Performance of different rubber tree clones against South American leaf blight (Microcyclus ulei)

This study was aimed to evaluate the behaviour of eighteen clones of Hevea brasiliensis (rubber) against South American leaf blight and to study progress of the disease. The experiment was conducted in Cachoeiro de Itapemirim‐ES, where 18 clones were evaluated. The experimental design was a randomized block with four replicates; each experimental unit consisted of three plants. Evaluations were performed at 15‐day intervals on 30 leaflets per tree. Disease incidence was quantified and infection classified according to the stages of development and type of damage. Leaf blight occurred during the entire experimental period; however, disease intensity varied with the resistance level of the clones and the time of year. Clones FX 3864, RRIM 725, RRIM 711, IAC 300 and IAN 873 exhibited the highest resistance to leaf blight.     

Evaluation of the resistance of 36 Hevea clones to Microcyclus ulei and relation to their capacity to accumulate scopoletin and lignins

Thirty-six Hevea clones were inoculated with conidia of Microcyclus ulei, the causal agent of South American Leaf Blight in an air-conditioned chamber. Components of disease resistance such as latent period, infectious period, lesion size, percentage of damaged leaf area, number of lesions, spore production and stromatic generation period were studied during a single infection cycle. The clones were easily separated on the basis of these characters that were evaluated under controlled conditions. The main components that were highly correlated were the spore production, lesion size and number of lesions with the percentage of damaged leaf area. Others, such the stromatic generation period, were slightly correlated with all other components; latent period and infectious period was slightly correlated with the lesion size; and lesion size was slightly correlated with lesion density. For screening of varieties, damaged leaf area and spore production were the two components that should be considered the most important. Furthermore, the clones were tested for their capacity to produce scopoletin, a phytoalexin of Hevea, and to produce lignins in their infection sites. A strong correlation was observed between scopoletin accumulation and clone resistance. Moreover, strong lignin accumulation was often associated with a longer stromatic generation period. These two physiological reactions could interfere by limiting fungal development in several clones. However, neither scopoletin nor lignin accumulation could individually explain the behaviour of all clones.     

Disease progress of South American leaf blight of rubber in different brazilian regions

An analysis of 13 epidemics caused by Microcyclus nlei in rubber trees was made. The possibilities of chemical control, the influence of climatic factors on disease development, and the fitness of three disease growth models to the held data are discussed.     

Calonectria metrosideri,a highly aggressive pathogen causing leaf blight,root rot,and wilt of Metrosideros spp. in Brazil

The genus Metrosideros includes several tree, shrub and vine species, native to the Pacific Islands. Seedlings from 25 seed lots of Metrosideros polymorpha and two seed lots of M. tremuloides with symptoms of root rot, stem girdling, wilting and round, purple leaf spots were observed in the Forestry Nursery at the Universidade Federal de Viçosa, Brazil. In the original disease site, seedling mortality reached up to 71% in M. polymorpha and 34% in M. tremuloides. Single conidial cultures obtained from infected leaf, root and stem samples of M. polymorpha were used to identify the fungal species. Morphological characters and DNA sequences of four loci, containing partial sequences of β‐tubulin (TUB2), histone H3 (HIS3), calmodulin (CAL) and the elongation factor (tef‐1α) genes of three isolates, indicated that they belong to a new species, described here as Calonectria metrosideri sp. nov. Potting medium infestation and inoculation of seedlings of M. polymorpha with an inoculum suspension at 1 × 10⁴ conidia ml^?1 induced typical symptoms of the disease (leaf spots, root rot and wilt), similar to those observed under natural conditions. Calonectria metrosideri was re‐isolated, which fulfilled Koch's postulates, and confirmed its status as a pathogen.     

Relative susceptibility of Eucalyptus provenances to Cylindrocladium leaf blight in Kerala,India1

Susceptibility of 46 provenances belonging to 16 species of Eucalyptus to Cylindrocladium leaf blight caused by Cylindrocladium quinqueseptatum, C. clavatum and C. ilicicola differed significantly in detached leaf inoculations. Generally, susceptibility of a provenance to the three species of Cylindrocladium showed significant differences; only a few provenances gave either equally resistant or susceptible reactions to all the three species. C. clavatum was the most virulent species, C. ilicicola the least and C. quinqueseptatum intermediate.     

