Experiments with MBC derivatives for the control of Dutch elm disease

Preparations of methyl benzimidazol-2-ylcarbamate (MBC) hydrochloride stabilized with HC1, MBC nitrate stabilized with lactic acid and MBC bisul-phate stabilized with KHS0₄ were made from technical MBC. As it was the least phytotoxic to elm shoots, the hydrochloride was selected for field experiments on the control of Dutch elm disease using 6 m elms. In protectant experiments using 1.51 of 0.25 or 0.5 % MBC per tree, only five of eighteen injected trees became infected while all the control trees were severely diseased. In curative experiments, injection with 0.25 % MBC 2 and 4 wk after inoculation with Ceratocystis ulmi kept symptoms to < 1 and 5% respectively, compared with 76% in untreated inoculated trees. MBC at 0.5 % Save similar results.     

Role of birds in dissemination of the thread blight disease caused byCylindrobasidium argenteum

The thread blight disease of broad leaved trees caused byCylindrobasidium argenteum occurred in laurel forests over 20 yr old after clear cutting in Kyushu. Finding fruit bodies of the causal fungus was possible but very difficult in the forests. In inoculation tests using spores and infected branches harvested in the forests, we succeeded in transmission only with branches. In the forests, the disease is transmitted almost entirely by contact with infected branches. During 1989 to 1992 we found four brown-eared bulbul nests containing branches infected with the disease. In one nest, mycelia of the fungus had been transmitted to the host tree. The occurrence of the disease in forests over 20-yr-old was considered to be due to the nesting of birds in trees which provided the necessary height and closed environment.     

Feeding by Scolytus bark beetles to test for differently susceptible elm varieties

Dutch elm disease (DED), caused by the fungi Ophiostoma ulmi and O. novo‐ulmi, has reduced elm populations severely in Europe and North America. Breeding programmes are in action to find less susceptible elm varieties suitable for re‐establishing elm stands. Bark beetles, mainly Scolytus spp., are the only known natural vectors of DED. During twig feeding, beetles transfer Ophiostoma spores to healthy elms. Thus, less palatable elms should run a lower risk of DED infections. In feeding preference bioassays, we offered twigs from elms exhibiting different degree of susceptibility to O. novo‐ulmi, together with non‐host trees to Scolytus beetles. Scolytus multistriatus preferred wych elm, Ulmus glabra, to 100% in two‐choice tests, whereas S. laevis did not discriminate between a tolerant and a susceptible variety of field elm, U. minor. We suggest that the feeding assay is useful as a low‐tech method in breeding programmes for evaluating the suitability of promising elm genotypes to vector insects.     

Metabolic distinction of Ulmus minor xylem tissues after inoculation with Ophiostoma novo-ulmi

Dutch elm disease (DED) is the most devastating and widespread disease of elms. The pathogen, Ophiostoma novo-ulmi, spreads systemically causing xylem vessels blocking and cavitation, and ultimately resulting in the development of a wilt syndrome. Twig samples from susceptible and resistant Ulmus minor trees were harvested at 0, 5, 15, 30, 60, and 120 days post-inoculation (dpi) with O. novo-ulmi. Fourier transform-infrared (FT-IR) spectroscopy, in tandem with chemometrics, was used to monitor changes in wood chemistry as consequence of infection. Principal component analysis distinguished between spectra from inoculated and control elms, and from susceptible- and resistant-inoculated elms. By 30 dpi, infected xylem showed reduced relative levels of carbohydrates and enhanced relative levels of phenolic compounds, probably due to the degradation of cell wall polysaccharides by fungal enzymes and the synthesis of host defence compounds. On 15 dpi, samples from resistant-inoculated elms showed higher levels of starch than samples from susceptible-inoculated elms, suggesting that availability of starch reserves could affect the tree's capacity for defensive responses. The results showed the power of FT-IR spectroscopy for analysing changes in the major components of elm xylem as consequence of infection by DED, and its potential for detecting metabolic profiles related to host resistance.     

The pathogen causing Dutch elm disease makes host trees attract insect vectors

Dutch elm disease is caused by the fungal pathogen Ophiostoma novo-ulmi which is transmitted by the native elm bark beetle, Hylurgopinus rufipes. We have found that four semiochemicals (the monoterpene (-)-beta-pinene and the sesquiterpenes (-)-alpha-cubebene, (+)-spiroaxa-5,7-diene and (+)-delta-cadinene) from diseased American elms, Ulmus americana, synergistically attract H. rufipes, and that sesquiterpene emission is upregulated in elm trees inoculated with O. novo-ulmi. The fungus thus manipulates host trees to enhance their apparency to foraging beetles, a strategy that increases the probability of transportation of the pathogen to new hosts.     

