Occurrence Of Downy Mildew Research Articles

Detection of cucumber downy mildew spores based on improved YOLOv5s

Cucumber downy mildew is caused by the infection of leaves with downy mildew spores. However, research on the prevention and control of cucumber downy mildew often focuses on the stage after symptoms have appeared on the leaves, that is, once disease spots have already formed. Since the occurrence of downy mildew is closely related to the quantity of spores, early-stage research on the quantity of downy mildew spores is of great significance for the prevention and control of cucumber downy mildew. Consequently, developing a rapid, accurate, and efficient method for detecting cucumber downy mildew spores is critical for advancing disease control. This study introduces an improved YOLOv5s model for spore detection. The model incorporates a transformer module into YOLOv5s’s backbone, enhancing global feature information extraction. It also adds a small object detection head to counter YOLOv5s’s extensive down-sampling and difficulty in learning features of small objects. Integration with the Convolutional Block Attention Module (CBAM) further refines detection precision for small objects like mildew spores. Upon evaluation with an image dataset collected through a microscope, the improved YOLOv5s model demonstrated superior performance metrics across various resolutions. At a resolution of 1440px × 1440px, it achieved the highest mean Average Precision (mAP@.5) of 95.4 %, a precision (P) score of 89.1 %, and a recall (R) rate of 90.3 %. These metrics surpassed the original YOLOv5s model at the same 1440px × 1440px resolution by 1.6 % in mAP@.5, 1.6 % in P, and 0.5 % in R. Additionally, the model’s mAP@.5 across various resolution scales indicates superior detection precision compared to other leading models like YOLOv7. In the context of microscopic images with small spores and complex backgrounds, the improved YOLOv5s model effectively detects cucumber downy mildew spores, offering valuable insights and technical support for advancing the prevention and control measures against cucumber downy mildew.

Development of an Occurrence Prediction Model for Cucumber Downy Mildew in Solar Greenhouses Based on Long Short-Term Memory Neural Network

The occurrence of cucumber downy mildew in solar greenhouses directly affects the yield and quality of cucumber. Chemical control methods may cause excessive pesticide residues, endanger food quality and safety, pollute the ecological environment, etc. Therefore, it is very important to predict the disease before its occurrence. To provide farmers with better and effective guidance for the prevention and control work, minimize the loss of disease damage, this article took cucumber ‘Lyujingling No. 2′ as the experimental material and acquired greenhouse environmental factors data by wireless sensors, including Temp (Temperature), RH (Relative Humidity), ST (Soil Temperature) and SR (Solar Radiation). LSTM (Long Short-Term Memory) neural network structure was constructed based on Keras deep learning framework to develop a prediction model with time-series environmental factors. Combined with the occurrence of downy mildew from manual investigation and statistics, through debugging the parameters, this article developed an occurrence prediction model for cucumber downy mildew and compared it with KNN (K-Nearest Neighbors Classification) and ANN (Artificial Neural Network). In the prediction model, the forecasted results of the four environmental factors were consistent with the true value distributions, and R2 (R-Squared) were all above 0.95. Among them, the ST variable predicted the best results, e.g., R2 = 0.9982, RMSE (Root Mean Square Error) = 0.08 °C, and MAE (Mean Absolute Error) = 0.05 °C. In the disease occurrence prediction model, the training accuracy was 95.99%, the Loss value was 0.0159, the disease occurrence prediction Accuracy was 90%, Precision was 94%, Recall was 89%, F1-score was 91%, the AUC (Area Under Curve) value was 90.15%, and Kappa coefficient was 0.80. It also had obvious advantages over other different models. In summary, the model had a high classification accuracy and performance, and it can provide a reference for the occurrence prediction of cucumber downy mildew in actual production.

Influence of weather variables on the development of pearl millet downy mildew

The present study was undertaken during 2016 to 2018 to find out the effect of different weather variables on the initiation and development of downy mildew in pearl millet in Punjab. The maximum temperature ranged from 32.8ºC to 36.9ºC and minimum temperature ranged from 17.2ºC to 27.8ºC during the crop season. The correlation analysis showed significant negative correlation of maximum temperature (r = -0.665*), minimum temperature (r = -0.776**), wind speed (r = -0.898**), rainfall (r = -0.625**) and non-significant negative correlation of evening relative humidity (r = -0.523) with downy mildew incidence. The positive correlation with morning relative humidity (r = 0.871**) was significant and sunshine hours (r = 0.321) were non-significant with per cent disease incidence. A multiple regression model was developed using two years (2016 and 2017) data to predict the occurrence of downy mildew with R2 = 0.981, indicating that all weather parameters contributed 98.1 per cent towards disease development. The model was validated with 2018 data which shows that equation can be used in the disease forecasting for taking timely actions for control measures.

