Crown Wilt Research Articles

Pathogenicity, Symptom Development, and Colonization of Metrosideros polymorpha by Ceratocystis lukuohia.

Extensive mortality of Metrosideros polymorpha (`ōhi`a) trees has been associated with Ceratocystis spp. on Hawai`i Island and was named rapid `ōhi`a death (ROD). Both C. lukuohia and C. huliohia have been associated with ROD, although C. lukuohia appears to be the more important pathogen. Crown observations and dissections of forest trees either wound-inoculated with, or naturally infected by, C. lukuohia were conducted to confirm pathogenicity and document patterns of host colonization. In pathogenicity trials, one of three and two of three trees inoculated with the fungus in February and August, respectively, exhibited crown wilt symptoms at 92 and 69 days after inoculation. Extensive, radial, black staining of the sapwood was found in main stems, while no crown wilt or xylem staining was found in control trees. Xylem staining, necrotic phloem, and fungus presence was noted in six trees inoculated in May to June and harvested 37 to 42 days later, and these observations were compared with those in two naturally infected trees felled in early August. Contiguous xylem staining was found in the main stems and into crowns of all diseased trees, while discontinuous streaks of xylem staining extended into the main forks and side branches. Necrotic phloem associated with xylem staining occurred on the lower stems of inoculated trees. Aside from the necrotic phloem and radial staining of the sapwood, symptom development in `ōhi`a infected with C. lukuohia is similar to other systemic wilt diseases on hardwood trees. We propose Ceratocystis wilt of `ōhi`a as the official name of the disease.

Collar Rot and Crown Wilting by Phytophthora pachypleura on Aucuba japonica in Italian Nurseries

Collar Rot and Crown Wilting by <i>Phytophthora pachypleura</i> on <i>Aucuba japonica</i> in Italian Nurseries

Phaeoacremonium species associated with olive wilt and decline in southern Italy

Six Phaeoacremonium species (spp.) were isolated from symptomatic wood of olive trees (Olea europea) in Apulia (southern Italy) that showed crown wilt and twig and branch dieback. These Phaeoacremonium spp. were identified according to their morphological characteristics and by analyses of partial sequences of the actin and β-tubulin genes. Combining these cultural, morphological and molecular data, three Phaeoacremonium spp. were isolated that are already known to be responsible for severe decline of olive in Apulia, Phaeoacremonium aleophilum, Phaeoacremonium alvesii and Phaeoacremonium parasiticum, together with three other Phaeoacremonium spp. that are associated for the first time with wilt, decline and dieback of olive orchards in Italy and worldwide: Phaeoacremonium italicum, Phaeoacremonium sicilianum and Phaeoacremonium scolyti. To understand and to confirm their involvement in wilt and decline of olive trees, pathogenicity assays were performed on shoots of young olive plants. The data indicate that all six of these Phaeoacremonium spp. can cause discolouration, necrotic wood, and death of shoots, although different levels of virulence were observed, with Pm. italicum, Pm. aleophilum and Pm. sicilianum producing greater necrotic lesions than the other Phaeoacremonium spp. investigated here.

Patterns and severity of crown dieback in young even-aged stands of european ash (Fraxinus excelsior L.) in relation to stand density, bud flushing phenotype, and season

The extent and temporal pattern of crown damage (attributed to Hymenoscyphus pseudoalbidus) in even-aged stands of Fraxinus excelsior in relation to bud flushing phenotype, stand density, and season was investigated. Data were collected in 2007 in four statistically designed thinning experiments located in 12&amp;ndash;15-years old plantations of ash in Denmark. The study included 21 plots of four contrasting, residual stand densities: (1) 1700&amp;ndash;5500 trees/ha (unthinned control plots), (2)&amp;nbsp;1500 trees/ha, (3) 500 trees/ha, and (4) 100&amp;ndash;150 trees/ha. Assessments included estimation of flushing phenotype in May, followed by evaluation of severity of crown damage (percentage of crown killed) in June and September. Simultaneously, for each tree, the presence or absence of crown wilt and dead tops were recorded. The seasonal pattern of disease severity (average crown damage) was similar in all stands, and disregarding stand density the extent of tree crown damage increased significantly towards the end of the growing season (P &amp;lt; 0.005). Disease severity was the worst in unthinned plots, but otherwise unrelated to stand density. Late-flushing trees were most severely affected (P &amp;lt; 0.001). The observed patterns of disease severity are probably associated with ecological features of the pathogen that still remain largely unknown. &amp;nbsp;

First Report of Botryosphaeria iberica Associated with Dieback and Tree Mortality of Monterey Cypress (Cupressus macrocarpa) in Algeria.

