The mango sudden decline pathogen, Ceratocystis manginecans, is vectored by Hypocryphalus mangiferae (Coleoptera: Scolytinae) in Oman

In Oman, the bark beetle Hypocryphalus mangiferae is closely associated with trees affected by mango sudden decline disease caused by Ceratocystis manginecans. Although it has previously been assumed that this beetle plays a role in the dispersal of the pathogen, this has not been established experimentally. The aim of this study was to determine whether H. mangiferae vectors C. manginecans from infected to healthy mango trees. A survey conducted in northern Al Batinah region of Oman revealed that H. mangiferae was closely associated with mango sudden decline disease symptoms and it was found on trees in the early stages of the disease. Healthy, 2-year-old mango seedlings were exposed to H. mangiferae collected from diseased mango trees. Seedlings were infested by the bark beetles and after 6 weeks, typical mango sudden decline disease symptoms were observed. Ceratocystis manginecans was isolated from the wilted mango seedlings while uncolonized control seedlings remained healthy. The results show that H. mangiferae vectors C. manginecans in Oman and is, therefore, an important factor in the epidemiology of this disease.     

Accumulation of phytoalexins in leaves of plane tree (Platanus spp.) expressing susceptibility or resistance toCeratocystis fimbriata f. sp.platani

Inoculation of leaves of resistantPlatanus occidentalis and susceptiblePlatanus acerifolia leaves withCeratocystis fimbriata f. sp.platani, the canker stain disease agent, induced foliar necrosis and biosynthesis of two phytoalexins, scopoletin and umbelliferone. Foliar symptoms keep localized and accumulation of coumarin phytoalexins was rapid for incompatible interactions. Necrosis spread widely and accumulation of these phenolic compounds was much later and lower for compatible interactions. The differential response could be used in a genetic improvement program for resistance against canker stain.     

Assessment of resistance to <Emphasis Type="Italic">Ceratocystis cacaofunesta</Emphasis> in cacao genotypes

Ceratocystis wilt of cacao (caused by Ceratocystis cacaofunesta) is a dangerous disease and results in the death of the plant. This fungus was recently identified in the major cacao-producing regions of Brazil, and was observed to be more aggressive than isolates from other geographical locations. The objective of this study was to develop and test a consistent method to assess cacao genotype response to C. cacaofunesta, based on young plants (seedlings or cuttings). The fungus was inoculated by the deposition of propagule suspensions on cut stems. The parameters to assess disease progress were (a) disease incidence, (b) differences in mortality between the most contrasting cacao genotypes for resistance and susceptibility, (c) disease index, (d) consistency of response over time and (e) relative lesion heights. When seedlings were used for the analyses, the ICS-1 and TSH-1188 genotypes proved to be useful as genetic standards for susceptibility and resistance to C. cacaofunesta, respectively. Inoculum concentrations between 10⁴ and 10⁵ propagules ml⁻¹ and the moment at which the disease incidence stabilized provided appropriate conditions for genotypic comparison. When ten cacao genotypes propagated by cuttings (clones) were assessed, the results confirmed TSH-1188 as the reference genotype for resistance to C. cacaofunesta, while the remaining clones could be grouped as resistant (CEPEC-2008), moderately resistant (CEPEC-2002, CEPEC-2007) and susceptible (CEPEC-2009, CCN-10, CCN-51, HW-25, PH-16, SJ-02). The analytical concepts and results were discussed in terms of their application in breeding programmes aimed at developing genetic resistance to Ceratocystis wilt of cacao.     

Histopathological aspects of mango resistance to the infection process of Ceratocystis fimbriata