Yield and quality of grapes cultivated under plastic coverings with different downy mildew control strategies

AbstractViticulture 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.

Climate change and the occurrence of downy mildew in Brazilian grapevines

Abstract: The objective of this work was to evaluate the potential impact of climate change on the occurrence of grapevine downy mildew in Brazil. Seedlings containing four to six leaves were sprayed with a sporangia suspension containing 105 sporangia per milliliter. After spraying, the seedlings were subjected to temperatures of 26, 28, 29.1, 30.4, and 31.8°C for 24 hours. The percentage of diseased leaf area and the latent period were evaluated. Maps of the geographic and temporal distribution of the disease were made considering the monthly average of the mean air temperature and leaf wetness duration for the reference climate or climate normal (1961-1990) and the future climates (2011-2040, 2041-2070, and 2071-2100), considering the A2 and B1 gas emission scenarios, designed by the Intergovernamental Panel on Climate Change (IPCC). Favorability ranges were set and used in logic functions of the geografical information system (GIS) to generate monthly maps for grapevine downy mildew. Rising temperatures interfered with the grapevine downy mildew infections, reduced the disease severity, and increased the latent period. Future climate scenarios indicate a reduction of favorability of downy mildew in Brazil, with variability in the different grape producing regions.

Produção e características físico-químicas dos cachos da videira 'BRS Clara' sob cobertura plástica e sombrite em safra fora de época

Devido às condições climáticas favoráveis à ocorrência de doenças fúngicas em uvas de mesa, tem-se buscado a adoção de tecnologias que propiciem a redução nos custos de produção, sendo uma alternativa o cultivo de uvas sob cobertura plástica. O objetivo deste trabalho foi avaliar a produção e as características físico-químicas dos cachos da videira 'BRS Clara' enxertada sobre o porta-enxerto IAC-766 'Campinas', em cultivo protegido durante a safra fora de época, visando à redução da aplicação de fungicidas para o controle do míldio. Os experimentos foram realizados em pomares comerciais localizados em Uraí e Marialva-PR. As videiras foram conduzidas no sistema latada, em espaçamento de 4,0 x 4,0 m, em Uraí, e de 2,0 x 5,0 m, em Marialva. O delineamento experimental foi o inteiramente casualizado, com dois sistemas de cultivo protegido (sob cobertura plástica e sob sombrite) e sete repetições. No experimento conduzido em Uraí, não foram verificadas diferenças entre os sistemas de cultivo protegido quanto às características produtivas e químicas das bagas, como o teor de sólidos solúveis totais, índice de maturação e pH. Verificou-se a ocorrência do míldio somente nas folhas, sendo a incidência e a severidade menor nas videiras sob cobertura plástica (0,5 e 0,02%, respectivamente). Em Marialva, também não houve influência das coberturas nas características produtivas das videiras. Entretanto, o teor de sólidos solúveis totais das bagas sob cobertura plástica foi superior em relação àquelas sob sombrite (19,6 e 17,2ºBrix, respectivamente). Não foi detectada a ocorrência de míldio em nenhum dos sistemas de cultivo protegido nessa localidade. Conclui-se que o uso da cobertura plástica permite a redução do número de aplicações de fungicidas para o controle do míldio, sem alterar as características produtivas da uva 'BRS Clara'.

Occurrence of Downy Mildew Caused by Peronospora belbahrii on Sweet Basil in Hungary.

