Characterization of host–fungus interactions among wood decay fungi associated with Khaya senegalensis (Desr.) A. Juss (Meliaceae) in Singapore

Tree pruning creates wounds that are amenable for wood decay fungi colonization. To characterize the dynamic host–fungus interactions at this location in Senegal mahogany (Khaya senegalensis), in vitro and in vivo pathogenicity tests were conducted with wood decay fungi associated with this tropical tree species. Fomitiporella caryophylii, Hymenochaete murina and Phellinus noxius isolates were included in this experiment following their frequent isolation from Senegal mahogany pruning wounds. The evaluated isolates demonstrated unique host interactions in laboratory tests that suggest equally divergent prognoses for living Senegal mahoganies affected by these fungi. Although all evaluated fungal isolates successfully breached naturally induced reaction zones, P. noxius alone caused significant mass loss to incubated wood blocks. In addition, P. noxius caused extensive wood decay after inoculation in living hosts, successfully illustrating Koch's postulates for this host–fungus relationship. The wood decay ability, invasiveness and facultative parasitism demonstrated by P. noxius suggest its dominant role in wood decay columns below pruning wounds on living Senegal mahoganies. These results highlight the importance of characterizing specific host–fungus interactions and their implications for wood decay severity below pruning wounds in living trees.     

Occurrence of brown root rot in Ocean Expo Park,Okinawa, Japan: Infection route and preventive control measures

Ocean Expo Park, established in 1976 on subtropical Okinawa Island, Japan, has approximately 8000 planted or naturally grown trees in an area of 77.2 ha. Windfall of these trees occurs mainly due to typhoons; wood chips made from the trunks and roots of windfall trees are commonly used as mulching material throughout the park areas, despite possible infection by pathogenic fungi such as Phellinus noxius, the pathogen causing brown root rot. P. noxius is distributed in tropical and subtropical areas worldwide and has a broad host range. The fungus can infect host plants with mycelia via root-to-root contact or with basidiospores. Here, we report the current status of tree damage caused by brown root rot in the park and infer the infection routes of P. noxius based on microsatellite markers. Among a total of 294 trees surveyed in the park, P. noxius was isolated from 13 trees of five species. P. noxius was observed more frequently on Ficus microcarpa than on other tree species. Ficus superba var. japonica was identified as a new host species, and Bombax ceiba was first recorded as a host plant of P. noxius in Japan. Among the 13 P. noxius isolates from the diseased trees, 2 isolates from adjacent diseased trees were considered to be of the same genet, while the other 11 isolates were different genets, indicating that infection by basidiospores occurred frequently among trees in the entire park, although spread via root systems also occurred between at least two adjacent trees. An identical genet was not detected at distant locations, which suggests that the disease does not spread via chips. However, mulching with chips can lead to wood decay due to decaying fungi other than P. noxius. Therefore, in accordance with the precautionary principle, the park currently prohibits the chipping and mulching of windfall or damaged trees and is considering disposal methods such as burning.     

Genotype distribution of Raffaelea quercivora in the oak galleries and its composition in the mycangia of Platypus quercivorus

Raffaelea quercivora is the pathogenic fungus that causes Japanese oak wilt. The female monogynous ambrosia beetle, Platypus quercivorus, carries this fungus in mycangia on the pronotum. These beetles bore galleries in oak trees with their partners to produce offspring, and they deposit fungus on the gallery walls from their mycangia. The offspring mature in the gallery, before loading the fungal pathogen and flying from the gallery to other healthy trees. To investigate the unloading and loading modes of the fungus within the gallery, we developed four polymorphic microsatellite markers for R. quercivora and identified the fungal genotypes in the galleries and mycangia of the beetles. Small wood chips were sampled at 5–10‐mm intervals from the walls of five galleries in a dead Quercus serrata tree. The pronota were also sampled from five female adult beetles. The genotypes of the R. quercivora isolates from the wood chips and pronota were identified using the microsatellite makers. The genotypic analysis showed that each gallery was inhabited patchily by 5–10 genotypes of R. quercivora, and the mycangia of each beetle contained 3–6 genotypes. These results indicate that diverse R. quercivora genotypes are unloaded repeatedly from the mycangia of female beetles onto the gallery wall, which results in their patchy distribution on the walls. When the offspring leave the host tree, the fungal clones that proliferate in the walls are also loaded repeatedly into the mycangia of the mature beetles.     

