Powdery Mildew Severity Research Articles

Characterization of Cucumber (cucumis sativus) genotypes through principle component and regression analyses

Thirty diverse genotypes of cucumber (Cucumis sativus L.) collected from different indigenous sources were characterized with respect to economically important traits by using principal component and regression analyses during kharif 2009-10. The effect and contribution of each character on fruit yield per plot was measured. Principal component analysis characterized the genotypes into four principal components based on their total variation (83.72%). The first principal component accounted for more than 48% of the total variation and was the combination of number of marketable fruits per plant, fruit length, harvest duration, total soluble solids, seed germination, seed vigour index-I and II and yield per plot. The second, third and fourth principle components contributed only 15.27%, 13.50% and 6.72% of total variations, respectively. To quantify the importance of each variable in predicting average fruit weight and yield per plot, multiple linear regression models were developed. Model-I indicated that average fruit weight can be predicted satisfactorily on the basis of number of marketable fruits per plant, fruit length and breadth, while, Model-II indicated that yield per plot can be best predicted by with the help of number of marketable fruits per plant, fruit length, average fruit weight, harvest duration, seed germination, seed vigour index-II and severity of powdery mildew and anthracnose. Therefore, on the basis of information on genetic diversity through principal component and regression analyses, suitable selection strategy can be formulated for getting higher yield in cucumber.

Efficacy of fungicides and organic oils to control powdery mildew disease of jujube (Ziziphus mauritiana Lam.)

Powdery mildew (Oidium erysiphoides f.sp. ziziphi) is the major disease of Indian jujube (Ziziphus mauritiana) in Bangladesh. An experiment was conducted to test the efficacy of six fungicides, two organic oils, and a detergent against the disease. Tested fungicides were Tilt (Propiconazole) @ 0.05%, Folicur (Hexaconazole) @ 0.1%, Bavistin DF (Carbandazim) @ 0.2%, Dithane M-45 (Mancozeb) @ 0.3%, Thiovit 80 WG (Sulpher) @ 0.3%, and Cupravit (Copper) @ 0.3%, the oils were Mustard oil @ 0.5% and Neem oil 0.5%, and the Detergent (Trix) @ 0.5%. The materials were applied as foliar spray for seven times at an interval of 15 days. All of the fungicides and two oils gave significant decrease in severity of powdery mildew and increased fruit yield of Indian jujube irrespective of varieties, locations and over times. Among the treatments, Folicur, Tilt, Thiovit, and Dithane M-45 sprays were found effective than others. The severity index values on two jujube varieties were 3.89-4.50 at Mowna and 4.00-4.53 at Ishurdi in control treatment. The severity indices were reduced to 1.45-1.96 at Mowna and 1.33-2.07 at Ishurdi due to application of Tilt, Folicur, Thiovit, and Dithane M-45, which gave increase in fruit yield over control by 68.88, 63.69, 63.04, and 54.63% in Apple Kul and 83.25, 77.87, 77.39, and 70.36% in BAU Kul, respectively. Most of the treatments were able to reduce number of spotted fruits. The best effective fungicide was found to be Tilt followed by Folicur and Thiovit in reducing disease severity of powdery mildew as well as other fruit diseases like fruit spot and fruit rot and increase fruit yield of Indian jujube. Therefore, Tilt/Folicur may be recommended for jujube growers to control the powdery mildew disease in commercial orchard. DOI: http://dx.doi.org/10.3329/bjar.v38i4.19032 Bangladesh J. Agril. Res. 38(4): 659-672, December 2013

New Optimized Spectral Indices for Identifying and Monitoring Winter Wheat Diseases

The vegetation indices from hyperspectral data have been shown to be effective for indirect monitoring of plant diseases. However, a limitation of these indices is that they cannot distinguish different diseases on crops. We aimed to develop new spectral indices (NSIs) that would be useful for identifying different diseases on crops. Three different pests (powdery mildew, yellow rust, and aphids) in winter wheat were used in this study. The new optimized spectral indices were derived from a weighted combination of a single band and a normalized wavelength difference of two bands. The most and least relevant wavelengths for different diseases were first extracted from leaf spectral data using the RELIEF-F algorithm. Reflectance of a single band extracted from the most relevant wavelengths and the normalized wavelength difference from all possible combinations of the most and least relevant wavelengths were used to form the optimized spectral indices. The classification accuracies of these new indices for healthy leaves and leaves infected with powdery mildew, yellow rust, and aphids were 86.5%, 85.2%, 91.6%, and 93.5%, respectively. We also applied these NSIs for nonimaging canopy data of winter wheat, and the classification results of different diseases were promising. For the leaf scale, the powdery mildew-index (PMI) correlated well with the disease index (DI), supporting the use of the PMI to invert the severity of powdery mildew. For the canopy scale, the detection of the severity of yellow rust using the yellow rust-index (YRI) showed a high coefficient of determination ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\mbi{R}}^{\bf 2 =} {\bf 0.86}$</tex> </formula> ) between the estimated DI and its observations, suggesting that the NSIs may improve disease detection in precision agriculture application.

