Incidence and geographical distribution of downy mildew on maize caused by Peronosclerospora sorghi in Nigeria

Abstract

Incidence and geographical distribution of downy mildew (Peronosclerospora sorghi) on maize (Zea mays) were determined in a systematic survey of 181 maize fields in the major maize‐growing regions and ecological zones of Nigeria. Downy mildew was observed in the forest and Guinea savanna ecologies, but no disease was detected in other ecologies. Highest levels of disease incidence (63%) were observed in the forest zone, and progressively less disease incidence was found at the southern and northern Guinea savanna zones. Spatial pattern analysis indicated an aggregation and randomness of infected plants in the northern Guinea savanna and the forest zone, respectively. Disease incidence was positively correlated with the presence of downy mildew infected sorghum plants and relative amount of sporulation on infected sorghum (Sorghum bicolor) but negatively correlated with plant age and cropping pattern. Relative sporulation on maize plants was negatively correlated with age of maize plants. Higher levels of disease incidence were observed when the previous crop was either maize or sorghum than when previous crops were cassava, okra, tomatoes, or rice.     

Chitosan enhances disease resistance in pearl millet against downy mildew caused by Sclerospora graminicola and defence-related enzyme activation

BACKGROUND: The present study investigated the effect of chitosan seed priming on the induction of disease resistance in pearl millet against downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroet. RESULTS: Pearl millet seeds were primed with chitosan at different concentrations: 0.5, 1.5, 2.5 and 3 g kg^?1 seed. Of the different concentrations, 2.5 g kg^?1 was found to be optimum, with enhanced seed germination of 99% and seedling vigour of 1782, whereas the untreated control recorded values of 87% and 1465 respectively. At optimum concentration, chitosan did not inhibit sporulation and release of zoospores from sporangia. Furthermore, pearl millet seedlings raised after seed treatment with chitosan showed an increased level of the defence‐related enzymes chitosanase and peroxidase as compared with the untreated pearl millet seedlings on downy mildew pathogen inoculation. The effect of chitosan in reducing downy mildew incidence was evaluated in both greenhouse and field conditions, in which respectively 79.08 and 75.8% disease protection was obtained. CONCLUSION: Chitosan was effective in protecting pearl millet plants against downy mildew under both greenhouse and field conditions by inducing resistance against the pathogen. Thus, chitosan formulation can be recommended for seed treatment in the management of downy mildew disease. Copyright © 2008 Society of Chemical Industry     

Reaction of maize,sorghum and Johnson grass to Peronosclerospora sorghi

Development of sorghum downy mildew, incited by Peronoscleospora sorghi (Weston and Uppal) C.G. Shaw, on maize, sorghum and Johnson grass was investigated at two locations in Uganda during three seasons (1994 and 1995). More sorghum downy mildew developed on the Johnson grass and sorghum than on the maize at all locations and in all seasons. No significant differences were observed in sporulation of P. soghi on the three hosts. Leaf shredding occurred on the three hosts but was the least on maize. Cross-inoculation with both conidia and oospores was achieved on the three hosts. Since the fungal population formed oospores and sporulated readily on the three hosts, which is typical of the sorghum strain, the disease in Uganda is attributed to the sorghum strain.     

Characterization of resistance mechanisms activated by Trichoderma harzianum T39 and benzothiadiazole to downy mildew in different grapevine cultivars

Downy mildew, caused by Plasmopara viticola, is one of the most destructive diseases of grapevine and is controlled with intense application of chemical fungicides. Treatment with Trichoderma harzianum T39 (T39) or benzothiadiazole‐7‐carbothioic acid S‐methyl ester (BTH) has been previously shown to activate grapevine resistance to downy mildew and reduce disease symptoms in the Pinot noir cultivar. However, enhancement of plant resistance can be affected by several factors, including plant genotype. In order to further extend the use of resistance inducers against downy mildew, the physiological and molecular properties of T39‐ and BTH‐activated resistance in different cultivars of table and wine grapes were characterized under greenhouse conditions. T39 treatment reduced downy mildew symptoms, but the degree of efficacy differed significantly among grapevine cultivars. However, efficacy of BTH‐activated resistance was consistently high in the different cultivars. Expression profiles of defence‐related genes differed among cultivars in response to resistance inducers and to pathogen inoculation. T39 treatment enhanced the expression of defence‐related genes in the responsive cultivars, before and after P. viticola inoculation. A positive correlation between the efficacy of T39 and the expression level of defence‐related genes was found in Primitivo and Pinot noir plants, while different genes or more complex processes were probably activated in Sugraone and Negroamaro. The data reported here suggest that the use of a responsive cultivar is particularly important to maximize the efficacy of resistance inducers and new natural inducers should be explored for the less responsive cultivars.     

