Giovanni Nicolotti

Invasion of European pine stands by a North American forest pathogen and its hybridization with a native interfertile taxon

It was recently reported that North American (NA) individuals of the forest pathogen Heterobasidion annosum were found in a single pine stand near Rome, in association with the movement of US troops during World War II. Here, we report on some aspects of the invasion biology of this pathogen in Italian coastal pinewoods, and on its interaction with native (EU) Heterobasidion populations. Spores of Heterobasidion were sampled using woody traps in pine stands along 280 km of coast around Rome. DNA of single‐spore colonies was characterized by two sets of nuclear and one set of mitochondrial taxon‐specific polymerase chain reaction primers. NA spores were found not only in a single site, but in many locations over a wide geographic area. Invasion occurred at an estimated rate of 1.3 km/year through invasion corridors provided by single trees, and not necessarily by sizable patches of forests. Within the 100‐km long range of expansion, the NA taxon was dominant in all pure pine stands. Because abundance of the EU taxon is low and identical among stands within and outside the area invaded by NA individuals, we infer that the exotic population has invaded habitats mostly unoccupied by the native species. Discrepancy between a mitochondrial and a nuclear marker occurred in 3.8% of spores from one site, a mixed oak‐pine forest where both taxa were equally represented. Combined phylogenetic analyses on nuclear and mitochondrial loci confirmed these isolates were recombinant. The finding of hybrids indicates that genetic interaction between NA and EU Heterobasidion taxa is occurring as a result of their current sympatry.

A multiplex PCR‐based method for the detection and early identification of wood rotting fungi in standing trees

Aims:  The goal of this research was the development of a PCR‐based assay to identify important decay fungi from wood of hardwood tree species in northern temperate regions.

Soil contamination by crude oil: impact on the mycorrhizosphere and on the revegetation potential of forest trees.

In vitro and greenhouse biotests were carried out to study the effects of various concentrations of crude oil on the mycorrhizosphere and the ability of ectomycorrhizal fungi to colonise Norway spruce and poplar seedlings grown on contaminated soil. Ectomycorrhizal fungi grown in pure cultures showed a variety of reactions to crude oil, ranging from growth stimulation to total inhibition of growth, depending on the species of fungi. Germination of poplar and spruce seeds was not significantly affected. The growth of spruce seedlings was not affected by crude oil, whereas that of poplar seedlings was significantly reduced at high concentrations. None of the concentrations had any effect on the degree of ectomycorrhizal and endomycorrhizal colonisation of poplar. With spruce, however, the ectomycorrhizal fungi showed species-specific reactions to increasing concentrations, in accordance with the results of the pure culture test. The length of time between soil contamination and seeding affects both seedling growth and the mycorrhizal infection potential of the soil. The results confirm the importance of mycorrhizal fungi in the bioremediation of soils contaminated by crude oil.

Pathogen introduction as a collateral effect of military activity.

489–497). Three papers utilize molecular phylogenetic approaches to systematics. Traditional groupings and most species of Physconia are confirmed as distinct, although doubt is shed on the monophylly of two species pairs (pp. 498–505). The Lecanora rupicola group is shown to be distinct from Lecanora s. str., with the species containing sordidone as well as having pruinose apothecial discs (pp. 506–514). ITS data is used in a revision of the marine Collemopsidium species in north-west Europe, along with statsitical analyses of morphological and habitat variables, leading to the recognition of five species (pp. 515–532). A critical revision of the non-yellow species of Rhizocarpon with hyaline muriform ascospores in the Nordic countries is presented; 16 species are accepted and keyed, along with maps, descriptions, synonyms, spore drawings and habit photographs (pp. 533–570). Finally, a survey of Trichothelium species on bark in the neotropics revealed three new species, bring the known number to five (pp. 571–575). The increased inclusion of lichenological papers in Mycological Research in recent years reflects the continuing integration of lichenologists into the broader mycological community. However, now that The Lichenologist, has a new publisher (Cambridge University Press) and is expected to provide an improved service, Mycological Research will in future give priority to lichen papers which will also be of interest to a wider mycological audience.

Comparing the influences of ecological and evolutionary factors on the successful invasion of a fungal forest pathogen.

The fungal forest pathogen Heterobasidion annosum has been introduced from North America into Italy and is now associated with high mortality of Italian stone pines. Due to the presence of a closely related native H. annosum taxon, this pathosystem presents an unusual opportunity to test specific ecological and evolutionary factors influencing fungal invasions. Comparative inoculation experiments on Scots pine cuttings and on seedlings of European and North American pines failed to identify significant increased pathogenicity of North American genotypes on European hosts congruent with lack of host-pathogen co-evolution. However, spore trappings indicate that while reproductive potential of native H. annosum was significantly reduced in the dry season, that of the invasive taxon was consistently high regardless of season. Ecological differences between the native and exotic taxon may therefore facilitate this invasion. Understanding which factors enhance this emerging forest disease is important both for biotic invasion theory and for disease control.