Diversity and host association of the tropical tree endophyte Lasiodiplodia theobromae revealed using simple sequence repeat markers

Lasiodiplodia theobromae is a cosmopolitan fungus with a worldwide distribution in the tropics and subtropics, where it causes shoot blight and dieback of trees and shrubs and imparts blue stain in timber. In this study, eight simple sequence repeat (SSR) markers were used to evaluate the genetic diversity and gene flow between populations of L. theobromae. The relationships between isolates from different hosts were considered using three populations from different tree species in Venezuela (VEN) and the relationships between isolates from different geographical origins included populations from VEN, South Africa (RSA) and Mexico (MEX). A small number of predominant genotypes were encountered in the VEN and RSA populations and thus genotypic diversity was low. There was no evidence of host specificity for isolates of L. theobromae and there was very high gene flow between populations from different hosts. Geographical isolation existed between populations of the pathogen from different regions, with unique alleles fixed in the different populations. Gene flow was, however, less restricted between isolates from MEX and the other populations, consistent with MEX as a common source of seed in both VEN and RSA. Genetic analysis suggested predominantly clonal reproduction with some genotypes widely distributed within a region. The broad host range of L. theobromae and the lack of evidence for host specialization, coupled with its endophytic nature and the common appearance of symptoms only after harvest, is likely to hinder disease management strategies.     

Variation in virulence of Cryphonectria hypovirus 1 in Macedonia

We investigated variation in virulence of Cryphonectria hypovirus 1 (CHV‐1) to the chestnut blight fungus, Cryphonectria parasitica, in Macedonia by inoculating chestnut stems in the field. We inoculated trees with two isolates of C. parasitica, each infected with one of five isolates of CHV‐1, four of which were the same for both fungal isolates. Two virus isolates, [Sk28] and [Sk47], were significantly more virulent than the others when compared in the same fungal host isolates, as measured by reduced canker growth and increased callus formation. Mycelial growth rate in vitro was weakly correlated to canker growth or callus formation and is therefore not a reliable predictor for virulence. We found significant fungus × virus interactions for canker growth and callus formation, which seems due mainly to one virus isolate. Significant interactions were not expected because the two fungal host isolates are members of the same clone that is dominant in Macedonia and most of southeastern Europe. Phenotypic variation for response to viruses, therefore, is greater than variation revealed by the genetic markers used to define clones. More than half of the trees inoculated with virus‐free controls were dead within 2 years, and the 30% still alive after 5 years had cankers with extensive callus formation, indicating that natural virus transmission had occurred after inoculation. In contrast, only 2% of the trees inoculated with virus‐infected isolates were dead after 5 years. Hypoviruses naturally occurring in Macedonia reduce canker development and tree mortality similarly to those in other parts of southern Europe, and therefore, may have good potential for biological control of chestnut blight.     

Diversity of Cryphonectria parasitica in callused chestnut blight cankers on European and American chestnut

Infection of American and European chestnuts with the chestnut blight fungus Cryphonectria parasitica results in the formation of cankers, lesions caused by the growth of mycelia within bark tissue of the host plant. Infection of the fungus with Cryphonectria hypovirus 1 (CHV‐1) results in conversion of the mycelial phenotype from virulent to hypovirulent, thus allowing production of callus around cankers as a reaction by infected trees, rendering active into inactive cankers. In this study, we sampled one USA and six European chestnut stands and assessed frequency of hypovirulent C. parasitica and diversity of vegetative compatibility (vc) types present in calluses and randomly sampled cankers. Callused cankers on C. dentata at West Salem in the USA yielded significantly more hypovirulent C. parasitica isolates compared with four sampled populations on C. sativa, while all six sampled European populations did not show any statistically significant differences among themselves. We observed no correlation between hypovirulence frequencies in randomly sampled cankers and calluses, as well as no correlation of C. parasitica vc type diversity in calluses and residential populations of the fungus. Furthermore, even though we have observed calluses with more than one vc type, they do not occur regularly. Even when present in C. parasitica populations with high vc type diversity, no more than three different vc types were observed in a single callus.     

