Incidence of dieback disease following fungal inoculations of sexually and asexually propagated shisham (Dalbergia sissoo)

Shisham (Dalbergia sissoo) is an important multipurpose tree with great economic importance, but this tree has been devastated by dieback disease. Seedlings and asexually propagated (cuttings) plants were artificially inoculated with four fungi (Fusarium solani, Botryodiplodia theobromae, Curvularia lunata and Ganoderma lucidum) to evaluate the potential role of these fungi in shisham dieback disease. Results at 2 years revealed that highest disease was caused by inoculation of F. solani (31.39%), followed by B. theobromae (19.042%) and C. lunata (12.22%), but no dieback disease was caused by G. lucidum. During both years, seedlings exhibited greater susceptibility to disease (17.24%) compared to cuttings (7.83%). In particular, F. solani caused more disease in seedlings (46.18%) compared to cuttings (16.61%). With the F. solani inoculations, maximum disease rate was observed at 8 weeks post‐inoculation both in seedlings (77%) and in cuttings (31%), but the maximum disease increase was observed at 4–5 weeks post‐inoculation. Analysis of variance showed significant differences among the different fungi and also between seedlings and cuttings. F. solani can be considered as a major fungal pathogen contributing to dieback disease of shisham, and asexual propagation can reduce the severity of dieback.     

Development of Melampsora ciliata rust on nursery‐grown poplars in north‐western Himalayas

Development of leaf rust (Melampsora ciliata) in different species, hybrids and cultivars of poplar (Populus spp.) was studied in nursery‐grown plants. Five different criteria were used to assess the disease development. The mean disease index on 10 August was 9.4% which increased to 70.0% on 10 October. The lowest disease index (5.5%) was recorded in P. yunnanensis whereas the maximum was recorded in P. × euramericana‘Rubra‐Poiret’ (59.5%). The apparent infection rate per unit per day was highest in P. nigra × P. trichocarpa (9.7 × 10^–2) whereas the minimum occurred in P. maximowiczii × P. berolinensis‘Oxford’ (3.3 × 10^–2). The area under the disease progress curve was a maximum in P. × euramericana‘Rubra‐Poiret’ (26.7) and a minimum in P. yunnanensis (1.6). Complete defoliation by the first half of October occurred in P. nigra × P. trichocarpa, which also had the maximum apparent infection rate and area under the disease progress curve. Inoculum production was highest in P. nigra × P. trichocarpa and lowest in P. maximowiczii × P. berolinensis‘Oxford’.     

Artificial inoculation and susceptibility of Pinus armandii to Dothistroma septosporum

Dothistroma needle blight (DNB) is a serious needle disease of conifers that primarily affects pine species (Pinus spp.). Dothistroma septosporum is one of the DNB pathogens that has a diverse range of host species excluding Pinus armandii. In 15 inoculated P. armandii seedlings, D. septosporum acervuli were observed in 43 infected needles of ten seedlings with a mean disease severity of 1.11% at 25 weeks after inoculations, demonstrating the potential of D. septosporum to cause symptoms on the needles of P. armandii via artificial inoculation. The disease severity of P. armandii was similar to the positive control, Pinus nigra (median 0.75 for P. armandii to 0.70 for P. nigra), thus, P. armandii acts under artificial conditions as a susceptible host species.     

Lesion size induced by Chrysoporthe fungal pathogens varies between Eucalyptus species and geographic locations in Zambia

