Downy Mildew

During the second two weeks of February 2013, plants of green pack choi var. Cantón with foliar chlorosis and necrosis were detected in Organopónico 23 de Diciembre, Sancti Spíritus province. A characteristic downy mildew growth was evident on the lower surface of infected leaves. With the objective of identified the causal agent of these symptoms, chlorotic leaves were analyzed by blotter test method. Conidiophores and conidia were morphologically characterized. Pathogenicity tests were carried out three times by inoculating leaves healthy plants of green pack choi var. Cantón, with a conidial suspension (1 × 105 conidia/mL). Non-inoculated plants served as controls. In all analyzed and inoculated plants, hyaline conidiophores, 350-520 x 10-20 μm, with final branches usually strongly curved were observed. Conidia hyaline, 23-29 x 20-24 μm (length/width =1.15-1.21) are similar to those described for Hyaloperonospora parasitica. This is the first report of a H. parasitica on green pack choi in Cuba.

ABSTRACT: In the present study, status of downy mildew of cucumber was ascertained in Jammu division of Jammu & Kashmir (India) and the disease incidence and severity was recorded up to 70.29 per cent and 56.01 per cent respectively at 80 days after transplanting. Among the twenty two cucumber germplasm evaluated for resistance to downy mildew, eleven were observed to be moderately susceptible and another eleven susceptible. However, none fell in the category of resistant, moderately resistant or highly susceptible. Among the fungicides tested with varying number of sprays, metalaxyl + mancozeb (five sprays) was most effective and reduced the disease intensity up to 94.23 per cent over control. Plant extract of Allium sativum was most effective causing disease reduction of 49.88 per cent. An extra dose of potash reduced the disease by 30.93 per cent. An integration of these measures can be utilized for developing an integrated disease management module for management of downy mildew...

Downy mildew (Plasmopara halstedii (Farlow) Berlese & de Toni) is widely observed years in sunflower planted areas in Trakya region depending on climatic conditions in some years. Although genetically resistant hybrids to downy mildew have just started to plant recently in Turkey, they have been planting many years in European countries. In the study, to determine the situation of downy mildew in Trakya region, enough leaf samples were collected from mildew infested plants in different areas representing complete region. Consequently, a mixture of all different races was constituted and these leaf samples were dried at shadow at 24-48 hours period, and then they were saved in the refrigerator at -80 ºC. Mildew spore solution from these saved plant samples. This spore solution was infested to experimental materials. In the research, HA-89 and 6626-A female lines were found to sensitive to downy mildew and RHA-419, HA-460, RHA-436, RHA-437 and RHA-340 inbred lines were observed as resistant to the disease. As a result, some resistant lines were observed in the early generations and it was determined that these resistant inbred lines could be used as donor lines in Trakya region in mildew resistance research

Downy mildew (Plasmopara halstedii (Farlow) Berlese & de Toni) is widely observed in sunflower planted areas in Trakya region depending on climatic conditions in some years. Although genetically resistant hybrids to downy mildew have just started to plant recently in Turkey, they have been planting many years in European countries. In the study, to determine the situation of downy mildew in Trakya region, leaf samples were collected from mildew infested plants in different areas representing complete region. Consequently, a mixture of all different races was constituted and these leaf samples were dried at shadow at 24-48 hours period, and then they were stored in the refrigerator at -80 oC. Mildew spore solution from these stored plant samples. This spore solution was infested to experimental materials. In the research, HA-89 and 6626-A female lines were found to be to downy mildew and RHA-419, HA-460, RHA-436, RHA-437 and RHA-340 inbred lines were observed as resistant to the dise...

Cucumber production is threatened by heavy incidence of downy mildew disease during rainy and autumn-winter seasons in the tropics. Identifying and deploying tolerant germplasm are required for cucumber geneticists to develop promising hybrid/variety against this disease. The experiment was undertaken to study different components of genetic variability for 20 growth and yield component traits employing 20 genotypes as well as to screen genotypes against downy mildew disease in Randomized Block Design with three replications. Three genotypes Debstar, Samrat 7 star, and Pusa Barkha showed resistant reactions with less than 10% leaf infection under open field condition. High magnitude of GCV and heritability coupled with high genetic advance as percentage of mean was observed for vine length, intermodal length, nodal position of female flower, number of fruits per plant, average fruit weight, sex ratio, seeds per fruit, 100 seed weight, total sugar content, vitamin C content and perce...