Sawadaea tulasnei Powdery Mildew of Norway Maple (Acer platanoides) in Oregon.

In August 2012, Norway maple 'Crimson Century' trees affected by powdery mildew were observed in Portland, OR. A majority of leaves throughout the crowns on each of the five trees planted in the street terrace on one side of a single city block were affected. White mycelium was present in irregular, discrete, scattered spots or almost continuously on the upper surfaces of leaves and also was present on some petioles. The affected area of the upper surface of leaf blades was estimated to typically be >50%. Chasmothecia were present singly or in groups on the mycelium, and bore simple and bifid appendages (originating from the upper half of the chasmothecia) including some with uncinate or circinate apices that allowed tentative identification to the genus Sawadaea (1). Mean diameter of the chasmothecia was 160 (standard error [SE] = 3.9) μm, and mean appendage length was 72 (SE = 4.9) μm. Asci averaged 77 (SE = 1.2) × 52 (SE = 1.2) μm and ascospores averaged 24 (SE = 0.4) × 12 (SE = 0.3) μm. Braun (1) reported ranges in dimensions of these features as: chasmothecia, (min. 125) 140 to 190 μm; appendages, 40 to 80 μm; asci, 60 to 80 (max. 100) × (min. 30) 35 to 50 (max. 55) μm; and ascospores 15 to 25 (max. 30) × 10 to 15 μm. Nuclear rDNA sequence data was obtained for ITS1, 5.8S, and ITS2 regions using primers PMITS1 and PMITS2. A BLASTn search revealed that the data (430 bp) obtained (GenBank Accession No. KF258718) exactly matched respective sequences of Sawadaea tulasnei (AB193363, AB193385, AB193390, AB193391, and EU247884), and differed from respective sequence data for S. bicornis (AB193380) by 22 nucleotides. S. tulasnei is a European species previously found on maples including Acer platanoides. However, this pathogen has been reported only rarely in North America in the states of New York, Ohio, and Wisconsin, and the province of Quebec (2,3,4). Although not likely to seriously affect the growth or survival of established trees, severe powdery mildew can detract from the aesthetic value of trees. Further, S. tulasnei might seriously damage small seedlings, and detection of this exotic pathogen in nurseries should restrict movement of stock. To our knowledge, this is the first report of S. tulasnei in western North America, and it indicates the distribution of this pathogen is transcontinental. Specimens have been deposited in the U.S. National Fungus Collections (BPI 892675). References (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena-Stuttgart-New York, 1995. (2) S. Hirose, et al. Mycol. Res. 109:912, 2005. (3) B. Hudelson, et al. Plant Dis. 92:485, 2008. (4) J. Weiland and G. Stanosz. Plant Dis. 90:830, 2006.

Lr67/Yr46 confers adult plant resistance to stem rust and powdery mildew in wheat