Chrysoporthe canker disease is one of the serious threats facing planted Eucalyptus in southern Africa. In order to manage this disease, planting of less susceptible species of Eucalyptus has been promoted in many countries but it is not clear which species are less susceptible for Zambian environments. The purpose of this study was to test the response of different Eucalyptus species to Chrysoporthe fungal pathogens under field conditions to identify the least susceptible species to the disease. Two-year-old Eucalyptus trees (E. grandis, E. camaldulensis, E. cloeziana and E. tereticornis) growing in low- and high-rainfall locations were inoculated separately with three Chrysoporthe fungal species (C. austroafricana, C. syzygiicola and C. zambiensis) and the induced lesion size was measured six months after inoculation. Analysis of variance revealed that lesion size differed significantly between Eucalyptus species (F_3,948 = 1 978.8, p < 0.001). Lesion size on Eucalyptus species increased in the order E. camaldulensis < E. teriticornis < E. cloeziana < E. grandis. On average, trees growing in the higher-rainfall site produced significantly larger lesions than trees growing in the low-rainfall site (F_1,948 = 565, p < 0.001), suggesting that location influences disease severity. Smaller lesions on E. camaldulensis indicate lower susceptibility to Chrysoporthe canker disease, providing an opportunity to use this species in the selection and breeding for resistant Eucalyptus genotypes for plantation development in high disease-risk sites in Zambia.     

立地条件对毛竹林枯梢病感病指数的关系效应研究

[目的]研究毛竹林的立地条件和枯梢病发生的关系。[方法]对江西省不同立地条件的60块毛竹样地开展了监测调查,分析了坡度、坡位、坡向、海拔高度和土壤层厚度5个立地因子对毛竹林枯梢病感病指数的影响。[结果]表明,毛竹枯梢病的感病指数在不同坡度、不同海拔、不同土层厚度下均存在极显著的差异,且感病指数与坡度及海拔高度呈极显著正相关关系,与土层厚度呈极显著负相关关系;感病指数与坡向呈负相关关系;坡位对毛竹枯梢病的感病指数无显著影响。同时,为了探究这5个立地因子对毛竹枯梢病感病指数的综合影响,利用数量化理论,以这5个立地条件为自变量,毛竹枯梢病的感病指数为因变量,建立多元线性回归预测方程,该预测方程复相关系数R=0.854,复相关系数的F检验得F=10.432F_(0.01)(11.48)=2.64,经T检验,与毛竹枯梢病感病指数关系最大的立地因子是土层厚度,其次是海拔高度和坡度,这3个因子是影响毛竹枯梢病的主导因子。[结论]综合分析得出,在急险坡、上坡位、阳坡面、高海拔、薄土层的立地条件下,毛竹枯梢病的感病指数最大;在平缓坡、下坡位、阴坡面、丘原、肥土层的立地条件下,毛竹枯梢病的感病指数最小。     

Mycosphaerella species associated with leaf disease of Eucalyptus globulus in Ethiopia

Eucalyptus spp. are among the most widely planted exotic trees in Ethiopia. Several damaging leaf pathogens are known from Eucalyptus spp. worldwide. Of these, Mycosphaerella spp. are among the most important, causing the disease known as Mycosphaerella leaf disease (MLD). Characteristic symptoms of MLD include leaf spot, premature defoliation, shoot and twig dieback. Recent disease surveys conducted in Ethiopian Eucalyptus plantations have revealed disease symptoms similar to those caused by Mycosphaerella spp. These symptoms were restricted to E. globulus trees growing in several localities in south, south western and western Ethiopia. The aim of this study was to identify the fungi associated with this disease. This was achieved by examining ascospore germination patterns, anamorph associations and sequence data from the Internal Transcribed Spacer (ITS) region of the rRNA operon, for representative isolates. Several different ascospore germination patterns were observed, suggesting that more than one species of Mycosphaerella is responsible for MLD on E. globulus in Ethiopia. Analysis of sequence data showed that three Mycosphaerella spp., M. marksii, M. nubilosa and M. parva were present. This is the first report of these three species from Ethiopia and represents a valuable basis on which to build further studies in the region.     

First report of Puccinia psidii on Corymbia citriodora and Eucalyptus in Colombia

A rust disease was observed during routine disease surveys of Eucalypt species in Colombia. The cause of the disease was identified, using morphology and DNA sequence data, as the myrtle rust pathogen, Puccinia psidii. We evaluated the susceptibility of Eucalyptus grandis and the hybrid Eucalyptus urograndis to P. psidii. This is the first report of this pathogen on Corymbia citriodora and Eucalyptus species in Colombia.     

