Powdery Mildew Severity Research Articles

Unlocking the potential of simulated hyperspectral imaging in agro environmental analysis: a comprehensive study of algorithmic approaches

This study focuses on identifying and evaluating the severity of powdery mildew disease in tomato plants. The uniqueness of this work lies in combining the imaging and advanced deep learning methods to develop a technique that transforms Red Green Blue (RGB) images into Simulated Hyperspectral Images (SHSI) to perform spectral and spatial analysis for precise detection and assessment of powdery mildew severity, thereby enhancing disease management. Furthermore, this research evaluates three advanced pre-trained VGG16 models, ResNet50 and EfficientNet-B7 algorithms for image preprocessing and feature extraction. Extracted features are passed to a neural network generator model to convert RGB image features into SHSIs, providing insights into the spectrum. This method enables the image analysis to perform assessments from SHSIs for health classification using Normalized Difference Vegetation Index (NDVI) values, which are meticulously compared with accurate hyperspectral data using metrics like mean absolute error (MAE) and root mean squared error (RMSE). This strategy enhances precision farming, environmental monitoring, and remote sensing accuracy. Results show that ResNet50’s architecture offers a robust framework for this study’s spectral and spatial analysis, making it a suitable choice over VGG16 and EfficientNet-B7 for transforming RGB images into SHSI. These simulated hyperspectral images offer a scalable and affordable approach for precise assessment of crop disease severity.

Green Alternatives for the Control of Fungal Diseases in Strawberry: In-Field Optimization of the Use of Elicitors, Botanical Extracts and Essential Oils

Finding safe and reliable alternatives to fungicides is currently one of the biggest challenges in agriculture. In this regard, this experiment investigated the effectiveness of different elicitors, botanical extracts and essential oils to control grey mold (Botrytis cinerea) and powdery mildew (Podosphaera aphanis) on strawberry plants. This trial was conducted in field conditions under a plastic tunnel with strawberry plants ‘Elsanta’. A first group of strawberry plants was treated before flowering with elicitors [acibenzolar-S-Methyl–(BTH), chitosan], botanical extracts (seaweed extract, alfalfa hydrolysate) and essential oils (thyme and juniper), and grey mold incidence on flowers was evaluated (Experiment 1). Furthermore, a second group of plants was treated before (Experiment 2) and after (Experiment 3) controlled inoculation with P. aphanis. The results indicated that the incidence of flower infected by B. cinerea was reduced by approximately 50% with thyme and juniper essential oils’ applications compared to the untreated control, with no significant difference observed compared to the commercial fungicide penconazole (positive control). As a consequence, the final yield of essential-oil-treated plants was +27% higher than that of non-treated plants. No significant differences emerged for other tested products against grey mold. However, gene expression analysis showed an up-regulation (>2 ÷ 5 folds as compared to control 4 days after application) of FaEDS1, FaLOX and PR gene expression (FaPR1, FaPR5, FaPR10) in leaves treated with BTH. The other natural substances tested also induced defense-related genes, albeit at a lower level than BTH. In Experiment 2, all treatments applied prior to inoculation significantly reduced the incidence and severity of powdery mildew as compared to control. At 28 days after inoculation, chitosan and thyme essential oil applications performed similarly to their positive controls (BTH and penconazole, respectively), showing a significant reduction in disease incidence (by −84 and −92%) as compared to control. Post-inoculum application of essential oils (Experiment 3) showed an efficacy similar to that of penconazole against powdery mildew. These results indicated that the tested substances could be used as alternatives to fungicides for the control of grey mold and powdery mildew in strawberry, therefore representing a valuable tool for the control of these fungal diseases under the framework of sustainable agriculture.

First Report of Powdery Mildew on Vitis bryoniifolia Caused by Erysiphe necator in China.

Grapes, belonging to the genus Vitis, are one of the world's most economically valuable fruit crops, which are widely used as the source of wine, raisins, and juice. The genus Vitis contains about 60 species mainly distributed in Asia, Europe, and North America to northern South America (Wan et al. 2013). In May 2022, severe powdery mildew symptoms were found on wild Vitis bryoniifolia plants at Guizhou Normal University, Guiyang, China. The incidence observed was approximately 85% among 50 V. bryoniifolia plants. Infected leaves appear white powdery patches, eventually leading to chlorosis to necrosis. Mycelia occurred on adaxial and abaxial leaf surfaces, petioles and young shoots. Upon microscopic observation hyphae were hyaline and 3.5-6 μm wide. Hyphal appressoria were solitary and lobed to multilobed. Conidiophores were erect, straight to somewhat flexuous and 80-130 µm long (n = 30). Foot cells were subcylindrical to curved-sinuous at the base, followed by 2-4 cells. Conidia formed singly (occasionally 2-6 in a chain) and were ellipsoid to ovoid in shape with dimensions of 22.5-38 × 12-19.5 µm (n = 50). No fibrosin bodies were observed on conidia. Based on these morphological characteristics, the powdery mildew fungus strongly resembled Erysiphe necator (Braun and Takamasu 2000; Zheng et al. 1987) that has been shown to cause powdery mildew on Vitis (Gadoury et al. 2012; Gaforio et al. 2011; Qiu et al. 2015). To confirm the identification, the ribosomal DNA internal transcribed spacer (ITS) and the ribosomal large subunit (LSU) region were amplified and sequenced using the ITS1/ITS4 primer pair (White et al. 1990) and the NL1/NL4 primer pair (Ziemiecki et al. 1990), respectively. The spliced 1250-bp ITS-LSU sequence (GenBank accession no. PP188565) shared 99.84-100% identity with ITS-LSU sequences of E. necator (LC028995, LC028996, ON073862, LC777882, and OM033353). Based on the phylogenetic analysis of the combined ITS-LSU dataset of Erysiphe species (Takamasu et al. 2015), PP188565 was grouped in a clade with E. necator strains MUMH530, MUMHs141, and VPRI19719. To perform pathogenicity analysis, leaves of three healthy, potted 1-year-old V. bryoniifolia plants were inoculated by gently pressing with diseased leaves. Three non-inoculated healthy plants served as controls. All plants were incubated in a greenhouse at 25 ± 2°C with 80% relative humidity. Powdery mildew symptoms, similar to field conditions were observed on inoculated plants 13 days after inoculation, whereas control plants remained symptomless. Fungus reisolated from inoculated V. bryoniifolia plants was morphologically identical to that on originally diseased plants, and the spliced ITS-LSU sequence of reisolated fungus shared 100% identity with PP188565, fulfilling Koch's postulates. Based on the morphological and molecular characterizations, the powdery mildew fungus was identified as E. necator. To our knowledge, this is the first report of powdery mildew caused by E. necator on V. bryoniifolia in China. This work further expands the host range of Erysiphe necator on Vitis species.