We demonstrate that Lr67/Yr46 has pleiotropic effect on stem rust and powdery mildew resistance and is associated with leaf tip necrosis. Genes are designated as Sr55, Pm46 and Ltn3 , respectively. Wheat (Triticum aestivum) accession RL6077, known to carry the pleiotropic slow rusting leaf and yellow rust resistance genes Lr67/Yr46 in Thatcher background, displayed significantly lower stem rust (P. graminis tritici; Pgt) and powdery mildew (Blumeria graminis tritici; Bgt) severities in Kenya and in Norway, respectively, compared to its recurrent parent Thatcher. We investigated the resistance of RL6077 to stem rust and powdery mildew using Avocet × RL6077 F6 recombinant inbred lines (RILs) derived from two photoperiod-insensitive F3 families segregating for Lr67/Yr46. Greenhouse seedling tests were conducted with Mexican Pgt race RTR. Field evaluations were conducted under artificially initiated stem rust epidemics with Pgt races RTR and TTKST (Ug99 + Sr24) at Ciudad Obregon (Mexico) and Njoro (Kenya) during 2010-2011; and under natural powdery mildew epiphytotic in Norway at Ås and Hamar during 2011 and 2012. In Mexico, a mean reduction of 41 % on stem rust severity was obtained for RILs carrying Lr67/Yr46, compared to RILs that lacked the gene, whereas in Kenya the difference was smaller (16 %) but significant. In Norway, leaf tip necrosis was associated with Lr67/Yr46 and RILs carrying Lr67/Yr46 showed a 20 % reduction in mean powdery mildew severity at both sites across the 2 years of evaluation. Our study demonstrates that Lr67/Yr46 confers partial resistance to stem rust and powdery mildew and is associated with leaf tip necrosis. The corresponding pleiotropic, or tightly linked, genes, designated as Sr55, Pm46, and Ltn3, can be utilized to provide broad-spectrum durable disease resistance in wheat.

Multiple disease resistance in greengram and blackgram germplasm and management through chemicals under rain-fed conditions

Field screening conducted during Kharif , 2008 and 2009 revealed that out of 31 genotypes of greengram, only 1 genotype ML 1299 and out of 14 genotypes of blackgram, only 3 genotypes viz, BS 2-3, IPU 02-43 and B 3-8-8 showed resistant or highly resistant response against multiple diseases including Cercospora leaf spot, web blight and powdery mildew. In another trial conducted for management of foliar diseases of greengram and blackgram through chemical revealed that two foliar sprays of propiconazole @ 0.1% at an interval of 8-10 days was most effective as it reduced severity of Cercospra leaf spot (85.77 and 80.10 %), web blight (77.87 and 85.29 %) and powdery mildew (100.00 % each) with average yield of 9.08 and 8.83q/ha of greengram and blackgram, respectively.

Controlling of Mango Powdery Mildew by some Salts, Growth Regulators and the Biofungicide AQ10 Compared with Punch Fungicide in Egypt

Two experiments on 10 years old mango trees, Saddeka cv. (high susceptible cultivar) were conducted under field condition during 2012 and 2013 growing seasons for management of powdery mildew at El Adleia district, Belbees county, El-Sharkia governorate. In these trials, mango trees were sprayed with two potassium phosphate salts , calcium chloride ,three commercial growth regulators ,i.e. Agrotone (NAA), Cultar (paclobutrazol) , and Berelex (GA3), the bio-fungicide AQ10 (Ampelomyces quisqualis) , the commercial systemic fungicide Punch (flusilazole) and an alternate among Cultar ( paclobutrazol ), monobasic phosphate and the fungicide Punch. The aforementioned treatments were applied at 14 days intervals during both growing seasons starting at bud flower burst stage till full bloom stage in order to evaluate their efficiency on management mango powdery mildew disease. The obtained results showed that spraying of mango trees ( Saddeka cv.) during 2012 and 2013 growing seasons with any of the tested treatments significantly reduced the severity of powdery mildew with significant increase to the produced fruit yield compared with control treatment.In addition, results of both seasons revealed that alternation spray among Cultar ( paclobutrazol ), mono basic potassium phosphate and the fungicide Punch was the most superior treatment in reducing severity of the disease and producing the highest fruit yield followed by spraying of the fungicide Punch then spraying of mono basic potassium phosphate . Meanwhile, Brelex was of the lowest efficiency treatment in this regard followed by spraying of Agrotone . The other treatments recorded intermediate figures. Control treatment recorded 44.3 % disease severity and produced poor fruit yield.