Phosphorus,nitrogen and potassium nutrition on Calonectria leaf blight in eucalypt plants

Calonectria pteridis causes Calonectria leaf blight (CLB), and consequently severe defoliation in eucalypt plantations, which results in losses in wood volume. To reduce the negative impacts of this disease in eucalypt, this study aimed to assess the application of different doses and combinations of the macronutrients N, P and K on the percentage of symptomatic leaf area (SLA) and defoliation induced by the pathogen. Cuttings of a clone of Eucalyptus grandis were transplanted to pots containing soil that received different dose combinations of N, P and K, according to an incomplete factorial design. At 200 days after transplanting, leaf samples were analysed for N, P and K contents, and then, the plants were inoculated. Forty‐five days post‐inoculation, SLA and percentage of defoliation were quantified. Potassium doses above 75 mg/dm³ of soil significantly reduced SLA and defoliation. The influence of N and P on defoliation was dependent on K doses, but both reduced symptomatic leaf area. The best control of the disease, expressed by decreased defoliation and symptomatic leaf area, was achieved with leaf content of N, P and K of 9.8, 0.8 and 10.4 g per kg leaf, respectively, obtained with doses of 55, 82.5 and 143 mg/dm³of soil, respectively. Therefore, N, P and K nutrition can be a component of an integrated management programme for the control of CLB in eucalypts.     

南京地区银杏叶枯病的发生及病原调查

于2017年10月—2018年11月间,对银杏叶枯病的发生以及银杏叶枯病发病原因进行了调查,结果表明:银杏叶枯病在南京地区发生较为普遍。从5月开始发生(平均病情指数为7.28),7,8月病害达高发期(平均病情指数分别为24.15,41.57),10月病害发生较为严重,此时大量病树叶片枯黄脱落,平均病情指数达到62.35;对采集的银杏叶枯病病叶进行标本镜检,并参考相关的资料,认为叶枯病病原或致病因素包括真菌性病原、细菌性病原和环境因素,而真菌性病原包括链格孢菌、镰刀菌、盘多毛孢菌、盘圆孢和叶点霉菌;另有部分患病植株叶片,未发现和分离出相关病原。推测可能是由环境因素或营养条件所造成的非侵染性病害,具体原因尚需进一步研究。     

Pestalotiopsis biciliata,a new leaf pathogen of Eucalyptus spp. recorded in Italy

The present paper describes new symptoms on Eucalyptus spp. in Central Italy associated with the fungal pathogen Pestalotiopsis biciliata. This fungal species has been previously recorded in Italy on grape associated with fruit rot. Artificial inoculation trials on leaves confirmed the pathogenicity of the fungus to Eucalyptus camaldulensis. P. biciliata is included in the list of Pestalotiopsis spp. responsible for leaf disease on eucalypts worldwide.     

Screening of Corymbia and Eucalyptus species for resistance to Calonectria pteridis leaf blight

Calonectria leaf blight (CLB), caused by Calonectria pteridis, is a major foliar disease of eucalypt plantations in warm and high rainfall regions in Brazil. The use of resistant genotypes is the best method for disease control in the field, so identification of sources of resistance is strategic for the long‐term genetic breeding programmes of eucalypt. In this study, resistance of 13 species of Eucalyptus and 3 species of Corymbia to CLB was evaluated by spray inoculation of a spore suspension (1 × 10⁴ conidia ml^?1) of the pathogen, under controlled conditions. Eucalyptus brassiana, E. saligna, E. scias and E. agglomerata were the most resistant, while E. robusta, E. urophylla, E. camaldulensis, E. longirostrata and C. toreliana were moderately resistant and E. cloeziana, E. pellita, E. tereticornis, E. pilularis, C. maculata, E. grandis, E. dunnii and C. citriodora were the most susceptible. The broad inter and intraspecific variability of the species tested demonstrates the potential for introgression of resistance genes into valuable genotypes as a strategy for the breeding programmes and commercial plantation of eucalypt.     

Selection of Pinus spp. in South Africa for tolerance to infection by the pitch canker fungus

The increasing threats from pests and diseases demand that the South African forest industry explores options to deploy alternative pine species in plantation development. This is especially true for species, such as Pinus patula Schiede and Deppe ex Schltdl. and Cham., which are highly susceptible to the pitch canker fungus Fusarium circinatum. Losses due to F. circinatum have been confined mostly to nurseries and at field establishment resulting in a significant cost to the industry. Although, the fungus has not as yet resulted in stem and branch infections on established P. patula in South Africa, it has caused pitch canker on other, more susceptible species such as P. radiata D. Don., and P. greggii Engelm. ex Parl. As alternatives to P. patula, on the warmer and cooler sites in South Africa, families of P. elliottii Engelm var. elliottii, P. tecunumanii (Schw.) Eguiluz and Perry, P. maximinoi H. E. Moore and P. pseudostrobus Lindl. were screened for tolerance to infection by F. circinatum in greenhouse studies. Seedlings were wounded and inoculated with spores of F. circinatum. Lesion development following inoculation was used to differentiate the levels of tolerance between families. The results showed that P. maximinoi, P. pseudostrobus, and the low elevation variety of P. tecunumanii are highly tolerant to infection with very little family variation. The narrow sense heritability estimates for these species were less than 0.06. In contrast, P. elliottii showed good tolerance with some family variation and a heritability of 0.22, while the high elevation source of P. tecunumanii showed a high degree of family variation and a heritability of 0.59. These results provide the industry with valuable information on pine species tolerant to F. circinatum that could be used as alternatives to P. patula in South Africa.     