PREVALANCE AND MANAGEMENT OF SOME MAJOR DISEASES OF MANGO AT AFGOYE AND BALAD DISTRICT IN SOMALIA

The experiments were conducted in different mango orchards of Afgoye and Balad districts in Somalia under the faculty of Agriculture, Zamzam Universityof Science and Technology during February to April, 2020 on prevalence and management of mango diseases. Altogether, seven different diseases viz. Anthracnose, die-back, powdery mildew, sooty mold, red rust, bacterial leaf blight and bacterial leaf spot were recorded. All the diseases were common in both regions but these varied from orchard to orchard. Among the diseases, severity of Anthracnose (35.3%), die-(20.67%), powdery mildew (45.17%), red rust (13.75%) and bacterial leaf sight (54.33%) were found major problem in Balad districts. In Afgoye , Anthracnose (16.033%), sooty mold (18.90%), bacterial leaf blight( 19.833%) and bacterial leaf spot (8.927%) were found the highest severity. fungicides Caroozate 45, Carbazim, respectively, were evaluated and found that Carbazim were good effect in controlling Anthracnose, sooty mold, red rust and bacterial leaf spot. Caroozate 45 was also effective in controlling Anthracnose, die-back, powdery mildew, red rust al leaf spot disease. like similarly weused botanicals fungcide, Such as Neemand Garlic well cake.respectively,were evaluated and found that Neem with Garlic were good effect in controlling Anthracnose, sooty mold, red rust and bacterial leaf spot. Neem was also effective in controlling Anthracnose, die-back, powdery mildew, red rust al leaf spot disease.

Impact of Weather Variables on the Severity and Progression of Powdery Mildew on Rapeseed-mustard in Haryana

Impact of Weather Variables on the Severity and Progression of Powdery Mildew on Rapeseed-mustard in Haryana

Change of Flavonoid Content in Wheatgrass in a Historic Collection of Wheat Cultivars.

Wheatgrass is recognized for its nutritional and medicinal properties, partly attributed to its flavonoid content. The objective of this study was to assess the flavonoid content and antioxidant properties of wheatgrass obtained from a wide range of 145 wheat cultivars, which included Chinese landraces (CL), modern Chinese cultivars (MCC), and introduced modern cultivars (IMC). The flavonoids were extracted using a solution of 80% methanol, and their content was evaluated using ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS). The results revealed the assessed cultivars showed significant variation in their total flavonoid content (TFC), with MCCs generally having higher amounts compared to CLs. PCA analysis demonstrated clear variations in flavonoid profiles between different cultivar groups, emphasizing the evolutionary inconsistencies in wheat breeding. The antioxidant assays, ABTS, DPPH, and FRAP, exhibited robust abilities for eliminating radicals, which were found to be directly associated with the amounts of flavonoids. In addition, this study investigated the correlation between the content of flavonoids and the ability to resist powdery mildew in a collection of mutated wheat plants. Mutants exhibiting heightened flavonoid accumulation demonstrated a decreased severity of powdery mildew, suggesting that flavonoids play a protective role against fungal infections. The results highlight the potential of wheatgrass as a valuable source of flavonoids that have antioxidant and protective effects. This potential is influenced by the genetic diversity and breeding history of wheatgrass. Gaining insight into these connections can guide future wheat breeding endeavors aimed at improving nutritional value and in strengthening disease resistance. The current finding provides critical information for developing wheatgrass with high flavonoid content and antioxidant activity.