Stem cankers and branches showing bark discoloration, fissuring, resin exudation leading to dieback, crown wilting, and tree mortality have been observed since late spring 2008 on 40-year-old Cupressus macrocarpa (Hartw.) trees planted in forests mixed with Juniperus oxycedrus L. and Acer monspessulanum L. in Taffet, near Ain Abbessa, in the district of Bougaa, Algeria (36°18'57″N; 05°06'33″E; 1,400 m elevation). In 2010, approximately 60% of the C. macrocarpa trees were diseased. For fungal isolations, cankered branches were surface sterilized with ethanol. After removal of the outer bark, fragments of necrotic inner bark taken from the margin of cankers were plated on potato dextrose agar (PDA). Most of the colonies were identified as Botryosphaeria iberica (Phillips, Luque & Alves) based on comparison of morphological traits and DNA sequences with known isolates of the fungus (1). Pestalotiopsis funerea colonies were also obtained, although with less frequency. B. iberica colonies on PDA were dark green with aerial mycelium and optimum growth at 25°C. Pycnidia were produced after 3 weeks of incubation at 20°C under a 12-h near UV light photoperiod on water agar amended with autoclaved cypress seeds. Conidia were brown, one-septate, oval to oblong, and 24.2 (20.1 to 27.4) × 11.2 μm (8.8 to 14.1) (n= 50). An isolate was deposited at the Centralbureau voor Schimmelculture as CBS 130984. DNA was extracted from freeze-dried mycelium and amplified using primers ITS1 and ITS4. The amplified DNA sequence of B. iberica isolate CBS 130984 from Algeria (GenBank Accession No. JN836991) showed 100% homology with sequences of B. iberica isolates obtained from dead and cankered bark of oaks from Spain and Italy (GenBank Accession Nos. AY573216, AY573214, AY573213, AY573210, AY573202, and AY573201). Stem inoculations were performed in the greenhouse on 10 4-year-old, grafted plants of C. macrocarpa growing in 5-liter pots using isolate CBS 130984. A 3-mm plug taken from the margin of a colony grown on PDA for 1 week was inserted in a circular wound of the same size made in the bark with a cork borer where the stem diameter was approximately 1 cm. Inoculations were repeated in June 2010 and June 2011. Five months after inoculations, small rounded to elongated lesions (1.0 to 2.5 cm long), sometimes with resin exuding cracks, were visible on all inoculated stems. Control trees, inoculated with sterile PDA plugs, showed no canker development. B. iberica was successfully reisolated from the necrotic bark surrounding the inoculation sites. No significant differences in canker size were observed between the two replicated experiments. Some Botryosphaeria species that are found on a variety of hosts are also known to cause cankers and dieback of cypress; among these are B. stewensii, B. obtusa, B. dothidea, and B. ribis, often acting as weak pathogens (2,3). Considered weakly virulent in causing dieback of grapevine (4) and, to our knowledge, reported here for the first time on Cupressaceae, B. iberica caused cankers and dieback of C. macrocarpa trees that had probably been weakened by repeated drought events occurring in Algeria during the last 10 years.

Effect of Propiconazole on Laurel Wilt Disease Development in Redbay Trees and on the Pathogen In Vitro

Laurel wilt is a vascular disease of Lauraceous plants caused by a fungus (Raffaelea spp.) that is vectored by a recently introduced, nonnative ambrosia beetle (Xyleborus glabratus). The disease is devastating to redbay (Persea borbonia) trees in forests, parks, and residential landscapes in the southeastern United States, and management strategies for reducing its impact are needed. In this study, the systemic fungicide propiconazole completely inhibited mycelial growth of Raffaelea spp. in vitro at concentrations 0.1 parts per million (ppm) or greater and was fungitoxic at 1 ppm or greater, whereas the fungicide thiabendazole was less inhibitory. None of the ten mature redbay trees that received root-flare injections of propiconazole developed crown wilt symptoms for at least 30 weeks after being inoculated with Raffaelea spp., whereas nine of ten untreated control trees wilted in more than one-third of their crowns. Propiconazole was retained in the stem xylem for at least 7.5 months after injection but was more frequently detected in samples from trees injected 4.5 months earlier and was not well detected in small-diameter branches. Results suggest that propiconazole may be useful in preventing laurel wilt in redbay, but limitations and questions regarding duration of efficacy, rate of uptake, and efficacy under different levels of disease pressure remain.

First Report of Root and Collar Rot by Phytophthora cryptogea on Sweet Cherry in Italy.