Yellowish lesions with downy, gray growth developed on the leaves of carnations (Dianthus caryo-phyllus) in a greenhouse in Hokkaido Prefecture, Japan, in March 2011. We identified the fungus on diseased plants as Peronospora dianthicola on the basis of the morphologies of the conidia, conidiophores, and oospores. To confirm pathogenicity of the fungus, we inoculated healthy plants with a conidial suspension of the fungus, and the plants developed the same signs and symptoms as the naturally infected plants. We then reidentified P. dianthicola from the diseased lesions. This is the first report of downy mildew of carnation in Japan.

We have compared the antiperonosporal activity of the ceveratrum alkaloids cevadine, veratridine, 3-O-oleoyl veracevine, and their parent alkamine veracevine, as well as the Solanum alkaloids -solanine and its aglycone, solanidine, against various biotrophic and abiotrophic developmental stages of the sunflower downy mildew pathogen, Plasmopara halstedii. The known Na+ ion channel activator ceveratrum alkaloids effectively inhibited the asexual spores and the systemic invasion of the parasitising thallus, while the known cell membrane disruptant Solanum alkaloids also affected the asexual spores and the biotrophic stages but to a lesser extent. The asexual spores responded rapidly to the alkaloids. Inhibition of the motion of zoospores was followed by changes in the semipermeability of plasmalemma leading to cell disruption. These amphiphilic steroid alkaloids are thought to act by direct incorporation into the microbial membrane disrupting its structural and functional integrity. Examination of the effect of veratridine on the alkali metal salt tolerance of P. halstedii showed that this steroid alkaloid dramatically impaired the tolerance of microbes to Li+, Na+, Cs+ and, especially, to K+.
Evaluation of a series of piperidine and related non-steroidal structural analogues, designed by molecular modeling, revealed that the anti-oomycete activity of these synthetic compounds is comparable to that of the natural ceveratrum alkaloids. Our results suggest that plasmalemma is a viable target site for plant disease control agents and extend the structural arsenal of compounds with novel mode of action.

Ujváry I. and Oros G. (2002): Ceveratrum Alkaloids as Fungal membrane Disruptants and Models for New Anti-Oomycota Agents. In: "Modern Fungicides and Antifungal Compounds III"  Eds. Dehne H.W. , Gisi U., Kuck H., Russel P.E. and Lyr H., AgroConcept Gmbh, Bonn, pp.307-316,

Plasmopara viticola (Berk. and M. A. Curtis) Berl. and De Toni, is a serious disease of grapevines in general and King Ruby seedless cultivar in particular, affecting their growth and yield. Magnesium carbonate (MgCO 3) is an untransparent, which induces stomatal closing and enhances plant growth and physiology. In this study, effect of foliar application of MgCO 3 at 1 and 3% on plant resistance, growth, yield and physiology of grapevines (cv. King Ruby seedless) infected with downy mildew was investigated under !eld conditions. The obtained results showed that foliar application of MgCO 3 at 3% led to upregulation of the transcription factor JERF3 (9.6-fold), and the defense-related genes GLU (6.3-fold), POD (8.7-fold), PR1 (9.6fold), and CHI II (8.6-fold). In addition, this treatment led to a reduction in the disease severity (78%), and an increment in the yield per grapevine (20%). Furthermore, biochemical properties of berries, total contents of the photosynthetic pigments, phenolic compounds, and activities of the antioxidant enzymes peroxidase and polyphenol oxidase also enhanced. In contrast, lipid peroxidation, and H 2 O 2 content in grapevines leaves reduced in response to MgCO 3 spraying. Light microscope observations revealed that average number of closed stomata increased and the average stomatal pore area decreased in grapevines leaves as a result to MgCO 3 spraying. Based on these results, we can conclude that spraying with MgCO 3 at 3% has effective roles in inducing the plant resistance against downy mildew, and improving the growth and yield of grapevines.

