potential alternative to visual assessment of resistance levels in breeding programmes. [ABSTRACT FROM AUTHOR]

Late blight, caused by Phytophthora infestans, is the most devastating disease of potato worldwide that can cause up to 100% crop loss under disease conducive conditions. The present study was carried out to evaluate and identify effective Trichoderma isolates against the disease. Thirty‐nine isolates of Trichoderma spp. isolated at Nepal Plant Disease and Agro Associates (NPDA), Kathmandu from Likhu areas of Nuwakot, Nepal were screened against P. infestans in detached leaf assay for their efficacy in reducing the lesion size of late blight. Fifteen isolates significantly reduced lesion size by 19%–46% compared with the control (water spray). Of them, top 10 isolates along with Sanjeevni (T. viride), a commercial product were tested in field experiments under natural epiphytotic conditions at Thansing and Dhikure of Likhu Rural Municipality in 2020–2021 and 2022–2023 crop years, respectively. The Trichoderma isolates significantly (p <.001) increased plant growth, tuber yield and reduced disease severity in both years. In 2020–2021, isolates, TL1‐2A, TL4‐81A and TL5‐21A reduced disease severity by 37.3%, 37.2% and 30.4%, respectively. The isolate TL1‐2A also significantly increased plant height, ground coverage and tuber yield by 41.2%, 30.3% and 72.3%, respectively compared with the control (water spray). In 2022–2023, TL1‐2A reduced disease severity by 40.2% and increased tuber yield by 46.4%. Other isolates, though significantly different from control, did not have satisfactory effect on disease control and tuber yield. In both years, the isolate TL1‐2A significantly reduced the disease, and increased plant growth and tuber yield. Thus, TL1‐2A isolate can be a potential candidate as a biocontrol agent for the integrated management of potato late blight in Nepal. [ABSTRACT FROM AUTHOR]

Fusarium rot is one of the main postharvest diseases of melons, directly interfering with the quality and commercial use of the fruit. The purpose of this study was to assess the effect of environmental factors (temperature, pH and salinity) and the pathogenicity of four Fusarium species (F. falciforme, F. kalimantanense, F. pernambucanum and F. sulawesiense) belonging to three different species complexes on disease development on melon, as well as the in vitro and in vivo sensitivity of these species to the fungicides azoxystrobin + fludioxonil, imazalil and thiabendazole. The results showed optimum fungal growth temperatures from 24.5 to 27.2°C, and optimum pH from 6.10 to 8.37 for all Fusarium species. NaCl concentrations (250–1000 mM) significantly reduced in vitro mycelial growth for all isolates. All species were pathogenic to melon plants and fruit, with an isolate of F. falciforme being the most aggressive, causing the highest disease severity in plants and fruit (43.3% and 62.5%, respectively). The isolate of F. sulawesiense tested showed high in vitro sensitivity to two fungicides (azoxystrobin + fludioxonil and imazalil), with EC50 values below 1 mg/L of a.i. Fruit inoculated with the selected isolates of F. falciforme and F. pernambucanum showed a reduction in the disease severity on the peduncle when treated with the fungicide thiabendazole (9.0% and 4.0%, respectively). Azoxystrobin + fludioxonil was responsible for the lowest disease severity in the epicarp caused by the same isolates (0.0% and 2.5%, respectively). These results are relevant to improve management strategies for diseases of melon caused by Fusarium spp. [ABSTRACT FROM AUTHOR]

Bacterial wilt caused by the Ralstonia solanacearum species complex (RSSC) is a disease that negatively affects the cultivation of Solanaceae crops in Burkina Faso. Knowledge of the pathogen diversity is essential to deploy locally adapted control methods. In this study, diseased plants showing typical bacterial wilt symptoms were collected in the three main agroclimatic zones of Burkina Faso for the detection of RSSC isolates. Strain characterization was achieved through a phylogenetic and pathogenicity diversity assessment. A total of 102 isolates were sampled, and Phylotype I (Ralstonia pseudosolanacearum) was predominant (n = 101; sequevars 14, 31, 34, and 46). The remaining isolate was characterized as Phylotype IIA‐35 (Ralstonia solanacearum). Phylotypes I‐31 and I‐46 were predominant and both characterized as the most the aggressive group of strains amongst a subset of 33 representative isolates. Our findings provide valuable information as regard RSSC diversity that breeders and resistance programme should target in order to fight this pathogen in Burkina Faso and around the world. [ABSTRACT FROM AUTHOR]

Alternaria leaf spot is a common disease on various plants worldwide. In this study, an Alternaria species, A. hydrangeae causing leaf spot on Cucumis sativus (cucumber) and Ipomoea purpurea in China was identified based on morphology and multi‐locus analysis of the partial ITS, GAPDH, Alt a 1, TEF1, and RPB2 gene regions. The pathogenicity of the present isolates and a representative isolate of A. hydrangeae were assessed on living leaves of C. sativus, I. purpurea and Hydrangea paniculata. Similar symptoms were observed on every plant inoculated with the isolates. The same fungus was re‐isolated from inoculated leaves fulfilling Koch's postulates. Morphology of the original and re‐isolated isolates showed characteristics similar to A. hydrangeae with some variations. Multi‐locus analysis indicated that the present isolate fell into A. hydrangeae clade. This study is the first report of A. hydrangeae as an agent of Alternaria leaf spot in C. sativus and I. purpurea in China, which extends the host range of the fungus. [ABSTRACT FROM AUTHOR]