Sweet cherry (Prunus avium L.) cultivation has increased in Italy and ≈30,000 ha are now in production. In the spring of 2006, a disease survey was conducted in orchards of central Italy. Decline symptoms of Prunus avium 'Durone' grafted on wild rootstocks of Prunus avium consisted of reduced tree vigor, yellowing of leaves, and development of root and collar rot. A reddish brown discoloration of the inner bark and wood was observed on symptomatic trees. Symptoms were recorded in three cherry orchards seasonally submitted to soil saturation conditions. In one orchard, symptoms were observed on approximately 30% of 170 surveyed trees. A Phytophthora species was consistently isolated on PARPH-V8 medium (2) from collar lesions of five cherry trees over nine trees randomly chosen among symptomatic trees in the three orchards. Colonies (20) were isolated and all appeared fluffy on potato dextrose agar and did not grow at 35°C. The morphological characteristics fit the descriptions of Phytophthora cryptogea Pethybr. & Lafferty (1). Sequence analysis of the internal transcribed spacers region of isolates shared 100% homology with P. cryptogea (GenBank Accession Nos. EF418948.1, EF418943.1, and EF153671.1). Pathogenicity of two P. cryptogea isolates (AN1 and AN2, Accession Nos. EF661576 and EF661577, respectively) was tested by soil infestation in a growth chamber at 22°C using 15 1-year-old rooted seedlings of wild rootstock of Prunus avium for each isolate. Noninoculated seedlings (15) were used as negative controls. The inoculum was produced by growing isolates on autoclaved millet grains moistened with V8 juice for 4 weeks. Each plant was inoculated with 30 cm3 of inoculum per liter of soil. Each seedling was randomly assigned to isolates AN1, AN2, or the noninoculated control and arranged in a complete random design. All plants were flooded for 24 h every 2 weeks for 8 weeks. At the end of the experiment, all inoculated seedlings showed crown wilting and root rot. Control plants showed no symptoms. Percentage of necrotic lateral roots expressed as dry weight (±SE) was 19.9 ± 0.6, 17.5 ± 0.2, and 4.4 ± 0.5, respectively, for seedlings inoculated with isolates AN1, AN2, and controls (analysis of variance F = 7.48, P < 0.01). Values of inoculated seedlings were significantly different from the control plants with the Tukey Post-Hoc test. No difference in virulence was observed between the two isolates. P. cryptogea was always reisolated from the roots of inoculated plants. Although pathogenicity of P. cryptogea on sweet cherry has been reported in the United States and other European countries (3,4), to our knowledge, this is the first record of P. cryptogea on sweet cherry orchards in Italy. The presence of P. cryptogea in cherry orchards is of significant concern because of its aggressiveness to this host and woody hosts such as apple, apricot, peach, walnut, and kiwi.

Screening European Elms for Resistance to Ophiostoma novo-ulmi

Abstract Resistance breeding of the native elms against Dutch elm disease, caused by the fungus Ophiostoma novo-ulmi Brasier, is a major objective in Europe for the conservation of this tree species. More than 2,500 cuttings of 324 elm clones (Ulmus minor Miller, U. glabra Huds., U. laevis Pall., U. pumila L., U. minor x U. glabra, and U. minor x U. pumila) from eight European countries, planted in several randomized two-block designed plots were inoculated with various O. novo-ulmi strains. Crown wilting and dieback were recorded during the first year after inoculation. The wilting of the control trees varied among the plots, making the results difficult to compare, but analysis of variance (ANOVA) within each plot showed significant differences in disease severity among the clones tested, allowing study of the variation of the response among elm taxa. Results showed that 19 European inoculated clones recovered from O. novo-ulmi attack, giving hope for the reestablishment of native elms in countryside hedges and forests. FOR. SCI. 51(2):134–141.

Bioecology of the fungus Sphaeropsis sapinea dyko &amp; Sutton - agents of pinus species decline