Effect of Combination between Bioagents and Antioxidants on Management of Tomato Powdery Mildew

Isolation of microorganisms occurring on the phyllopane of tomato leaves yielded many Basillus and Trichoderma strains. The isolated Bacillus spp. were purified and identified as B. chitinosporus, B. megaterium, B. pumilus, B. subtilis and B. thuringiensis and the isolated Trichoderma spp. were, T. album, T. hamatum, T. koningii, T. harzianum and T.veredi. All the tested Bacillus and Trichoderma strains caused significant inhibition to the germinated conidia of Leveillula taurica (imperfect stage = Oidiopsis taurica) the causal of tomato powdery mildew compared with control treatment. In addition, B. thuringiensis B. subtilis and B. chitinosporus were the most efficient bacteria in this regard and T. harzianum and T. veredi were the most efficient fungi. The inducer resistance chemicals (IRCs) bion, chitosan, humic acid, salicylic acid and zinc sulphate resulted in significant reduction to the germinated conidia of the causal fungus compared with control treatment. This reduction was gradually increased by increasing the tested concentration. In plastic house experiments, spraying tomato plants with the tested bioagents B. thuringiensis and T. harzianum and the IRC salicylic acid resulted in significant reduction to powdery mildew severity during 2012/2013 and 2013/ 2014 growing seasons. Spraying of the bioagents B.thuringiensis and T. harzianum and the IRC salicylic acid, each alone or in different combinations, resulted in significant reduction to the severity of the disease with significant increase to the produced fruit yield. Furthermore, spraying any of these compounds alone was of less effect in this regard compared with spraying their combinations. However, the fungicide Sumi-8 was the superior in this regard, being 3.7 % disease severity and fruit yield 16.2 k g. / plant followed by the mixture of the three treatments, being 4.6% disease severity and fruit yield 13.7 kg. / plant. The three oxidative-reductive enzymes, i.e. PAL, PO and PPO were greatly increased in the leaves of all sprayed treatments compared with control treatment. In addition, plants sprayed with salicylic acid recorded the highest activity of the three enzymes followed by that sprayed with B. thuringiensis then T. harzianum. Meanwhile, untreated leaves (control) recorded the lowest activity followed by that sprayed with Sumi-8.

Herança da resistência do mamoeiro a doenças fúngicas com base em análise dialélica de Hayman

Neste trabalho foram estimados parâmetros genéticos e estudou-se a herança da resistência do mamoeiro às doenças pinta-preta, oídio e mancha-de-phoma, em cruzamentos dialélicos no campo. Avaliaram-se 56 combinações (F1s e recíprocos) e oito genitores, quatro do grupo Formosa (Maradol, JS12-N, JS12-4 e Sekati) e quatro do grupo Solo (Waimanalo, Golden, Sunrise Solo 72-12 e São Mateus). Quantificaram-se a severidade de pinta-preta em folha e em fruto, e a severidade de oídio e mancha-de-phoma em folha. Efetuou-se análise de variância conjunta dos dados, considerando-se, além dos cruzamentos, a época de avaliação como fontes de variação. A severidade de pinta-preta em folha e em fruto e a severidade de oídio em folha tiveram ausência de significância nos três testes de suficiência do modelo aditivo-dominante. Observou-se a existência de pelo menos quatro genes ou blocos gênicos com dominância para severidade de oídio e ao menos um para severidade de pinta-preta em folha e fruto. Para severidade de oídio, os efeitos gênicos aditivos foram mais importantes. Efeitos gênicos aditivos e não aditivos, por sua vez, foram igualmente importantes tanto para severidade de pinta-preta em folha, quanto para severidade em fruto. Constatou-se efeito de dominância parcial para severidade de oídio e dominância completa para severidade de pinta-preta em folha e em fruto. Sekati foi o genitor que apresentou a maior concentração de alelos favoráveis para a redução da severidade de pinta-preta e de oídio.

Response of mulberry accessions to major foliar diseases in temperate conditions of Jammu and Kashmir, India

Thirty-three indigenous and 24 exotic mulberry accessions belonging to five Morus spp. originated from seven countries distributed in temperate and tropical climates were observed for their response to two major foliar diseases during 2010 and 2011 under temperate conditions of Jammu and Kashmir, India. Leaf spot and powdery mildew severity (Percent Disease Index (PDI)) ranged from 0.00 to 74.90% and 0.00 to 59.85%, respectively. Indigenous and exotic accessions responded similarly to leaf spot, but varied too much to powdery mildew. Irrespective of origin, response in ascending order of PDI for leaf spot is M. multicaulis, M. indica, M. alba, M. kayayama and M. bombycis and for powdery mildew is M. multicaulis, M. kayayama, M. bombycis M. alba and M. indica. Among indigenous accessions, Brentul Kashmir offered highest resistance to both the diseases. Nadigam offered maximum resistance only to leaf spot followed by Himachal local; while Chinarpati followed by Mysore local only for powdery mildew. Among exotic accessions, Ichinose offered maximum resistance to both the diseases followed by Kokusou-21 and Tagowase.