Emerging fungal pathogens could bring irreversible damage to economically important plant species resulting in yield losses. One method of control of plant diseases is crop rotation, whereby the main cultivated crop is rotated with other crops. However, for crop rotation to be successful, the alternative crop must be a non‐susceptible or non‐host plant of the pathogen. In January 2021, for the first time, Corynespora cassiicola was reported to cause leaf spots and fruit rot in eggplant (Solanum melongena) in the Philippines. This study investigated the potential host range of newly reported C. cassiicola in controlled, repeated pathogenicity assays. Of the 36 plant species (19 plant families) assayed for leaf infection, 26 and 23 plant species were pathogenic to C. cassiicola in wounded and unwounded conditions, respectively. Of the 27 plant species (13 plant families) assayed for fruit/head/bulb/tuber infection, 16 and 6 were susceptible to C. cassiicola in wounded and unwounded conditions, respectively. Among all plant species assayed, mango, tomato, and beans were considered very susceptible as infection occurred in both leaves and fruits and wounded and unwounded treatments. The related species, tomato and pepper, were also susceptible to diseases caused by C. cassiicola. This is the first report of the pathogenicity of the C. cassiicola Philippine strain to various plant species assessed in controlled conditions. [ABSTRACT FROM AUTHOR]

The grey blight disease is a common disease of tea plants and camellias (Camellia spp.). It is caused by Pestalotiopsis‐like fungi, which were mostly identified as species of Pestalotiopsis and Pseudopestalotiopsis. In this study, four strains of Neopestalotiopsis were isolated from brown and grey‐white spots of leaves of Camellia oleifera and C. sasanqua in China. These strains belong to Neopestalotiopsis longiappendiculata and are characterized by morphology and multi‐loci phylogenetic analysis (ITS‐tef‐tub2). This is the first report of N. longiappendiculata as agent of grey blight disease on Camellia spp. Pathogenicity tests indicated that N. longiappendiculata infects not only Camellia oleifera and Camellia sasanqua but also Eucalyptus polyanthemos and Euonymus japonicas. Given the broad host range and pathogenic nature, it is time to focus on management aspect to control the disease. [ABSTRACT FROM AUTHOR]

False smut of rice is an emerging disease and a potential threat to hybrids and inbred rice cultivars grown in Asian countries. The aim of the study was to avoidance of false smut incidence by manipulating the planting date in rice. The genotypes including five rice hybrids, namely, KRH 2, US 312, DRRH 3, PHB 71, PA 6644 and three pure‐line cultivars, namely, BPT 5204, PR 116 and HKR 47 were evaluated in different planting dates (PD1: June 25, PD2: July 5, PD3: July 15). All the tested genotypes flowered during 100–110 days, except BPT 5204, which took 115 days to flower. False smut was quantified on rice genotypes using different disease variables such as infected panicle/plant, total false smut ball/plant and disease score. Disease variables were significantly and positively correlated to each other. The significant interaction between the genotype and planting date was observed. The early planting date (June 25) showed higher incidence than late planting (July 15). Overall mean of disease variables was higher in hybrids than pure‐line cultivars. Weather factors such as rainfall, rainy days and high relative humidity during the flowering period were favourable for disease development. The manipulation in the planting date can be utilized as a potential non‐monetary cultural approach for minimizing the incidence of false smut in rice. Cultivar HKR 47 with lower disease variables in different planting date can be used in diseases resistance breeding program. [ABSTRACT FROM AUTHOR]

Extracellular vesicles (EVs) are nanometric, lipid membrane‐bound vesicles released outside the cell. Plants have not been traditionally regarded to have EVs due to the presence of a cell wall. However, since the mid‐1960s, EVs have been reported in various plant species. They are often shown as vesicles in multivesicular bodies (MVBs) that later fuse with the plasma membrane (PM). Plant EVs have been commonly visualized using electron microscopy. Using membrane‐spanning domains, plant EVs can be fluorescence‐detected. They were observed near the infection sites in host tissues attacked by pathogens or at the interfaces with symbiotic fungi. Plant EVs could be taken up by bacteria and fungi. Proteins, lipids and nucleic acids, including small ribonucleic acids (RNAs), were found in plant EVs. Plant EVs have been isolated from the symplast and apoplast of various organs and purified after density gradient ultracentrifugation. Improved protocols and technologies for EV visualization provide a basis for the future applications of EVs in plant pathology. [ABSTRACT FROM AUTHOR]

Corynespora cassiicola is the causal agent of target spot of several cultivated species, among which cucumber is highlighted for frequent reports of yield losses under greenhouse conditions. Given the difficulties managing this disease due to the lack of information about the resistance of cucumber cultivars, the aim of the present study was to evaluate the response of ten cucumber cultivars to C. cassiicola based on epidemiological components of the disease in a greenhouse. Symptoms of target spot were apparent in all cucumber cultivars from the second day of inoculation of C. cassiicola, demonstrating the short incubation period of the disease and the susceptibility of the crop. The components latent period, number of lesions, lesion diameter, disease severity, number of sporulating lesions, number of spores per affected leaf area and number of spores per sporulating lesion varied according to the cucumber cultivar. The monomolecular model showed the best fit to the number of target spot lesions during the ten days of evaluation, showing differences between cultivars for initial inoculum and disease progression rate parameters. Multivariate analysis with the epidemiological components combined identified three groups of cultivars: one group that was less affected by the disease, represented by Safira and Diplomata cultivars; a second group showing intermediate behaviour, including Valent, Eureka, Taiko, Yamarashi and Darlington cvs., and a third group that was most susceptible to the pathogen and was represented by Soldier, Vulcano and Exocet cvs. Safira and Diplomata cultivars showed low level of susceptibility to target spot and can be recommended for areas with high disease intensity. [ABSTRACT FROM AUTHOR]