Abstract Many elicitors (silicon, chitosan, bion or fungicide) were investigated on grapevines grown under natural infestation to evaluate their capacity on inducing defense from downy mildew disease and enhancing growth, yield, berries quality as well as some physiological and anatomical characteristics of Roumy Ahmar grapevines. Foliar application of any elicitors used, in special, silicon was significantly increased yield per vine, cluster weight, 100 berry weight, soluble solids%, total anthocyanin and total phenols while reducing the total acidity% in berries as well as increasing leaf area and potassium percentage in leaves and antioxidant enzyme activities comparing with control. Chitosan application was significantly superior than using other elicitors in increasing shoot length, nitrogen and phosphorous percentage, photosynthetic pigment, ascorbic acid, proline and phenolic compounds in the leaves, and decreased hydrogen peroxide and lipid peroxidation leading to improved membrane permeability. All tested elicitors, in special, Si reduced downy mildew disease severity as compared with untreated control vines. Also, the chloroplast exhibited different degrees of malformation and lysis. The mitochondria were highly vacuolated and the nucleus was misshapen in infested vines. It could be suggested that spraying Roumy Ahmar grapevine with 1000 mg/l silicon four times controlled downy mildew disease in grapevine as well as improving its growth, yield and quality.

In Cuba, sweet basil (Ocimum basilicum) is used fresh, dried and processed for flavouring and fragrances, and as insect repellent in greenhouses. In February 2009 a foliar disease was observed in plots of sweet basil cv. “Genovesa”, located at the Horticulture Research Institute “Liliana Dimitrova” in Quivican, Havana province, and in greenhouses for vegetable production in Siboney, Havana City, Cuba.  Leaves of infected plants were initially slightly chlorotic, especially near the central vein. Within two to three days, a characteristic grey downy growth was evident on the lower surface of infected leaves. Microscopic observations revealed conidiophores 2-7 times dichotomously branched, with length 250 - 500 µm (average 350 µm) and sterigmata bearing a single conidium. Conidia measured 25-35 x 20-28 µm and were elliptical and greyish in mass. No oospores were found. Pathogenicity tests were carried out twice by inoculating leaves of 40-day-old healthy plants of sweet basil and sage with a conidial suspension. Non-inoculated plants served as controls. After six days, typical symptoms of downy mildew developed only in the inoculated plants of sweet basil, and Peronospora-type conidiophores were observed developing on the leaves. The conidiophores and conidia of Peronospora sp. found in sweet basil were similar in shape, color, and size range as the previously unnamed Peronospora sp. reported by Garibaldi et al. (2005) and are not pathogenic to sage. This pathogen had previously been reported in Italy and France. This is the first report of a Peronospora sp. on sweet basil in Cuba.

Quinoa (Chenopodium quinoa) is an important export of the Andean region, and its key disease is quinoa downy mildew, caused by Peronospora variabilis. P. variabilis oospores can be seedborne and rapid methods to detect seedborne P. variabilis have not been developed. In this research, a polymerase chain reaction (PCR)-based detection method was developed to detect seedborne P. variabilis and a sequencing-based method was used to validate the PCR-based method. P. variabilis was detected in 31 of 33 quinoa seed lots using the PCR-based method and in 32 of 33 quinoa seed lots using the sequencing-based method. Thirty-one of the quinoa seed lots tested in this study were sold for human consumption, with seed originating from six different countries. Internal transcribed spacer (ITS) and cytochrome c oxidase subunit 2 (COX2) phylogenies were examined to determine whether geographical differences occurred in P. variabilis populations originating from Ecuador, Bolivia, and the United State...