Mango wilt, caused by Ceratocystis fimbriata, is one of the most important diseases affecting mango yields in Brazil. Information regarding the infection process of C. fimbriata in the stem tissues of mango from different cultivars and the basis of host resistance to the pathogen is rare in the literature. Thus, the objective of the study was to investigate how infection by two isolates of C. fimbriata can be affected by mango cultivar‐specific mechanisms of resistance. Disease progress on the inoculated stem tissues of the mango cultivars was evaluated and stem sections were obtained from the site of inoculation and prepared for histopathological observations using light microscopy. The factors mango cultivars and C. fimbriata isolates and their interaction were significant for all measures of disease development. Plants from the cultivars Espada, Haden and Palmer inoculated with isolates of C. fimbriata were more susceptible, whereas plants from the cultivars Tommy and Ubá were moderately resistant and resistant, respectively. Histopathologically, fungal isolates apparently massively colonized the stem tissues of plants from the susceptible cultivars Espada, Haden and Palmer, starting from the collenchyma and moving in the direction of the cortical parenchyma, xylem vessels and pith parenchyma. By contrast, on stem tissues of plants from the resistant cultivars Tommy Atkins and Ubá, most of the cells reacted to C. fimbriata infection by accumulating amorphous material. The results from the present study strongly indicated the importance of phenolic compounds for mango cultivar resistance against infection by Brazilian C. fimbriata isolates.     

Genetic diversity and interfertility among highly differentiated populations of Ceratocystis fimbriata in Brazil

Mating studies showed that isolates of the insect‐associated wilt pathogen Ceratocystis fimbriata from Eucalyptus spp., mango, fig, inhame (Colocasia esculenta), Gmelina arborea and sweet potato were interfertile, and progeny from those crosses showed normal segregation for microsatellite markers. Genetic diversity was compared among 13 populations of C. fimbriata collected from six states in Brazil using 15 highly polymorphic microsatellite markers. The gene diversity values of most eucalyptus and mango populations from Minas Gerais, Bahia, Rio de Janeiro and São Paulo states were similar to putatively native populations of Ceratocystis platani and C. cacaofunesta, two other species in the C. fimbriata complex that are homothallic. Index of association values indicated substantial asexual reproduction or selfing in populations on mango and eucalyptus. Most of these eucalyptus and mango populations were not highly differentiated from each other, and these populations and genotypes appeared to be more closely related to each other than to other populations by upgma analyses. By contrast, the G. arborea population from Pará and the fig and inhame populations from São Paulo had relatively low levels of diversity and were highly differentiated from each other and all other studied populations, suggesting that they were from different origins and had gone through genetic bottlenecks. One of the eucalyptus populations in Bahia consisted of a single genotype and may have been introduced to the site in infected cuttings from another Bahia location. Similarly, a mango population from Mato Grosso do Sul consisted of a single genotype, which was identical to one of the genotypes found on mango in São Paulo. Aside from introductions by humans, mating studies and genetic analyses suggest that limited dispersal distance and a high degree of selfing or asexual reproduction lead to local populations of C. fimbriata that have limited diversity but are highly differentiated from other populations.     

海南省芒果可可球二孢对多菌灵的敏感性及菌株适合度研究

针对中国海南地区芒果蒂腐病致病菌可可球二孢对多菌灵的抗性水平及菌株的适合度进行了研究。采用区分剂量法,测定了2016年从海南省芒果园采集、分离的90株可可球二孢对多菌灵的敏感性,并对抗性及敏感菌株在菌丝生长、致病力、渗透压及相对渗率等方面进行了比较。结果表明:海南地区芒果可可球二孢对多菌灵的抗性频率为65.56%,且以高抗菌株为主（8个中抗菌株,51个高抗菌株）;该病菌对芒果危害甚大,其中具强致病力的菌株达65株,占72.22%。高抗菌株的菌丝生长优于敏感菌株,存在极显著差异（P0.01）;抗性菌株的致病力与敏感菌株无显著差异;敏感菌株的相对渗率高于抗性菌株,表明敏感菌株细胞膜的透性较高,胞内电解质渗出较多。研究表明,海南地区芒果可可球二孢对多菌灵的抗性水平较高,且抗性菌株适合度高于敏感菌株,易形成优势群体。     

Ceratocystis fimbriata‐induced changes in the antioxidative system of mango cultivars