First report of Ceratocystis huliohia causing mortality of Metrosideros polymorpha trees on the Island of Kauaʻi,Hawaiʻi USA

The fungus Ceratocystis huliohia was detected for the first time in dead and dying Metrosideros polymorpha trees on the Island of Kaua?i, Hawai?i, U.S.A. Fungal isolates were recovered from diseased trees into culture, and identities were confirmed by diagnostic qPCR assay and DNA sequencing. Growth chamber inoculations confirmed C. huliohia pathogenicity on M. polymorpha seedlings and subsequently the same fungus was recovered, completing Koch's postulates. DNA sequence analysis revealed a unique ITS haplotype for Kaua?i isolates of C. huliohia that has not been found on Hawai?i Island.     

Variations in virulence and hyphal growth of four Raffaelea quercivora isolates within Quercus crispula

Mass mortality of fagaceous trees caused by Japanese oak wilt has occurred widely in Japan. Although virulence of the causal fungus, Raffaelea quercivora, appeared to differ among isolates, its relation to the fungal growth within trees was unknown. To clarify the differences in fungal virulence against susceptible Quercus crispula, we examined fungal growth of four R. quercivora isolates within trees and the resulting virulence. In our study, the isolates were multiple‐inoculated in seedlings and single‐inoculated in twigs of mature trees. In the multiple‐inoculation test, mortality rates were examined by the observation of external symptoms. In the single‐inoculation test, water conductance and hyphal growth within the trees were examined by applying aqueous dyes and fluorescence microscopy, respectively. Mortality rates, the proportion of the cross‐sectional area comprising non‐conductive sapwood and horizontal hyphal growth differed significantly among the isolates. Univariate logistic regression analyses showed that both the proportion of non‐conductive sapwood and hyphal growth were significantly positively related to mortality rates. For three isolates, hyphal growth was significantly positively correlated with the proportion of non‐conductive sapwood. These results suggested that the virulence against Q. crispula varies among R. quercivora isolates and that the extent of fungal colonization of the tree determines fungal virulence.     

Brown root rot of trees caused by Phellinus noxius in the Ryukyu Islands,subtropical areas of Japan

The fungus Phellinus noxius has a broad host range and causes brown root rot in a variety of tree species of various ages, irrespective of their original health. The fungus is widely distributed in tropical countries of Southeast Asia, the Pacific Islands and Australia, Central America and Caribbean, and Africa. Since 1988, when brown root rot was first found on Ishigaki Island, Okinawa Prefecture, the disease has been reported on several islands in Okinawa and Kagoshima Prefectures, and it has been causing serious problems to shade, windbreak, ornamental and landscape trees in the Ryukyu Islands, located in the subtropical region of southern Japan. Here, we report on the current status of P. noxius‐caused brown root rot in the Ryukyu Islands, Japan, including symptoms, occurrence, dispersal, distribution and host tree species of the disease, pathogenicity and/or virulence of the pathogen, and disease management based on our surveys and previously published reports from Japan. Brown root rot has been confirmed in 53 tree species from 32 plant families at different sites on 10 of the 12 islands surveyed. Among the 53 tree species, 34 were first recorded in Japan as host plants of P. noxius. The disease occurs mainly in shade, ornamental and windbreak trees at sightseeing places, parks, roadsides, agricultural land such as sugar cane fields, and around residences or other places associated with human activities.     

Molecular phylogeny of Ganoderma lucidum isolates collected from northern India

Ganoderma lucidum has been found to be a pathogen on a wide range of tree species in India. Because of large variations found in both macro‐ and microscopic characters, traditional identification and characterization methods are unreliable for this genus. We analysed nrDNA internal transcribed spacer (ITS) sequences of 52 isolates in the G. lucidum complex by the parsimony method, finding 17 lineages. The maximum parsimony analysis showed that the isolates of G. lucidum from the same host species had high similarity in ITS sequences, compared to isolates from other tree species. The result was also supported by high values of population differentiation parameters such as N_ST and F_ST values. Genetic analysis suggests the occurrence of host‐mediated genetic differentiation in G. lucidum isolates, which requires further investigation.     