The high severity of plant diseases has hampered the implementation of straw incorporation technology in practice. To clarify the relationship between the nitrogen deficiency caused by wheat straw decomposition and Fusarium head blight (FHB) occurrence, five nitrogen levels as 0%, 25%, 50%, 75% and 100% were set to simulate the nitrogen changing after straw incorporated into soil and its effects on the pathogenicity of Fusarium graminearum. Nitrogen starvation degree was characterized by autophagy. Seedling infection and toxin production were used to test pathogenicity. The results showed that biomass of F. graminearum cultured in 25% nitrogen level medium for 72 hr and 120 hr were 0.39 g/ml and 0.29 g/ml, respectively, and were greater than those of other treatments at the same time (p <.05). The spore germination in 0%, 25%, 50% and 75% nitrogen level media were greater than those in 100% nitrogen level medium, in which the total nitrogen deficiency was the greatest (p <.05), reaching 64.5%. Total nitrogen deficiency would lead to F. graminearum autophagic death, while other treatments displayed different starvation responses in F. graminearum. F. graminearum cultured in 25% and 50% nitrogen levels media for 48 and 72 hr or in 75% nitrogen level medium for 168 hr produced more deoxynivalenol (DON). The lesion lengths caused by F. graminearum treated with 25%, 50% and 75% nitrogen levels for 72 hr were 18.33 mm, 15.78 mm and 14.96 mm, respectively, which were significantly longer than the lesions at the 0% (10.57 mm) and 100% (12.18 mm) nitrogen levels. The results indicated that the pathogenicity of F. graminearum was affected by nitrogen levels significantly and partial nitrogen deficiency could prompt the severity of FHB. [ABSTRACT FROM AUTHOR]

The natural bacterial communities of the soil–plant system are relevant in the process of suppressing diseases caused by soilborne plant pathogens. However, little is known regarding the structure of these communities in soils cultivated with brassica vegetables and their relationship with clubroot severity, a disease caused by Plasmodiophora brassicae. In the present study, the composition of bacterial communities in soils cultivated with cauliflower with distinct levels of disease severity was compared. The bacterial composition in soils with lower and higher clubroot severity differs in phylum and genera levels. Soils associated with plants with lower disease severity showed predominance of Kaistobacter, Flavisolibacter, Sphingobacterium, Koribacter, Nitrospira, Bradyrhizobium and Bacillus. Our study reinforces the importance of management strategies that promote improving the physical–chemical characteristics of soil, which are essential to modulate bacterial populations correlated with plant disease suppression. [ABSTRACT FROM AUTHOR]

Sterculia lanceolata, an important tropical woody plant, has high ornamental and medicinal value. To our knowledge, only brown root disease in this plant has been reported. In Nanning, Guangxi, China, an outbreak of leaf blight disease was observed on S. lanceolata in June 2019, with the leaf infection rate ranging from 80% to 100%. The disease seriously affected the leaves of trees and caused economic loss. Eight isolates were recovered from the infected leaves of different trees, and the pathogenicity was then determined by the methods of mycelial disc and conidial suspension, fulfilling Koch's postulates. According to the morphological and molecular biological characteristics of isolates, the pathogen causing leaf blight on S. lanceolata was identified as Colletotrichum siamense. Accurate identification of the pathogen provides a reliable basis for the control of the disease. [ABSTRACT FROM AUTHOR]

Recent reports of plant diseases that result in yield reduction and increasing demand for dragon fruits raise concerns of fruit supply shortage. Emerging plant diseases may play an important role in increasing yield losses and reducing the availability of stem cuttings (source of planting materials). Understanding the aetiology of current and new diseases of dragon fruit is important to address production issues and to formulate effective disease control measures. This study reports Epicoccum sorghinum as a potential emerging pathogen of dragon fruit. Epicoccum sorghinum MBDF0024a was isolated from dragon fruit stems (Hylocereus monacanthus) showing brown spot symptoms. DNA sequence of the internal transcribed spacer (ITS‐rDNA), beta tubulin and actin gene regions of fungal isolate MBDF0024a had high similarities to E. sorghinum stains. Epicoccum sorghinum MBDF0024a was pathogenic to three cultivated dragon fruit species (Hylocereus undatus, H. monacanthus and H. megalanthus) in repeated laboratory and glasshouse trials. Large brown lesions developed on 3‐week‐old inoculated rooted stem cuttings 3 days postinoculation (dpi). Yellowing of the lesion (advance part) started at five dpi, and at seven dpi, yellowing was observed in the stem. As there are no reported control measures for diseases caused by E. sorghinum, this study screened chemicals with antifungal properties. A biopesticide containing B. subtilis (2 ml/400 ml), and chemicals isoprothiolane (2.25 ml/400 ml), mancozeb (2 g/400 ml) and pyraclostrobin (1 ml/400 ml) (chemical control) completely inhibited the in vitro growth of E. sorghinum MBDF0024a. The results establish E. sorghinum as a new and emerging pathogen of dragon fruit that could be a major yield‐limiting disease if left uncontrolled. The biopesticide can be considered a fairly safe option for disease management, but glasshouse and field studies are needed for validation. [ABSTRACT FROM AUTHOR]

Ralstonia solanacearum (RS) race 1 biovar 4 (R1bv4), causal agent of bacterial wilt in vegetable sweet potato (VSP), is often latent in VSP vines and is important in introduction of the pathogen to newly planted fields. In this study, the effects of biological and environmental factors on the distribution and multiplication of R1bv4 in VSP tissues were examined. Based on stem‐injection inoculation, the R1bv4strain of NC01 could cause 49.0% and 33.0% wilting on VSP cultivars TN71 and WS, respectively. The populations of NC01 in diseased TN71 and WS were 108–109 cfu/g tissue at 28th day after inoculation. On the other hand, the R1bv4 could not cause symptom in cultivars of TN57 and VSPSL‐1 vine and the NC01 was confined to near the injection sites. Temperature tests indicated that NC01 could cause 28.0% and 14.0% wilting on cultivar TN71 at 28 and 20°C, respectively. Moreover, the populations of NC01in diseased plants were 1.6 × 109 and 7.9 × 108 cfu/g tissue at 28 and 20°C, respectively. The distribution of NC01 in VSP stem indicated that the isolation frequency of NC01 was lower than 31.0% in terminal shoots or erect stems and 45.0 to 100.0% in creeping stem after 8 wks planted in infested soil (106 cfu/g soil). The results demonstrated that terminal shoots or erect stems were not common carrier for transmitting R1bv4. Furthermore, two R1bv4 strains, NC01 and HsinT01, were examined the ability for latent infection on cv. TN71. The results revealed that NC01 and HsinT01 showed different ability of latent infection on cultivar TN71. NC01 had lower percentage (46.8% and 45.1%) than HsinT01 (93.4% and 75.3%) at 20 and 28°C. [ABSTRACT FROM AUTHOR]

