Parasitism and saprotrophic wood decay are two fungal strategies fundamental for succession and nutrient cycling in forest ecosystems. An opportunity to assess the trade-off between these strategies is provided by the forest pathogen and wood decayer Heterobasidion annosum sensu lato. • We report the annotated genome sequence and transcript profiling, as well as the quantitative trait loci mapping, of one member of the species complex: H. irregulare. Quantitative trait loci critical for pathogenicity, and rich in transposable elements, orphan and secreted genes, were identified. • A wide range of cellulose-degrading enzymes are expressed during wood decay. By contrast, pathogenic interaction between H. irregulare and pine engages fewer carbohydrate-active enzymes, but involves an increase in pectinolytic enzymes, transcription modules for oxidative stress and secondary metabolite production. • Our results show a trade-off in terms of constrained carbohydrate decomposition and membrane transport capacity during interaction with living hosts. Our findings establish that saprotrophic wood decay and necrotrophic parasitism involve two distinct, yet overlapping, processes.
THREE crops — corn, soybeans and wheat — account for a vast majority of the value of America’s agricultural crop output. But wheat is different in one important respect. While more than 90 percent of the nation’s corn and soybean acres are now planted with seeds genetically engineered to resist insects, herbicides or both, there is not a single acre of genetically engineered wheat being grown commercially in the United States.
This unique book covers a broad diversity of fungal systems and provides unique insight into the functions of those fungi in various ecosystems - from soil, to plant, to human. Bringing together fungal genomic information on a variety of lifestyles and traits, the book covers saprotrophism, pathogenesis (including biotrophs, hemibiotrophs, necrotrophs) and symbiosis. Advances in high-throughput sequencing now offer unprecedented opportunities for identification of novel key molecular mechanisms controlling plant-microbe interactions, evolution of fungi and developmentally- and ecologically-relevant traits, this book explores how these massive streams of fungal sequences can be exploited to gain a deeper understanding of the evolution of fungi and their ecological role.
Although tremendous progress has been made in recent years in fungal genomics, thanks to the sequencing of over one hundred fungal genomes, until now no book has used this information to bridge fungal genomics, molecular ecology and ecology. Edited by a recognized leader in fungal genomics and soil metagenomics with over a decade of experience, Genomics & Metagenomics for Harnessing the Ecology of Fungi will be a useful resource for the experienced as well as the new researchers entering the field.
Hybrid species of fungal pathogens that infect wild and cultivated plants are emerging with new virulence and host ranges, posing a threat to agriculture and forestry1. Here we show that the virulence of hybrid species of the basidiomycete fungus Heterobasidion annosum (Fr) Bref, a causal agent of root and butt rot in conifers and one of the most economically important forest pathogens, is controlled by their mitochondrial genome. Our results indicate that cooperation between organelles that contain genetic information may influence the phenotype of hybrid phytopathogens.
The root and butt rot caused by Heterobasidon annosum is one of the most destructive diseases of conifers in the northern temperate regions of the world, particularly in Europe. Economic losses attributable to Heterobasidion infection in Europe are estimated at 800 million euros annually. The fungus has been classified into three separate European intersterile species P (H. annosum), S (H. parviporum) and F (H. abietinum) based on their main host preferences: pine, spruce and fir, respectively. In North America, two intersterile groups are present, P and S/F, but these have not been given scientific names. The ecology of the disease spread has been intensively studied but the genetics, biochemistry and molecular aspects of pathogen virulence have been relatively little examined. Recent advances in transcript profiling, molecular characterization of pathogenicity factors and establishment of DNA-transformation systems have paved the way for future advances in our understanding of this pathosystem.
Taxonomy: Heterobasidion annosum (Fr.) Bref., H. parviporum Niemelä & Korhonen and H. abietinum Niemelä & Korhonen; kingdom Fungi; class Basidiomycotina; order Aphyllophorales; family Bondarzewiaceae; genus Heterobasidion.
Identification: presence of the fungus fruit bodies, basidiocarps whitish in the margins, upper surface is tan to dark brown, usually irregular shaped, 3.5 (−7) cm thick and up to 40 cm in diameter; pores 5–19, 7–22 and 13–26 mm2 for the P, F and S groups, respectively. Small brownish non-sporulating postules develop on the outside of infected roots. Asexual spores (conidiospores) are 3.8–6.6 × 2.8–5.0 µm in size. Mating tests are necessary for identification of intersterility groups.
Host range: The fungus attacks many coniferous tree species. In Europe, particularly trees of the genera Pinus and Juniperus (P), Picea (S), Abies (F) and in North America Pinus (P) and Picea, Tsuga and Abies (S/F). To a lesser extent it causes root rot on some decidous trees (Betula and Quercus).
Disease symptoms: symptoms (e.g. exhudation of resin, crown deterioration) due to Heterobasidion root rot in living trees are not particularly characteristic and in most cases cannot be distinguished from those caused by other root pathogens. Heterobasidion annosum s.l. is a white rot fungus. Initial growth in wood causes a stain that varies in colour depending on host tree species. Incipient decay is normally pale yellow and it develops into a light brown decay to become a white pocket rot with black flecks in its advanced stage.