Sweet basil (Ocimum basilicum L.) is an important medicinal and aromatic plant in Hungary that is cultivated over a large area. During field surveys conducted in 2010, significant incidence of downy mildew was observed in two plant stands at Budapest-Soroksár and Tordas. In 2003, the disease occurred in a greenhouse at Albertirsa as well. By the end of September, on full-grown leaves of two sweet basil cultivars, the frequency of disease occurrence and the percentage of infected leaf area reached 80 to 90% and 17 to 20%, respectively, at Budapest-Soroksár. Symptoms appeared mainly on cvs. Genovese and Milita among others. On leaves, large chlorotic lesions with soft margins developed, followed by necrotization from the middle. Chlorosis often involved the entire leaf surface. Necrotic spots were irregular, variable in diameter, and limited by the main veins. A typical grayish white furry growth could be observed mainly on abaxial leaf surfaces both in chlorotic and necrotic regions. Most abundant growth developed on the leaves of cv. Genovese. Premature leaf fall on diseased plants occurred as well. The fungus was identified as Peronospora belbahrii Thines on the basis of morphological investigation suggested by Thines et al. (4). Sporangiophores were colorless with a long, straight trunk and monopodially branched five to seven times with a length of 416 to 784 μm (average 572 μm). Sporangiophores ended with two slightly curved acute branchlets, the longer one measured 12.5 to 25.0 μm (average 17.1 μm) and the shorter one measured 5.0 to 18.8 μm (average 9.5 μm) long. Ratio of longer to shorter branchlets was 0.7 to 3.0, the average ratio was 1.9. Sporangia were rounded or slightly ovoid, olive to dark brown, and measured 29.3 × 25.6 (23.8 to35.0 × 20.0 to 31.3 μm). Length/width ratio was 1.2 (1.0 to 1.4). Molecular investigation of two isolates was performed. DNA extraction from sporangiophores was followed by PCR using ITS5 and ITS4 primers. The obtained sequence (GenBank Accession No. HQ702191) showed 99.8 to 100.0% similarity with sequences of P. belbahrii (e.g., Accession Nos. FJ394335 and HN462241) and Peronospora sp. (e.g., Accession Nos. AY884605, AY919301, and FJ346561) isolated from sweet basil. In Europe, the disease was reported from Italy (2), France (3), Germany (4), and Switzerland (1). To our knowledge, this is the first report of downy mildew on sweet basil in Hungary.

An unnamed Hyaloperonospora sp. causing downy mildew on arugula (rocket) in Korea

Arugula or rocket (Eruca vesicaria ssp. sativa) is a leafy vegetable for salad use worldwide. In March 2009, plants showing typical symptoms of downy mildew were found in plastic greenhouses in Yongin, Korea. Severely affected plantings were unmarketable and had to be abandoned before harvest. Infection resulted in chlorotic leaves with a white fungallike growth developing on the lower surfaces typical of downy mildew. A sample was deposited in the herbarium of Korea University (KUSF24009). Conidiophores were hyaline, 200–600 · 10–17 lm, straight, monopodially branched in 7–9 orders, and emergent from stomata. Ultimate branchlets were mostly in pairs, flexuous to curved, 15–30()40) lm long and had obtuse or subtruncate tips. Conidia were subglobose, hyaline, and measured 20AE0–23AE8 · 17AE5–21AE5 lm (length ⁄ width ratio = 1AE06–1AE15). These characteristics unequivocally indicate the genus Hyaloperonospora. The amplification and sequencing of the ITS rDNA were performed with procedures outlined by Cooke et al. (2000), and the sequence of the region was deposited in GenBank (Accession No. GQ919015). Comparison with the sequences available in the GenBank database revealed that the ITS sequence is identical to sequence EU049271 from Hyaloperonospora sp. on Eruca sativa in Spain, but is significantly different from the sequence AY210987 of H. parasitica on Capsella bursa-pastoris. Based on morphological and molecular data, the arugula ⁄ rocket pathogen is clearly distinct from H. parasitica, to which it was previously attributed in most studies. The Korean accession is identical to the unnamed Hyaloperonospora sp. reported from arugula in Spain (Goker et al., 2009). There is no previous record of a downy mildew on arugula in Korea, although it has been previously recorded from Argentina, Iran, Pakistan, Spain, and the USA (Farr & Rossman, 2009; Goker et al., 2009). The first occurrence of downy mildew on arugula in East Asia was recently recorded in Japan (Sato et al., 2004). It suggests that the pathogen is capable of rapid spread into Asian countries. Since cultivation of arugula was recently started on a commercial scale in Korea, the downy mildew poses a serious threat to production of this leafy crop.

First Occurrence of Downy Mildew on Boxleaf Veronica Caused by Peronospora grisea in Italy.