To evaluate the anti-mildew activity of the commercial essential oils (EOs) against pathotypes ‘771’ and ‘773’ of P. halstedii in mineral salt medium, the EOs obtained from different parts of Greek sage, black cumin, bay, mustard, St. John’s wort, French lavender, garlic, grape, and ginger plants were examined at concentrations of 0.2%, 0.4%, 0.6%, 0.8%, and 1% on leaf discs of susceptible sunflower variety ‘08-TR-003’. The ginger EO had the highest anti-mildew activity at a concentration of 1% and was found to be the most effective with a decrease in sporangium quantity above 90% for pathotypes ‘771’ and ‘773’. The EOs of garlic, St. John’s wort, and grape followed it, respectively, with a decrease in sporangium quantity above 80%.

Downy mildew (Plasmopara halstedii (Farlow) Berlese & de Toni) is widely observed years in sunflower planted areas in Trakya region depending on climatic conditions in some years. Although genetically resistant hybrids to downy mildew have just started to plant recently in Turkey, they have been planting many years in European countries. In the study, to determine the situation of downy mildew in Trakya region, enough leaf samples were collected from mildew infested plants in different areas representing complete region. Consequently, a mixture of all different races was constituted and these leaf samples were dried at shadow at 24-48 hours period, and then they were saved in the refrigerator at -80 ºC. Mildew spore solution from these saved plant samples. This spore solution was infested to experimental materials. In the research, HA-89 and 6626-A female lines were found to sensitive to downy mildew and RHA-419, HA-460, RHA-436, RHA-437 and RHA-340 inbred lines were observed as resistant to the disease. As a result, some resistant lines were observed in the early generations and it was determined that these resistant inbred lines could be used as donor lines in Trakya region in mildew resistance research

Many elicitors (silicon, chitosan, bion or fungicide) were investigated on grapevines grown under natural infestation to evaluate their capacity on inducing defense from downy mildew disease and enhancing growth, yield, berries quality as well as some physiological and anatomical characteristics of Roumy Ahmar grapevines.
Foliar application of any elicitors used, in special, silicon was significantly increased yield per vine, cluster
weight, 100 berry weight, soluble solids%, total anthocyanin and total phenols while reducing the total acidity% in berries as well as increasing leaf area and potassium percentage in leaves and antioxidant enzyme activities comparing with control. Chitosan application was significantly superior than using other elicitors in increasing shoot length, nitrogen and phosphorous percentage, photosynthetic pigment, ascorbic acid, proline and phenolic compounds in the leaves, and decreased hydrogen peroxide and lipid peroxidation leading to improved membrane permeability. All tested elicitors, in special, Si reduced downy mildew disease severity as compared with untreated control vines. Also, the chloroplast exhibited different degrees of malformation and lysis. The mitochondria were highly vacuolated and the nucleus was misshapen in infested vines.
It could be suggested that spraying Roumy Ahmar grapevine with 1000 mg/l silicon four times controlled
downy mildew disease in grapevine as well as improving its growth, yield and quality.

Downy mildew of grapevine, caused by Plasmopara viticola, is a foliar disease of global importance. Control of downy mildew of grapevine (Roumy Ahmar cultivar) using Streptomyces viridosporus, S. violatus, Trichoderma harzianum, T. viride and the commercial yeast of Saccharomyces cerevisiae was investigated. In addition to the disease control, all treatments significantly enhanced the plant growth, nutrient content, total phenol, activities of antioxidant enzymes, yield and fruit quality. Changes in some physiological and anatomical characteristics of the treated plants were also recorded. Compared to the control treatment, the maximum reduction of the disease severity (67.3%) was achieved by S. viridosporus or T. harzianum, while the best growth and yield parameters were recorded for S. violatus. Treatment of S. viridosporus showed the highest total phenol content (66.3%) as well as the highest activity of the antioxidant enzyme peroxidase (45.8%), over the control. S. violatus increased the contents of nitrogen (10.2%), phosphorus (37.2%), potassium (7.3%), and total soluble sugars (26.5%) in grapevine leaves over the control. Moreover, all treatments led to an improvement of the leaf anatomical features. In this regard, the treatment of S. violatus led to the increment of the thickness of mid-vein (47.1%) and lamina (56.8%) of the grapevine leaf blade over the control. Based on their efficiency and eco-safety, we recommend the use of S. viridosporus or T. harzianum for control of the downy mildew disease of grapevine, as well as to improve its growth, yield, and fruit quality.