Susceptibility of Zucchini Cultivars to Powdery Mildew (Podosphaera xanthii) Under High- and Low-Nitrogen Regimes

Powdery mildew, primarily caused by Podosphaera xanthii, threatens cucurbit crop yield and longevity. Fungicides and resistant cultivars cannot fully manage or prevent the disease. Previous work has shown that powdery mildew incidence and severity can increase under high soil nitrogen. This study was conducted in Kentucky to determine disease severity and yield using a split plot design with nitrogen fertility (high: 140 kg/ha; low: 84 kg/ha) and zucchini cultivar (Cash Machine, Cue Ball, Desert, Dunja, Eight Ball, Emerald Delight, Golden Glory, Mexicana, and Spineless Perfection) as the main plot and subplot factors, respectively. In year 1, powdery mildew severity was significantly higher in high soil nitrogen and varied significantly among cultivars. Yield was significantly lower in high soil nitrogen. Significant differences in fruit count, but not fruit weight, were observed among the cultivars. In year 2, nitrogen did not significantly affect disease severity, but fruit weight and count were significantly lower in the high soil nitrogen treatment. Golden Glory had significantly higher powdery mildew severity, while Mexicana and Eight Ball had significantly lower severity compared to all other cultivars. Spineless Perfection had the highest fruit weight and was significantly higher than all other cultivars except for Cue Ball and Eight Ball. Golden Glory had the highest fruit count and was significantly higher than all others except for Dunja. Nitrogen did not consistently affect disease severity throughout the study. The effects of powdery mildew on yield should be explored further, as heavily diseased plants did not always have low yield.

First Report of Powdery Mildew on Sophora flavescens Caused by Erysiphe diffusa in China.

Sophora flavescens (Fabaceae) is a deciduous subshrub which has been used in Chinese popular medicine for a long history (He et al. 2015). In June 2023, severe powdery mildew symptoms were observed on wild S. flavescens plants on Longwen hill of Guizhou Normal University, Guiyang, China. The incidence was approximately 80% among 100 S. flavescens plants observed. Almost all leaves were infected. Mycelia occurred on both adaxial and abaxial leaf surfaces, petioles, and stems, forming small-to-large patches. Hyphae were hyaline, 5 to 7 μm wide. Hyphal appressoria were solitary. Conidiophores were erect, straight to somewhat flexuous, and 45 to 120 µm long (n = 50). Foot cells were subcylindrical to slightly curved, followed by 2 to 3 shorter cells. Conidia formed singly, were ovoid to cylindrical, 26 to 42 × 12 to18 µm (n = 50). Based on these morphological characteristics, the powdery mildew fungus was tentatively identified as Erysiphe diffusa (Braun and Cook 2012). To confirm the identification, the ribosomal DNA internal transcribed spacer (ITS) and the ribosomal large subunit (LSU) region were amplified and sequenced using primer pairs ITS1/ITS4 (White et al. 1990) and NL1/NL4 (Ziemiecki et al. 1990), respectively. The obtained 647-bp ITS sequence (GenBank accession no. PP130131) displayed 100% identity with the ITS sequences of E. diffusa. The obtained 618-bp LSU sequence (GenBank accession no. PP693303) displayed 100% identity with the ITS sequences of E. diffusa (MT325922 and MT628019) and E. manihoticola (MT106658 and MT106660). Using a phylogenetic tree based on the combined ITS-LSU data, the isolate was grouped in a clade with the E. diffusa strain (GenBank accession no. LC777871). To fulfill Koch's postulates, leaves of three healthy potted S. flavescens plants were inoculated by gently pressing with diseased leaves. Non-inoculated plants were used as controls. All plants were incubated in a greenhouse at 25 ± 2°C, 80% relative humidity. After 15 days, typical powdery mildew symptoms were observed on the inoculated plants, whereas no symptoms were found on the control plants. The reisolated fungus from the inoculated S. flavescens was morphologically identical to that on naturally diseased plants, and the ITS sequence of the reisolated fungus showed 100% identity with PP130131. As the causal fungus of soybean powdery mildew, E. diffusa is known to infect papaya and other legumes, including Lens culinaris and Mimosa caesalpiniifolia (Attanayake et al. 2009; Luz et al. 2019). Particularly, E. diffusa has been previously reported to infect S. flavescens in the United Kingdom (Jones and Baker 2007; Bradshaw et al. 2023), but this is the first report of S. flavescens powdery mildew caused by E. diffusa in China. This work further expands the geographical range of E. diffusa-infected S. flavescens plants.

Impact of Weather Parameters and Time of Sowing on Severity of Powdery Mildew in Cluster Bean

Background: Powdery mildew of cluster bean causes considerable yield loss upto 50-55%. Studies carried on cluster bean powdery mildew are very few and as such there is no information related to epidemiology of the disease. Environmental factors decide the epidemic of the disease and are being used to forecast the disease severity. Methods: Five different dates of sowing of cluster bean were evaluated in a randomized complete block design with four replications at Main Agricultural Research Station, College of Agriculture, Dharwad. Observations on the first appearance of the disease and severity were recorded at weekly intervals using disease scoring scale 0-9 and along with pod yield were considered for statistical analysis. The weather data was used to correlate with the disease severity and correlation matrix was worked out. Further, the observations were converted to % disease index to calculate rate of infection and area under disease progress curve (AUDPC) for each date of sowing. Result: Sowing of crop in first fortnight of September recorded the minimum mean disease severity of 19.10% and recorded pod yield of 4.72 t/ha with lower value of area under disease progress curve (1270.50) as against crop sown in first fortnight of November that recorded the 39.39 % of maximum mean disease severity, 3.82 t/ha pod yield and 2583.88 of area under disease progress curve. The mean maximum temperature was positively correlated (0.89) with % disease index whereas, minimum temperature (-0.87), morning relative humidity (-0.81) and evening relative humidity (-0.88) were negatively correlated with % disease index. Disease progression was started at 35 days after sowing and the maximum ‘r’ value of 0.157 was observed during the II fortnight of September followed by an ‘r’ value of 0.142 during the I fortnight of September whereas, a lower ‘r’ value of 0.009 was observed in I fortnight of September sown crop at 63-69 days after sowing.

