Eastern filbert blight disease resistance from <Emphasis Type="Italic">Corylus americana</Emphasis> ‘Rush’ and selection ‘Yoder #5’ maps to linkage group 7

Eastern filbert blight (EFB), caused by the pyrenomycete Anisogramma anomala, is a serious threat to the hazelnut industry in the Pacific Northwest. EFB is endemic in eastern North America where it occasionally produces small cankers on the wild American hazelnut (Corylus americana). In contrast, most cultivars of European hazelnut (Corylus avellana) are susceptible. Genetic resistance is the most promising disease control method and is an objective of the Oregon State University hazelnut breeding program. ‘Gasaway’ resistance, which is governed by a dominant allele at a single locus, has been extensively used in the program. However, ‘Gasaway’ and some of its offspring have been infected by EFB isolates from New Jersey, Minnesota, and Michigan. Efforts to create new cultivars with durable EFB resistance include identifying and studying new resistance sources. In this study, resistant accessions C. americana ‘Rush’ and interspecific hybrid selection ‘Yoder #5’ were crossed with susceptible C. avellana selections and the resulting segregating seedling populations were inoculated by either exposure of potted trees under a structure topped with diseased branches or field exposure supplemented by tying diseased branches to each tree. Disease response was scored when cankers were visible 20 months after inoculation. Resistance from both sources segregated in a 1:1 ratio, indicating control by a single locus and a dominant allele for resistance. DNA extracted from the seedlings was amplified with previously mapped microsatellite markers. Resistance from both C. americana ‘Rush’ and ‘Yoder #5’ was placed on linkage group 7 in the same position as resistance from C. avellana ‘Ratoli.’ Linked microsatellite markers B753, GB372, and B509 will be useful for marker-assisted selection and the pyramiding of genes for durable EFB resistance. Assessing response to EFB is challenging, whether the plants are inoculated under a structure topped with diseased wood or in a humidity chamber in the greenhouse, or by exposure in the field. The pathogen has a 2-year life cycle, and there is a 15-month wait between inoculation and symptom expression. A small number of escapes is commonly encountered, and resistant plants occasionally develop small cankers. Our approach of studying segregation ratios and then mapping with microsatellite markers should be a useful approach for disease resistance studies in many tree crops.     

Real-time PCR for detection and quantification,and histological characterization of <Emphasis Type="Italic">Neonectria ditissima</Emphasis> in apple trees

Key message

We designed a pair of primers from a region of the β-tubulin gene to detect and quantify Neonectria ditissima in wood of some infected apple cultivars, and optimized light microscopy to study fungal-plant interactions.

Abstract

Neone ctria ditissima, the causal pathogen of fruit tree canker, is a sordariomycete fungus that affects apple orchards, especially in north-western Europe. To prevent serious disease epidemics, an accurate, rapid, and sensitive method for detection of N. ditissima is needed for pathogen identification. A quantitative real-time PCR (qPCR) assay was developed for both detection and quantification of this pathogen in infected apple cultivars. Several primer sets were designed from regions of the β-tubulin gene. One primer set passed several validation tests, and the melting curve confirmed species-specific amplification of the correct product. In addition, the N. ditissima biomass could be detected at variable amounts in samples from the infection sites of six different cultivars, with ‘Aroma’ having the lowest amount of N. ditissima biomass and ‘Elise’ the highest. To complement the qPCR results, tissue from detached shoots and 1-year-old trees of ‘Cox’s Orange Pippin’ (susceptible) and ‘Santana’ (partially resistant) was used in a histopathology study. In both detached shoots and trees, fungal hyphae were found in cells of all tissues. No qualitative differences in the anatomy of the infected samples were observed between the cultivars. In the detached shoot experiment, both cultivars were affected but differences in the rate of disease progression suggest that the partially resistant cultivar could resist the fungus longer. The qPCR assay developed in our study produced reproducible results and can be used for detection of N. ditissima in infected trees.

