Powdery mildew disease of rubber tree

Powdery mildew disease of rubber trees affects young rubber leaves, buds, inflorescences and other immature tissues reducing rubber latex yields by up to 45%. The disease is present in all rubber‐growing regions, with a high incidence rate in subtropical environments. The causal agent of powdery mildew disease of rubber trees was first described as Oidium heveae, but later research on the morphological characteristics suggests that O. heveae was in the past confused with Erysiphe quercicola. However, the most appropriate classification is still under debate between the genera Golovinomyces or Podosphaera. Molecular and phylogenetic analyses have established some relationships between rubber powdery mildew fungus and other powdery mildew species, but the generic sexual state of rubber powdery mildew fungus has not yet been established. Rubber powdery mildew conidia are wind‐spread spores that are produced in great numbers when growth conditions of the disease are favourable. The optimum conditions for conidial germination are 97–100% relative humidity and temperatures between 25 and 28°C. While some newly bred rubber clones have shown resistance to the disease, it can also be controlled with a number of fungicides and biological control agents. It is clear from recent knowledge about climate–fungus relationships that changes in weather strongly influence disease incidence and severity. The aim of this review is to highlight the classification conflicts, main causes and influencing factors behind the disease spreading, as well as draw attention to the impact of weather changes on the outbreaks of the disease. The information in this review will be helpful to adopt better control measures of the powdery mildew disease of rubber, especially in higher humidity areas, thereby minimizing the loss of rubber yields due to this disease.     

Molecular identification of the powdery mildew fungus infecting rubber trees in China

Powdery mildew is a foliar disease of rubber trees. It is one of the most important leaf diseases in rubber plantations worldwide. The causal agent of this powdery mildew, previously known as Oidium heveae, has been identified under various names. To precisely identify the causal agents of this disease, 57 conidial samples were collected from 2013 to 2017 in Hainan, Yunnan and Guangdong provinces, the main rubber tree planting regions in China. Based on morphological observations using light and scanning electron microscopy, pathogenicity testing, and nrDNA ITS and 28S sequences, Erysiphe quercicola is suggested as the only causal agent of rubber tree powdery mildew in China.     

Erysiphe australiana: the cause of powdery mildew on Lagerstroemia speciosa in Brazil

Powdery mildew symptoms and signs were observed on seedlings of Lagerstroemia speciosa within an ornamental plant nursery in Viçosa, State of Minas Gerais, Brazil. Signs were most prominent as intense mycelial growth and sporulation on the shoots, new branches and leaves, which led to tissue necrosis. Based on morphological characteristics and phylogenetic analyses of ITS and 28S rDNA sequences, the powdery mildew pathogen of L. speciosa was identified as Erysiphe australiana, a well‐known powdery mildew pathogen infecting Lagerstroemia spp. worldwide. To our knowledge, this is the first report of E. australiana causing powdery mildew on L. speciosa in Brazil.     

石羊河下游干旱荒漠区梭梭人工林病害发生种类及防治对策

通过对石羊河下游干旱荒漠区梭梭人工林病害的调查,结果表明:梭梭人工林发生的各类病害有7种,其中:叶部病害有白粉病和枯萎病2种,枝干病害有枝枯病、瘤锈病、黑枯病和干桔病等4种,根部病害有根腐病1种.危害梭梭人工林主要病害有白粉病和枝枯病,有针对性地提出了防治对策.     

Outbreak of powdery mildew caused by Sawadaea negundinis on boxelder in Iran

Boxelder (Acer negundo) is planted as ornamental and shade tree in many countries including Iran. During July 2016, boxelder trees in parks and streets of different localities in East Azarbaijan province, Iran were found to be heavily infected with powdery mildew. Whitish powdery fungal mass developed mainly on the lower leaf surface. The infected young leaves became bubbled, curled and crinkled, giving affected plants an unpleasant appearance. During September, scattered, dark brown, spherical chasmothecia were produced on the lower leaf surface. The causal agent was identified as Sawadaea negundinis based on a combination of morphological characteristics of sexual and asexual morphs and sequence data of the rDNA internal transcribed spacer region (ITS1‐5.8S‐ITS2). This study provides the first report on the occurrence of S. negundinis on boxelder in Iran.     

Erysiphe alphitoides causes powdery mildew on Eucalyptus gunnii

In June 2016, pot‐grown Eucalyptus gunnii plants showing typical symptoms of powdery mildew disease were found in a greenhouse in Korea. Morphological characteristics of the anamorph and molecular sequence analyses of the ITS regions and 28S rDNA verified the fungus as Erysiphe alphitoides, which is known as common and widespread powdery mildew on Quercus spp. Although E. alphitoides has been reportedly associated with powdery mildew diseases of tropical trees and shrubs other than Quercus spp., this is the first finding of E. alphitoides on a Eucalyptus tree worldwide.     