Monitoring of QoI fungicide resistance in Plasmopara viticola populations in Japan

BACKGROUND: The increasing occurrence of QoI fungicide resistance in Plasmopara viticola (Berk. & MA Curtis) Berl. & DeToni populations is becoming a serious problem in the control of grapevine downy mildew. In Japan, the existence of QoI‐fungicide‐resistant P. viticola was reported in 2009. RESULTS: The QoI fungicide resistance in P. viticola samples collected from vineyards in Japan in 2008 and 2009 was monitored. Resistant P. viticola were detected in the regions where QoI fungicides have been introduced in accordance with the pest management programme, whereas in Hokkaido vineyards, where QoI fungicides have not yet been introduced, QoI‐fungicide‐resistant P. viticola were not found. CONCLUSION: Japan comprises thousands of islands and is physically isolated from other countries by the sea. Monitoring the emergence, incidence and distribution of QoI fungicide resistance in P. viticola populations in Japan is necessary to improve pest management strategies for downy mildew disease in Japanese vineyards. Copyright © 2010 Society of Chemical Industry     

Resistance mechanism to carboxylic acid amide fungicides in the cucurbit downy mildew pathogen Pseudoperonospora cubensis

BACKGROUND: Pseudoperonospora cubensis, the causal oomycete agent of cucurbit downy mildew, is responsible for enormous crop losses in many species of Cucurbitaceae, particularly in cucumber and melon. Disease control is mainly achieved by combinations of host resistance and fungicide applications. However, since 2004, resistance to downy mildew in cucumber has been overcome by the pathogen, thus driving farmers to rely only on fungicide spray applications, including carboxylic acid amide (CAA) fungicides. Recently, CAA‐resistant isolates of P. cubensis were recovered, but the underlying mechanism of resistance was not revealed. The purpose of the present study was to identify the molecular mechanism controlling resistance to CAAs in P. cubensis. RESULTS: The four CesA (cellulose synthase) genes responsible for cellulose biosynthesis in P. cubensis were characterised. Resistant strains showed a mutation in the CesA3 gene, at position 1105, leading to an amino acid exchange from glycine to valine or tryptophan. Cross‐resistance tests with different CAAs indicated that these mutations lead to resistance against all tested CAAs. CONCLUSION: Point mutations in the CesA3 gene of P. cubensis lead to CAA resistance. Accurate monitoring of these mutations among P. cubensis populations may improve/facilitate adequate recommendation/deployment of fungicides in the field. Copyright © 2011 Society of Chemical Industry     

The reliability of leaf bioassays for predicting disease resistance on fruit: a case study on grapevine resistance to downy and powdery mildew

This study was designed to assess the reliability of grapevine leaf bioassays for predicting disease resistance on fruit in the field. The efficacy of various grapevine quantitative trait loci (QTLs) for conferring resistance to downy and powdery mildew was evaluated in bioassays and in a 2‐year field experiment for downy mildew. The resistance genes studied were inherited from Muscadinia rotundifolia (Rpv1 and Run1) and from American Vitis species through cv. Regent (QTLRgP and QTLRgD). In bioassays, genotypes carrying Run1 blocked powdery mildew development at early stages. Genotypes combining Run1 with QTLRgP displayed no greater level of resistance. For downy mildew, genotypes carrying Rpv1 and/or QTLRgD were more resistant than the susceptible cv. Merlot, and showed a high level of leaf resistance in the field (<10% severity). Disease levels on bunches were much higher than those on leaves, with a high variability between Rpv1 genotypes (1–48%). A Bayesian decision theory framework predicted that an OIV‐452 threshold of 5 in leaf bioassays allowed accurate selection of grapevine genotypes (P = 0·83) with satisfactory disease severity on bunches. Therefore, this study validates that the use of early bioassays on leaves, as currently performed by grapevine breeders, ensures a satisfactory level of resistance to downy mildew of bunches in the field.     