Mango wilt is one of the most important diseases affecting mango production, yet the physiological mechanisms underlying host responses to this fungal infection are poorly known. The disease attenuation displayed by some mango cultivars might be related to higher antioxidant capacities in leaves. To test this hypothesis, the activities of a range of enzymes (e.g. superoxide dismutase and catalase) and metabolites (e.g. ascorbate and glutathione) involved in the antioxidant system, as well as some markers for oxidative stress (e.g. hydrogen peroxide and malondialdehyde equivalents), were evaluated for 30 days after the inoculation of mango plants with Ceratocystis fimbriata. Tommy Atkins plants displayed higher values for the upward, downward and radial fungal colonization of the stem tissues than Ubá plants. In contrast to the working hypothesis, Tommy Atkins plants exhibited more prominent increases in enzyme activities and metabolite concentrations related to oxidative stress responses. These increases were minimal, if any, in Ubá plants. These results suggest that Tommy Atkins plants are less effective at restraining fungal spread through vascular tissues and thus trigger leaf antioxidant defences to cope with the developing stress.     

Populations of Ceratocystis fimbriata on Colocasia esculenta and other hosts in the Mata Atlântica region in Brazil

Ceratocystis fimbriata is native to Brazil, where it is able to cause serious diseases on numerous hosts, especially on non‐native plants. Because C. fimbriata is soilborne and not wind dispersed, highly differentiated populations are found in different regions of Brazil. The present study compared populations of C. fimbriata on taro, mango, eucalyptus and kiwifruit from the coastal Mata Atlântica region with native populations of the fungus from the Cerrado‐transition region in Brazil by using 14 SSR markers and DNA sequences of ITS and mating type genes. Microsatellite and phylogenetic analyses were performed to test the hypothesis that populations on different hosts from the Mata Atlântica region are related to each other and are native to the region. The ITS sequences varied greatly among the taro isolates, with six sequences identified, from which two had not been previously reported. For mating type genes, four sequences were identified among the isolates on taro, mango, eucalyptus and kiwifruit. Phylogenetic analyses showed that Mata Atlântica populations formed a monophyletic group distinct from Cerrado‐transition region populations, although earlier studies had shown that isolates from the two regions are interfertile and are considered as a single biological species. Microsatellite analysis revealed low gene diversity for each of the three Mata Atlântica populations on taro, mango and kiwifruit, suggesting that these populations had gone through genetic bottlenecks, probably by dispersal of select genotypes in vegetative propagation material. Also, microsatellite markers showed that two microsatellite genotypes from taro are widely spread in Brazil, probably by infected corms.     

Cigar‐end disease of banana in the southern region of Oman (Dhofar)

Abstract

Cigar‐end disease of banana, Verticillium theobromae has become apparent in the southern region of Oman, and is prevalent under warm and humid conditions. Benomyl and thiabendazole were found to effectively control V. theobromae in artificially induced cigar‐end disease.     

<Emphasis Type="Italic">Fusarium mangiferae</Emphasis> associated with mango malformation in the Sultanate of Oman

Mango malformation, caused by Fusarium mangiferae, represents the most important floral disease of mango. The first symptoms of this disease were noticed in the beginning of 2005 in plantations at Sohar in the Sultanate of Oman. The affected inflorescences were abnormally enlarged and branched with heavy and dried-out panicles. Based on morphology and DNA-sequence data for the genes encoding translation elongation factor 1α and β-tubulin, the pathogen associated with these symptoms was identified as F. mangiferae.     

Assessment of the spread of chestnut ink disease using remote sensing and geostatistical methods

Chestnut ink disease, caused by Phytophthora cinnamomi and P. cambivora, is responsible for important economic losses and limits the establishment of new chestnut (Castanea sativa) groves in Portugal. Although the differences in soil properties and in cropping practices affect ink severity, the regional spread of disease is not known. Data for monitoring C. sativa decline were obtained by using field surveys and Small Format Aerial Photography (SFAP), a reliable tool which provides large-scale imagery obtained at low altitude. Visible colour and near-infrared images were obtained with different cameras with an average ground resolution of 22, 14 and 39 cm. The spatial distribution of ink disease in northern Portugal for the years 1995–2004 was estimated through a geostatistical method, and the estimation of precision was determined. From 1995–2002, the chestnut population in the study area increased by 18.5% due to new orchard plantations. After 2002 the population decreased because the new plantations were not sufficient to recover the number of dead chestnut trees, killed mostly by ink disease. The directional semivariograms indicated anisotropy with a greater disease spread in the NE–SW direction. This direction corresponds to site areas at the same altitude, where soil tillage and human mobility are higher.     