河口地区橡胶白粉病防治技术研究

研究认为河口地区～年橡胶白粉病防治失败的一个重要原因,是由于多年单一使用粉锈宁使19982000病原菌产生抗药性。采用以硫磺粉为主防药物,以古铜叶病率～作首次施药指标,叶片老化、病10%20%50%率达时进行一次全面喷防的防治技术,取得良好效果。40%     

Coffee‐leaf extract and phosphites on the curative control of powdery mildew in eucalyptus mini‐stumps

The aim of this study was to evaluate the effectiveness of a plant extract obtained from the leaves of coffee plants infected by Hemileia vastatrix (NEFID), different formulations of phosphites and the combination of the extract and phosphites in controlling powdery mildew in eucalyptus mini‐stumps, as well as to study the effects on the production of mini‐cuttings and their rooting percentage. The experiments were conducted on two eucalyptus hybrids (‘urocam’ and ‘urograndis’) in a clonal garden and greenhouse. First, the NEFID plant extract and phosphites of copper, zinc, potassium and potassium/manganese were evaluated to determine their effectiveness in controlling powdery mildew and their toxic effect on the fungus' morphology. Subsequently, we analysed the direct fungitoxicity, curative efficiency and anti‐sporulating action of the NEFID extract and various combinations of phosphites with or without the extract, and we also evaluated their effects on shoot production and rooting in eucalyptus mini‐cuttings. The NEFID plant extract and phosphites of Cu, Zn and K/Mn were more effective than the fungicide pyraclostrobin + epoxiconazole in the control of powdery mildew. Potassium phosphite was not effective in controlling the pathogen. Among the tested mixtures, the combination of 50% NEFID plant extract and 50% copper phosphite was the most effective because it exhibited direct toxicity on powdery mildew, a high curative efficiency, anti‐sporulating action and no adverse effects on the production of shoots or rooting in eucalyptus mini‐cuttings.     

New insights into the identity and origin of the causal agent of oak powdery mildew in Europe

Powdery mildew is the most common disease on oaks in Europe where it was first recorded at the beginning of the 20th century. Yet, little is known about the origin of the causal agent. In this study, we analysed the variability of the ribosomal DNA (rDNA) of the pathogen. The internal transcribed spacer (ITS) region, the 5.8S rRNA coding gene and the intergenic spacer (IGS) of the rDNA of 33 European (mostly French) samples of oak powdery mildew were amplified using polymerase chain reaction (PCR) and PCR products were subsequently sequenced. Four different haplotypes were obtained for ITS among the various samples (ITS_A, ITS_B, ITS_C and ITS_D). Each ITS sequence corresponded to a different IGS sequence. The comparison of ITS sequences obtained with sequences accessible in the GenBank database revealed very high homologies with different taxa. Of these, three taxa had already been described on oaks in Europe, i.e. Erysiphe alphitoides (100% homology with ITS_A), Erysiphe hypophylla (99.4% homology with ITS_C) and Phyllactinia guttata (97.64% homology with ITS_D). Our data also confirmed the 100% homology between ITS_A and the sequence described for Oïdium mangiferae, the agent of mango powdery mildew. The fourth haplotype, i.e. ITS_B, represented by nearly 25% samples, showed 100% homology with the recently described Erysiphe quercicola from Quercus spp. in Asia, and several tropical and sub‐tropical powdery mildew species, including Oïdium heveae, a major pathogen of rubber trees worldwide. Our results suggest that oak powdery mildew might originate from host shifts of tropical Erysiphe species introduced to Europe through infected exotic host plants.     

Relationships between Oak powdery mildew incidence and severity and commensal fungi

Oak (Quercus robur) powdery mildew is a common and damaging fungal disease. In a local survey at Reading, UK, oak powdery mildew was common on trees of all height classes but was most common on trees of 3–9 m. A variety of other fungal species were commonly found growing in association with oak powdery mildew colonies. The abundance of such fungi was estimated through stratified sample surveys for 2.5 years. The taxa most commonly associated with oak powdery mildew were Acremonium sp., Trichoderma sp., Ampelomyces/Phoma sp. and Leptosphaerulina australis. Nearly 90% of mildew colonies were associated with L. australis, which is not generally considered as a mycoparasite or antagonist, in contrast with the other three fungi. Abundance varied between June and October surveys. Acremonium sp. abundance was greater in summer samplings, whereas L. australis and Trichoderma sp. abundances were greater in autumn samplings. Ampelomyces/Phoma sp. was never observed in the absence of powdery mildew. Relationships between the mildew‐associated fungi and oak powdery mildew appeared curved and differed significantly between sampling years. L. australis was positively correlated with the other three associated fungi studied when powdery mildew was also present . The variety and high population densities of the mildew‐associated fungi suggest that they may be important in determining the final density of oak mildew and the damage caused by it.     