Problems in control of Rottboellia exaltata L.f. in maize in Bukidnon Province, Mindanao, Philippines

Various methods were tested to control the annual grass Rottboellia exaltata L.f. in maize (Zea mays L.) under small-farm conditions in Bukidnon Province, Mindanao, Philippines during 1977 and 1978. No single method was satisfactory. Despite adequate early season control, late-germinating Rottboellia tillered profusely. By harvest, plots had heavy infestations and were carpeted with seed. At harvest, untreated controls averaged 8·6 t Rottboellia dry matter ha^?1 and only half the maize yield of handweeded plots. The ‘karase’ spike-tooth harrow, or 0·2 kg paraquat ha^?1, effectively removed Rottboellia flushes before maize emergence, but these techniques delayed planting, which can intensify downy mildew disease (Sclerospora sp.). Even though handweeding increased maize yields and decreased Rottboellia dry weights, it is impractical on typical 3- to 5-ha maize farms. Mungbean (Vigna radiata (L.) Wilczek var. aureus), intercropped with maize, suppressed Rottboellia initially. Openings caused by mungbean harvest, however, allowed explosive late-season weed growth in maize. Three herbicide treatments were as effective as handweeding: pendimethalin plus atrazine, either banded over the maize row (followed by cultivation), or broadcast; and pendimethalin followed by 2, 4-D, both broadcast. In one experiment, low-cost practices, including weed flush removal, cultivation, or handweeding, provided high net returns, whereas expensive herbicide treatments produced low net returns. Fertilizer, applied without weed control, increased maize yield 62%. Without fertilizer, weed control increased yield 107%. Combining the two raised yield 167%.     

Crop damage caused by powdery mildew on hop and its relationship to late season management

Powdery mildew of hop (Podosphaera macularis) may cause economic loss due to reductions in cone yield and quality. Quantitative estimates of crop damage from powdery mildew remain poorly characterized, especially the effect of late season disease management on crop yield and quality. Field studies in Washington State evaluated cone yield, bittering acid content and quality factors when fungicide applications were ceased at different stages of cone development. The incidence of cones with powdery mildew was linearly correlated with yield of cones, bittering acids and accelerated cone maturation. In cultivar Galena, the cumulative effect of every 1% increase in cones powdery mildew incidence was to reduce alpha‐acid yield by 0·33%, which was due to direct effects on cone yield but also indirect effects mediated by dry matter. In the more susceptible cultivar Zeus, alpha‐acid yield was increased 20% by controlling powdery mildew through the transition of bloom to early cone development compared to ceasing fungicide applications at bloom: additional applications provided only modest improvements in alpha‐acid yield. In both cultivars, the impact of powdery mildew on aroma characteristics and bittering acid content were less substantial than cone yield. The damage caused by powdery mildew to cone colour and alpha‐acid yield, as well as the effectiveness of fungicide applications made to manage the disease, appears inseparably linked to dry matter content of cones at harvest. Realising achievable yield potential in these cultivars requires control of the disease through early stages of cone development and harvest before maturity exceeds c. 25% dry matter.     