The use of resistance inducers is a promising development in the management of plant diseases, owing to their ability to control a broad spectrum of pathogens and improve the efficacy of fungicides. This study evaluates different sources of phosphonates (potassium, manganese, copper), a formulation prepared from the by‐products of the coffee industry (Greenforce CuCa), as well as the effects of their application, alone or in association with fungicide, in the management of two important coffee fungal diseases in Brazil: leaf rust and brown eye spot, caused by Hemileia vastatrix and Cercospora coffeicola, respectively. The effect of these products on defoliation, productivity and chemical composition of coffee beans (content of trigonelline, chlorogenic acid, caffeine and total soluble solids) was evaluated. Among all the alternative products tested individually, potassium phosphonate (P2O5—33.6% + K2O—29%) stood out, particularly for rust control, which was similar to the results of fungicide treatments. Treatments with fungicide, Greenforce CuCa and cuprous oxide, individually, caused less plant defoliation. Regarding the chemical composition of the coffee beans, the manganese phosphonate treatment showed the highest values for trigonelline, chlorogenic acid, caffeine and total soluble solid content. The results of this study show that resistance inducers can be useful in disease management, may come to eventually replace traditional fungicides and can also contribute to the beverage quality. [ABSTRACT FROM AUTHOR]

Viticulture has been expanding in tropical regions. However, the climate in these areas is generally favourable to the incidence of plant diseases, especially downy mildew. Plastic covers and warning systems have shown very positive results in disease control, but they are tools that have never been used simultaneously in a tropical area. The Vitis vinifera cv. BRS Morena table grape was evaluated as regards yield and quality under different downy mildew control strategies as carried out on vineyards trained on an overhead trellis system, covered by a black shading screen (BSS) or a braided polypropylene film (BPF), over a 3‐year period. Different grapevine downy mildew management approaches defined the treatments: Co) Control (no spraying); Ca) Conventional control (calendar); Ba) "Rule 3–10" (Atti Istituto Botanico, 8, 1947, 45); Ma25) Low‐infection efficiency—i0>25%; and Ma75) High‐infection efficiency—i0>75% (Plant Disease, 84, 2000, 549). The occurrence of downy mildew and the amount of damage inflicted on vine yield and grape quality are directly related to the period of the crop cycle when there is rainfall. The use of the Ma75 warning system (Plant Disease, 84, 2000, 549) under braided polypropylene film resulted, for the most part, in similar vineyard productivity compared to Ca, but did not influence the number of branches and its fertility. The other warning systems decreased productivity by 31.9% compared to Ca. It was not possible to establish a relationship between the occurrence of downy mildew and its influence on grape sweetness and acidity. The use of warning systems led to a substantial reduction in fungicide sprays, approximately 66.7 to 71.3%, compared to the calendar system commonly used by the vine growers, with the Ba (Atti Istituto Botanico, 8, 1947, 45) and Ma75 controls (Plant Disease, 84, 2000, 549) leading to the highest fungicide saving. [ABSTRACT FROM AUTHOR]

Field experiments were carried out in 2016 and 2017 to determine the effect of crop rotation on the onset of early blight in three potato varieties in Denmark. Six and seven fields with different histories with potato (rotation‐fields) were used for the experiments in 2016 and 2017, respectively. The results showed that variety and the interaction between variety and rotation‐field had no significant effect on the onset of early blight. Rotation‐field, on the other hand, had a significant effect on the onset of early blight in both years of the study. Early blight occurred earlier in fields with <2 years between subsequent potato crops than in fields where potatoes have not been grown for at least 2 years. The onset of early blight was not different between the fields where there had not been potatoes for at least 2 years. For fields that were preceded by potatoes, early blight occurred earlier in fields in which the severity of early blight in the previous years was higher than that in the fields in which the severity of early blight in the previous years was low or moderate. In conclusion, the results of this study suggest that at least a 2‐year interval between subsequent potatoes in a rotation cycle is necessary to delay the onset of early blight. Moreover, the severity of early blight in the previous years can affect the onset of early blight. [ABSTRACT FROM AUTHOR]

The parasitic pathogenic fungus Stagonosporopsis cucurbitacearum (Sc.) is the main cause of pumpkin gummy stem blight (GSB), one of the most devastating pumpkin crop diseases in north‐east China. In the present study, transcriptome analyses of the GSB‐susceptible strain commonly grown in that region, zq‐1, were performed to identify differentially expressed genes (DEGs) relevant to GSB infection. Using RNA‐seq of six fungal samples, we obtained 44.62 Gb of clean sequence data with a Q30 base percentage of 92.38% or higher. We carried out functional annotation by comparing sequences against NR, Swiss‐Prot, KEGG, COG, KOG, GO, and Pfam databases and obtained annotation results for 38,110 unigenes. From these unigenes, a total of 341 DEGs were identified and subjected to GO functional annotation and KEGG pathway analysis. Subsequently, 52 genes possessed putative pathogenic functions, with 34 genes assigned to molecular function (including hydrolase, protein kinase, phosphatase, cellulase, etc.), 15 genes assigned to biological process, and 3 genes assigned to mitogen‐activated protein kinase pathways, ABC transport proteins and cellular endocytosis. Identification of DEGs should enhance our understanding of pathogenic genes involved in pumpkin infection by Sc. and should facilitate the systematic investigation of pathogenic gene expression patterns and host–pathogen interactions. [ABSTRACT FROM AUTHOR]