Boxleaf veronica (Hebe buxifolia (Benth.) Cockayne & Allan), native to New Zealand, is an annual or perennial shrub widely cultivated in Mediterranean zones. During late spring 2003, after seasonably wet and cool weather, a downy mildew epidemic occurred on potted, overhead irrigated, 1-year-old seedlings at a commercial nursery in eastern Sicily (southern Italy). Infections affected boxleaf veronica at first, but spread to variegated boxleaf (H. buxifolia cv. variegata). Initial symptoms on the upper side of leaves were small, gray brown patches that gradually spread, eventually resulting in necrosis in the center of infected areas. At that point, brown patches were evident on both sides of the leaves. Lesions on the lower leaf surface became covered with a fairly dense, pale gray-to-brown layer of conidia and conidiophores. As the disease progressed, these spots coalesced into large and conspicuous brown lesions. The youngest, most succulent shoots withered and died. The large brown lesions on the leaves were disfiguring and affected 95 to 100% of plants in the nursery. All diseased nursery stock had to be discarded. Oospores were not observed in leaf tissues. The fungus recovered from leaves with abundant gray brown sporulation was identified as Peronospora grisea (Unger) Unger. Microscopic observations revealed conidiophores that branched dichotomously five to seven times with branch ends 6 to 10 × 2 to 3 μm, slightly curved, and tapered to a blunt apex. Hyaline conidia were ellipsoid, brownish when mature, and measured 23 to 27 × 15 to 18 μm (mean = 25.2 × 17.1 μm), falling within the range of those reported for P. grisea (1). Pathogenicity was confirmed by inoculating 10 1-yr-old seedlings (10 cm tall) by gently pressing infected leaves with abundant sporulation onto healthy leaves and maintaining inoculated plants in a humid chamber at 21°C. An equal number of noninoculated plants served as controls. After 9 to 11 days, symptoms similar to those originally observed developed onto inoculated plants, and after 12 to 15 days, grayish mildew grew on leaves. Microscopic examination of the developing mycelium confirmed that leaves were infected with P. grisea. Uninoculated control plants did not develop any symptoms. The disease was also confirmed in this way on variegated boxleaf veronica (H. buxifolia cv. variegata). Downy mildew of Hebe spp. has been recorded in New Zealand, Britain, France, Germany, and more recently, West Sussex (2). Heavy rainfall during the spring of 2003 in eastern Sicily could have favored disease development. To our knowledge, this is the first report of downy mildew of boxleaf veronica and variegated boxleaf veronica caused by P. grisea in Italy.

BREMCAST: Development of a system to forecast risk levels of downy mildew on lettuce (Bremia lactucae)

A forecasting system was developed to predict risk levels of downy mildew of lettuce ( Bremia lactucae ). The criteria for the forecasting system were derived from the relationships of weather variables to sporulation, dissemination and infection processes of B. lactucae . In addition the presence of inoculumsource, or the disease, in the field was taken into consideration. User-friendly software (BREMCAST) for use within the Windows (Microsoft Corp.) operating system was developed to calculate sporulation, infection, disease severity and cumulative disease severity values. The system predicted the occurrence of downy mildew on 84 and 80% of the days, under commercial and field plot conditions, respectively. The potential of the system for use as an intelligent decision tool in managing downy mildew is discussed.

Occurrence of Downy Mildew on Sunflower in South Africa.

Downy mildew, caused by Plasmopara halstedii (Farl.) Berl. & De Toni in Sacc., is an economically important disease of sunflower (Helianthus annuus L.) in Europe and the United States (1). The disease was first noticed in South Africa in a commercial field near Standerton and in a seed production field near Kroonstad during the 1993 to 1994 planting season. During the 1995 to 1996 season, downy mildew was found in experimental hybrids near Heilbron, and in commercial fields near Heil-bron, Marikana, and Potchefstroom. At Heilbron, five hybrids were infected with P. halstedii, whereas three others showed symptoms of downy mildew at Potchefstroom and Marikana. All commercially cultivated hybrids have been developed in South Africa. Disease incidence in all the fields was low, with less than 1% of plants affected by the disease. Diseased plants were dwarfed and displayed veinal chlorosis of leaves typically associated with downy mildew of sunflower. White fungal growth commonly occurred on lower leaf surfaces. Sunflower seedlings inoculated with P. halstedii produced symptoms characteristic of downy mildew. The occurrence of the disease in many geographic areas and on various hybrids in South Africa suggests that the fungus is well established. Recent outbreaks can be attributed to the cool, wet, climatic conditions of the 1993 to 1994 and 1995 to 1996 seasons. The susceptibility of local hybrids suggests that downy mildew is a potentially dangerous disease of sunflower in South Africa. Reference: (1) J. F. Miller and T. J. Gulya. Crop Sci. 27:210, 1987.

１９８３年福岡県におけるイネ黄化い縮病の多発生について

１９８３年福岡県におけるイネ黄化い縮病の多発生について