Identification of the Armillaria root rot pathogen in Ethiopian plantations

Armillaria root rot is a well‐known disease on a wide range of plants, world‐wide. In Ethiopia, the disease has previously been reported on Pinus spp., Coffea arabica and on various native hardwoods. The causal agent of the disease has been attributed to Armillaria mellea, a species now known to represent a complex of many different taxa. The aim of this study was to determine the extent of Armillaria root rot and the identity of the Armillaria sp. in Ethiopian plantations. As part of a plantation disease survey in 2000 and 2001, samples were collected in plantations at and around Munessa Shashemene, Wondo Genet, Jima, Mizan and Bedele, in south and south‐western Ethiopia. Basidiocarps were collected and their morphology studied. Morphological identification was confirmed by sequencing the intergenic spacer (IGS‐1) region of the ribosomal rRNA operon and comparing data with published sequences of Armillaria spp. Armillaria isolates were collected from Acacia abyssinica, Pinus patula, Cedrela odorata and Cordia alliodora trees. Sporocarps were found on stumps of native Juniperus excelsa. Basidiocarp morphology and sequence data suggested that the fungus in Ethiopia is similar to that causing disease of Pinus spp. in South Africa and previously identified as A. fuscipes. This identification was confirmed for all isolates, based on sequence data. Armillaria fuscipes is known to be common in southern Africa. Its widespread occurrence in Ethiopia suggests that it is also the major cause of Armillaria root rot in that country.     

A single dominant Ganoderma species is responsible for root rot of Acacia mangium and Eucalyptus in Sumatra

Ganoderma root rot is the most serious disease affecting commercially planted Acacia mangium in plantations in Indonesia. Numerous Ganoderma spp. have been recorded from diseased trees of this species and to a lesser extent Eucalyptus, causing confusion regarding the primary cause of the disease. In this study, a large collection of Ganoderma isolates were obtained from the roots of A. mangium showing early signs of root rot in disease centres in South Sumatra plantations. Isolates were also collected from Eucalyptus roots at Lake Toba in North Sumatra showing similar symptoms as well as from sporocarps connected to these samples. Phylogenetic analyses showed that a single Ganoderma sp., identified as G. philippii, is the major causal agent of Ganoderma root rot on A. mangium. Results from this study also showed that the isolates obtained for Eucalyptus trees in North Sumatra belong to G. philippii. Isolates from roots and connected fruiting bodies together with the morphology of the fruiting structures confirmed this identification. Symptoms associated with this pathogen are obvious and it should not be confused with other diseases. Other Ganoderma spp. found in disease centres are considered to be of minor importance and management strategies for root rot should be focused on G. philippii.     

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

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

First report of Mycosphaerella dearnessii in Switzerland

Brown-spot needle blight caused by Mycosphaerella dearnessii [syn. Scirrbia acicola; anamorphic state: Lecanosticta acicola (syn. Septoria acicola)] was observed for the first time in Switzerland. So far, the disease seems to be confined to planted Pinus mugo and Pinus uncinata near Zurich. Pinus sylvestris adjacent to diseased P. uncinata did not show any disease symptoms.     

Management of fungal root‐rot pathogens in tropical Acacia mangium plantations

Acacia mangium is a fast‐growing tree species. It is mainly planted in large monocultures for pulpwood in South‐East Asia. Root rot has become the most economically damaging disease of this species with high tree mortality rates observed during second and third rotations. Two main types of root rots have been found in A. mangium, viz. brown root‐rot and red‐root disease caused by Phellinus spp. and Ganoderma spp., respectively. To assess the future management options for root rot of A. mangium, we review past and current disease‐management strategies for root rot in different temperate and tropical industrial tree crops. The efficacies of a wide range of silvicultural, chemical and biological options are detailed, and their potential utilization in managing root rot of A. mangium is discussed. We conclude that the current gaps in knowledge regarding identification, biology and disease epidemiology of the root‐rot pathogens will need to be addressed so that effective management options can be developed.     