     

Phytophthora collar rot of apple: seasonal effects on infection and disease development

One-to three-year-old trees of the apple variety Cox's Orange Pippin were highly resistant to infection by Phytophthora cactorum except during the spring from March to May. A rapid increase in resistance occurred after this time from the commencement of shoot growth. The period of susceptibility to infection by P. syringae was from October to December, when trees were dormant. Inoculations with either fungus during the respective susceptible periods caused rapidly extending lesions which girdled and killed the trees; established lesions continued to enlarge in months when trees were resistant to infection. Similar seasonal fluctuations in resistance to infection by P. cactorum also occurred in mature (35-year-old) Cox trees but the susceptible period was longer. Lesions resulting from inoculations at the optimum time (the ‘mouseear’ to ‘pink-bud’ stages of development) extended at similar rates in both young and old trees. The infrequent incidence of collar rot in young trees is probably related to factors other than inherent resistance. In resistance and pathogenicity studies young trees gave reliable and consistent results, provided that inoculations were correctly timed in relation to bud development.     

Old park trees as habitat for saproxylic beetle species

Very old trees harbour a diverse fauna of saproxylic insects, many of which are classified as threatened due to the scarcity of this kind of habitat. Parks, which often contain many old trees, are therefore considered to be important sites for this fauna. However parks are intensively managed and dead wood is often removed. Therefore this study compares if the saproxylic beetle fauna in parks is as diverse as it is in more natural stands. Eight ‘Park’ sites at manor houses around lake Mälaren, Sweden were compared with trees in wooded meadows: eight grazed sites, here termed ‘Open’, and 11 sites regrown with younger trees, termed ‘Re-grown’. The comparison was made on lime trees (Tilia spp.): one of the most frequent tree species in old parks which host a diverse beetle fauna. Beetles were sampled with window traps, which in total caught 14,460 saproxylic beetles belonging to 323 species, of which 50 were red-listed. When comparing all saproxylic species, ‘Park’ sites had significantly fewer species than ‘Open’ sites. However, for beetles in hollow trees and for red-listed species there was no significant difference, the number in ‘Park’ being intermediate between ‘Open’ and ‘Re-grown’. Species composition differed between sites, but only marginally so. Therefore, the conclusion is that old park trees on average are as valuable for faunal diversity as trees in more natural sites. Large conservation benefits can be obtained by combining cultural and conservational values in the management of park habitats.     

PATHOLOGY OF CYST-NEMATODES

1. The cyst-nematodes, which belong to the genus Heterodera Schmidt, are obligate plant parasites. Several species cause crop diseases of economic importance. These nematodes differ greatly in structure from the other, vermiform, plant-parasitic and soil-inhabiting nematodes, for although the migrant larval phase of cyst-nematodes is vermiform, this phase is only transient. The principal phases are the sedentary female, which feeds upon the plant root, and the cyst, which derives from the female and consists of the eggs surrounded by mucilage within the dead female cuticle. The term ‘egg’ includes the contents within the shell, which at maturity is usually a coiled, second stage, larva. 2. The migrant larva may be parasitized by many species of predacious and endozoic fungi which have been much studied, but these do not parasitize the females or cysts. Until 1974 only one parasite of the females was known, and that imperfectly. On the other hand, many fungi have been cited as parasites of eggs inside cysts, notably the species now known as Phialophora malorum and Cylindrocarpon destructans. Insect-pathogenic fungi have also been cited as egg parasites but evidence is now against their pathogenicity to Heterodera. No other classes of organism are known to parasitize the females or cysts, although Collembola have been reported as predators. 3. Studies published since 1973, including the present, show a total of seven (or eight) pathogenic fungi. There are two (or three) pathogens of the females, two major and three minor pathogens of the eggs. The former comprise Catenaria auxiliaris and two Entomophthora-like fungi, possibly the same species but both imperfectly known. The major egg pathogens are Verticillium chlamydosporium and an incompletely known species termed the ‘contortion fungus’ from the symptoms on infected larvae newly hatched from eggs. The minor egg pathogens are a ‘black yeast’ taxonomically fairly similar to but not identical with Phialophora malorum; a sterile ‘crystal-forming fungus’ and Cylindrocarpon destructans. The main features of these pathogens are described and illustrated. 4. Mycorrhizal fungi belonging to Glomus Tulasne & Tulasne are sometimes associated with cysts. They ordinarily sporulate inside empty cysts, but in one remarkable example from Heterodera schachtii growing on tomato host in glasshouse culture a Glomus apparently behaved as a pathogen. Pythium species may invade cysts maintained under unfavourable conditions. Miscellaneous other fungi are also found occasionally in eggs. 5. In addition to undergoing disease caused by fungi, eggs sometimes undergo oily degeneration. This disorder is not of numerical significance, but a high proportion of cysts are diseased through apparently non-specific causes whose symptoms can be summarized as ‘lysed, shrivelled, coagulated or decayed’. Although the majority of diseased females are killed by fungal pathogens, some 25–40% of diseased cysts are destroyed through non-specific causes. Overall disease in ten populations of Heterodera schachtii examined from roots was 9% of females and 26% of young cysts; in 76 populations sieved from soils a mean of 14% of older cysts were diseased. Where the cyst-nematode host had been grown in monoculture for 11 years higher proportions of cysts were diseased although few pathogens of females were present. Heterodera avenue cysts were parasitized to a similar extent. 6. Of the pathogens of females, Catenaria auxiliaris was widespread in H. schachtii and uncommon in H. avenue, whereas Entomophthora-like fungi were widespread in H. avenue and rare in H. schachtii. Of egg pathogens, Verticillium chlamydosporium and the ‘contortion fungus’ were common in H. schachtii and H. avenae, and the ‘contortion fungus’ was also found in H. glycines. The minor egg pathogens were much less common.     