Fungal colonization patterns in necrotic rootstocks and stem bases of dieback‐affected Fraxinus excelsior L.

European ash (Fraxinus excelsior) trees currently face the major threat of ash dieback caused by an invasive fungus, Hymenoscyphus fraxineus. Collar rots in F. excelsior have been increasingly associated with infections by this pathogen. However, the aetiology of the collar rots is still unclear and remains heavily debated. In contrast to most studies of this kind, entire rootstocks of four diseased ash trees were dug out to examine necrotic tissues in these rootstocks and stem bases in detail and to sample necrotic wood for fungal isolation. With the aid of morphological and molecular identification techniques, five to twelve fungal taxa were detected per tree. Members of the Nectriaceae family and Botryosphaeria stevensii, the causal agent of stem and branch cankers on many tree species, were frequently isolated from outer xylem. In contrast, H. fraxineus was the dominating species in interior wood layers. Microsatellite genotyping of 77 H. fraxineus isolates helped to identify up to six different genotypes per tree. The role of H. fraxineus and other isolated fungi in the aetiology of ash collar rots are discussed.     

Multilocus phylogenetic analysis revealed a new cryptic lineage of Serpula himantioides in Japan

Serpula himantioides is a widely distributed saprotrophic fungus that causes root and butt rot in various tree species. In Japan, butt rot associated with S. himantioides is observed in Chamaecyparis pisifera and Abies sachalinensis. Previous studies have shown that S. himantioides includes five phylogenetically defined cryptic lineages, but the placement of Japanese isolates remains unclear. To clarify the phylogenetic relationship between Japanese S. himantioides and the five known lineages, we conducted a phylogenetic analysis using three newly collected Japanese isolates along with 74 S. himantioides isolates, based on the internal transcribed spacer (ITS) region, the 28 S large subunit (LSU) rDNA, the beta-tubulin (tub) gene, and the heat stress protein (hsp) gene. The concatenated phylogenetic tree showed that Japanese isolates composed a clade with a high bootstrap value distinct from the known lineages, indicating the Japanese isolates present a new cryptic lineage of S. himantioides.     

Pathogenicity of Ceratocystis resinifera to Norway spruce

The blue‐stain fungus Ceratocystis resinifera colonizes wounds on living Picea spp. and other conifers in Europe and North America. Little is known regarding the pathogenicity of this fungus and consequently, four Norwegian C. resinifera isolates were inoculated on to Norway spruce (Picea abies) using two different techniques. These included single‐point inoculations on young trees (two inoculations per tree on 14‐year‐old trees) and mass‐inoculations on older trees (～200 inoculations per tree on 34‐year‐old trees). In both experiments, C. resinifera induced minor symptoms that in most cases did not differ significantly from inoculation with sterile agar. The virulent blue‐stain fungus C. polonica, which was inoculated for comparative purposes, induced extensive symptoms, causing 83% dead cambium circumference and 82% blue‐stained sapwood, and long necrotic lesions in the phloem. The results suggest that C. resinifera is non‐pathogenic or only mildly pathogenic to Norway spruce and does not present a threat to these trees.     

A preliminary report on decay and canker of Acacia richii caused by Inonotus rickii in China

An epidemic wood‐decaying fungus, Inonotus rickii, originating from South America, has spread to the Mediterranean area and southern China. We report the first observation of this fungus on Acacia richii in Panzhihua, southern China. It causes serious canker and decay on urban trees in the investigated area. In addition, phylogenetic analysis showed that the fungus from Panzhihua is closely related to isolates from Europe, South America, Mianyang and Hainan of China. Moreover, it was concluded that the isolates of the species previously reported from the USA do not belong to I. rickii.     