Sudden Oak Death, A New Forest Disease in California

A forest disease caused by a newly described pathogen, Phytophthora ramorum, is presently affecting a number of woody plant species in central and northern coastal California and southern Oregon, U.S.A. Among the most severely affected tree species are coast live oak, Quercus agrifolia, and tanoak, Lithocarpus densiflorus. In March 2000, we established plots in Marin County, CA, to assess symptom progression and the association of other organisms with diseased trees. Symptomatic trees exhibit 'bleeding' of viscous sap from apparently intact bark, typically within approximately 2 m of the soil. At least three species of bark and ambrosia beetles colonize bleeding oaks. These beetles colonized every bleeding tree that died during the first year of the study (N = 23) while the foliage was still green. By March 2001, numbers of symptomatic and dead trees increased for both coast live oak and tanoak. Symptomatic coast live oaks totaled 26% in March 2000 and 27% in March 2001. During the same period, mortality increased from 6% to 10%. For tanoaks, 41% were symptomatic in 2000, rising to 49% in 2001. Mortality was 11% in 2000 and 13% in 2001. The values for coast live oak are broadly consistent with independently acquired infection and mortality estimates derived from an unbiased transect method.     

Spatial and temporal analysis of coffee wilt disease caused by Fusarium xylarioides in Coffea canephora

Coffee wilt disease (CWD) caused by Fusarium xylarioides, considered to be a soil-inhabiting fungus, is endemic in several African countries, affecting commercially important coffee species and causing serious economic losses. Coffee wilt disease development in naturally infected Coffea canephora fields at the Coffee Research Institute in Uganda was assessed from April 2001 to March 2006 to generate information about temporal and spatial spread of the disease. Maps of diseased trees were also generated from the data. Semi-variance analysis was performed on the data to show the spatio-temporal structure of disease. Host influence on the spatio-temporal structure was deduced from the distribution pattern of diseased and healthy trees and analysis of variance. Results show that the temporal disease epidemic progress was slow. The disease was found to spread from initial infections to healthy neighbouring trees, resulting in an aggregated pattern. An infected tree could infect up to three healthy trees away, in any direction. Disease foci formed and expanded with time, coalescing but punctuated in spots planted with resistant hosts. There were varying levels of susceptibility among host genotypes, affecting the rates and levels of epidemic development. The implications of the findings to the control of CWD are discussed.     

Scytalidium Wilt of Citrus

In July 1998, a sudden wilt of Star Ruby grapefruit (Citrus paradisi Macf.) occurred in Israel in a region with a warm Mediterranean climate. The wilt of the middle and upper canopy of main limbs was accompanied by gum oozing from the affected branches. The bark of these branches attained a dark colour and the epidermis sloughed off easily revealing a mass of black powder, resulting from copious sporulation of dark conidia. Both the bark and the xylem were intensively colonized with mycelium. The fungus was identified as Scytalidium lignicola Pesante, based on the characteristic mixture of some colourless and dark conidia, produced in branched chains by conversion of the vegetative hyphae. Artificial inoculations induced typical disease symptoms and the fungus was reisolated, thus confirming Koch's postulates. Similar symptoms appeared in Star Ruby interim segments which had been cut and top grafted with various citrus cultivars. This is the first detailed report of pathogenicity of S. lignicola to citrus trees. It is postulated that the disease developed after predisposition of Star Ruby grapefruit trees by comprehensive pruning followed by extremely hot conditions.     