Mechanisms and metabolomics of the host–pathogen interactions between Chestnut (Castanea species) and Chestnut blight (Cryphonectria parasitica)

Chestnut blight is a stem‐girdling disease of Castanea caused by the fungal pathogen Cryphonectria parasitica. Chestnut blight affects all Castanea species to some degree. In Asian species, chestnut blight is a commercially relevant disease which primarily affects nut production. In American and European species, chestnut blight has caused significant declines in wild populations and continues to negatively affect nut production in the European chestnut (C. sativa). Despite the profound effect of this disease in the Castanea genus, very little is known concerning the factors involved in the host–pathogen interaction between C. parasitica and its Castanea hosts. This review summarizes information on known mechanisms and metabolites involved in the host–pathogen interaction and contributes original information on the pathogen in relation to susceptible and putatively resistant genotypes with a view to furthering research that will promote a better understanding of this devastating disease and enable its control.     

Cylindrocarpon cylindroides var. tenue als Pathogen an Abies concolor und einigen Tannenbastarden

Cylindrocarpon cylindroides var. tenue as a pathogen of Abies concolor and some Abies hybrids . By artificial inoculations it was proved that Cylindrocarpon cylindroides Wollenw. var. tenue Wollenw. is the cause of a disease of Abies concolor and the progenies of the species-combinations A. concolor×A. procera and A. concolor×A. nordmanniana. The disease finally can cause the death of the trees.     

早竹丛枝病的调查及病原菌的分子鉴定

[目的]对早竹丛枝病进行调查及病原菌分子鉴定,为早竹丛枝病的病害诊断和防治提供科学依据。[方法]采用单株水平和单枝盘水平的2种病害分级标准对早竹丛枝病进行调查。使用植原体16S rDNA和真菌rDNA-ITS序列的特异性PCR引物,对早竹丛枝病的病原菌进行分子鉴定。[结果]调查的6块样地早竹丛枝病的平均发病率为18.59%,平均病情指数为6.67。感病的早竹DNA样品能够扩增出真菌的rDNA-ITS序列,而不能够扩增出植原体的16S rDNA序列;扩增出的序列与报道的竹针孢座囊菌的序列同源性达到99.00%,与其它真菌的序列同源性最高仅为94.00%。[结论]浙江省德清县早竹丛枝病的病原菌为竹针孢座囊菌。     

First report of Rhytisma filamentosum causing tar‐spot disease on Salix koriyanagi

The occurrence of previously unknown tar‐spot disease on Salix koriyanagi was observed during surveys for forest disease outbreaks in Korea. The fungus associated with tar‐spot disease was identified as Rhytisma filamentosum based on morphological characteristics of the fungus and molecular sequencing of the ITS and 28S rDNA regions of two samples. To our knowledge, this is the first report of R. filamentosum on S. koriyanagi from Korea, following its first discovery on Salix integra in Japan.     

Effect of environment on the response of Eucalyptus clones to inoculation with Cryphonectria cubensis

The ascomycete Cryphonectria cubensis causes severe losses in Eucalyptus plantations in South Africa and selection programmes for disease tolerance are necessary. The aim of this study was to use two C. cubensis inoculation trials, planted at different locations to assess the disease susceptibility of the clones and the effect of the environment on disease development. These two trials consisted each of 21 Eucalyptus clones (E. grandis, E. grandis × camaldulensis and E. grandis × urophylla). All trees were inoculated with a single virulent strain of C. cubensis and lesion widths measured 6 and 12 months after inoculation. Clones differed significantly in their tolerance to C. cubensis. Further, disease severity differed depending on the geographical location of the trial. A significant clone × locality (genotype × environment) interaction was observed. Therefore, screening for disease resistance should take place only in areas where clones will be commercially grown.     