Chitosan nanoparticle encapsulation of celery seed essential oil: Antifungal activity and defense mechanisms against cucumber powdery mildew

The objective of the current study was to explore the antifungal potential of celery seed essential oil (CSEO) in a nano-carrier system against Podosphaera fusca, the causal agent of cucumber powdery mildew. We assessed the physicochemical characterization of CSEO-loaded chitosan nanoparticles (CSEO-LCNPs) using dynamic light scattering, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. The successful loading of various concentrations of CSEO into chitosan nanoparticles (1:0, 1:0.25, 1:0.5, 1:0.75, and 1:1) has been verified. The particles exhibited a spherical shape, with an average diameter of 113 nm, and a negatively charged surface with a zeta potential of -31.5 mV. The Korsmeyer-Peppas model well described the release behavior of CSEO from nanoparticles. Additionally, we examined the defense mechanism, as well as biochemical/molecular responses following foliar treatment with CSEO-LCNPs. In vivo, results revealed that CSEO-LCNPs foliar application on the cucumber seedlings inoculated with P. fusca significantly reduced the disease severity of powdery mildew. Treatment with CSEO-LCNPs led to an increase in phenolic and flavonoid compounds, chlorophyll concentration, enzyme activities, and gene transcriptions in inoculated cucumber seedlings. In our study, we observed a positive correlation between antioxidant compounds and the defense-associated enzymes as well as their corresponding gene expressions. Our study underscores the potential of CSEO-LCNPs as an eco-friendly and effective solution for managing cucumber powdery mildew.

Investigation of genetic diversity using molecular and biochemical markers associated with powdery mildew resistance in different flax (Linum usitatissimum L.) genotypes

Under greenhouse conditions, the resistance of 18 different genotypes of flax to powdery mildew was evaluated. To investigate genetic diversity and identify the molecular and biochemical markers linked to powdery mildew resistance in the tested genotypes, two molecular marker systems—start codon targeted (SCoT) and inter-simple sequence repeat (ISSR)—as well as a biochemical marker (protein profiles, antioxidant enzyme activity, and secondary metabolites) were used. Based on the results, the genotypes were classified into four categories: highly susceptible, susceptible, moderately susceptible, and moderately resistant. The genotypes differed significantly in powdery mildew severity: Polk had a severity of 92.03% and Leona had a severity of 18.10%. Compared to the other genotypes, the moderately resistant genotypes had higher levels of flavonoids, antioxidant enzymes, phenolics, and straw yield; nevertheless, their hydrogen peroxide and malondialdehyde levels were lower. Protein profiles revealed 93.75% polymorphism, although the ISSR marker displayed more polymorphism (78.4%) than the SCoT marker (59.7%). Specific molecular and biochemical markers associated with powdery mildew resistance were identified. The 18 genotypes of flax were divided into two major clusters by the dendrogram based on the combined data of molecular markers. The first main cluster included Leona (genotype number 7), considered moderate resistance to powdery mildew and a separate phenetic line. The second main cluster included the other 17 genotypes, which are grouped together in a sub-cluster. This means that, besides SCoT, ISSR markers can be a useful supplementary technique for molecular flax characterization and for identifying genetic associations between flax genotypes under powdery mildew infection.

First Report of Powdery Mildew on Viburnum chinshanense Caused by Erysiphe pseudoviburni in China.

Viburnum chinshanense, a deciduous shrub in the family Caprifoliaceae, is a dominant tree distributed mainly in the North-Central and South-Central regions of China (Zhu et al. 2023). Because of its lush white flowers and vibrant red fruits, V. chinshanense is used widely as ornamental tree in China. In May 2022, severe powdery mildew symptoms were observed on V. chinshanense on the Huaxi Campus of Guizhou Normal University, Guiyang, China. The incidence was approximately 75% among 80 V. chinshanense plants observed. White mycelia were present on both adaxial and abaxial leaf sides, but not on fruits, petioles, or stems. Infected leaves showed slight chlorosis and twisting. The mycelia were amphigenous, forming small-to-large patches, often sparse on the upper leaf surface, but mostly confluent on the lower leaf surface. Hyphae were hyaline, 4-7 μm wide. Hyphal appressoria were lobed to multilobed, in opposite pairs or solitary. Conidiophores were erect, straight, or somewhat flexuous, 60-130 µm long (n = 30). Foot cells were subcylindrical to slightly curved-sinuous at the base, 20-40 × 6-10 µm (n = 30) in size, followed by 1-3 shorter cells. Conidia formed singly, occasionally two to three in a chain. Conidia were ellipsoid to ovoid, cylindrical, and 24-40 × 16-20 µm (n = 50). No fibrosin bodies were observed on the conidia. Chasmothecia were subglobose, 56-115 µm in diameter. The appendages were 35-70 µm long. Based on these morphological characteristics, the powdery mildew fungus was identified as Erysiphe pseudoviburni (Bradshaw et al. 2020). To confirm the identification, the ribosomal DNA internal transcribed spacer (ITS) and the ribosomal large subunit (LSU) region were amplified and sequenced using the ITS1/ITS4 primer pair (White et al. 1990) and the NL1/NL4 primer pair (Ziemiecki et al. 1990), respectively. The obtained 643-bp ITS sequence (GenBank accession no. ON729292) had 99.84% identity with E. pseudoviburni strains KUS-F27310 (MN431595) and MUMH0001 (LC009904). The obtained 593-bp LSU sequence (ON729293) had 99.83% identity with E. pseudoviburni (LC009904 and MN431595). Based on the phylogenetic analysis of the combined ITS and LSU dataset (Bradshaw et al. 2020), the isolate (GZVD-1) was grouped in a clade with the E. pseudoviburni strains KUS-F27319, KUS-F27310, and MUMH0001. To fulfill Koch's postulates, leaves of three healthy potted V. chinshanense plants were inoculated by gently pressing with diseased leaves. Non-contact plants were used as controls. All plants were incubated in a greenhouse at 25 ± 2°C, 80% relative humidity. Similar powdery mildew symptoms were observed on the inoculated plants 12 days after inoculation, whereas the control plants remained symptomless. The reisolated fungus from the inoculated plants was morphologically identical to that on originally diseased plants. ITS and LSU sequences of the reisolated fungus showed 100% identity with ON729292 and ON729293, respectively. E. pseudoviburni has previously been reported to infect some Viburnum species, including V. sieboldii in Japan (Takamatsu et al. 2015) and V. odoratissimum in South Korea (Bradshaw et al. 2020). To the best of our knowledge, this is the first report of powdery mildew caused by E. pseudoviburni on V. chinshanense in China. This work expands the known host range of E. pseudoviburni in the Viburnum genus.