Water-borne spore dispersal in coffee berry disease and its relation to control*

Devices are described which were used to catch rain-dispersed Colletotrichum conidia within and between coffee trees infected with coffee berry disease (CBD). The amount of CBD inoculum dispersed was related to the number of diseased and sporulating berries but not to the sporulating capacity of the fungus in maturing bark. Wet conditions encouraged spore production and dispersal, and spraying with fungicides prolonged sporulation of diseased berries. The amount of pathogenic inoculum, subsequent disease development and crop losses were greatly increased by the presence of only a few diseased berries during growth of the young crop. Spore concentrations were greatest close to diseased berries, but most spores within trees were dispersed downwards through the canopy. Some spores were dispersed between trees by wind-driven rain-splash and vectors such as pickers. Inoculum sources in tree tops are most important during CBD epidemics and disease can be restricted by removing or spraying the tops of multiple-stem trees. Fungicide applied to tree tops effectively controls CBD, because spores dispersed during rain are accompanied by redistributed fungicide     

VIRUS DISEASES OF CACAO IN WEST AFRICA IX. STRAIN VARIATION AND INTERFERENCE IN VIRUS 1A

Cacao virus iA, the most important and prevalent of the viruses that attack cacao in the Gold Coast, occurs in strains that differ widely in their virulence towards cacao. Outbreaks usually contain trees infected with different strains and individual trees are often infected simultaneously with more than one strain; this can be demonstrated by coppicing the trees, and by inoculating sets of test plants with grafts from different parts of one tree. Neither mild nor virulent strains seemed to be consistently dominant in roots or in other parts of cacao trees.
Cacao plants infected with mild strains were nearly always protected against the effects of infection by virulent strains; however, virulent strains entered hosts already infected with mild strains, but usually without causing any symptoms unless the plants were coppiced. The severe symptoms that developed on new growth from such coppiced plants were seldom repeated in later growth. Mealybugs transmitted the virulent strains from leaves with symptoms characteristic of infection by the latter, but not from leaves free from such symptoms. These results suggest that the multiplication of a virulent strain is impeded in plants infected with a mild strain.
In the field, infection with a mild strain protected mature trees against the effects of virulent strains spread by mealybugs. During 3 years in which 273 out of 387 previously uninfected trees became severely diseased, only 35 out of 416 infected with themildstrain developed symptoms of infectionwiththevirulent strain. Five years after infection with the mild strain, trees were yielding I pod per tree more than in the year they were infected, whereas the decrease on trees infected with the virulent strain was 16 pods per tree. Some limitations in the practical application of protection by mild strains, and objections to its use as a control measure, are discussed.     

COPPICING EXPERIMENTS ON THE SPREAD AND CONTROL OF CACAO SWOLLEN-SHOOT DISEASE IN NIGERIA

A coppicing technique was used to determine the incidence and distribution of latent and unrecognized infection around naturally occurring outbreaks of cacao swollen-shoot virus disease in Western Nigeria. All the apparently healthy trees within 30 yards of eighty outbreaks of various sizes were coppiced and most of the infected stumps which regenerated showed symptoms within a year.
The distribution of the infected stumps around thirty-five outbreaks studied in detail is expressed by the equation log₁₀ I = a + bx. I is the estimated intensity of infection in the coppiced stumps at distance x from the nearest infected tree removed at the time of coppicing. The constant a determines the height of the peak of the infection gradient and increases with outbreak size, whereas the slope of the gradient, determined by the negative constant b , is similar around all outbreaks.
The results are consistent with information on the movement of the mealybugs and spread of cacao swollen-shoot virus in outbreaks. Moreover, they indicate that outbreaks are controlled most economically by removing all obviously infected trees and adjacent apparently healthy ones. Control does not require the destruction of all the trees around outbreaks up to a distance of 30 yards as done previously, but can be achieved by felling fewer trees, the actual number depending on the size of the outbreak.     