Xylem sap flow of Norway spruce after inoculation with the blue-stain fungus Ceratocystis polonica

In a field experiment, the sap flow of Norway spruce ( Picea abies ) was measured in response to inoculation with Ceratocystis polonica , a virulent fungal associate of the spruce bark beetle Ips typographus. Four vigorous, mature Norway spruce trees were mass-inoculated with C. polonica at a density of four inoculations per dm² within a 120-cm-wide band on the lower bole. Two other trees were inoculated with sterile agar and served as controls. Sap flow of the six trees was measured by the thermal dissipation method from three weeks prior to inoculation until five months after inoculation. In three trees that had been inoculated with the fungus, sap flow density decreased dramatically within the first weeks after inoculation until no sap flow was measurable 4–6 weeks after inoculation. No marked changes in sap flow density were recorded in the fourth tree that had been inoculated with C. polonica , and this tree survived the inoculation. Inoculation with sterile agar did not have any apparent influence on the sap flow of the control trees. The results confirm the ability of C. polonica to kill mature Norway spruce trees. Sap flow measurements by the thermal dissipation method provided a direct and nondestructive method for monitoring the effects of fungal infection on sapwood functionality. Its application for further studies on vascular wilt and vascular stain diseases of trees is therefore recommended.     

Effect of phenology on susceptibility of Norway spruce (Picea abies) to fungal pathogens

Ceratocystis polonica and Heterobasidion parviporum are important fungal pathogens in Norway spruce (Picea abies). Tree susceptibility to these pathogens with respect to phenology was studied using artificial fungal inoculations at six stages of bud development, and assessed by measuring phloem necroses in the stems of 2‐ and 8‐year‐old trees. Tree capacity for resistance was assessed by measuring phloem nonstructural carbohydrates at each stage. Phloem necroses were significantly larger in trees with fungal versus control inoculations and increased significantly over time. Changes in nonstructural carbohydrates occurred in the trees; a significant decline in starch and a slight but significant increase in total sugars occurred over time. These results suggest that susceptibility to fungal pathogens and carbohydrate levels in the stems of the trees were related to fine‐scale changes in bud development. A trade‐off may occur between allocation of starch (the major fraction of the stem carbohydrate pool) to bud development/shoot growth versus defence of the stem. Previous tests of plant defence hypotheses have focused on herbivory on plants growing under different environmental conditions, but the role of phenology and the effect of pathogens are also important to consider in understanding plant resource allocation patterns.     

Pine Wilt Disease Caused by the Pine Wood Nematode: The Induced Resistance of Pine Trees by the Avirulent Isolates of Nematode

Since the beginning of the 20th century, pine trees in Japan have been seriously damaged by the pine wilt disease. This disease is caused by the pine wood nematode, Bursaphelenchus xylophilus, which is transmitted by the Japanese pine sawyer, Monochamus alternatus. The control of disease depends to a large extent on chemicals, but the public is now demanding environmentally friendly control methods. The virulence of B. xylophilus varies very widely. Pre-inoculation of young pine trees in a nursery with avirulent B. xylophilus has induced systemic resistance of trees against a subsequent inoculation with virulent B. xylophilus. This induced resistance was considered a hopeful means for developing a biological control for the disease. The induced resistance by the avirulent nematodes was also expressed in mature pine trees in a forest where the disease was naturally epidemic. However, the effects of induced resistance were not satisfactory for practical biological control. Since the inoculation with higher concentrations of the avirulent B. xylophilus induced the resistance more effectively, the pre-inoculation method will need to be improved to develop the biological control. The induced resistance of pine trees by avirulent B. xylophilus should be one of the candidate biological control methods against pine wilt disease. This induced resistance also provides an experimental system to clarify physiological interactions between the nematodes and pine trees.     

Spongy tissue development in Alphonso mango: association with <Emphasis Type="Italic">Staphylococcus xylosus</Emphasis>

A Gram-positive and catalase positive Staphylococcus strain was found to be associated with spongy tissue defect of Alphonso mango. The organism was identified to species level by physiological, morphological and biochemical characterization and fatty acid profile. The strain was identified as Staphylococcus xylosus (IMTECH, India, Accession No. MTCC 7441). The optimal growth of the organism was observed in the pH range of 5.0–9.0 and temperature range of 10–45°C. It was mannitol and arabinose-positive and able to produce acid from various sugars. The organism was able to grow in a medium containing 2–10% NaCl. It was further identified to species level by genomic sequencing of 1,387 base pairs of DNA (Gene Bank accession No. EU019195). Based on nucleotide homology and phylogenetic analysis, the microbe was found to be S. xylosus. The survey of Alphonso mango trees with a known history of producing spongy fruits showed that some of the twigs, leaves and flowers were coated with a honeydew-like sticky substance and mango hopper insects were observed over the inflorescence. The source of contamination of spongy fruits by S. xylosus was in the sticky mass. Gram staining, the catalase test and morphological features of the culture isolated from the sticky mass exhibited characteristics identical to the Staphylococcus strain isolated from the spongy pulp. Pathogenicity tests on different varieties of mangoes, apples and guavas indicated that the disease was experimentally transmitted from infected to healthy fruits. This observation suggested that this organism develops spongy symptoms in the fruits post-harvest and lacks specificity. In inoculated fruits, catalase and peroxidase enzymes were expressed as in naturally infected fruits. This report shows that the infection by S. xylosus could be a major initiating factor for spongy tissue development in Alphonso mangoes.     

