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.

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. Methods and Results:  Eleven taxon‐specific primers were designed for PCR amplification of either nuclear or mitochondrial ribosomal DNA regions of Armillaria spp., Ganoderma spp., Hericium spp., Hypoxylon thouarsianum var. thouarsianum, Inonotus/Phellinus‐group, Laetiporus spp., Perenniporia fraxinea, Pleurotus spp., Schizophyllum spp., Stereum spp. and Trametes spp. Multiplex PCR reactions were developed and optimized to detect fungal DNA and identify each taxon with a sensitivity of at least 1 pg of target DNA in the template. This assay correctly identified the agents of decay in 82% of tested wood samples. Conclusions:  The development and optimization of multiplex PCRs allowed for reliable identification of wood rotting fungi directly from wood. Significance and Impact of the Study:  Early detection of wood decay fungi is crucial for assessment of tree stability in urban landscapes. Furthermore, this method may prove useful for prediction of the severity and the evolution of decay in standing trees.

This chapter focuses on the epidemiology and management of Dothistroma needle blight (DNB), which is one of the most important foliar diseases of pines (Pinus spp.) worldwide, caused by D. septosporum and D. pini (Mycosphaerella pini). Information is given on the pathogen distribution, host range, detection and infection biology, as well as management strategies and tactics, which include avoidance, exclusion, eradication, protection (using fungicides and biological control agents), genetic resistance, and integrated method of control.

In Europe the forest pathogen Heterobasidion annosum (Fr.) Bref. includes the S, P, and F intersterility groups (ISGs), each displaying a preferential specialization on Norway spruce (Picea abies (L.) Karst.), pine, and silver fir (Abies alba Mill.), respectively. In this paper, we present data about (i) H. annosum ISGs frequency in different forest types, (ii) the degree of host specificity of each ISG, (iii) the significance of the potential movement of airborne spores among forests, and (iv) the occurrence of S–P chimeras in the northwestern Alps. Using woody spore traps, we sampled natural pure spruce and fir forests and a mixed spruce-fir forest. The ISG of 582 spores was determined by ISG-diagnostic taxon-specific competitive priming (TSCP) polymerase chain reaction (PCR) combined with PCR-mediated detection of ISG-specific introns in the ML5–ML6 DNA region of the mitochondrial large ribosomal RNA (mt LrRNA). All three ISGs were found, and a strong correlation was observed between the F ISG and fir and the S ISG and spruce. In the mixed forest, no clear relationship between tree host species and host-specialized ISGs was found. In spite of a relative dominance of fir in the overstory of the mixed stand, the fir-associated F ISG represented only 11% of the total number of spores collected. This discrepancy was explained by the recent establishment of firs at this site. No S–P nuclear-mitochondrial chimeras were found. This suggests limited gene flow between these ISGs.Key words: Heterobasidion annosum, host specificity, ISGs, gene flow, PCR, Alps.

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.

The effectiveness against Heterobasidion natural airborne infections on Norway spruce stumps was tested for six treatments: aqueous suspension of Phlebiopsis gigantea oidiospores, 10%, 20% and 30% aqueous urea solutions, 4% copper oxychloride aqueous solution, and borax powder. The experiment was carried out in four naturally regenerated forests in the western Alps, each characterized by a different airborne inoculum potential. Within each stand, all treatments, with the exception of urea 10%, were effective and resulted in colonized areas of stumps significantly lower than controls. The effect of ambient spore loads on the stump colonization is discussed.

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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.