Spatial analysis and incidence–density relationships for downy mildew on hop

The spatial pattern of downy mildew (Pseudoperonospora humuli) on hop (Humulus lupulus) was characterized over 4 years to aid in deriving an appropriate incidence–density relationship. From 472 disease assessments (datasets), discrete distributions were fitted to the datasets to determine aggregation of disease density. Where distributions were able to be fitted, the Poisson distribution fitted 4% of the datasets and the negative binomial distribution fitted 87% of the datasets. Larger‐scale patterns of disease were assessed by autocorrelation and runs analysis; both indicated aggregation of diseased plants was less common than aggregation of disease within plants. Taylor’s power law indicated disease density was aggregated and related to mean disease density in all years. Disease incidence and density were linked by saturation‐type relationships based on the zero term of the negative binomial distribution or an empirical regression. Certain individual datasets were not described well by any incidence–density model, particularly when disease density was greater than about 0·8 diseased shoots per plant with the cultivar Cascade. When applied to 56 validation datasets, 88% of the variation in observed disease incidence was explained by the incidence–density models. Under conditions where sampling would be implemented for disease management, the requisite conditions appear to be in place for a binomial sampling plan for downy mildew.     

Department of Crop Science,Herbicide Section,Report October 1967 - August 1968

Abstract

A serious outbreak of muskmelon (Cucumis melo L.) downy mildew caused by Pseudoperonospora cubensis (Berk. &; Curt) Rostow, occurred in the Punjab (India) due to unusual rain showers accompanied by high humidity. Nine different fungicides were evaluated and of these zineb 75% (Dithane Z-78) and copper oxychloride (Blitox 50%) gave reasonable control of the disease.     

Activity of the New Fungicide Benthiavalicarb Against Plasmopara viticola and its Efficacy in Controlling Downy Mildew in Grapevines

Benthiavalicarb is a new fungicide active against Oomycetes fungal plant pathogens. The present study shows that benthiavalicarb is effective for controlling the Oomycete fungal pathogen Plasmopara viticola, which causes downy mildew in grapevines. The fungicide did not affect zoospore discharge from sporangia of P. viticola, but strongly inhibited zoospore encystment, cystospore germination in vitro and mycelial growth, together with sporangial production in vivo. Benthiavalicarb showed strong prophylactic and local activity in intact plants or detached leaves and low translaminar activity. The compound was not translocated from leaf to leaf in either a acropetal or basipetal direction. Benthiavalicarb applied at 1, 3 and 6 days post-inoculation protected grapevine plants against downy mildew and inhibited sporulation of the pathogen. Similar results were obtained on leaf disks if benthiavalicarb was applied up to 96 h post-inoculation. Benthiavalicarb diminished the sporulation of P. viticola when applied to established disease in the tissue. Benthiavalicarb remained active on leaves for a period up to 28 days. Two foliar applications of benthiavalicarb, 2 weeks apart, to field-grown grapevines inhibited downy mildew development and were as effective as the standard metalaxyl-Cu treatment in controlling the disease. A formulated mixture of benthiavalicarb + Folpet was similar or superior in performance to metalaxyl-Cu and the new strobilurin trifloxystrobin in controlling downy mildew. The effectiveness of benthiavalicarb makes it well suited for integration into a control programme against downy mildew disease in vineyards, and as a component to delay resistance buildup.     

一体化智能孢子捕捉系统在黄瓜霜霉病和黄瓜白粉病预测上的应用

为探索国内研制的新型一体化智能孢子捕捉系统在黄瓜霜霉病和黄瓜白粉病预测预报上的应用,在田间自然发病情况下,通过对捕捉孢子的形态进行识别,优化一体化智能孢子捕捉系统主要工作参数如有/无空气切割头、空气采集口高度和空气采集时间;通过病害及孢子的动态监测分析大棚黄瓜霜霉病和黄瓜白粉病病情指数与孢子捕捉量的关系。结果表明,当不加装空气切割头、空气采集口高度为70 cm、孢子捕捉时间在10:00—10:30时段有利于孢子的捕捉。黄瓜霜霉病和黄瓜白粉病病情指数与连续7 d孢子捕捉总量具有强正相关性。连续多日监测到黄瓜霜霉病菌孢子囊且数量快速增加是黄瓜霜霉病发生或快速上升的一个预测指标。黄瓜白粉病发病之前没有监测到黄瓜白粉病菌分生孢子,且在病害盛发期分生孢子捕捉量仍较少。研究表明,一体化智能孢子捕捉系统适用于黄瓜霜霉病的预测,但在黄瓜白粉病的预测上尚存在一定问题。     