Perpetuation of Cherry Leaf Spot Disease in Ornamental Cherry

Cherry leaf spot disease, caused by Blumeriella jaapii (Rehm) Arx., is an increasing concern to nursery producers of ornamental cherry in the south‐eastern United States. Spores were trapped starting in late March before symptoms were observed in the field, which indicates that leaf debris from diseased trees are an important source of primary inoculum. Previously infected trees of six cultivars (‘Kwanzan’, ‘Yoshino’, ‘Okami’, ‘Snowgoose’, ‘Autumnalis’ and ‘Akebono’), which were overwintered in a controlled environment protected from airborne spores, developed disease symptoms in late spring, indicating that dormant buds may also be a source of primary inoculum. Because ornamental cherry trees are propagated by budding and cuttings, disease management should incorporate cultural practices that focus on propagation from disease‐free trees and fungicide applications beginning at petal drop to protect emerging leaves.     

Figured grain in aspen is heritable and not affected by graft-transmissible signals

Figure can add value to wood products, but its occurrence is unpredictable. A first step in reliably producing figured wood is determining whether it is faithfully transmitted to progeny via sexual and asexual reproduction. We describe a 26-year-old male aspen genotype, designated ‘Curly Poplar’, which was shown to be a Populus × canescens hybrid using microsatellite markers. All rooted cuttings of this genotype exhibited an undulating pattern on the radial surface that was not seen in the control trees, all of which showed a smooth radial surface and straight grain. We observed spiral grain with a magnitude of 2.77 ± 0.12°/cm from vertical in 11-month-old, field-grown rooted Curly Poplar cuttings, but spiral grain was not apparent in wood from the 26-year-old mature ortet that supplied these cuttings. Veneer cut from the mature tree exhibited a novel type of figure that we called ‘Scattered Moiré’. Reciprocal grafts between Curly Poplar and various non-figured aspens showed that a graft-transmissible signals did not appear to be involved in figure formation in Curly Poplar or the induction of figure in straight-grained trees. Curly Poplar was crossed to a straight-grained clone to test the inheritance of the gene(s) responsible for figure. Samples from the resulting population revealed that 79 out of 377 seedlings exhibited figure. A Chi-square test led to the rejection of a 1:1 segregation ratio between figured and non-figured phenotypes (p < 0.01), but not of a 1:3 segregation ratio (p 0.0793). Overall, these analyses showed that figure in Curly Poplar is under genetic control, but its inheritance may not be simple.     