Effectiveness of Rhodococcus erythropolis strain OPI-01 on the fungal development in winter wheat

Abstract. Behzad A, Diakite S, Astarkhanova TS, Pakina EN, Allen D, Mohammadi PM, Diarra O, Saquee FS. 2024. Effectiveness of Rhodococcus erythropolis strain OPI-01 on the fungal development in winter wheat. Biodiversitas 25: 1063-1070. One of the means of sustainable wheat production is using bacterial pesticides, which can synthesize phytohormonal substances with antibacterial and antifungal action. Therefore, the work aimed to study the effect of different doses of a new growth regulator Restart, ZH (Rhodococcus erythropolis D strain OPI-01) on winter wheat yield. The findings of field experiments on the effect of plant growth regulator R. erythropolis strain OPI-01 method of pre-sowing treatment of seeds (at 0.1 L/t and 0.2 L/t), and soil spraying just before sowing (-0.5 l/ha) revealed that on average, during the 2020-2021 and 2021-2022 seasons, the number of productive stems increased by a margin of 23-30, the number of grains in 1 ear increased in the experimental units by 16.2-19.4%, and the length of the ear by 0.3-0.7cm, gluten varied from 32.3 to 33.8%, yield increased from 27.8-33.0% relative to the control. Disease severity and incidence of powdery mildew, brown rust and Septoria disease in plots amended withR. erythropolis strain OPI-01 was 2-fold less than in the control plots. Research trials show the efficacy of R. erythropolis strain OPI-01 under field conditions as a plant growth regulator and a potential microbial fungicide against some foliar diseases of winter wheat. It would be exciting to study the mechanism of R. erythropolis on wheat pathogens in vitro and in planta which are still less developed in the literature.

Aerial and terrestrial digital images for quantification of powdery mildew severity in Ayocote bean (Phaseolus coccineus)

Objective/Background. Epidemiological research on Phaseolus coccineus is lacking. The aim was to develop and validate digital methods to quantify the severity associated with powdery mildew in ayocote bean. Materials and Methods. An ayocote bean plot with 65.3 % incidence and 22.7 % average powdery mildew foliar severity was selected. Based on 250 leaves collected in field with varying severity degrees, eight 7- and 8-class logarithmic-diagrammatic scales (ELD) were designed and validated in a controlled environment (CEV) and field (FV). In Rstudio®, accuracy (β), precision (R2), reproducibility (r), and agreement level were determined with Cohen’s kappa index (kw) and Lin’s concordance coefficient (LCC). Additionally, a Hierarchical Cluster Analysis (HCA) was performed by scale and assessment environment for clustering by similarity evaluation. In ArcMap® v10.3, in a 15-quadrant block, an ‘image segmentation’ analysis was performed using supervised classification and maximum likelihood to estimate powdery mildew severity and an indicator of canopy coverage index (VCI). Results. In VEC-1, v1r2 (ELD-7c; β=1.07, R2=0.93, r=0.87) and v1r1 (ELD-8c; β=0.97, R2=0.85, r=0.87) scales were best evaluated. In VEC-2, comparing clusters conformed in the HCA, the ELD-7c was the best scored with perfect accuracy (β>0.96), very high precision (R2>0.94), very high reproducibility (r=0.97-0.99) and very high agreement (κw>0.96; LCC>0.97); and in ELD-8c reproducibility and agreement decreased. In VCa, ELD-7c maintained optimal metrics, but ELD-8c reached ideal parameters for preventive ELD in early stages of powdery mildew (β>0.98, R2>0.98, r=0.99, κw=0.99-0.999, LCC=0.98-0.999). Image analysis estimated severity = 8.4 % (CI = 5.3 - 12.6 %) and ICV = 0.88 (CI = 0.76 - 0.99), contrasting with field assessment 47% (CI = 38.8 - 55.3%) and 0.46 (CI = 0.76 - 0.99), respectively, mainly with ICV > 0.94 due to less symptomatic leaf exposure. Suggests applicability for canopy estimation with restrictions for severity based on pathogen expression. Conclusion. A methodology for ELD development is proposed, comprising: image acquisition, processing and quantification; controlled validation and field validation. Validation statistics included precision (R2); accuracy (β); reproducibility (Pearson’s coefficient and Hierarchical Cluster Analysis); and agreement (Lin’s Coefficient and Kappa Index), proposed in a comprehensive approach for first time. RGB-drone images are proposed to estimate a comprehensive vigor and severity coverage index.