Host range of Erwinia psidii and genetic resistance of Eucalyptus and Corymbia species to this pathogen

Dieback caused by Erwinia psidii is currently one of the most important emerging diseases in eucalypt plantations in Brazil. However, little is known in terms of the host range of this pathogen or the potential sources of resistance against the disease it causes. In this study, we inoculated plants of species from nine families to gain insight into the host range of E. psidii. Plants of all inoculated species of Myrtaceae except Acca sellowiana exhibited disease symptoms and therefore represent potential hosts for the pathogen under natural conditions. In addition, the response of four Corymbia species, 29 Eucalyptus species and three interspecific Eucalyptus hybrids to inoculation with E. psidii was evaluated. All Corymbia henryi, Corymbia maculata, Eucalyptus thozetiana, Eucalyptus cloeziana, Eucalyptus viminalis, Eucalyptus dalrympleana and Eucalyptus pilularis plants were highly resistant to the pathogen, whereas differential disease resistance was observed in the other species. This study provides important information on sources of resistance to Erwinia psidii with potential use in the development of clones with enhanced resistance in eucalypt species of economic importance.     

Changes to relative stand composition after almost 50 years of Heterobasidion root disease in California true fir and pine forests

The Agaricomycete Heterobasidion annosum sensu lato (s.l.), a species complex of fungal pathogens, causes root and butt rot on conifers throughout the northern hemisphere, thereby shaping structure, composition, and evolution of vast and diverse forest ecosystems. We analyze forest change 48–49 years following Heterobasidion root disease emergence in 63 permanent plots first established in 1970–1972 and measured at least once every decade through 2020. We use this dataset to infer the long-term consequences of Heterobasidion root disease in a set of common forest types that reflect some of the most important hosts for this set of diseases in western North America. We contrasted three host–pathogen systems located within the Sierra Nevada, southern Cascades Mountain Range and the Modoc Plateau: (1) H. irregulare in host communities dominated by several Pinus (pine) species and Calocedrus decurrens (incense cedar) in Yosemite Valley, on the Sierra Nevada Range western slope; (2) H. irregulare in a largely single species (Pinus jeffreyi) host disease system on the eastern slopes of the Sierra Nevada and southern Cascades as well as the Modoc Plateau; and (3) H. occidentale—also on the western slope of the Sierra Nevada—in stands with a mixture of susceptible Abies (true fir) and a diversity of non-hosts for this Heterobasidion species. Approximately 50 years after disease emergence, relative basal area and stem density were significantly reduced within disease centres in all three pathosystems, but changes to forest composition and relative species dominance were determined by pre-disease host and non-host diversity. In the western-slope H. occidentale system, the disease increased the dominance of non-susceptible species, Pinus species and C. decurrens. In the multi-genus Yosemite pathosystem, H. irregulare did not significantly shift species dominance, and as expected, species shifts did not occur in the largely single-genus eastern-slope forests. In these widespread California forest ecosystems, two factors appeared to determine forest conditions almost 50 years after Heterobasidion root disease monitoring: the size of the disease centre and the initial diversity of non-hosts. Along with pathogen species, these factors appear to affect the local severity of disease as well as the degree of species shifts relative to initial plot compositions, reaffirming host susceptibility classifications associated with these forest types.     

Effects of elevated atmospheric CO<Subscript>2</Subscript> on two southern forest diseases

Research into the effects of rising atmospheric carbon dioxide (CO₂) on plant diseases remains limited despite the economic importance of this subject. Loblolly pine (Pinus taeda) seedlings were exposed to ambient and twice ambient levels of atmospheric CO₂ prior to inoculation with the fusiform rust fungus (the obligate pathogen Cronartium quercuum f.sp. fusiforme, CQF) or the pitch canker fungus (the facultative pathogen Fusarium circinatum, FC). Additionally, northern red oak seedlings (Quercus rubra; an alternate host of CQF) were exposed to ambient or elevated levels of atmospheric CO₂ prior to inoculation with CQF. In all cases, disease incidence (percent of plants infected) and disease severity (proportion of each plant affected) were determined; with the oak seedlings, the latent period (time to sporulation) was also monitored. In general, disease incidence was decreased by exposure to elevated CO₂. This exposure also increased the latent period for CQF on oak seedlings. In no instance did exposure to elevated CO₂ affect disease severity. This research demonstrated that plants may benefit from exposure to the increasing concentration of CO₂ in the atmosphere through decreases in fungal disease incidence.