<Emphasis Type="Italic">Sporothrix inflata</Emphasis>, a root-inhabiting fungus of <Emphasis Type="Italic">Quercus robur</Emphasis> and <Emphasis Type="Italic">Q. petraea</Emphasis>

The anamorphic fungus Sporothrix inflata, known as a soil-borne fungus with worldwide distribution, was isolated for the first time from the cortex and central cylinder of living and dead roots of healthy and diseased oak trees (Quercus robur and Q. petraea). Isolation frequencies of S. inflata from oak roots varied according to the health status of trees, oak species, study sites, soil depth and root diameter. Colony morphology and growth rate of isolates are influenced by colony age and type of culture medium.     

Molecular phylogenetic identification of endophytic fungi isolated from resinous and healthy wood of Aquilaria malaccensis,a red listed and highly exploited medicinal tree

Aquilaria malaccensis is a fast-growing, tropical tree belonging to the family Thymelaeaceae and is locally known as Agar. Agarwood formation takes place in the stem or main branches of the tree where an injury has occurred. It is believed that the tree is first attacked by a pathogenic fungus, which causes it to weaken. Most fungal diversity studies have previously been based on morphological examination and cultivation methods. In this study, we used both culture-dependent and culture-independent approaches (metagenomic) to study the endophytic fungi on wood chips of A. malaccensis. The culture-based approach revealed Alternaria, Cladosporium, Curvularia, Fusarium, Phaeoacremonium and Trichoderma as members of the agarwood community. Also analysis of ITS sequencing of these culture isolates provided further verification of the identity of the cultured groups. Analysis of community DNA (metagenome) extracted from both infected and healthy wood samples revealed that the majority of fungi present had highest sequence similarity to members of Dothideomycetes, followed by Sordariomycetes and Saccharomycetes. Thus, morphological and genetic characteristics showed that most isolates from agarwood belong to phylum Ascomycota. A neighbour-joining tree showed the relationships between the isolates sequence data and the closest identified relatives from GenBank.     

Wood‐rotting basidiomycetes associated with declining native trees in timber‐harvesting compartments of the Garden Route National Park of South Africa

Trees in the Garden Route National Park (GRNP) indigenous forests in South Africa are selectively harvested for timber based on criteria that include signs and symptoms induced by wood‐rotting fungi. However, virtually nothing is known regarding the identity and host associations of these macro‐fungi in this natural ecosystem. Surveys were conducted in three harvesting compartments in the GRNP to investigate the taxonomic affiliation and species richness of these fungi on standing and recently harvested trees. Samples were collected from basidiomes on infected trees and tree stumps, and from diseased tissues on symptomatic trees. Phylogenetic analyses using ITS sequences characterized the isolates obtained into 26 Operational Taxonomic Units (OTUs) belonging to 17 genera after clustering the sequences at a 97% identity threshold. Ganoderma (Ganodermataceae) and Inonotus (Hymenochaetaceae) were the most species‐rich genera and the Bloukrans compartment, with 22 OTUs, showed the highest species richness. A fungus (OTU1) affiliated with Ganoderma pfeifferi was the most abundant in the surveyed areas. Its predominance was also evidenced on host trees since it occurred on 15 of the 20 tree species sampled, with Olea capensis subsp. macrocarpa (Oleaceae) being the most colonized host. Given the wide variety of wood‐rotting basidiomycetes revealed by this study and particularly the preponderance of species with pathogenic potential, more attention should be given to better understand their ecological role in this natural ecosystem as well as the effects of logging that may enhance their dissemination or negatively affect their diversity and the health of trees in the region.     

Search for Viroids and Other Small RNAs Associated with Forest Damage

We examined whether viroids may be involved as the causative agents of forest damages which have been observed in Germany during the last decade. A crude RNA extract was prepared from healthy and diseased copper beech, spruce, and pine trees and was analysed by two-dimensional gel electrophoresis which resolves RNA bands in the molecular weight range from 25,000 to 10⁶. Viroids are known to consist of single stranded circular RNA and are clearly differentiable in the electrophoresis used here from cellular RNA. Viroids could not be found in any of the samples investigated. In all samples from diseased trees, however, other additional RNA bands were discovered which were more similar to cellular RNA than to viroids in their electrophoretic properties. It is uncertain whether these diseased-associated RNAs are due to an infection or originate from a modified nucleic acid metabolism.     