Sphaeropsis sapinea is a cosmopolitan fungus, identified in more than 50 countries of the world, on all continents, but it is primarily the species of warm lands. It is also a polyphagous fungus recorded from 11 coniferous genera. The most endangered and the most frequent host plants are Pinus species - it occurs on 48 pine species, among which the most susceptible are Pinus Radiata, P. nigra, P. sylvestris, P. ponderosa, P. resinosa, P. mugo, P. pinaster and P. elliotti. The greatest damage is caused on the introduced Pinus species and on those cultivated in artificial plantations, shelterbelts and in urban environments. In Yugoslavia S. sapinea is widely distributed both in the continental and in the Mediterranean parts. It was identified from ten pine species and six hosts from other coniferous genera. By the study in our country, the new hosts of this fungus were detected - Pinus jeffrey, P. peuce and P. heldreichii. The most endangered species in our country is Austrian pine, both in urban environments, and in plantations The symptoms of the disease are bud wilt, curling, stunting and necrosis of current year shoots and needles, dieback of top shoots, parts of crown or tree tops, branch and stem bark canker, root collar rot on the young plants in nurseries and their dying. This fungus also prevents seed germination of Pinus species and causes blue sap stain of the freshly cut wood, although sap stain was also observed on standing trees. More rarely it causes root rot and crown wilt of Pinus species. The main symptoms of infection, both of young plants and older trees, are the dieback of current year shoots S. sapinea can penetrate through buds, bark of young shoots and needles. The critical time of infection is the period from mid April to mid May. Then infection mainly penetrates through the bark of young shoots, which results in their dying. Infection through the needles occurs mainly at the time of their sudden growth or during summer months. The first visible symptoms of infection of the young shoots are in the form of brown necroses, resin bleeding and several short pairs of needles at the place. S. sapinea can infect male and female flowers, current year and second-year cones. The pycnidia with mature conidia can form on the shoots, needles, first-year and second-year cones during the year of infection. The first mature fructifications are mostly formed in the bark of young shoots, in the zone of infection, and they were recorded in late June at the earliest. They were recorded on the cones at the beginning of the third decade of July. Pycnidia are formed in the bark, on the needles and on the second-year and older cones, on male and female flowers, as well as on the cones in the first year of development. The size of S. sapinea conidia on different Pinus species is very variable throughout the world and ranges widely from 16.8-55.0?7.0-21.0 ?m. Our study shows that the size of pycnospores in our country is also variable and it ranges 14.8-51.4?9.7-20.2 ?m The optimal temperature for spore germination and germ tube growth is 27?C, and the optimal temperature for mycelial growth on the media PDA and MEA is 28?C. The formation of fruiting bodies in the culture is affected by light and the presence of sterilised needles on the mycelium The correct and timely control measures can contribute to reduce the consequences of this serious disease, by the combined application of silvicultural and chemical measures. Chemical control is recommended in the nurseries, severely infected plantations and in urban environments. The fungicides which showed the greatest efficiency are the preparations based on copper and Benomil.

Diseases of Italian cypress caused by Botryodiplodia theobromae Pat.

Abstract Botryodiplodia theobromae was identified as the causal agent of three hitherto undescribed diseases of Italian cypress, Cupressus sempervirens: (i) crown wilt, on mature trees, (ii) Botryodiplodia stem tanker, on mature trees, and (iii) seedling blight, in nursery stands.

Effect of pruning intensity and season on Diplodia pinea infection of Pinus radiata stem through pruning wounds

AbstractIn a five‐year‐old Pinus radiata stand, trees were pruned to remove 50%, 40% or 25% of the crown and pruning stubs inoculated with Diplodia pinea. Infection occurred in 65–68% of the intensely pruned trees some of which also developed crown wilting and died, but in lightly pruned trees (25% crown removal) only 8% of the trees were infected and no mortality occurred.Pruning and inoculation every two weeks for a whole year cycle showed an infection peak in summer, but extremely low infection level during the rest of the year.A vertical gradient of resistance of infection was apparent along the stem with the basal part being extremely resistant, becoming more susceptible towards the top. Within limits infection also increased with increasing stub diameter.

Seasonal Detection of Visible Dutch Elm Disease Symptoms

Most of the lightly diseased American elms (10% or less crown wilt) that were suitable candidates for fungicide injection and/or pruning therapy for Dutch elm disease were discovered in surveys during June and early July. More treatable elms were found in areas where diseased elms were removed promptly (up to 20 work days after discovery) than where removal was delayed until fall and winter, and in areas where the smaller European elm bark beetle is the primary vector of Dutch elm disease rather than where the native elm bark beetle is the primary vector.

TRANSLOCATION OF CACODYLIC ACID IN DUTCH ELM-DISEASED AMERICAN ELMS AND ITS EFFECT ON SCOLYTUS MULTISTRIATUS (COLEOPTERA: SCOLYTIDAE)

AbstractCacodylic acid was injected into hatchet-made frill girdles 60 cm above the ground on Dutch elm-diseased American elms (Ulmus americana L.) at the rate of 0.8 ml/cm circumference measured 1.3 m above the ground. Cacodylic acid was translocated up the trees into the phloem. Arsenic residue analyses at several different heights in each tree indicated an inverse relationship between height and amount of cacodylic acid residue in the phloem. Largest amounts were translocated in trees with 75% wilted crowns.Cacodylic acid injection into elms had no significant inhibitory effect on Scolytus multistriatus (Marsham) brood development. Cacodylic acid residues as high as 1700 ppm caused little or no beetle mortality. Highest numbers of beetles/dm2 bark surface area emerged from acid-treated elms with 75% crown wilt and from untreated elms with 100% crown wilt.