Root‐colonizing ophiostomatoid fungi associated with dying and dead young Scots pine in Poland

Ophiostomatoid fungi are carried by various bark beetles. However, very little is known about the role of these fungi in conifer roots. We studied ophiostomatoid fungi in roots of dying and dead Pinus sylvestris trees and tested the potential phytotoxicity of some isolates using a sensitive bioassay with Lepidium sativum in Poland. Fungi were identified based on their morphology and DNA sequencing. Three ophiostomatoid fungi, Leptographium procerum, Sporothrix inflata and Ophiostoma pallidulum, were isolated from the roots. The most abundant soil‐borne fungus, S. inflata, and relatively rare O. pallidulum were isolated for the first time from roots of dying and dead pine trees. The frequency of S. inflata and O. pallidulum correlated with tree decline. The fungi were isolated more frequently from roots of dead than dying trees. Sporothrix inflata and O. pallidulum slightly reduced the stem and root growth of L. sativum. Leptographium procerum reduced more significantly root than stem growth. This species reduced root elongation 32–54% after 10–17 days of incubation.     

Wood-inhabiting fungi in stems of Fraxinus excelsior in declining ash stands of northern Lithuania,with particular reference to Armillaria cepistipes

Abstract

Stem bases of 210 Fraxinus excelsior trees of three different health categories were sampled by the means of an increment borer in declining ash stands in northern Lithuania. From this number, 15 sound-looking, 132 declining and 63 dead trees from three discrete plots yielded 352 isolates, representing 75 fungal species. In addition, mycelial fans and rhizomorphs typical of Armillaria spp. from 205 and 20 trees, respectively, were sampled and subjected to fungal isolations. Species richness was similar in trees from each health category, but community structures differed, indicating that species composition of wood-inhabiting fungi in stems changes along with the changes in tree health condition. Armillaria cepistipes was the most common species (86 isolates from 210 wood samples, or 41.0%), isolated more frequently and consistently than any other potential tree pathogen. It also showed abundant occurrence on a majority of trees in the form of mycelial fans and rhizomorphs, from which 64 and 14 isolates of the fungus were obtained, respectively. The population structure of A. cepistipes revealed the presence of 53–93 genets per hectare, some of which extended up to 30–55?m.     

接种菌根菌对桉树生长的影响

以尾叶桉和巨尾桉为材料 ,1993和 1994年在广东省开平市镇海林场建立了 2个外生菌根菌接种试验 ,均采用裂区设计 ,4次重复 ,每试验均 2个树种为主区 ,菌根菌处理为副区。试验 1有 8个外生菌根菌处理 ,每处理小区 6株或 9株 ,试验 2有 3个外生菌根菌处理 ,每处理小区 9株。造林后 ,定期观测树高、地径或胸径。试验结果表明 :树种内菌根菌效应分析发现 ,巨尾桉所有指标在菌根菌间存在显著差异 ,尾叶桉只是某些指标在菌根菌间有显著差异 ,表明两树种对相同菌根菌处理的反应不同 ;树种联合方差分析表明 ,试验 1中所有指标在区组间、树种间、菌根菌处理间均有显著差异 ,从方差分量看 ,树种效应 >树种×菌根菌互作效应或菌根菌效应 ;试验 2中树高指标在树种间和菌根菌处理间均存在显著差异 ,而 2 4个月时胸径指标在树种间无显著差异 ,但胸径在菌根菌处理间有极显著差异 ,树高指标的方差分量为树种效应 >树种×菌根菌互作效应或菌根菌效应。胸径的方差分量为菌根菌效应 >树种×菌根菌互作效应 >树种效应。分析表明树种×菌根菌互作效应存在时间上的不稳定性 ;同时 ,讨论了外生菌根菌应用中树种因素的重要性。     

Pruning enhances the susceptibility of Picea abies to infection by the bark beetle‐transmitted blue‐stain fungus,Ophiostoma polonicum

Defoliation of conifers occasionally precedes bark beetle attacks, suggesting that a severe loss of foliage and ensuing reductions in carbohydrate availability may enhance host tree susceptibility. To shed light on this question, different degrees of defoliation on young Picea abies were simulated by removing whole whorls of branches from below, the trees retaining 100, 50, or 25% of their original crown biomass. After one week or one year, the trees were inoculated with Ophiostoma polonkum, a tree‐killing fungus transmitted by Ips typographus.