Overwintering form of the causal agent of shot hole disease in Khorasan Razavi, Iran

Shot hole disease of stone fruit trees caused by some plant pathogenic fungi is a major constraint to stone fruit production worldwide where the trees are grown. Identification of the causal agents of the disease and their overwintering forms in stone fruit trees of Khorasan Razavi was necessary for disease management programs. Buds, twigs, fallen leaves and fruits were collected from the infected peach, apricot, nectarine and almond trees in winter 2007. The samples were superficially disinfested in 1% sodium hypochlorite for 2-3 min and then in 70% ethanol for 45 sec. Two to three fragments of 4x4 mm from each tissue were separately cultured on 2% water agar and potato dextrose agar (PDA), and purified on PDA. Just a pathogenic fungal species, Wilsonomyces corpophilus was isolated from the infected buds and twigs. No microorganism was isolated from the fallen leaves and fruits collected from underneath of the infested stone fruit trees. Pathogenicity of the fungus was examined on detached shoots of current year of four varieties of stone fruit trees. Fungal discs were placed under the bark of the bud base. Control shoots were similarly treated with sterile PDA discs. Inoculated shoots were placed in a humid growth chamber at 25 degrees C. Fungal hyphae appeared at 30 days post inoculation. Control shoots were asymptomatic. Pathogenicity intensities or lesion lengths were significantly different among the four varieties tested. A completely randomised design with five replicates was employed to measure the number of spores in infested buds and twigs of each variety of stone fruit tree. The samples were sliced and placed into a glass tube of centrifuge containing 3 ml of sterile distilled water. They were mixed on a vortex mixer for 30-40 min and centrifuged at 3000 rpm for 5 min. Pelleted material from each sample was suspended in 500 microl of sterile distilled water and the spores were counted using a hemocytometre. Results revealed that the fungus overwinters as hyphae and conidia in the infected buds, and as hyphae and globular chlamydospores in twig lesions.     

A Review of the Biology and Pathogenicity of Rosellinia necatrix– The Cause of White Root Rot Disease of Fruit Trees and Other Plants

Rosellinia necatrix, an ascomycete soil‐inhabiting fungus, causes white root rot disease in a large number of plant species, especially fruit trees. The fungus, which occurs worldwide, is very aggressive and can kill infected trees. The biology and pathogenicity of the fungus are reviewed here, together with the current principal methods of disease control used in different pathosystems.     

Exogenous phenol increase resistance of Ulmus minor to Dutch elm disease through formation of suberin-like compounds on xylem tissues

The survival of some elms to Dutch elm disease (DED) epidemics could be related with the application of disinfectant products based on simple phenols. To test this hypothesis, the protective effect of different phenolic treatments in Ulmus minor trees was evaluated through inoculations with Ophiostoma novo-ulmi, the current DED pathogen. During spring 2004 and spring 2005, 4-year-old elms were: (i) watered with a 0.02% solution of the phenolic fraction of phenolic oil, (ii) watered with a 0.02 and 0.2% solution of a phenol–cresol mixture, and (iii) trunk injected with a 0.2% solution of phenol–cresol mixture. In May, trees were artificially inoculated with O. novo-ulmi. At the end of the 2004 and 2005 vegetative periods, phenol-treated trees showed significantly lower wilting values than control trees. One week of bud break delay was observed in trees watered with the 0.2% solution of phenol–cresol mixture. Fourier transform-infrared spectroscopy and electrospray ionisation mass spectrometry evidenced enhanced levels of suberin-like compounds in phenol-treated trees with respect to non-treated trees. The deposition of suberin in xylem tissues, as a response to phenol treatments, might be considered as one of the mechanisms of resistance of elms to O. novo-ulmi.     

VALSA EUGENIAE IN RELATION TO THE SUDDEN-DEATH DISEASE OF THE CLOVE TREE (EUGENIA AROMATICA)

The sudden-death disease of the clove tree is invariably associated with the fungus Valsa eugeniae. The pathogenicity of this fungus has been investigated experimentally, and it has been shown that it is a primary parasite on mature clove trees, that saplings are resistant to it, and that seedlings are immune. It has been experimentally demonstrated that water-borne spores of the fungus can invade the absorbing and the fibrous roots of the clove tree. The slow-decline disease, which affects clove saplings only, is associated with a slow and progressive root-rot over a period of many years. Valsa is also invariably associated with this disease, which occurs only in areas which have been replanted after the previous stand has been killed by sudden death. It is thought that slow decline is the symptom-expression of Valsa attack on young trees when these still retain some measure of juvenile resistance to it.     