Relative efficacy of strobilurin formulations in the control of downy mildew of sunflower

The efficacy of three commercial formulations of strobilurins, viz., trifloxystrobin, kresoxim-methyl, and azoxystrobin was evaluated against sunflower downy mildew disease caused by Plasmopara halstedii under laboratory, greenhouse, and field conditions. Complete inhibition of sporangial sporulation, zoospore release, and motility was observed with 2 μg ml⁻¹ in trifloxystrobin, and 5 μg ml⁻¹ for azoxystrobin and kresoxim-methyl. Seed treatment with different concentrations of strobilurins enhanced seed germination and seedling vigor of sunflower to varying degrees compared to control. Highest seed germination was recorded at 10 μg ml⁻¹ in kresoxim-methyl, and maximum seedling vigor was noticed with trifloxystrobin at 30 μg ml⁻¹. The effect of strobilurins was tested as seed treatment, foliar application, and seed treatment followed by foliar application. Under greenhouse conditions none of the concentrations used, either as seed treatment and foliar application, were phytotoxic. For the three strobilurins, the seed treatment along with foliar application enhanced the protection of the plants as compared to only the treatment of seeds. Foliar spray treatments alone provided an intermediate control of the disease. Trifloxystrobin showed a better effect than kresoxim-methyl and azoxystrobin. Disease curative activity of trifloxystrobin was higher compared to kresoxim-methyl and azoxystrobin. Tested fungicides when applied on adaxial leaf surface showed partial translaminar activity, and disease inhibition was marginal. Loss of trifloxystrobin and azoxystrobin activity over time was low, indicating stable rainfastness residual activity. A trend in protection against downy mildew disease similar to greenhouse results was evident in the field trials. This is the first report of strobilurins exhibiting high activity against P. halstedii and is a promising fungicide for controlling sunflower downy mildew disease by seed treatment and foliar spray.     

First report of Leveillula clavata causing powdery mildew on Euphorbia leucocephala from India

In December 2020, Euphorbia leucocephala plants exhibiting symptoms of powdery mildew were observed in the Botanical Garden of Tuljaram Chaturchand College, Baramati, Maharashtra, India. Based on morphological identification, DNA sequence analysis, and pathogenicity, the fungal pathogen of the disease was identified as Leveillula clavata. This is the first report of L. clavata on Euphorbia leucocephala from India and in general.     

大花月季白粉病发生情况研究

为给大花月季白粉病的预防提供理论依据,选取河南省南阳市常见的7个大花月季品种作为试验材料,对这7个大花月季品种白粉病的发生情况进行了调查,并对其抗性进行了对比分析结果发现:‘摩纳哥公主’属白粉病高抗品种,‘亚历克红’和‘希望’均属白粉病中抗品种,‘金凤凰’与‘香欢喜’均属白粉病感病品种,‘梅郎口红’与‘查克红’属白粉病严重感病品种;月季白粉病受温湿度的影响极为明显,5月为白粉病发病初期,6—8月气温较高,白粉病发病率较低,9—10月气温降低、温差增大,是月季生长的最佳时期,但此时也最容易发生白粉病,11月发病率明显下降。     

平榛白粉病发生规律的研究

采用野外定点观察、抽样调查和室内试验测定等方法,对平榛白粉病的发生规律进行了研究,结果显示:平榛白粉病各个发生阶段症状特点明显,每年发病初期为5月下旬~6月初,叶面和叶背均能出现明显的褐斑,表面覆盖白粉状物;发病高峰期为6月下旬~7月下旬;8月末秋季在白粉层上散生闭囊壳。病原菌侵染循环周期为1年,1、2年生植株相对抗侵染能力较弱,随着林龄增加,抗侵染能力增强。榛林密度大,病害发生率较高,北坡榛林病害发生程度较南坡严重。可通过调整榛林密度增加通风透光度,控制病害发生与发展。     

Severity of Xanthomonas axonopodis leaf blight on eucalypt cuttings under different levels of nutrients

Bacterial leaf blight of eucalypt, caused by Xanthomonas axonopodis, occurs mainly in forest nurseries, but also affects young plants in the field. Avoidance of leaf wetness for long periods of time over the whole nursery and using drip irrigation for clonal hedges are, currently, the most effective measures for controlling bacterial leaf blight on eucalypt. However, as these techniques are very costly, alternative management measures are required. We hypothesized that the management of mineral nutrients could reduce disease severity on eucalypts. To examine this hypothesis, rooted cuttings of Eucalyptus urophylla × E. grandis were irrigated with nutrient solutions containing different concentrations of copper (Cu), boron (Bo), potassium (K), calcium (Ca) and nitrogen (N) before inoculation with X. axonopodis 30 days after starting the nutrient solution treatments. Concentration of K higher than that recommended, commonly used in miniclonal hedges, reduced the severity of bacterial leaf blight. However, disease severity increased with an increasing of N/K ratio. The management of mineral nutrition solution, especially K, has great potential for integrated disease management of X. axonopodis in eucalypt nurseries.     