Essential oils and whole milk in the control of soybean powdery mildew

This research aimed to evaluate the potential of essential oils (EOs) and cow's whole milk (CWM) in order to control soybean powdery mildew and to estimate the most effective concentrations of these natural products in reducing the disease severity on soybean plants. Three experiments were carried out: The first experiment evaluated and selected the most effective treatments to reduce the severity of soybean powdery mildew under greenhouse conditions; the second experiment evaluated the effect of CWM and EOs of citronella, lemongrass, eucalyptus, cinnamon and tea tree on the pathogen through the ultrastructure analysis of soybean leaflets infected by Erysiphe diffusa using the scanning electron microscope (SEM) and light microscope (LM) technology. In the third experiment, the most effective products were tested at several concentrations in order to define the most effective concentrations to reduce disease severity under greenhouse conditions. The treatments CWM (100mL L-1) and EOs of citronella, lemongrass and eucalyptus (1.0mL L-1), reduced the disease severity from 67 to 74%. Direct effects from all natural products tested on the structures of E. diffusa were demonstrated through the SEM and LM analysis. Concentrations at 1.5mL L-1 for EOs of citronella, lemongrass and eucalyptus and also at 180mL L-1 for the treatment CWM were the most effective against E. diffusa on soybean.

CONTROL OF CHAMOMILE POWDERY MILDEW DISEASE USING POTASSIEN, CITRIEN AND CHITOSAN

The effect of three resistance inducers, i.e. chitosan, citrien and potassien were studied under both greenhouse (2009/2010) and field condition in 2010/2011 and 2011/2012 growing seasons to control powdery mildew disease caused by Sphearotheca fuliginea in chamomile (Matricaria chamomilla).Results showed that all used inducers had decreased disease severity compared to non-treated control. In this respect, chitosan showed the highest effect on decreasing disease severity followed by citrien. Meanwhile, potassien gave the lowest effect. The decrease in disease severity of powdery mildew was positively expressed by an increase in crop parameters, i.e numbers, inflorescences weights, fresh, dry weights of plants and the principal components of chamomile essential oil.

Application of Geographic Information Systems to Identify the Oversummering Regions of Blumeria graminis f. sp. tritici in China.

Blumeria graminis f. sp. tritici, the pathogen that causes wheat powdery mildew, can oversummer as mycelia or conidia on leaves of volunteer wheat plants in cool mountainous areas in China. In this study, the regions in China where B. graminis f. sp. tritici can oversummer were identified on the basis of the probability that temperature remains below a critical temperature that is lethal to B. graminis f. sp. tritici. Two methods, one describing the relationship between the average temperature (20 to 26°C) in a given continuous 10-day period and wheat powdery mildew severity, the other describing the relationship between the average temperature (26 to 33°C) and the number of lethal days on powdery mildew development, were used to calculate the oversummering probability using weather data for 743 sites across China. Spatial interpolation based on the ordinary kriging method was conducted for the regions without observation. Oversummering probability values were similar for most locations estimated between the two methods. The B. graminis f. sp. tritici oversummering regions in China were identified to be in mountainous or high-elevation areas, including most regions of Yunnan, west and central areas of Guizhou, south and northwest Sichuan, south and east Gansu, south Ningxia, north and west Shaanxi, central-north Shanxi, west Henan and Hubei, and some regions in Qinghai, Tibet, and Xinjiang. When the oversummering sites from this study were compared with observed survey data for some of these sites, about 90% of sites where B. graminis f. sp. tritici oversummering was observed had been found suitable by both methods. The coincidence frequency and the area under the receiver operating characteristic curve for model 2 were higher, albeit only slightly, than those for model 1. Thus, both methods may be used to assist in disease management and further investigation on pathogen oversummering.