The effects of cocoa swollen-shoot virus on the growth and yield of Amelonado and Amazon cocoa (Theobroma cacao) in Ghana

The virulent strain A of cocoa swollen-shoot virus (CSSV) severely decreased the growth and yield of Amelonado cocoa (Theobroma cacao) trees kept free of capsids (Distantiella theobroma and Sahlbergella singularis) and the dieback fungus (Calonectria rigidiuscula) in Ghana. Fifteen per cent of graft-inoculated Amelonado trees showed symptoms within 4 months, and 48, 80 and 100% within 6, 12 and 20 months, respectively. Infected trees, whether shaded or unshaded, began to decline 6 months after infection, and deteriorated rapidly during the next 27 months by which time 16 % had died and most others were moribund; fertilizer applications had no significant effect on the rate at which infected trees deteriorated. Yields of pods and dry cocoa were greatly reduced 2 yr after infection and were very low after 3 yr; yields were significantly reduced by virus infection but there were no significant further effects of applying fertilizer. These results confirm that CSSV strain A alone is very damaging and often eventually lethal to Amelonado trees in Ghana, and indicate that the conflicting results obtained previously in Ghana and Nigeria were probably due to differences in the virulence of the CSSV strains tested. In contrast, the virus had much less effect on cocoa trees of the Amazon type; only 3% of graft-inoculated Amazon trees showed symptoms within 4 months, and 43, 84 and 97% after 1, 2 and 3 yr, respectively. Slight deterioration of tree canopies was first detected c. 15 months after infection and, although it continued slowly during the next 21 months, the decline was much less severe than that of Amelonado trees. Yields of both unshaded and shaded trees were apparently reduced by virus infection, but yield losses were much smaller than those of Amelonado trees. These results support the present objectives of controlling the spread of CSSV in Ghana by roguing infected trees, and selecting cultivars with greater tolerance to infection for future use.     

Chemical changes in Ulmus minor xylem tissue after salicylic acid or carvacrol treatments are associated with enhanced resistance to Ophiostoma novo-ulmi

Application of endogenous plant hormone salicylic acid (SA) or essential oil component carvacrol (CA) in elms enhances tree resistance to the Dutch elm disease pathogen, although the effect of these compounds on tree metabolism is unknown. The chemical changes induced by SA or CA treatments in Ulmus minor were studied through gas chromatography–mass spectrometry (GC–MS) analysis of xylem tissues. Treatments consisted of fortnightly irrigating seedlings with water, SA or CA at 600 mg L⁻¹. The chemical composition of the xylem tissues sampled from treated trees was significantly altered depending on the treatment type. SA treatment induced an accumulation of the sinapyl alcohol, a precursor of lignin and other phenylpropanoid-derived products. CA treatment induced an accumulation of the methyl esters of palmitic, linoleic and stearic acids. Both treatments resulted in early bud burst and SA significantly reduced sapwood radial growth, possibly as a consequence of a trade-off between tree growth and tree defence. The enhanced resistance provided by these treatments is discussed.     

Can Norway spruce trees be ‘vaccinated’ against attack by Ips typographus?

1 A field experiment was carried out to test the hypothesis that treatment of Norway spruce trees with the Ips typographus-transmitted blue-stain fungus Ceratocystis polonica enhances tree resistance to later mass attack by this bark beetle. 2 Twenty-five mature trees were pretreated by inoculating a non-lethal dose of the fungus into the bark, while 18 trees served as untreated controls. Three and a half weeks after treatment a bark beetle attack was initiated by attaching dispensers with I. typographus pheromone to the tree trunks. 3 A significantly larger proportion (67%) of the control trees than of the pretreated trees (36%) were killed by the beetle attack. The result is discussed in relation to recent results regarding defence mechanisms in Norway spruce trees.     

Biocontrol of almond bark beetle (Scolytus amygdali Geurin-Meneville, Coleoptera: Scolytidae) using Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes)

AIMS: To formulate the entomopathogenic fungus Beauveria bassiana in invert emulsion, then apply it against adults of almond bark beetle (Scolytus amygdali) under laboratory and field conditions. METHODS AND RESULTS: The effect of formulated B. bassiana in invert emulsion against S. amygdali adults was shown by comparing the mortality percentage of adults exposed to the formulated fungus using a Petri dish treatment method and by field applications to infested peach trees with mortality of adults exposed to the unformulated fungus or the untreated control. Results obtained from both exposure methods have indicated that treatment of S. amygdali adults with the formulated fungus resulted in a significantly higher mean mortality percentage (P < 0.05) when compared with the treatment with the unformulated fungus or the untreated control. This mortality ranged from 81.2 to 100%, 10 days after treatment with the formulated fungus when compared with 6.7 to 49.6% mortality, 10 days after treatment with the control or the unformulated fungus, respectively. Viability of the fungus conidia in invert emulsion was assessed by calculating the germination percentage of the conidia over time. Results indicated a high storage stability shown by a small loss of germination percentage for the formulated conidia of both strains (5.8 to 8.4% over a 12-week period) vs a low storage stability shown by a high loss of germination percentage for the unformulated conidia of the same strains (58.9 to 61.0% over the same period). The presence of B. bassiana in the galleries of beetles following the treatment of infested trees was shown in the present research. CONCLUSIONS: The results obtained have demonstrated a significantly higher level of efficacy of formulated B. bassiana in invert emulsion against S. amygdali adults under laboratory and field conditions. The ingredients of invert emulsion used in the formulation of the fungus had a negligible effect on the viability of formulated conidia when compared with the unformulated. SIGNIFICANCE AND IMPACT OF THE STUDY: Results obtained in the present research are promising and may be exploited commercially to control S. amygdali adults on various species of stone fruit trees, especially peach trees. This type of biocontrol of this insect may be used as an alternative means to chemical control for management of the insect. No adverse environmental impacts of the fungus or its formulation have been observed during application.     