First report of Powdery Mildew Caused by Podosphaera xanthii on Siraitia grosvenorii in Guizhou, China.

Swingle (Siraitia grosvenorii), a member of the Cucurbitaceae family, stands out as a distinctive plant with both economic and medicinal significance. In October 2023, severe powdery mildew were observed on S. grosvenorii in Guiyang City (26.50°N; 106.66°E), Guizhou Province, China. About 80 % of the plants in the greenhouse showed powdery mildew symptoms. Three infected plant samples were selected for morphological and molecular analysis (GZAAS 23-0801, GZAAS 23-0802 and GZAAS 23-0803). The voucher specimens are deposited in the Key Laboratory of Agricultural Biotechnology of Guizhou Province. The symptoms initially manifested as irregular to nearly circular, small yellow spots, with distinct depressions as well as surfaces covered in white mycelium. Over time, these spots gradually expanded and merged patches. In the final stages, the entire leaves turned into yellow and withered. Microscopic observations showed that fungal hyphae were septate, branched, and flexuous to straight and 5 to 9 µm wide, and appressoria were indistinct to slightly nipple-shaped. Conidia were hyaline and ellipsoid to oval with fibrosin bodies and measured 31 to 43 × 18 to 24 μm (n = 50) with a length/width ratio of 1.3 to 2.3. Conidiophores were unbranched, straight, 120 to 268 × 14 to 22 µm (n = 30), producing two to five immature conidia in chains. Foot cells of conidiophores were cylindrical, 39 to 84 × 8 to 14 μm (n = 30), followed by one to three short cells. Short cells were cylindrical, 12 to 32 × 8 to 15 μm (n = 50). The morphological characteristics were identical with the previous description of Podosphaera xanthii (Braun and Cook, 2012). Total DNA was extracted from conidia and mycelia by the Chelex method (Walsh et al., 1991). The ribosomal DNA internal transcribed spacer (ITS) and nuclear ribosomal large subunit (LSU) were amplified by using the primers ITS1/ITS4 (White et al., 1990) and LSU1/LSU2 (Scholin et al., 1994), respectively. The ITS (OR825802, OR825803 and OR825804, respectively) and LSU (OR825805, OR825806 and OR825807, respectively) sequences of three isolates, were deposited in GenBank. The BLAST results revealed that both the ITS and LSU region sequence were 100% identical to those of P. xanthii (ITS: MF043939, MG754404 and KJ698669; LSU: OQ061319, AB936277and OP218411). Phylogenetic analyses of ITS and LSU sequences showed that our three isolates were clustered with P. xanthii (KX842351, LC270782 and LC270779) with high statistical support (ML/MP/BI: 100%/97%/1.00). Combined with their morphological characteristics, these three isolates were identified as P. xanthii. Pathogenicity tests were performed by gently brushing conidia onto the leaves of five healthy S. grosvenorii plants. Five non-inoculated plants were used as the control. All plants were maintained in a greenhouse at 25 ± 2°C. One week after inoculation, similar symptoms were observed in the inoculated plants, whereas no symptoms occurred on the control plants. By microscopic observation, the fungus on the inoculated plants was morphologically identical to those on originally diseased plants. Powdery mildew caused by P. xanthii has been reported on Vernonia cinerea (Wu et al., 2023), Vigna unguiculata (Zhang et al., 2023), Cucumis melo (Meesam et al., 2023). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on S. grosvenorii in Guizhou, China. The occurrence of powdery mildew on S. grosvenorii may pose a potential threat to its large-scale cultivation. The pathogen could become a threat to other Cucurbitaceae members in the future.

Epidemiological etiology of Erysiphe sp. and putative viral and phytoplasma-like symptoms in Ayocote bean (Phaseolus coccineus)