Non-chemical agents provide tenable, eco-friendly alternatives for the management of the major diseases devastating Indian mustard (Brassica juncea) in India

India is a leading producer of oilseed Brassicas, contributing approximately 23 percent of the country's total oilseed production. In India, the Indian mustard [Brassica juncea (L.) Czern. & Coss.] crop is ravaged by various diseases, including Alternaria blight, white rust, downy mildew, Sclerotinia rot and powdery mildew, which can contribute to fluctuations in crop yields. A field experiment examining an integrated disease management system for Indian mustard (B. juncea) was conducted under the All India Coordinated Research Project on Rapeseed-Mustard (Indian Council of Agricultural Research or ICAR) during three crop seasons (2006–09) at 11 locations to assess treatments suitable for the management of crop disease. The data from the different locations and years regarding disease severity and incidence were pooled and analyzed. Seed treatments with freshly prepared Allium sativum bulb aqueous extract (1 percent w/v) resulted in significantly higher initial plant stands, across locations and years. Seed treatment with A. sativum bulb extract, followed by its use as a foliar spray, resulted in significantly reduced Alternaria leaf and pod blight severity, reduced white rust severity, fewer stag heads per plot, reduced downy mildew and Sclerotinia rot incidence, and reduced powdery mildew severity, across locations and years. The combination also provided significantly higher seed yields compared with the control across locations and years and was at par with treatment by chemical fungicides. The combination used in the present study was as effective as the combination of seed treatment with Trichoderma harzianum and foliar spraying with Pseudomonas fluorescens and T. harzianum. Economic returns were higher when using biorational treatments (A. sativum bulb extract, T. harzianum, P. fluorescens) compared with chemical fungicides. The combination of seed treatments with T. harzianum followed by its use as a foliar spray (17.22), and the similar combination of seed treatments and foliar spraying with the A. sativum bulb extract (17.18), resulted in a higher benefit to cost ratio. This eco-friendly technology can help oilseed Brassica growers in India safeguard the crops from major diseases and increase the stability and productivity of the Indian mustard crop.

The effect of quinone outside inhibitor fungicides on powdery mildew in a grape vineyard in Hungary

Powdery mildew, caused by Erysiphe necator Schwein., is one of the most important diseases of grapes worldwide. In the present study, nine treatments consisting of chemical compounds and combinations of these compounds were tested against powdery mildew on Vitis vinifera cv. Merlot CI 181 and cv. Italian Riesling GK1. The aim of this study was to examine the effect of quinone outside inhibitor (QoI) fungicides, also called strobilurins, on powdery mildew and to see if resistant strains of the fungus were present. QoI inhibitors had never been used before in the vineyard or a nearby vineyard. Powdery mildew infection severity was monitored in the experimental vineyard in Cserszegtomaj, Hungary. At the same time, weather conditions and their effect on powdery mildew infection levels were monitored. No differences were found between the cultivars Merlot CI 181 and Italian Riesling GK1 in powdery mildew severity. However, there were differences in powdery mildew severity depending on the chemical compound and combination of compounds tested. The QoI fungicides provided little or no control of powdery mildew infection, and powdery mildew severity was not significantly different from that in the untreated vines. This suggests that the population of powdery mildew in this experimental vineyard was resistant to QoI fungicides. In the other treatments the level of powdery mildew infection was either significantly lower than in the untreated vines or there was no infection at all. These results show that the use of QoI fungicides selected for QoI resistance in the powdery mildew population. These results provide a warning that, QoI-resistant powdery mildew strains are likely to be a problem in Hungary in the future.

First Report of Powdery Mildew of Snow Lotus (Saussurea involucrata) Caused by Leveillula taurica in China.