我国新天敌资源——小蠹蒲螨形态与生物学研究

小蠹蒲螨Pyemotes scolyti(Oudemans,1936)为我国新纪录种。在河北,是核果类果树毁灭性害虫果树小蠹Scolytus japonicus Chapuis和多毛小蠹S.seulensis Mu-rayamy的有效天敌。该螨胎生,1年多代(25℃,8d完成1代),雌雄性比30:1～2,每雌产后代平均60余头,有较高的利用价值。     

Lecanosticta acicola, causal fungus of brown spot needle blight inPinus thunbergii, new to Japan

A needle blight disease with brown spots was found on ornamental trees ofPinus thunbergii in Shimane Prefecture, Japan. The causal fungus was identified asLecanosticta acicola, known as causal fungus of brown spot needle blight of pines recorded in the Americas, Europe, and China.Pinus thunbergii was heavily infected following inoculation with the fungus in June, but only slightly infected following inoculation in September. The mycelia of the fungus were raised and produced conidial masses on potato-dextrose and Waksman agars. They grew well at 20–25°C within the range of 5 to 35°C.     

METHODS OF CONTROLLING BLACK-POD DISEASE (CAUSED BY PHYTOPHTHORA PALMIVORA) OF THEOBROMA CACAO IN NIGERIA

Supplementary methods of controlling black-pod disease ( Phytophthora palmivora ) of cocoa in Nigeria are considered, because fungicide application is not always economic.
There is no evidence that resistance occurs within the local population of Amelonado-type trees.
Although the percentage of diseased pods was greater with trees closely spaced (5 times 5 ft. to 8 times 8 ft.), than with widely spaced trees (10 times 10 ft. to 15 times 15 ft.), the closer spacings often gave more healthy pods per acre.
Loss of pods from black-pod was decreased when trees were inspected frequently (alternate days) and infected pods were removed when showing the earliest symptoms. However, this procedure may not be economic, except when potential yields are relatively small (fewer than twelve pods per tree).
Satisfactory control of black-pod was obtained with copper fungicides, applied with either hand-sprayers or a power-sprayer. The monetary return depends on yield level, rather than on disease incidence or on spraying costs. It is recommended that spraying should be practised when the potential yield is twelve or more pods per tree.     

Elm defence against herbivores and pathogens: morphological,chemical and molecular regulation aspects

Elms (Ulmus spp.) have long been appreciated for their environmental tolerance, landscape and ornamental value, and the quality of their wood. Although elm trees are extremely hardy against abiotic stresses such as wind and pollution, they are susceptible to attacks of biotic stressors. Over 100 phytopathogens and invertebrate pests are associated with elms: fungi, bacteria and insects like beetles and moths, and to a lesser extent aphids, mites, viruses and nematodes. While the biology of the pathogen and insect vector of the Dutch elm disease has been intensively studied, less attention has been paid so far to the defence mechanisms of elms to other biotic stressors. This review highlights knowledge of direct and indirect elm defences against biotic stressors focusing on morphological, chemical and gene regulation aspects. First, we report how morphological defence mechanisms via barrier formation and vessel occlusion prevent colonisation and spread of wood- and bark-inhabiting fungi and bacteria. Second, we outline how secondary metabolites such as terpenoids (volatile terpenoids, mansonones and triterpenoids) and phenolics (lignans, coumarins, flavonoids) in leaves and bark are involved in constitutive and induced chemical defence mechanisms of elms. Third, we address knowledge on how the molecular regulation of elm defence is orchestrated through the interaction of a huge variety of stress- and defence-related genes. We conclude by pointing to the gaps of knowledge on the chemical and molecular mechanisms of elm defence against pest insects and diseases. An in-depth understanding of defence mechanisms of elms will support the development of sustainable integrated management of pests and diseases attacking elms.