Seasonal Patterns of Spore Deposition of Heterobasidion Species in Four Forests of the Western Alps

ABSTRACT Patterns of spore deposition by Heterobasidion species were studied between the spring of 1998 and December 2000 in four forests in the western Alps using woody traps. The maximum spore deposition rate (DR) ranged from 169 to 1,550 spores m(-2) h(-1). Although spores were captured from February to October at most sites, inoculum concentration consistently peaked in the late summer or early fall. In one of the four study sites, similar patterns of DR were recorded in 2 years of sampling. A significant correlation (r = 0.654, P = 0.001) was found between DR and the average minimum air temperature in the 4 weeks before sampling. Approximately 1,200 spores were isolated and identified at the species level by polymerase chain reaction-based methods. Single-spore isolates were consistently clampless, indicating the sampled airspora was almost exclusively composed of haploid basidiospores. No significant variations of basidiospore frequencies were detected for either H. abietinum or H. annosum among sampling periods. However, the frequency of H. parviporum spores was always significantly higher in the summer. These findings suggest different patterns of sporulation among Heterobasidion species.

FEASIBILITY OF ULTRASONIC TOMOGRAPHY FOR NONDESTRUCTIVE TESTING OF DECAY ON LIVING TREES

Both laboratory and field ultrasonic measurements were carried out to assess the feasibility of ultrasonic tomography for non-invasive testing of living trees. Trees with internal decay were investigated and later cut down. The laboratory measurements, performed on wood disks and specimens, led to the quantitative assessment of the reliability of the tomographic result. Statistical analysis of data allowed considerations to be made on the main aspects connected to the tomographic imaging, such as uncertainty, spatial resolution and anisotropy. The obtained results show that the tomographic image of the ultrasonic velocity distribution is in good agreement with the distribution of the wood decay in the investigated section and the proposed methodology therefore seems to be an improvement on currently used surveying methods.

A PCR‐based method for the identification of important wood rotting fungal taxa within Ganoderma, Inonotus s.l. and Phellinus s.l.

Two multiplex PCRs, based on 10 taxon-specific primers designed on rRNA gene regions, were developed for the identification of taxa within the lignivorous genera Ganoderma, Inonotus s.l. and Phellinus s.l., each comprising both secondary and primary aggressive decay fungi. Each multiplex PCR proved to correctly identify 1 x 10(-2) pg of fungal target DNA directly from wood. This method can be helpful in detecting decay in standing trees independent of its stage of advancement, and to identify the associated decay agents.

Ecological Constraints Limit the Fitness of Fungal Hybrids in the Heterobasidion annosum Species Complex

ABSTRACT The ability of two closely related species to maintain species boundaries in spite of retained interfertility between them is a documented driving force of speciation. Experimental evidence to support possible interspecific postzygotic isolation mechanisms for organisms belonging to the kingdom Fungi is still missing. Here we report on the outcome of a series of controlled comparative inoculation experiments of parental wild genotypes and F1 hybrid genotypes between closely related and interfertile taxa within the Heterobasidion annosum fungal species complex. Results indicated that these fungal hybrids are not genetically unfit but can fare as well as parental genotypes when inoculated on substrates favorable to both parents. However, when placed in substrates favoring one of the parents, hybrids are less competitive than the parental genotypes specialized on that substrate. Furthermore, in some but not all fungus × plant combinations, a clear asymmetry in fitness was observed between hybrids carrying identical nuclear genomes but different cytoplasms. This work provides some of the first experimental evidence of ecologically driven postzygotic reinforcement of isolation between closely related fungal species characterized by marked host specificity. Host specialization is one of the most striking traits of a large number of symbiotic and parasitic fungi; thus, we suggest the ecological mechanism proven here to reinforce isolation among Heterobasidion spp. may be generally valid for host-specialized fungi. The validity of this generalization is supported by the low number of known fungal hybrids and by their distinctive feature of being found in substrates different from those colonized by parental species.

Screening of antagonistic fungi against air-borne infection by Heterobasidion annosum on Norway spruce

Abstract In vitro inhibition of Heterobasidion annosum by fungi isolated from the surface and inside of Norway spruce (Picea abies L.) stumps, ten Verticillium bulbillosum strains from Fagus sylvatica L. mycorrhizoplane, and three lignivorous basidiomycetes from culture collections was evaluated at 5, 10 and 15°C in a search for potential biocontrol candidates. Forty-nine strains from nine genera and hyaline sterile mycelia with or without clamp connections were isolated from spruce. Over 50% inhibition at one or more temperatures was displayed by 21 of 49 isolates. Fresh wood tests were also performed with the six fungi that displayed the highest in vitro activity and with the basidiomycetes. The best results were observed with Hypholoma fasciculare, Trichoderma harzianum 7 AO , Verticillium bulbillosum (culture filtrate) and Phanerochaete velutina.