Control: silvicultural methods (e.g. stump removal), chemicals (urea, borates) and biological control agent (Phlebiopsis gigantea, marketed as PG Suspension® in the UK, PG IBL® in Poland and Rotstop® in Fennoscandia) are commonly used approaches for minimizing the disease spread.
... damages annually from the fungal pathogen Heterobasidion annosum. Aside from the economic losses, scientists are concerned by the white rot fungus that not only breaks down the wood for nutrients, but also releases the ...
Heterobasidion annosum sensu lato is a species complex comprising five species that are widely distributed in coniferous forests of the Northern Hemisphere and are each characterized by a distinct host preference. More than 1,700 papers have been published on these fungi in the past four decades, making them perhaps the most widely studied forest fungi. Heterobasidion species are at different levels on the saprotroph-necrotroph gradient, and the same individual can switch from one mode to the other. This offers a unique opportunity to study how genomic structure, gene expression, and genetic trade-offs may all interact with environmental factors to determine the life mode of the organism. The abilities of Heterobasidion spp. to infect stumps as saprotrophs and to spread to neighboring trees as pathogens have resulted in significant damages to timber production in managed forests. This review focuses on the current knowledge of the biology, ecology, evolution, and management of these species and is based on classical and modern studies.
The pattern of gene expression of the basidiomycete Heterobasidion annosum, causal agent of the root rot of conifers, was analysed during its interaction with pine roots. A complementary DNA (cDNA) library was constructed from total RNA extracted from H. annosum mycelia challenged with Scots pine seedling roots for 6 and 72 h. Single pass sequencing of 1148 randomly selected cDNA clones resulted in 923 expressed sequence tags (ESTs). Contig analysis and sequence comparisons identified 318 unigene sequences, of which 62 were repeatedly sampled. A putative cellular function was assigned to 223 contigs (70%) that showed a moderate to high homology to protein sequences from public databases. Variations in expression levels during the infection process were monitored on a set of 96 unigenes by reverse northern using dot hybridisation. Seven unigenes (7%) were shown to be either up (4) or down (3) regulated during interaction of the fungus with pine roots. Fungal genes differentially expressed during contact with roots include genes encoding mitochondrial proteins, a cytochrome P450 and a vacuolar ATP synthase.
Stump protection using chemical or biological agents is the main control measure against root and butt rot caused by Heterobasidion annosum s.l. in northern and temperate conifer forests. Long-term effects of urea treatment of stumps are poorly known and here we describe a 15-year study of urea treatment on the rot incidence on Norway spruce (Picea abies). We also tested the effect of urea protection on tree growth and on the resistance of stands against strong winds. Four treatments were made in two replications in two first-rotation P. abies stands in southern Sweden; after first-thinning stumps were (i) treated with urea 35% (w/v), (ii) artificially infected with H. annosum conidia, (iii) half urea treated and half artificially conidia infected, (iv) untreated, therefore naturally infected. After 15 years, the trees were sampled at 20 cm above ground using an increment borer and observed for presence of rot and, following incubation, presence of H. annosum conidia. Tree growth was calculated by measuring the diameter before and after the treatment. Urea treated plots showed the lowest incidence of rot (3%) as well as of H. annosum incidence (0%). Conidia treatment showed the highest incidence of rot (68%), its incidence was higher than that observed in natural infection treatment (43%), but did not differ from that of the 50% conidia treatment (47%). On about 30% of the rotted trees we observed conspicuous H. annosum fruiting. We did not observe growth reduction associated with tree rot. H. annosum was the only fungus observed associated with rotted trees which suggest that it was responsible for most of the rot observed in the investigated plots. Urea treated plots showed the lowest incidence of windthrown trees, and 59% of the windthrown tree incidence among the plots was explained by the incidence of H. annosum. Urea can be regarded as a reliable long-term protection method against root and butt rot of Norway spruce.
We investigated two hypotheses for the origin of the root rot fungus Heterobasidion annosum species complex: (i) that geology has been an important factor for the speciation (ii) that co-evolutionary processes with the hosts drove the divergence of the pathogen species. The H. annosum species complex consists of five species: three occur in Europe, H. annosum s.s., Heterobasidion parviporum and Heterobasidion abietinum, and two in North America, Heterobasidion irregulare and Heterobasidion occidentale; all with different but partially overlapping host preferences. The evolution of the H. annosum species complex was studied using six partially sequenced genes, between 10 and 30 individuals of each species were analysed. Neighbour-joining trees were constructed for each gene, and a Bayesian tree was built for the combined data set. In addition, haplotype networks were constructed to illustrate the species relationships. For three of the genes, H. parviporum and H. abietinum share haplotypes supporting recent divergence and/or possible gene flow. We propose that the H. annosum species complex originated in Laurasia and that the H. annosum s.s./H. irregulare and H. parviporum/H. abietinum/H. occidentale ancestral species emerged between 45 and 60 Ma in the Palaearctic, well after the radiation of the host genera. Our data imply that H. irregulare and H. occidentale were colonizing North America via different routes. In conclusion, plate tectonics are likely to have been the main factor influencing Heterobasidion speciation and biogeography.