Fungal proliferation and tree mortality increased with increasing levels of pruning. Pruning reduced stem diameter growth, but not carbohydrate reserves in foliage and bark. Foliar N, P, and Ca increased with increasing pruning. The results lend support to the hypothesis that a reduction in the photosynthesis capacity increases host tree susceptibility to a beetle‐fungus attack, and that induced defence against infection depends on efficient translocation of assimilates to the sites of infection.     

寄主树木、寄主和环境因子对松褐天牛深沟茧蜂寄生率的影响研究

[目的]松材线虫病是我国对森林危害和威胁最严重的病害,控制其传播媒介昆虫松褐天牛是防治松材线虫病的主要手段。作者发现的松褐天牛深沟茧蜂(Iphiaulax monochamusi Yang)是寄生松褐天牛中老龄幼虫的重要天敌。为明确松褐天牛深沟茧蜂的寄生率与寄主树木、寄主和环境因子的关系,开展了本研究。[方法]通过解剖46株松褐天牛危害致死的马尾松,调查了松褐天牛深沟茧蜂寄生率与马尾松、松褐天牛和环境因子之间的关系。[结果]调查研究表明:寄主树木的高度、胸径和树龄对松褐天牛深沟茧蜂寄生率没有显著影响,松褐天牛的数量对松褐天牛深沟茧蜂寄生率亦没有显著影响,而松褐天牛幼虫龄期和松褐天牛幼虫在树干上的位置显著影响松褐天牛深沟茧蜂寄生率。松褐天牛深沟茧蜂寄生率与松褐天牛龄期呈显著正相关,其偏好寄生3~5龄幼虫;就天牛在其危害寄主树木上的位置而言,松褐天牛深沟茧蜂偏好寄生马尾松主干上部和在韧皮部危害的松褐天牛幼虫,其对位于马尾松树干上部的寄主幼虫寄生率最高,达27.38%,对在韧皮部生活、危害的寄主幼虫寄生率为20.18%,显著高于位于木质部生活的寄主幼虫寄生率(5.46%)。逐步回归分析表明:影响松褐天牛深沟茧蜂寄生率的关键环境因子是寄主树木的坡位和其它天敌寄生率,其中,坡位与松褐天牛深沟茧蜂呈显著正相关,其它天敌寄生率与松褐天牛深沟茧蜂寄生率呈显著负相关。[结论]以上研究初步明确了松褐天牛深沟茧蜂的寄生率与寄主树木、寄主害虫和天敌之间的关系,为今后利用该重要天敌控制松褐天牛打下了基础。     

Parasitic association of the mycetophagous wood nematode,Bursaphelenchus fraudulentus with the honey fungus Armillaria ostoyae

Honey fungi, Armillaria spp. are common and economically important pathogens of a wide range of tree species grown both in the forest and orchard cultures worldwide. Our field research in 73 forest stands across Poland has shown a common association of the mycetophagous wood nematode, Bursaphelenchus fraudulentus with Armillaria‐infected trees. The data reported here provide the first insight into the parasitic interaction of a nematode and Armillaria ostoyae. In laboratory conditions, B. fraudulentus reproduced on A. ostoyae, caused substantial damage to its mycelium and, finally, killed the whole colony within a short time. In ageing cultures, the nematode produced resting (dauer) juveniles. After artificial inoculation to Armillaria‐infected trees, the nematode population persisted under the bark, continued feeding and mass reproduction on the mycelium, and dispersed over the mycelial fans. The ability of B. fraudulentus to develop and reproduce on the surface and inside the fungal rhizomorphs suggests that these structures could facilitate the nematode dispersion in the environment. Since B. fraudulentus is not pathogenic to the host tree, its parasitic association with A. ostoyae may contribute to natural regulation of this fungus in the environment. The observed characteristics of this nematode suggest that it could potentially be used as a biocontrol agent of honey fungi in forest and orchard trees.