A rapid, sensitive and visual loop‐mediated isothermal amplification (LAMP) method for detecting Acidovorax citrulli in cucurbit seed was developed in this study. The LAMP primers were designed to recognize the non‐ribosomal peptide synthetase (NRPS) gene (locus tag: Aave_4658) from A. citrulli. The LAMP assay was conducted at 64°C in 1 hr with calcein as an indicator. The sensitivity and specificity of the LAMP assay were further compared with those of a conventional polymerase chain reaction (PCR). The LAMP assay is highly specific to A. citrulli, and no cross‐reaction was observed with other bacterial pathogen. The sensitivity of the LAMP assay was 100‐fold higher than that of conventional PCR with a detection limit of 1 pg of genomic DNA. Using the LAMP assay, 7 of 12 cantaloupe seedlots collected from Xinjiang province were determined to be positive for A. citrulli. In contrast, only 2 of 12 seedlots showed positive for the pathogen with conventional PCR. Moreover, A. citrulli was detected in 100% of artificially infested seedlots with 0.01% infestation or greater. Our results demonstrated that the LAMP assay was simple, visual and sensitive for detecting A. citrulli, especially in seed health testing. Hence, this method has great potential application in routine detecting seed‐borne pathogens and reducing the risk of epidemics. [ABSTRACT FROM AUTHOR]

Anthracnose caused by Colletotrichum (CAD) is an economically important disease of cassava; however, research on its species diversity and geographical distribution of Colletotrichum in China remains limited. In this study, we investigated the phylogenetic diversity of Colletotrichum isolates associated with symptomatic leaf tissues of cassava from Guangxi and Yunnan provinces in China and aimed to confirm their identification using advanced techniques. Based on multi‐locus phylogenetic analyses and phenotypic characteristics, we identified four species from the isolates, comprising C. plurivorum, C. karstii, C. fructicola and C. siamense, and we found variation in degrees of virulence among the species and between cassava varieties. Our results are the first to report these species from cassava, and they provide a basis for the development of management strategies for CAD in cassava. [ABSTRACT FROM AUTHOR]

Abstract: Simple sequence repeats (SSRs) are preferred molecular markers because of their abundance, robustness, high reproducibility, high efficiency in detecting variation and suitability for high‐throughput analysis. In this study, an attempt was made to mine and analyse the SSRs from the genomes of two seed‐borne fungal pathogens, viz Ustilago maydis, which causes common smut of maize, and Tilletia horrida, the cause of rice kernel smut. After elimination of redundant sequences, 2,703 SSR loci of U. maydis were identified. Of the remaining SSRS, 44.5% accounted for di‐nucleotide repeats followed by 29.8% and 2.7% tri‐ and tetranucleotide repeats, respectively. Similarly, 2,638 SSR loci were identified in T. horrida, of which 20.2% were di‐nucleotide, 50.4% tri‐ and 20.5% tetra‐nucleotide repeats. A set of 65 SSRs designed from each fungus were validated, which yielded 23 polymorphic SSRs from Ustilago and 21 from Tilletia. These polymorphic SSR loci were also successfully cross‐amplified with the Ustilago segetum tritici and Tilletia indica. Principal coordinate analysis of SSR data clustered isolates according to their respective species. These newly developed and validated microsatellite markers may have immediate applications for detection of genetic variability and in population studies of bunt and smut of wheat and other related host plants. Moreover, this is first comprehensive report on molecular markers suitable for variability studies in wheat seed‐borne pathogens. [ABSTRACT FROM AUTHOR]

Abstract: Sclerotinia stem rot caused by Sclerotinia sclerotiorum is one of the most important diseases in oilseed rape‐growing areas of China. To determine the frequency of resistance of field isolates of S. sclerotiorum to carbendazim and dimethachlone, a total of 556 isolates from 10 different regions of Henan Province were obtained between 2015 and 2016. The frequency of isolates with a high‐resistance phenotype and a moderate‐resistance phenotype to carbendazim was 69.2% and 10.8%, respectively. However, S. sclerotiorum isolates resistant to dimethachlone were not detected. The baseline sensitivity of S. sclerotiorum to dimethachlone was distributed as a unimodal curve with a mean EC50 value of 0.39 ± 0.09 μg ml−1 for the inhibition of mycelial growth. Four dimethachlone‐resistant mutants were obtained from 20 wild‐type isolates induced by exposure to increasing concentrations of the fungicide in vitro. The mutants showed high levels of resistance to dimethachlone, with resistance factors that ranged from 179 to 323. Positive cross‐resistance occurred between dimethachlone and procymidone, iprodione, and fludioxonil; however, no cross‐resistance was observed for carbendazim and boscalid. The fitness of the dimethachlone‐resistant mutants was significantly lower than that of the wild‐type isolates, as measured by mycelial growth, hyphal dry weight, sclerotium number and dry weight, and pathogenicity. Additionally, based on osmotic tests, the inhibition of mycelial growth caused by NaCl applied at different concentrations was significantly higher for the dimethachlone‐resistant mutants than for their wild‐type parents. [ABSTRACT FROM AUTHOR]

Abstract: Previous research indicated that black and yellow leaf spots on Cymbidium, Ondontioda, Dendrobium and Cattleya could be caused by Fusarium proliferatum worldwide. However, the agent causing leaf spot on Cymbidium spp. plants is still obscure in Taiwan. Thirty‐five F. fujikuroi species complex (FFSC)‐like isolates were collected from Cymbidium leaf spot from different greenhouses in Taiwan. All isolates were identified as F. proliferatum based on morphological characteristics and molecular analysis. Sequence of translation elongation factor 1‐alpha gene showed 99%–100% homology with F. proliferatum. In addition, two assay techniques using either detached leaves or seedlings were used to evaluate the pathogenicity and host range of the isolates and consequently their effects on Cymbidium and other orchid plants. Pathogenicity assays revealed that all isolates induced black and necrotic spots on detached leaves of Cymbidium, showing 9.4%–29.5% severity on seedlings of Cymbidium. Results of host specificity tests on detached leaves of different plants indicated that the F. proliferatum isolates collected from Cymbidium plants caused severe black spots on Oncidium, Cymbidium, Dendrobium and Cattleya plants. The symptoms on Phalaenopsis plants were relatively mild. Results of host specificity tests on plant seedlings indicated that the F. proliferatum isolates of Cymbidium origin were also pathogenic to Oncidium, Cymbidium and Dendrobium, but not to Cattleya and Phalaenopsis. Phylogenetic analysis of the translation elongation factor (TEF) gene among all fungal isolates using maximum parsimony (MP) and Bayesian inference (BI) methods revealed that the isolates of F. proliferatum from Cymbidium spp. could be separated from other FFSC‐like species with high phylogenetic support. [ABSTRACT FROM AUTHOR]