Quambalaria eucalypti found on Eucalyptus in Indonesia

The Eucalyptus plantation industry in Indonesia has expanded rapidly during the last few decades. During routine nursery disease surveys, symptoms of a leaf and shoot blight disease were detected on Eucalyptus mother plants. Isolates were obtained from symptomatic tissues and identified using DNA sequence analyses. Phylogenetic analyses showed that the isolates were those of Quambalaria eucalypti. Pathogenicity tests were conducted with isolates of Q. eucalypti on clones of E. pellita and E. grandis × E. pellita hybrids. These resulted in symptoms similar to those observed on naturally infected plants. Eucalyptus genotypes tested showed variation in their susceptibility, highlighting the potential to select and breed for resistance and thus to manage future outbreaks of the disease. This is the first report of the pathogen in Indonesia as well as in Southeast Asia.     

Wind dispersal of Puccinia psidii urediniospores and progress of eucalypt rust

To identify and implement Puccinia psidii control strategies, it is essential to understand the role of environmental factors on rust‐disease development and spread among eucalypt (Eucalyptus spp.) plantations. In this study, we evaluated the wind dispersal of P. psidii urediniospores and the progress of eucalypt rust in a field trial in Brazil. Urediniospores of P. psidii were trapped in a Burkard^® spore trap from July 2004 to June 2005. To evaluate the progress of eucalypt rust, plots were established in March 2002 using a clonal hedge scheme. The incidence of both branches and leaves with rust was assessed weekly from February 2003 to October 2005. Disease progress was studied using time‐series analysis. Urediniospores were trapped on 77% of the days sampled. The highest average urediniospore concentration was detected from July to November, and most of the urediniospores (58%) were trapped at night. Urediniospore concentration was negatively correlated with rainfall, light intensity, minimum, average and maximum temperatures and wind speed, whereas urediniospore concentration was positively correlated with leaf‐wetness duration and relative humidity. From December 2004 to June 2005, average urediniospore concentration was 0.22 spores m^?3 air h^?1 and had no correlation with meteorological data. The highest average urediniospore concentration was associated with a combination of low average temperature, low light intensity, low wind speed, high relative humidity and high leaf wetness, which reflect conditions observed at night. The disease incidence was positively correlated with the urediniospores trapped at 12 days prior to disease assessment. According to the models obtained by the time series, a seasonal yearly effect was found on rust progress. Using our models, we were also able to forecast disease incidence up to 3 months after the last field assessment.     

膏桐苗圃病虫害调查初报

2008年7月对镇康县和双江县膏桐苗圃进行了病虫害调查,结果显示:苗圃地内膏桐幼苗主要受到象甲、潜叶蛾、红蜘蛛、地老虎以及白粉病、膏桐实生苗猝倒病等病虫危害.其中金边翠象容易发生在农田环境中,麻风树柄细蛾在几乎所有苗圃地内零星发生,这2种害虫是膏桐苗圃地内的主要食叶害虫;膏桐白粉病是膏桐苗圃中相对普遍发生的病害,主要发生在膏桐叶片和茎干上.针对膏桐主要病虫害提出了相应的病虫害防治措施,并就膏桐产业发展的迅猛势头进行了讨论.     

Foliar chemistry of juvenile Eucalyptus grandis clones does not predict chemical defence in maturing ramets

The tendency for managers of eucalypt plantations to plant large, homogeneous (i.e. clonal) stands presents a new suite of problems. Perhaps foremost among them is the elevated risk of disease or predation. One way to counter this risk is to select material with high natal resistance, such as material with high concentrations of plant secondary metabolites. This would be much simpler if we could predict future defences from the chemistry of juvenile plants. The present study aimed to determine the relationship between the concentrations of formylated phloroglucinol compounds (FPCs) in the leaves of newly established Eucalyptus grandis (Hill ex Maiden) clones in the nursery and those in the same genetic material in experimental plantations. There was almost no relationship between the concentrations of defensive chemicals in the leaves of newly established E. grandis clones growing in pots in the nursery and of those in the same genetic material growing in plantations. This implies that age effects and probable gene × environment interactions prevent evaluating the defensive qualities of clones until they are several years old and even then the results are site-specific.