The possible role of pathogenic fungi in local degeneration of Salvinia auriculata Aublet on Lake Kariba

A patchy degeneration of weed mats of Salvinia auriculata in the sheltered mouths of rivers draining into Lake Kariba was reported in 1962 to be associated with a fungal attack. Laboratory isolations from degenerating plants yielded a saprophytic Alternaria sp. and a parasitic Spicariopsis sp. Degenerating plants failed to transmit the disease when placed among healthy plants, and the results of inoculation experiments with spores of Spicariopsis sp. were inconsistent with this fungus being a primary pathogen. The characteristic feature of degeneration in the field was a mosaic of alternating ‘islands’ of diseased and healthy plants. Although the diseased plants showed the symptoms associated with Alternaria sp. and Spicariopsis sp., their characteristic distribution provided circumstantial evidence that degeneration was physiological in origin. This view was strengthened by the fact that sudd plants growing on degenerating areas of the Salvinia‘carpet’ were usually chlorotic. The presence of symptoms caused by the parasitic Spicariopsis sp. on degenerating plants could be explained by postulating that, after the plants have begun to degenerate, they are predisposed to infection by this fungus. The association of degeneration with a particular type of riverine site suggests that a seasonal investigation of the hydrobiological conditions accompanying the development of weed mats at such sites would indicate the type of factor responsible for the disease. The original hope for a biological control of Salvinia auriculata by means of a parasitic fungus remains a theoretical possibility.     

Wood of Tapirira (Anacardiaceae) from the paleogene Clarno Formation of Oregon

A new species of fossil wood, Tapirira clarnoensis, is described from a probable late Eocene deposit in the Clarno Formation of Oregon known locally as the Nut Beds. The wood represents, to the knowledge of the writer, the earliest occurrence of Tapirira in the fossil record and the only occurrence of the genus outside its present neutropical range of distribution.     

Quick Decline of Macadamia Trees: Association with Phytophthora capsici

Some macadamia trees in commercial orchards in Hawaii showing quick decline syndrome had bleeding from the trunk. Phytophthora capsici was isolated from c. 67% of such sites, and was shown to kill branches of artificially-inoculated healthy macadamia trees. The pathogen was detected in both diseased and apparently healthy bark and isolated from wood 80 mm away from the bark. Results suggest that trunk infection by P. capsici may lead to girdling and rapid decline, and attract insects which then cause some bleeding by making wounds at the sites of recent infection.     

Studies on the Relationship of Cowpea mosaic virus and its Vector Aphis cracdvora Koch

Chillies or Green peppers (Capsicum annuumL.) are extensively grown in this country during rainy and winter seasons. The crop brings good profit for the grower as it is widely used in green as well as in dried condition. A fruit spot disease of this valuable vegetable was noticed during the cold months of 1962 at Phule Market, Poona, on the sweet variety (which is usually bigger in size), stored in bamboo baskets and crates. On microscopical examination of such spots the fungus appeared to be a species of Helminthosporium. The pungent varieties of chilies such as‘Gauran’(long in size) and‘Dharwar round’wert; found to be free from infection. Affected fruits incubated in moist chambers gave abundant sporulation of the causal organism. Ripened and red chili-fruits were free from such infection in the markets. The present paper gives an account of the etiology of the disease, pathogen city and cultural behaviour of the fungus.     

Direct Detection of Fungal Siderophores on Bats with White-Nose Syndrome via Fluorescence Microscopy-Guided Ambient Ionization Mass Spectrometry

White-nose syndrome (WNS) caused by the pathogenic fungus Pseudogymnoascus destructans is decimating the populations of several hibernating North American bat species. Little is known about the molecular interplay between pathogen and host in this disease. Fluorescence microscopy ambient ionization mass spectrometry was used to generate metabolic profiles from the wings of both healthy and diseased bats of the genus Myotis. Fungal siderophores, molecules that scavenge iron from the environment, were detected on the wings of bats with WNS, but not on healthy bats. This work is among the first examples in which microbial molecules are directly detected from an infected host and highlights the ability of atmospheric ionization methodologies to provide direct molecular insight into infection.