Snow lotus (Saussurea involucrata Kar. et Kir.) is a rare and beneficial traditional Chinese medicinal herb, growing in the mountains at heights of 4,000 to 4,300 m in the Tianshan and A'er Tai areas in China (2). Because of its very slow growth and exhaustive plant collection, the wild population has been listed as a protected plant by the Chinese government. In recent years, it has succeeded in artificial cultivation. Since 2010, severe powdery mildew infections were repeatedly observed on leaves of the plant of artificial cultivation in Urumqi, Xinjiang Autonomous Region of China. White superficial mycelia were present epiphyllously on both sides of the leaves as well as on young stems, forming a thin, irregular covering. Infections often cause leaf yellowing, reduced growth, and premature defoliation. On the basis of microscopic examination, the morphology of the fungus can be described as follows: Conidiophores emerged through leaf stomata, singly or branched, and form dimorphic conidia. Primary conidia are lanceolate with distinct apical points and 44 to 63 × 12 to 22 μm. Secondary conidia are ellipsoid to cylindrical and 41 to 59 × 12 to 20 μm. The germ tube has indistinct appressoria, is longer than conidia length, and arises from the subterminal region of conidia. These morphological features are typical of the anamorphic stage description of Leveillula taurica (Lév.) Arnaud (1). No ascomata were observed. Representative voucher specimens were deposited in the fungal herbarium of Xinjiang Agriculture University (HMACC 40731). To verify the identity of the fungus, the internal transcribed spacer (ITS) rDNA was amplified and sequenced, and the sequences were deposited as GenBank Accession No. KC292212. Comparison with sequences in the GenBank database revealed that the ITS sequence showed 99% homology with the sequence of L. taurica on Helianthus sp. (AB044378) and Gundelia tournefortii (AB667874). Thus, the pathogen was identified as L. taurica on the basis of the morphological characters and the ITS sequence. Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of healthy potted plants. Three inoculated plants were kept under a plastic humid chamber, whereas the same number of non-inoculated plants served as the control. The plants were placed under natural conditions (25 to 28°C) with 80 to 90% humidity. At 5 days after inoculation, typical symptoms of powdery mildew developed on the inoculated plants. No symptoms were seen on the control plants. To our knowledge, this is the first record of L. taurica on S. involucrata in the world. Because the plant is becoming widely cultivated in the Urumqi for use as a Chinese medicinal herb, the occurrence of powdery mildew poses a potential threat to the health of snow lotus.

Response of mulberry accessions to major foliar diseases in temperate conditions of Jammu and Kashmir, India

Thirty-three indigenous and 24 exotic mulberry accessions belonging to five Morus spp. originated from seven countries distributed in temperate and tropical climates were observed for their response to two major foliar diseases during 2010 and 2011 under temperate conditions of Jammu and Kashmir, India. Leaf spot and powdery mildew severity (per cent disease index (PDI)) ranged from 0.00 to 74.90% and 0.00 to 59.85%, respectively. Indigenous and exotic accessions responded similarly to leaf spot but, varied too much to powdery mildew. Irrespective of origin, response in ascending order of PDI for leaf spot is M. multicaulis, M. indica, M. alba, M. kayayama and M. bombycis and for powdery mildew is M. multicaulis, M. kayayama, M. bombycis, M. alba and M. indica. Among indigenous accessions, Brentul Kashmir offered highest resistance to both the diseases. Nadigam offered maximum resistance only to leaf spot followed by Himachal local, while Chinarpati followed by Mysore local only for powdery mildew. Among ...

Characters of compost teas from different sources and their suppressive effect on fungal phytopathogens

Compost teas (CT) are fermented watery extracts of composted materials that are used to control plant diseases and on crop fertilization. In this work, aerated (ACT) and non-aerated compost teas (NCT) were obtained from four different composts: spent mushroom substrate compost, grape marc compost, greenhouse horticultural crop residues compost, and vermicompost. Physico-chemical and microbiological analysis were carried out to determine their properties. In vitro assays were performed to assess their suppressive effect on the mycelial growth of eight fungal phytopathogens. In vivo trials aimed to assess their effect on gummy stem blight (Didymella bryonae) and powdery mildew (Podosphaera fusca) in melon plants. Results showed that ACT and NCT filtrates inhibited the in vitro growth of all tested pathogens while autoclaved CT did not completely lose their inhibitory effect, and CT sterilized by microfiltration had no effect on the pathogen growth. The severity of powdery mildew was highly reduced by ACT and NCT from all sources, though in gummy stem blight assay only a delay in disease development was observed. In general, all compost teas showed a high level of microbial populations and nutrients. Results suggest that the efficacy of ACT and NCT firstly depend on the microbiota present in them. We consider compost teas from the four tested sources as a viable way to manage plant diseases and crop fertilization, throughout its integration in pest management programs and fertirrigation systems under different dilution rates.

Analysis of Incidence-Severity Relationships for Strawberry Powdery Mildew as Influenced by Cultivar, Cultivar Type, and Production Systems.