Introduction/Objective. Ayocote bean (Phaseolus coccineus) has potential as a source of resistance in breeding programs because it exhibits greater tolerance to plant pathogens than P. vulgaris. However, its sanitary characterization is insipient; therefore, the purpose of this work was to carry out an etiological-epidemiological diagnosis, with emphasis on presumptive symptoms of viral and phytoplasmic organisms, and a typical fungal signs of powdery mildew. Materials and Methods. A plot (50 x 62 m) of flowering Ayocote bean was selected. It was divided into 80 (8 x 10) quadrats (6 x 6 m) and 720 subquadrats (2 x 2 m). From 25 plants with powdery-mildew-type leaf symptoms, mycelium was collected with adhesive tape for light microscopy observation and taxonomic identification. Length-width measurements were made on 60 conidia. Pure mycelium collected in situ and ex situ from 1-5 leaflets/plant was used for genomic analysis by PCR with universal primers ITS1 and ITS4. Samples were sequenced in Macrogen Inc. Korea. A total of 63 plants and 121 trifoliate leaves with viral and phytoplasmic symptoms were collected by direct sampling. In 88/121 samples, genomic analysis was performed by PCR with universal primers for Potyvirus (1), Begomovirus (2), and Phytoplasmas (1). Sequence editing and analysis were performed in SeqAssem and BLASTn/GenBank. Phylogenetic constructions were developed in Mega 11 with MUSCLE, Maximum Likelihood (ML), and HKY substitution model (1000-Bootstrap). Putative powdery mildew severity (%), flower damage (%), Macrodactylus sp. adult density, and plant vigor (%) were evaluated in 80 quadrats (3subquadrats/quadrat) with App-Monitor®v1.1 configured with a 5-class scale. In GoldenSurfer® v10, Kriging geostatistical analysis was performed to determine the spatial interrelationship between these variables. Results. Erysiphe vignae was identified as associated with powdery mildew of P. coccineus. The fungus, with hyaline, ovoid to ellipsoid conidia measuring 31.74 ± 0.3419 μm x 15.11 ± 0.1579 μm, without the presence of fibrosin bodies, had 100% genomic homology. This is the first report in Mexico. With average July-August temperature and relative humidity of 16.3 °C (±5.8) and 92.8 % (±10.7), respectively, powdery mildew leaf incidence and severity were 65.3 and 22.7 % (±16.9, range: 0 - 66.5 %), respectively. The most inductive focus (60-80 % severity) had an aggregate e 4-quadrat pattern (96 m2, lag = 4 and σ2-s = 450). Inoculum dispersal was significantly associated with dominant North-South winds and plant vigor (lag = 4 and σ2-s = 470). Flower damage was inconclusive in its spatial association with powdery mildew and Macrodactylus sp. suggesting uncorrelated events. No Potyvirus, Begomovirus, or Phytoplasmas were detected associated with yellowing, leaf distortion, mosaic, internode shortening, and other symptoms observed in situ. This confirms the relative tolerance/resistance reported for P. coccineus. Conclusion. E. vignae (Erysiphales: Erysiphaceae) associated with P. coccineus is reported for the first time in Mexico with moderate to intense epidemic level, which indicates its susceptible condition to this fungus. However, negative results for Potyvirus, Begomovirus, and Phytoplasmas, validate the apparent tolerance/resistance of P. coccineus to these organisms.

Prevalence and Epidemiology of Apple Powdery Mildew in Northwest Himalayan Region of Himachal Pradesh

A survey was conducted to assess the incidence and severity of powdery mildew of apples during April to July of 2020 and 2021 at the different locations of Kinnaur district, Himachal Pradesh, India. Assessment scale of Hofer et al. (2019) with slight modification was used for cultivar screening. Apple seedlings were grown in the pots in the polyhouse of the Department of Plant Pathology in order to test the pathogenicity of Podosphaera leucotricha. Pathogenicity was confirmed through inoculation tests by gently pressing diseased leaves on young leaves of five asymptomatic, potted one-year-old Gale Gala seedlings of apple. Five non-inoculated plants were used for a control treatment. Overall, twenty different apple cultivars were screened against powdery mildew planted under field conditions at Krishi Vigyan Kendra Sharbo, Kinnaur, Himachal Pradesh, India. Out of these cultivars, five cultivars viz. Red Delicious, Royal Delicious, Red Velox, Auvil Early Fuji and Oregon Spur II, were found to be less susceptible to Podosphaera leucotricha, causing powdery mildew of apples, while Granny Smith, Golden Delicious, and Gale Gala were found extremely susceptible. Gala series of cultivars were found to be extremely susceptible to the pathogen. Incidence of the disease ranged from 25.42% to 53.80% and severity from 39.75% to 66.25%, respectively. According to the present study the disease initiated during the first week of May and peaked in the month of July in district Kinnaur. Temperatures between 18–24°C and RH between 50–65% were found to be favourable for the disease development. The conditions in the region were found to favourable for disease development and spread.

Chemical Control of Powdery Mildew of Bigleaf Hydrangea

The efficacy of the fungicide pydiflumetofen + difenoconazole (Postiva) was evaluated at varying application rates and intervals for the control of powdery mildew (Golovinomyces orontii, formerly Erysiphe polygoni) in bigleaf hydrangea (Hydrangea macrophylla ‘Nikko Blue’). Container-grown hydrangeas were arranged in a completely randomized design with six single-plant replications. Experiments were done in 2022 and 2023 under both greenhouse and shade house conditions (56% shade). Powdery mildew in hydrangea was developed naturally. Pydiflumetofen + difenoconazole at 1.1, 1.6, and 2.2 ml·L−1 and a standard fungicide azoxystrobin + benzovindiflupyr (Mural) at 0.5 g·L−1 were sprayed to runoff on 2-, 4-, and 6-week intervals. Plants that were not treated with fungicide served as the control. Plants were evaluated weekly for disease severity (0% to 100% foliage affected) and defoliation (0% to 100% defoliation). The season-long area under the disease progress curve (AUDPC) and defoliation progress curve (AUDFC) were calculated for the evaluation period. The initial and final plant height and width were recorded, and height and width increase were determined. Pydiflumetofen + difenoconazole and azoxystrobin + benzovindiflupyr significantly reduced final disease severity, AUDPC, and defoliation both in the greenhouse and shade house compared with control plants. In both greenhouse trials and the 2022 shade house trial, AUDFC was reduced in all treatments compared with the control plants. However, AUDFC was not reduced by all treatments in the 2023 shade house trial. Pooled over application intervals, the low rate of pydiflumetofen + difenoconazole was as effective as the medium and high rates of pydiflumetofen + difenoconazole and azoxystrobin + benzovindiflupyr in reducing final powdery mildew severity and AUDPC both in the greenhouse and shade house in both 2022 and 2023. No significant differences between application intervals were noted in final disease severity and progress. Control of powdery mildew with fungicides failed to increase plant dimensions (i.e., plant height and width) compared with the no fungicide control. Because all application rates and intervals of pydiflumetofen + difenoconazole provided comparable powdery mildew disease control, it is suggested that using a low rate of pydiflumetofen + difenoconazole with the longest application interval (6 weeks) is the most cost-effective approach for managing powdery mildew in bigleaf hydrangeas.