Non-Host Volatiles Disrupt the Response of the Stenographer Bark Beetle, Ips sexdentatus (Coleoptera: Scolytidae), to Pheromone-Baited traps and Maritime Pine Logs

Non-host volatiles (NHV) were tested on antennae of Ips sexdentatus with coupled gas chromatographic-electroantennographic detection (GC-EAD). Significant antennal responses were found to aggregation pheromone components, ipsdienol and amitinol, an attraction inhibitor, verbenone, and non-host bark volatiles extracted from Betula pendula, including trans-conophthorin (tC) and alcohols. The tC, a blend of three green leaf alcohols (C6-alcohols), and a blend of two bark alcohols (C8-alcohols) were tested in combination for their ability to disrupt the attraction of the stenographer bark beetle to pheromone-baited traps, unbaited and pheromone-baited maritime pine logs. The strongest disruptive effect resulted from the addition of the tC combined with the blends of NHV alcohols at high release rate, achieving an 83% reduction in trap catches, 89% reduction of attacks on unbaited pine logs, and 60% on baited logs. It is proposed that the two types of NHV have an additive effect, tC playing a major role in pheromone disruption while the alcohols would interrupt host specific signals. The results suggest that I. sexdentatus uses both bark and green leaf volatiles from non-host tree species in the host selection process. These NHV are promising disruptants, which could be used to prevent stenographer bark beetle attacks on log piles or standing trees in forest. A mixture of conifers and broad-leaved species would also disturb olfactory guided host selection supporting the assumption that more diverse forests are less prone to pest insect outbreaks.     

Induced cell death in Ceratocystis fimbriata by pro-apoptotic activity of a natural organic compound,perillaldehyde, through Ca2+ overload and accumulation of reactive oxygen species

Black rot caused by the fungus Ceratocystis fimbriata causes notable losses in sweet potato production. Perillaldehyde (PAE), a secondary metabolite in perilla, was studied to determine its antifungal effects on mycelial growth and spore germination of C. fimbriata. The effects of PAE on cell wall integrity and cell membrane permeability were also investigated. To elucidate the possible mechanisms of cell death triggered by PAE, sensitivity of C. fimbriata to PAE toxicity was determined by cytoplasmic and mitochondrial calcium ion concentrations ([Ca²⁺]c and [Ca²⁺]m), reactive oxygen species (ROS), mitochondrial membrane potential (MMP), cytochrome c (cyt c) release, metacaspase activation, phosphatidylserine (PS) externalization and DNA fragmentation. The results suggest that mycelial growth and spore germination were inhibited by PAE in a dose-dependent manner. Ceratocystis fimbriata spores treated with PAE experienced dramatic Ca²⁺ overload and elevated ROS production. Compared to untreated controls, the proportion of fluorescent cells stained with the ROS indicator DCFH-DA and treated with a range of PAE concentrations from 0.0625 to 0.50 μL mL⁻¹ increased by 2.9 ± 0.79% to 27.1 ± 0.38%. Ca²⁺ overload and ROS accumulation induced depolarization of the MMP, contributing to mitochondrial dysfunction. Cyt c was released from the mitochondria to the cytosol, triggering metacaspase activation. The significant antifungal activity of PAE on C. fimbriata was demonstrated by these studies, suggesting that PAE has the potential for wide application to postharvest management of tuber crops, in addition to the application to above-ground fruit and vegetables that have been previously investigated.