Infection approach of Diplodia sapinea,the causal agent of tip blight of Pinus tabulaeformis in China

To clarify the infection approach of Diplodia sapinea, a pathogen that causes tip blight of Pinus tabulaeformis, the infection process of the pathogen in needles was observed using scanning electron microscopy (SEM). In addition, the disease incidence on branches damaged by Aphrophora flavipes (Hemiptera: Cercopidae) and Dioryctria splendidella (Lepidoptera: Pyralidae) in the forest was also investigated. Then, branches and needles of P. tabulaeformis were inoculated using the D. sapinea spore suspension under indoor and field conditions. The results showed that the damage caused by A. flavipes could aggravate the occurrence of tip blight of P. tabulaeformis to some extent. Moreover, the pathogen could also penetrate 1‐, 2‐ and 3‐year‐old pine needles through stomata in the field. The pathogen infected the 1‐year‐old branches first and then gradually spread to 2‐ and 3‐year‐old branches.     

几种桉叶提取物的抗菌活性研究

研究了大叶桉、柠檬桉、尤曼桉(A、B)叶乙醇提取物和大叶桉、尤曼桉B叶提取物浓缩浸膏的石油醚、乙酸乙酯和正丁醇萃取组分对金黄葡萄球菌、大肠杆菌、枯草芽孢杆菌、黄瓜枯萎病菌的抗菌活性和以及这几种桉叶提取物的最低抑菌浓度。结果表明4种桉叶提取物对4种供试菌均有抑制作用,对金黄葡萄球菌、枯草芽孢杆菌抑制作用强,对黄瓜枯萎病菌作用弱。大叶桉、尤曼桉B提取物的抗菌活性强,这两种桉叶的乙酸乙酯和正丁醇萃取组分对4种供试菌抑菌作用最明显。     

Cherry leaf roll virus causing a disease of Betula spp. in the United Kingdom

A virus, serologically related to isolates of cherry leaf rollvirus (CLRV) from Prunus avium (L.) L. and Sambucus nigra L.was transmitted to a range of herbaceous plants from leavesor roots of thirty-one of forty-seven trees of Betula spp. growingat two heathland sites in Berkshire. Ageing leaves of virus-infectedindividuals which had mild chiorotic blotches or ring and linepatterns in July showed bright yellow ring and line patternsin October. In the season after B. verrucosa seedlings wereinoculated with CLRV isolates, leaves developed chlorotic ringand blotch patterns; the symptoms being similar whether theinocula were originally isolated from S. nigra, P. avium orB. verrucosa. Palisade and mesophyll cells of naturally infectedleaves of B. verrucosa contained chloroplasts in which granalorganization was appreciably less distinct than that of chloroplastsfrom virus-free leaves. In many instances, virus-infected leafcells had spherical virus-like particles about 30 mn in diametercontained within tubular structures in cell wall projections;these structures were not seen in virus-free material. An isolate of CLRV from B. verrucosa, purified from systemicallyinfected leaves of Nicotiana clevelandii Gray by ammonium sulphateprecipitation and differential centrifugation, contained twomajor components having sedimentation coefficients of 118s and130s. Each component was composed of spherical particles withdiameters in the range 26–30 nm and having buoyant densitiesin caesium chloride of 1·460 and 1·493 gm/cm³.Polyacrylamide gel electrophoresis of preparations from bothbuoyant components indicated that they each contained a singlespecies of protein whose molecular weight was in the range 53,000–54,000daltons.     

橡胶籽的化学成分与综合利用初探

以乙醚为溶剂测定了橡胶籽的含油率，并通过气相色谱对橡胶油的脂肪酸组成进行了定性定量测定，确证了８ 种脂肪酸的组成和它们的相对含量，同时，对橡胶饼中的化学组成也进行了定性定量分析，确定了氰甙的存在和蛋白质等组分的含量．分析了利用橡胶籽加工肥皂、食用油、油漆、润滑油、饲料等可行途径，为综合开发利用橡胶籽资源，提供了理论依据．     

Studies on conidial germination of Cylindrocladium quinqueseptatum,causing leaf blight of Eucalyptus in India1

In vitro germination of conidia of Cylindrocladium quinqueseptatum Boedijn & Reitsma, a cause of leaf blight of Eucalyptus spp., began after 4.5 h of incubation and attained approx. 95 % within 8 h; germination was optimal at 25°C. Conidial germination on the intact leaves of 2-month-old E. grandis occurred after 3 h of incubation. Formation of appressorium over the epidermal cells was recorded first on the abaxial surface of leaves at 6 h and later on the adaxial surface. Formation of appressorium over the stomata was found only very rarely and most leaf penetrations occurred directly through epidermal cells.     