The relationships between strawberry powdery mildew incidence (I) and severity (S) were investigated for various cultivars, for June-bearing and day-neutral cultivars, and for production systems (open-field and plastic-tunnel) with the objective of deriving a simple relationship for predicting severity (proportion of leaf area diseased [PLAD]) from incidence (proportion of diseased leaves). Data were collected from 2006 to 2011 at 11 commercial and experimental sites, for a total of 2,326 observations (n). For the cultivars grown in open fields, higher severity was observed on 'Seascape', with mean PLAD of 0.299 (n = 427); followed by 'Chambly', with 0.133 (n = 334); 'Cavendish', with 0.115 (n = 250); 'Darselect', with 0.111 (n = 321); and 'Jewel', with 0.105 (n = 276). In general, mean severity was higher when the strawberry plants were grown in plastic tunnels, with PLAD of 0.204, 0.199, and 0.181 for Chambly (n = 204), Darselect (n = 261), and Jewel (n = 253), respectively. A linear model based on complementary log-log transformation of I and S provided a good fit of the data (coefficient of determination [R2] adjusted for degrees of freedom from 0.82 to 0.96). A covariance analysis indicated that the sampling year and site of sampling did not significantly influence the estimated slope of the I-S relationship, nor did the specific cultivar among the June-bearing ones, whereas the production system (open-field versus plastic-tunnel) and the cultivar type (June-bearing versus day-neutral) significantly influenced the estimated slope. From this analysis, we were able to develop three specific models for open-field-grown June-bearing cultivars (R2 = 0.90), for the open-field-grown day-neutral cultivar (Seascape, R2= 0.91), and for June-bearing cultivars grown in plastic tunnels (R2 = 0.92). From these results, it was concluded that strawberry powdery mildew leaf severity can be accurately estimated from incidence of diseased leaves. The I-S relationships developed in the present study may be used in making practical disease management decisions, especially for management programs that use information on disease level in the field to initiate fungicide spraying programs or to time the interval between sprays.

Efficacy of Fungicides and Rotational Programs for Management of Powdery Mildew on Cantaloupe.

Powdery mildew of cucurbits, caused by Podosphaera xanthii (syn. Sphaerotheca fuliginia auct. p.p. (Schltdl.) Pollacci), is a common and often severe disease in most areas of the world. Field trials were conducted with cantaloupe to compare disease management success provided by conventional fungicides and biofungicides having different inherent efficacies and modes of action, when applied alone throughout the treatment period or as components of fungicide application programs. Additionally, the portion of total disease control provided by each component fungicide within selected rotational programs was determined. When applied alone throughout the treatment period, disease severity in 2008 and 2009 compared with nontreated plants was reduced by values of 100, 99.3, and 98.1% by wettable sulfur (Microthiol Disperss), triflumizole (Procure), and quinoxyfen (Quintec), respectively; 83.9, 76.4, and 57.4% by trifloxystrobin (Flint), pyraclostrobin (Cabrio), or azoxystrobin (Quadris), respectively; and 39.8, 31.1, 30.0, and 28.6% by thiophanate-methyl (Topsin M), potassium bicarbonate (Kaligreen), kresoxim-methyl (Sovran), and Bacillus subtilis (Serenade), respectively. Rotational application programs composed of Microthiol Disperss, Procure, and Quintec reduced powdery mildew severity on cantaloupe by 97.5 to 100% in both trials. In comparison, disease reduction of 86.0 to 100% was achieved when the first and third fungicide applications were Quintec or Procure and the second and fourth applications were Cabrio, Flint, Kaligreen, Quadris, Serenade, Sovran, or Topsin M. In field trials designed to elucidate the portion of total disease control provided by each component fungicide within a rotational program, application sequences of Procure, Streptomyces lydicus (Actinovate), Procure, and Actinovate or Procure, Kaligreen, Procure, and Kaligreen resulted in reductions in powdery mildew severity of 69.1 and 78.7%, respectively. In comparison, inclusion of only the two Procure applications brought about a mean disease reduction of 85%, whereas inclusion of only the two Actinovate or Kaligreen applications reduced the level of powdery mildew control to 17.6 and 12.9%, respectively. The usefulness of fungicides with low inherent efficacy as resistance management partners when applied with highly efficacious at-risk fungicides may be questioned; however, the importance of any fungicide as a resistance management partner should be measured by its ability to dilute the selection pressure of the at-risk fungicide and to inhibit the growth of any resistant biotypes that may arise, factors which may not be reflected by its inherent efficacy in controlling disease. Because less efficacious fungicides did not increase the overall level of disease control, encouraging growers and pest control advisors to incorporate them into powdery mildew treatment programs may be a challenge, because resistance management is not their top priority. An ongoing educational effort emphasizing the benefits of resistance management programs with respect to prolonging the effectiveness of single-site mode of action fungicides is essential.