A New Race of Spinach Downy Mildew in Japan

A new race of spinach downy mildew caused by Peronospora effusa occurred in Fukui, Japan. The fungus was capable of affecting spinach cultivars resistant to races 1, 2, 3 and 4, but not some other cultivars. Thus, the fungus had different pathogenicity from race 3 and race 4 of the pathogen and was considered to be a new race of spinach downy mildew in Japan. Received 26 April 2001/ Accepted in revised form 17 August 2001     

2020年北京房山酿酒葡萄霜霉病发生动态监测

霜霉病是世界范围内葡萄上的一种重要流行性病害.2020年,本研究系统调查了北京市房山区3个酿酒葡萄酒庄中4个不同葡萄品种的霜霉病发生情况,并记录了实时温湿度、降雨数据和用药时间,还分析了葡萄霜霉病的发生与降雨、相对湿度和用药时间的关系以及不同葡萄品种对霜霉病感病性的差异.结果 表明:房山3个酿酒葡萄酒庄在2020年5月...     

Occurrence and molecular characterization of azoxystrobin resistance in cucumber downy mildew in Shandong province of China

Cucumber downy mildew caused byPseudoperonospora cubensis (Berk. and Curt.) Rostov. limits crop production in Shandong Province of China. Since management of downy mildew is strongly dependent on fungicides, a rational design of control programs requires a good understanding of the fungicide resistance phenomenon in field populations of the pathogen. A total of 106 and 97 isolates ofP. cubensis were obtained in 2006 and 2007, respectively. The EC₅₀ values for the growth of all the 106 isolates collected in 2006 were 0.0063–0.0688μg ml⁻¹ (average: 0.0196±0.0048μg ml⁻¹) azoxystrobin and these were therefore considered sensitive isolates. However, 57 field isolates ofP. cubensis of the 97 collected in 2007 with EC₅₀ values that ranged from 0.609 to >51.2μg ml⁻¹ were considered resistant to azoxystrobin. Fragments of the fungicide-targeted mitochondrial cytochromeb gene from total pathogen DNA were amplified using polymerase chain reaction and their sequences analyzed to elucidate the molecular mechanism of resistance. A single point mutation (GGT to GCT) in the cytochromeb gene, resulting in substitution of glycine by alanine at position 143, was found in the three selected azoxystrobin-resistant isolates of downy mildew. This substitution in cytochromeb exhibited different resistance levels, with the resistance factor from 21.15 to greater than 2618.9. In addition, the different resistance levels seemed to appear within 1 year (between 2006 and 2007). Therefore, growers of Shandong Province in China now are faced with a challenge in managing the azoxystrobin resistance in cucumber downy mildew. http://www.phytoparasitica.org posting March 10, 2008.     

利用MAXENT预测玉米霜霉病在中国的适生区

玉米霜霉病是我国重要的对外植物检疫对象,本文用MAXENT软件对引起玉米霜霉病的5种检疫性病原菌Peronosclerospora maydis、P. sacchari、P. philippinensis、P. sorghi和Sclerophthora rayssiae var. zeae在我国的潜在分布进行了预测。结果表明,5种病原菌中P. sorghi在我国的适生范围最广,根据适生值的大小,其在华北平原、长江中下游平原、东北中部地区、两广、福建及云南西部,均有不同程度的发生风险。在这些地区内种植有大面积的玉米,为玉米霜霉病菌的定殖提供了良好的寄主。加强这些区域的调查监测和检疫对保护当地的玉米生产有重要意义。     

Spinach: better management of downy mildew and white rust through genomics

Spinach (Spinacia oleracea) has become an increasingly important vegetable crop in many parts of the world. Significant changes in production practices, particularly in the U.S. and E.U., have occurred in the past 10–15 years as a result of increased product demand. These changes likely increased the incidence and severity of downy mildew, caused by Peronospora farinosa f. sp. spinaciae. Recently, progress has been made to define the genetics of resistance to this pathogen and the closely related white rust pathogen, Albugo occidentalis. In this paper, we outline the genetic and genomic resources currently available for spinach, draw parallels between spinach diseases and more thoroughly characterized pathosystems, and describe efforts currently underway to develop new genetic and genomic tools to better understand downy mildew and white rust of spinach. Presently, many crucial tools and resources required to define the molecular underpinnings of disease are unavailable for either spinach or its pathogens. New resources and information for spinach genomics would provide a jumpstart for ongoing efforts to define (and deploy) genetic resistance against downy mildew and white rust.     