Abstract: We have explored the fungal diversity in asymptomatic twigs of apple, peach, pear and blueberry trees, with the objective of discerning between true endophytes and latent pathogens. Several fungal genera containing known bark pathogens were found. Seven Diaporthe species—D. oxe, D. infecunda, D. serafiniae, D. phaseolorum, D. terebinthifolii, D. foeniculina and D. brasiliensis—were identified, along with Botryosphaeria dothidea, Neofusicoccum parvum, Neofusicoccum australe, Cytospora sp., Cytospora acaciae and Pestalotiopsis spp. A pathogenicity trial was undertaken to determine the role of these species on apple, pear, blueberry and peach shoots. Diaporthe brasiliensis, D. foeniculina, Diaporthe inconspicua, D. terebinthifolii, Diaporthe sp.1, Cytospora‐like isolates and Pestalotiopsis spp. isolates produced no lesions on inoculated shoots, suggesting that they could be considered true endophytes on their respective hosts. Meanwhile, some of the isolates of Diaporthe—D. oxe, Diaporthe sp.2, D. infecunda and D. serafiniae, B. dothidea, N. parvum and N. australe could be regarded as latent pathogens in their respective hosts as they produced sunken cankers and necrosis on inoculated shoots. These results demonstrate that apple, pear, blueberry and peach healthy shoots can host many known endophytic fungi along with potential wood disease‐causing fungi that should be regarded as latent pathogens. [ABSTRACT FROM AUTHOR]

Abstract: A total of 54 samples of Brassicaceae crops showing symptoms of mosaic, mottling, vein banding and/or leaf deformation were collected in Kyiv region (northern central part of Ukraine) in 2014–2015. A half of collected samples was found to be infected with Turnip mosaic virus (TuMV), and TuMV was detected in samples from Brassica oleracea var. capitata (cabbage), Raphanus sativus, Brassica juncea, Raphanus sp., Sinapis alba, Camelina sativa and Bunias orientalis (weed). The full‐length sequence of the genomic RNA of a Ukrainian isolate (UKR9), which was isolated from cabbage, was determined. Recombination analysis of UKR9 isolate showed that this isolate was an interlineage recombinant of world‐Brassica and Asian‐Brassica/Raphanus phylogenetic groups. This study shows for the first time the occurrence of TuMV in Ukraine. [ABSTRACT FROM AUTHOR]

Abstract: Pathogenesis by Pectobacterium carotovorum and the other soft rot bacteria results mostly from the synthesis and secretion of a plethora of exoproteins including plant cell wall‐degrading enzymes and type III effectors. A mini‐Tn5 transposon mutant of P. carotovorum (KD200) was isolated that is highly increased in activity and transcript levels of extracellular cell wall‐degradative enzymes, pectate lyase, polygalacturonase, cellulase and protease. Accordingly, the mutant was more virulent as it macerated more host tissue than its parent. KD200 mutant harbours a Tn5 insertion directly upstream of nssAEcc71, a putative sodium/sulphate symporter gene and member of a family of divalent anion sodium symporters (DASS). The findings reported here suggest that DASS proteins may be involved in soft rot pathogenesis. [ABSTRACT FROM AUTHOR]

Dryopteris crassirhizoma dryocrassin ABBA treatment was tested for its effectiveness in controlling Fusarium solani var . coeruleum growth in vitro and for prevention of postharvest dry rot of potato tubers and slices. Dryocrassin ABBA strongly inhibited mycelial growth, resulting in reductions in both mycelium dry weight and per cent spore germination of F. solani var. coeruleum at concentrations of 2.0, 0.5 and 0.1 mg/ ml. Scanning electron microscopy ( SEM) observations showed that treatment induced abnormal, tightly twisted morphological changes in hyphae. Moreover, in vivo experiments demonstrated that dryocrassin ABBA treatment at 2 mg/ ml effectively controlled dry rot of potato tubers inoculated with mycelial discs of F. solani var. coeruleum. After dryocrassin ABBA treatment, the content of soluble proteins, peroxidase ( POD) and superoxide dismutase ( SOD) activity increased, and malondialdehyde ( MDA) content remained the stable situation. In addition, the expression level of plant lipid-transfer proteins ( LTPs) genes - St LTPa1, St LTPa7, St LTPb1 and St LTPb3 - was upregulated. These results collectively demonstrate that dryocrassin ABBA can inhibit growth of Fusarium pathogens to induce disease resistance. On the other side, dryocrassin ABBA maybe induce potato defence responses. [ABSTRACT FROM AUTHOR]

Virus particles of approximately 740-760 nm in length and 13 nm in diameter were observed from a diseased Nicotiana tabacum (tobacco) plant in Sichuan Province, China. The complete genomic sequence of the virus isolate XC1 was determined to contain 9659 nucleotides without 3′ terminal poly(A) tail. XC1 has a genome typical of members of the genus Potyvirus, encoding a large polyprotein of 3075 amino acids. Putative proteolytic cleavage sites and a number of well characterized functional motifs were identified by sequence comparisons with those of known potyviruses. Sequence comparison revealed that XC1 shared the highest level of nucleotide sequence identity (76.5%) with Wild tomato mosaic virus ( WTMV). Phylogenetic analysis showed that XC1 was closely related to the WTMV Guangdong isolate with an identity of 94.3% between CP gene sequence of the two viruses. We thus named XC1 WTMV- XC-1 as a novel isolate of WTMV. The full sequence of WTMV- XC-1 may serve as a basis for future investigations on the gene diversity of WTMV. [ABSTRACT FROM AUTHOR]