Vegetative compatibility types of Cryphonectria parasitica,causal agent of chestnut blight,in the Black Sea region of Turkey

Vegetative compatibility types (vc types) of 296 isolates of the chestnut blight fungus, Cryphonectria parasitica, were determined. The isolates had been obtained from 32 localities in 11 provinces in the Black Sea region of Turkey. Five vc types were detected: EU‐1, EU‐12, EU‐14, EU‐2 and EU‐5. The number of vc types found in single provinces varied between one and five. All of the five vc types were present only in the Kastamonu province. Vc type EU‐1 was detected in all the provinces. EU‐1 accounted for 90.8% of all isolates. Vc type EU‐12 was present in eight provinces and accounted for 6.8% of the isolates, whereas one or two isolates each of EU‐14, EU‐2 and EU‐5 were found in one or two provinces. Isolates possessing the white colony phenotype were considered to be hypovirulent. Hypovirulent isolates of each vc type were found, and they were detected in nine of 11 provinces.     

美洲栗抗疫病基因工程研究简介

该文介绍美国纽约州立大学环境科学院与林学院正在进行的美洲栗抗疫病基因工程研究 ,包括基因的选择、构建及初步结果     

Outbreak of shoot blight and dieback of Eucalyptus spp., caused by Pseudoplagiostoma eucalypti in Brazil

An outbreak of a new and severe disease was observed in Eucalyptus plantations of Bahia state, Brazil. An Ascomycota fungus has been frequently associated with the main symptoms of the disease namely leaf spot, branch cankers, shoot blight, defoliation, and dieback. Based on morphological characteristics, phylogenetic analysis (ITS and TEF-1α genes), and pathogenicity test on Eucalyptus plants, Pseudoplagiostoma eucalypti was identified as the causal agent of the disease. Although P. eucalytpi has been known from in Brazil since 1998, this is the first report of it causing severe disease and die-back on Eucalyptus spp. and we also record new symptoms associated with the pathogen.     

Allelopathy in agroforestry systems: the effects of leaf extracts ofCupressus lusitanica and threeEucalyptus spp. on four Ethiopian crops

The potential allelopathic effect ofCupressus lusitanica, Eucalyptus globulus, E. camaldulensis andE. saligna on seed germination, radicle and seedling growth was investigated with four crops:Cicer arietinum (chickpea),Zea mays (maize),Pisum sativum (pea) andEragrostis tef (teff). Aqueous leaf extracts of all the tree species significantly reduced both germination and radicle growth of the majority of the crops mostly starting from concentrations of 1% or 2.5%. The shoot and root dry weight increase of the crops was significantly reduced after 10 weeks treatment with leaf extracts. Among the four crops, chickpea and teff were most susceptible with respect to germination, and teff with respect to growth. From the overall data the leaf extracts of the four tree species can be arranged according to increasing allelopathic potential:C. lusitanica, E. globulus, E. saligna andE. camaldulensis. It is suggested that the planting ofE. camaldulensis andE. saligna in integrated land use systems should be minimized, whereas the use ofC. lusitanica andE. globulus seems less environmentally damaging in this respect.     

Identification and pathogenicity of Alternaria alternata causing leaf spot and blight disease of Ailanthus excelsa in India

Alternaria leaf spot of Ailanthus excelsa is generally considered as minor disease in India. Recently, severe disease outbreaks were recorded in the nursery of the Forest Research Institute, Dehradun, progeny trial at Jhumpa, Haryana, and in a nearby farm field. Leaf symptoms included small circular, brown, necrotic spots with a chlorotic halo. With severe infections, leaf spots coalesced and resulted in leaf blight. A small‐spored Alternaria with concatenated conidia was isolated consistently from the leaf samples with spot symptoms. Sequence analyses of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) and the translation elongation factor 1‐alpha (tef‐1α) gene region of two fungal isolates confirmed the species as A. alternata. In detached leaf assays, both isolates produced symptoms similar to those observed on the nursery/field‐grown plants. To validate the detached leaf assay result, pathogenicity was also demonstrated on whole plants in a glasshouse. Koch's postulates were fulfilled by re‐isolating A. alternata from the inoculated leaves. This work is the first to confirm that A. alternata is associated with leaf spot and blight disease of A. excelsa in India.