Comparison of lettuce diseases and yield under subsurface drip and furrow irrigation

ABSTRACT Subsurface drip and furrow irrigation were compared on lettuce (Lactuca sativa) cvs. Salinas and Misty Day for yield and incidence and severity of three important diseases of lettuce in the Salinas Valley, CA. Experiments were conducted between 1993 and 1995 during the spring and fall seasons. The diseases examined included lettuce drop (Sclerotinia minor), downy mildew (Bremia lactucae), and corky root (Rhizomonas suberifaciens). Replicated plots of subsurface drip and furrow irrigation were arranged in a randomized complete-block design. All plants were inoculated with S. minor at the initiation of the experiment during the 1993 spring season. Plots were not inoculated for downy mildew and corky root during any season nor were the plots reinoculated with S. minor. During each season, all plots were sprinkler irrigated until thinning, and subsequently, the irrigation treatments were begun. The furrow plots were irrigated once per week, and the drip plots received water twice per week. The distribution of soil moisture at two soil depths (0 to 5 and 6 to 15 cm) at 5, 10, and 15 cm distance on either side of the bed center in two diagonal directions was significantly lower in drip-irrigated compared with furrow-irrigated plots. Plots were evaluated for lettuce drop incidence and downy mildew incidence and severity at weekly intervals until harvest. Corky root severity and yield components were determined at maturity. Lettuce drop incidence and corky root severity were significantly lower and yields were higher in plots under subsurface drip irrigation compared with furrow irrigation, regardless of the cultivar, except during the 1994 fall season. Incidence and severity of downy mildew were not significantly different between the two irrigation methods throughout the study. The differential microclimates created by the two irrigation treatments did not affect downy mildew infection, presumably because the mesoclimate is usually favorable in the Salinas Valley. Subsurface drip irrigation is a viable, long-term strategy for soilborne disease management in lettuce in the Salinas Valley.     

不同栽培模式下葡萄霜霉病菌遗传结构的时间动态分析

为明确不同栽培模式下葡萄霜霉病菌Plasmopara viticola的遗传结构、遗传多样性及遗传分化水平,于2014-2015年定期采集露地和避雨2种栽培模式下的葡萄霜霉病菌菌株,利用6对SSR引物对该病菌基因型、遗传多样性及遗传分化进行对比分析。结果表明,露地和避雨栽培模式下葡萄霜霉病菌群体的Nei’s基因多样性指数大于0.14,香农多样性指数大于0.31,2种栽培模式下群体具有丰富的遗传多样性,但避雨栽培模式可显著降低群体等位基因数和等位基因频率。露地栽培模式下该病菌群体的流行模式呈现中等水平无性繁殖,2年初侵染和再侵染对病害流行的贡献率分别约占26.1%和73.9%;避雨栽培模式下葡萄霜霉病菌群体的流行模式则呈现高等水平无性繁殖,初侵染和再侵染对病害流行的贡献率分别约占4.3%和95.7%。卵孢子的形成对于葡萄霜霉病菌种群遗传变异和有效越冬起着关键的作用。2014-2015年露地栽培模式下葡萄霜霉病菌群体的主效流行基因型对病害流行的贡献率分别为44.5%和51.8%;而其在避雨栽培模式下葡萄霜霉病菌群体的贡献率分别可达84.2%和87.1%。同一年份的露地和避雨栽培模式下葡萄霜霉病菌群体的主效基因型种类相同,2个群体间的等位基因频率呈现显著正相关性,且二者之间存在频繁的基因交流,推测避雨栽培模式下葡萄霜霉病的初侵染源自于避雨设施附近的露地栽培病株上再侵染形成的飞散传播孢子囊。