Begomoviruses are one of the major pathogens in tomato crops worldwide. In Venezuela, six begomovirus species have been described infecting tomato: Potato yellow mosaic virus ( PYMV), Euphorbia mosaic Venezuela virus (Eu MVV), Merremia mosaic virus (Me MV), Tomato chlorotic leaf distortion virus (To CLDV), Tomato yellow margin leaf curl virus ( TYMLCV) and Tomato yellow leaf curl virus ( TYLCV). In this study, the occurrence of these viruses was analysed by PCR in 338 tomato plants exhibiting virus-like symptoms. Sixty-three per cent of the plants were positive at least to one of the begomoviruses tested. PYMV and TYLCV were the most frequent viruses showing 39.6 and 23.7% occurrence, respectively. Phylogenetic analyses revealed two groups of PYMV isolates from several Caribbean Basin countries. The first group clustered isolates from several countries, including Venezuela, and the second group clustered only Colombian isolates. Due to the high prevalence of PYMV and TYLCV in Venezuela, it is suggested that the surveillance and control strategies currently applied in the country should be focused on these two begomoviruses. [ABSTRACT FROM AUTHOR]

The stolbur phytoplasma ' Candidatus Phytoplasma solani' is responsible for the grapevine disease 'bois noir' affecting a number of wine-growing areas in Europe. Transmission of stolbur phytoplasma to different laboratory hosts can be difficult due to the requirement of transmitting insect vectors or parasite plants. Here, heterologous grafting was used as an alternative technique for transmission of common and strongly symptomatic stolbur genotypes CPsM4_At1 and CPsM4_At6 of ' Ca. P. solani' to experimental host plants such as Catharanthus roseus and tomato making phytoplasma strains more accessible for molecular and experimental investigations in different plant species. Transmission was confirmed by quantitative PCR, microscopy and nested PCR followed by marker gene sequencing. In our study, the transmission of different genotypes of ' Ca. P. solani' resulted in distinguishable symptom development in the laboratory host C. roseus. Symptom development in grafted rootstock was observed three to 7 weeks after heterologous grafting. Survival of the graft unit was influenced by the presence of ' Ca. P. solani' in the scions and was clearly reduced in phytoplasma free scion - rootstock combinations. [ABSTRACT FROM AUTHOR]

Cultivation of non-host crops after uprooting Xanthomonas campestris pv. musacearum ( Xcm)-infected banana plants has been advocated for breaking Xanthomonas wilt disease ( XW) cycle in fields. Knowledge on the interaction of these crops with Xcm is limited. Maize, beans and sweet potato were planted after uprooting Xcm-infected banana plants in Rwanda and eastern Democratic Republic of Congo ( DR Congo). A weed fallow (mixed species) served as the control. After one, two and/or four break-crop or fallow seasons, healthy plantlets were replanted and monitored for XW for 12-24 months. XW status in adjacent fields was monitored, and diseased stems within 100-300 m radius of the two- and four-season experiments were uprooted. In Rwanda, soil and plant parts from the one-season experiments were sampled for Xcm isolation and Xcm-like colonies confirmed with Xcm-specific primers using PCR. Pathogenicity tests were performed to confirm the ability of the PCR-positive isolates to infect healthy banana plantlets. XW was observed in all the one-season experiments, with higher cumulative incidences in maize and bean plots. However, no similar trends were observed in the two-season experiments, with a 6-8% incidence observed only in bean and potato plots in DR Congo. Lengthening time under break crops to two and four seasons, respectively, reduced the incidence to 3% and zero in Rwanda and 0-8% in the two-season experiments in DR Congo. Incidence in the first-season experiments highly correlated ( R = 88) to that in the adjacent fields, suggesting possible re-infections from these fields. Two season with break crop plus collective XW control are recommended in these agro-ecosystems. PCR-positive Xcm-like colonies from break crops only induced localized cell death on banana, while PCR-positive isolates from symptomatic banana plants caused full XW symptoms. Cross-infection/inoculation studies under controlled conditions are still needed to conclusively elucidate Xcm interaction with these crops. [ABSTRACT FROM AUTHOR]

The oomycete plant pathogen Phytophthora cinnamomi causes a highly destructive root rot that affects numerous hosts. Integrated management strategies are needed to control P. cinnamomi in seminatural oak rangelands. We tested how biofumigation affects crucial stages of the pathogen's life cycle in vitro, in infested soils under laboratory conditions and in planta. Different genotypes of three potential biofumigant plant species ( Brassica carinata, Brassica juncea, Brassica napus) were collected at different phenological stages, analysed for their glucosinolate contents, and subsequently tested. The most effective genotypes against mycelial growth and sporangial production were further tested on the viability of chlamydospores in artificially infested natural soils and in planta on Lupinus luteus, a host highly susceptible to P.cinnamomi. Brassica carinata and B. juncea genotypes inhibited mycelial growth, decreased sporangial production, and effectively inhibited the viability of chlamydospores in soil, but only B. carinata decreased disease symptoms in plants. Effective genotypes of Brassica had high levels of the glucosinolate sinigrin. Biofumigation with Brassica plants rich in sinigrin has potential to be a suitable tool for control of oak root disease caused by P. cinnamomi in Spanish oak rangeland ecosystems. [ABSTRACT FROM AUTHOR]

Many epidemics involve plants infected with more than one pathogen, but few experiments address climate change scenarios that influence mixed infections. This study addresses the interactive effects of co-infection and temperature on disease development in plants of the annual pasture species subterranean clover ( Trifolium subterraneum), which is widely sown in different world regions. Bean yellow mosaic virus ( BYMV) and the fungus Kabatiella caulivora are two important pathogens causing considerable production losses in pastures containing this species. Both occur together in such pastures causing a severe necrotic disease when mixed infection occurs. Effects of temperature on symptom expression were investigated in subterranean clover plants infected singly or in mixed infection with these pathogens. Plants were maintained in controlled environment rooms at 18°C, 20°C or 22.5°C after sap inoculation with BYMV. K. caulivora conidia suspensions were inoculated to plants once systemic BYMV symptoms developed. Plants were assessed for three disease assessment parameters, dead petioles numbers, marginal leaflet necrosis and overall plant damage. In general, mixed infection caused most severe symptoms, K. caulivora least severe symptoms, and BYMV symptoms of intermediate severity. In single infections, effects of temperature on disease severity differed between pathogens: BYMV symptoms were most pronounced at 18°C, but K. caulivora induced more severe symptoms at 20°C and 22.5°C. In mixed infections, disease severity generally followed the pattern developed with BYMV alone as temperature increased. Also, synergistic increase in disease severity sometimes occurred at 18°C, but increases were only additive at 20°C and 22.5°C. These results reflected the greater BYMV multiplication detected in infected leaves at 18°C compared with 20°C or 22.5°C. Our findings indicate that in rainfed subterranean clover pastures, as global warming progresses disease severity from infection with BYMV and K. caulivora alone may decline or increase, respectively, and mixed infection with them may become less damaging. [ABSTRACT FROM AUTHOR]