First report of powdery mildew caused by Podosphaera fusca on Coreopsis tinctoria in China.

Coreopsis tinctoria is an annual herb and commonly cultivated in gardens due to its attractive flowers, its capitula also have been used as a traditional medicine in China, Asia, North America and Europe (Shen et al. 2021). In June 2023, severe powdery mildew infection was observed on C. tinctoria in a hillside near headwork of the middle route of the South to North Water Diversion Project (32°40'55''N, 111°41'59''E). Abundant irregular white spots were found on adaxial surface of the leaves and tender stems. Approximately 75% of the observed C. tinctoria plants showed these signs and symptoms. Generative hyphae were thin-walled, smooth or almost so, and 5 to 9 μm wide. Conidiophores were unbranched, straight, 80.5 to 162.5 × 9.3 to 12.9 μm (n=25), and produced one to three immature conidia. Foot-cells of conidiophores were cylindrical, 38.5 to 62.3 μm (n=20) long. Conidia were ellipsoid to ovoid, 25.1 to 31.9 × 15.2 to 19.5 μm (n=30). The morphological characteristics of asexual structures corresponded to Podosphaera sp. (Braun and Cook 2012). For further identification, genomic DNA was extracted directly from the mycelia and conidia using Chelex 100 (Sigma Aldrich, Shanghai, China). The internal transcribed spacer (ITS) regions and 28S large subunit (LSU) of ribosomal DNA from the specimen (CT2302) were amplified using the primers ITS1/ITS4 (expected amplicon size 566 bp) (White et al. 1990) and NL1/NL4 (expected amplicon size 618 bp) (Baten et al. 2014), respectively. The sequences of ITS (GenBank accession no. OR649304) and LSU (GenBank accession no. OR649305) showed 99.63% and 100% identity values to the Podosphaera fusca isolate HMNWAFU-CF2012074 in the NCBI database (KR048109 for ITS and KR048178 for LSU), respectively. Phylogenetic analyses based on the combined ITS and LSU sequences using MEGA 7.0 software indicated that CT2302 formed a monophyletic clade together with isolates of P. fusca. Therefore, this fungus was identified as P. fusca based on the morphological and molecular characteristics. Pathogenicity tests were performed by gently pressing the infected leaves onto 15 young leaves of five healthy plants and three noninoculated plants were used as controls. All plants were maintained in a greenhouse (25℃ and 70% relative humidity). Powdery mildew symptoms similar to those of originally diseased plants were observed on all inoculated leaves after 12 days, whereas no symptoms were observed on the control leaves. Powdery mildew caused by P. fusca (previously Sphaerotheca fusca) on C. tinctoria has been reported in Russia, Poland, Korea, Romania and Ukraine (Cho and Shin 2004; Rusanov and Bulgakow 2008). To our knowledge, this is the first report of P. fusca on C. tinctoria in China. The identification of P. fusca as the causal agent on C. tinctoria is critical to the prevention and control of this disease in the future.

Produtos alternativos isolados e associados a fungicida em diferentes épocas de semeadura no controle do oídio da soja

ABSTRACT: Soybean (Glycine max) is the most important legume cultivated in the world. With the aim of studying alternative products isolated and associated with fungicide on the efficiency of controlling powdery mildew (Microsphaera diffusa), in two sowing seasons, field experiments were conducted in Ponta Grossa, PR, Brazil, during the 2016/2017 and 2017/2018 seasons. The treatments were: 1- control (water), 2- Bacillus subtilis lineage QST, 3- Bacillus subtilis lineage QST associated with fungicide, 4- 1% chitosan, 5- 1% chitosan associated with fungicide, 6- sulfur, 7- sulfur associated with fungicide, 8- sodium hypochlorite, 9- sodium hypochlorite associated with fungicide, 10- fungicide (2 applications) and 11- fungicide (3 apllications). In all fungicide treatments, azoxystrobin + benzovindiflupyr with adjuvant was used. The variables evaluated were: powdery mildew severity and yield. The severity data made it possible to calculate the area under the disease progress curve (AUDPC). AUDPC values were higher in the second sowing season. Sulfur, chitosan and B. subtilis, isolated, reduced AUDPC, but when associated with the fungicide they obtained superior results. Sulfur, whether or not associated with the fungicide, provided less severity of the disease. The fungicide applied three times showed better control than two applications. The highest yield averages were, obtained in the first sowing season. There was no difference between the treatments during sowing in October for yield, this was affected by the treatments, only in the second sowing season, highlighting the sulfur associated with the fungicide.