This study aimed to examine Brazilian M. oryzae populations using 18 microsatellites. Fifty cultivars were sown in plastic trays for the pathotyping of 847 isolates. The DNA of 494 isolates was extracted and purified using the modified Doyle and Doyle method, the genetic structure was determined by the software Structure, and the actual number was selected from the prediction method based on the K values. Nei's genetic distance among the subpopulations was determined with the aid of the program Genetix, and the amova was performed with the program Arlequin. Out of 847 inoculated monosporic isolates, 528 infected their respective cultivars; of the 528 isolates pathotyped, there was a prevalence of group IA and pathotype IF-1, which was the most frequent pathotype in the rice production areas of Brazil. The Bayesian clustering analysis indicated that 19 was the optimal value of K; this value was the lowest standard deviation and log (ln K) closest to zero, which predicted the 494 isolates of M. oryzae that were selected for molecular studies to be grouped into 19 subpopulations. The AMOVA detected a 37.13% variability within the 19 subpopulations and 62.87% variability among the subpopulations. The polymorphic information content ( PIC) ranged from 0 to 0.756. Thirty three rare alleles were found distributed among 15 out of 19 subpopulations. The Margalef index ranged from 38.69 to 79.21 for all 18 analysed locus. The results indicated that the identification of different blast resistance genes must consider the composition of each subpopulation and that the identification is most effective when performed within a subpopulation and then between subpopulations. [ABSTRACT FROM AUTHOR]

Rice blast, caused by the ascomycete fungus Magnaporthe oryzae, is one of the most destructive plant diseases in the world and a serious threat to global food security. Biofungicide physcion, extracted from roots of Chinese traditional herb rhubarb, has been commercialized to control cucumber powdery mildew ( Podosphaera fuliginea) in China as a new active and environmentally-friendly ingredient. This study investigated its bioactivity on rice blast and impact on the infection of M. oryzae. Physcion was effective on M. oryzae with 50% inhibition concentration of 18.19 mg/l on the fungus mycelium growth in vitro and provided 86 and 98% control efficacy in vivo at the concentrations of 40 and 60 mg/l, respectively. It inhibited the initial infection of M. oryzae by inhibiting growth of mycelia, the germination of conidia and the formation of appressoria. Moreover, it inhibited the secondary infection of the fungus at the concentration of 40 mg/l, but had no influence at the low concentrations of 1.25-20 mg/l. So physcion might be a promising natural plant extract that is worthy of being explored to apply on the control of rice blast. [ABSTRACT FROM AUTHOR]

Cucumber green mottle mosaic virus ( CGMMV; genus Tobamovirus) infects frequently the grafted watermelon and is widely distributed in China. Investigating the transmission modes and their efficiency is urgently needed to understand the factors contributing to the epidemiology of this viral disease. In the present study, we found that the occurrence of CGMMV in a bottle gourd seed production base reached 100%, while the contamination rate and transmission rate were 100 and 0.92%, respectively. The bottle gourd plants showed obvious mottle symptom on leaves starting 36 days after seed sowing. The long latent period of CGMMV in seedlings implies a potential risk to use contaminated seeds in the production of grafted watermelon. This virus could overwinter in soil with debris of infected plants, and the infection rate of CGMMV from contaminated soils was 10.30%. CGMMV could be transmitted from infected watermelon plants to healthy ones by pruning at least to the ninth plant during the whole growing season. The transmission distance was 1.87 m by drip irrigation and 2.31 m by flow irrigation. This study suggested that contaminated seeds, contaminated soil, pruning and irrigation could transmit CGMMV at different efficiency, and all contribute to the epidemiology of CGMMV. [ABSTRACT FROM AUTHOR]

Symptoms resembling those associated with phytoplasma presence were observed in pomegranate ( Punica granatum L.) trees in June 2012 in the Aegean Region of Turkey (Aydın province). The trees exhibiting yellowing, reduced vigour, deformations and reddening of the leaves and die-back symptoms were analysed to verify phytoplasma presence. Total nucleic acids were extracted from fresh leaf midribs and phloem tissue from young branches of ten symptomatic and five asymptomatic plants. Nested polymerase chain reaction assays using universal phytoplasma-specific 16S rRNA and tuf gene primers were performed. Amplicons were digested with Tru1I, Tsp509I and HhaI restriction enzymes, according to the primer pair employed. The phytoplasma profiles were identical to each other and to aster yellows (16SrI-B) strain when digestion was carried out on 16Sr(I)F1/R1 amplicons. However, one of the samples showed mixed profiles indicating that 16SrI-B and 16Sr XII-A phytoplasmas were present when M1/M2 amplicons were digested, the reamplification of this sample with tuf cocktail primers allowed to verify the presence of a 16Sr XII-A profile. One pomegranate aster yellows strain AY- PG from 16S rRNA gene and the 16Sr XII-A amplicon from tuf gene designed strain STOL- PG were directly sequenced and deposited in GenBank under the Accession Numbers KJ818293 and KP161063, respectively. To our knowledge, this is the first report of 16SrI-B and 16Sr XII-A phytoplasmas in pomegranate trees. [ABSTRACT FROM AUTHOR]