Phellinus noxius

Abstract: The survival of Phellinus noxius arthroconidia, basidiospores, and mycelia and of P. noxius-colonized wood was measured in soils with different soil matrix potentials. Survival of arthroconidia declined more slowly in soils with -0.50 and -0.42 MPa of soil matrix potential compared with soils with -0.15 and -0.025 MPa. However, arthroconidia were rarely recovered from the treatments after 3 months. Basidiospores were not recovered after 3, 3.5, 4, and 4.5 months in the -0.025, -0.15, -0.42, and -0.50 MPa soil matrix potential treatments, respectively. Mycelia that were buried in the soil with -0.025 MPa were not recovered after 4 weeks, whereas mycelia in soils with -0.50, -0.42, and -0.15 MPa were not recovered after 10 weeks. P. noxius was not recovered from pieces of artificially infested wood subjected to 1 month of flooding. However, in treatments with lower soil moisture, P. noxius survival ranged from 80% to more than 90% over 2 years. Colonies of P. noxius were not recovered from the rhizosphere of soils around the infested roots of three host species, Calophyllum inophyllum, Casuarina equisetifolia, and Cinnamomum camphora. However, P. noxius was recovered from naturally infected roots of these hosts 1 to 10 years after they were killed. These results indicated that woody debris in soils harboring P. noxius played an important role in the long-term survival of the fungus. Flooding infested fields may help control P. noxius in the field.

Abstract: Since the 1990s, brown root rot caused by Phellinus noxius (Corner) Cunningham has become a major tree disease in Taiwan. This fungal pathogen can infect more than 200 hardwood and softwood tree species, causing gradual to fast decline of the trees. For effective control, we must determine how the pathogen is disseminated and how the new infection center of brown root rot is established. We performed Illumina sequencing and de novo assembly of a single basidiospore isolate Daxi42 and obtained a draft genome of ~40 Mb. By comparing the 12,217 simple sequence repeat (SSR) regions in Daxi42 with the low-coverage Illumina sequencing data for four additional P. noxius isolates, we identified 154 SSR regions with potential polymorphisms. A set of 13 polymorphic SSR markers were then developed and used to analyze 329 P. noxius isolates collected from 73 tree species from urban/agricultural areas in 14 cities/counties all around Taiwan from 1989 to 2012. The results revealed a high proportion (~98%) of distinct multilocus genotypes (MLGs) and that none of the 329 isolates were genome-wide homozygous, which supports a possible predominant outcrossing reproductive mode in P. noxius. The diverse MLGs exist as discrete patches, so brown root rot was most likely caused by multiple clones rather than a single predominant strain. The isolates collected from diseased trees near each other tend to have similar genotype(s), which indicates that P. noxius may spread to adjacent trees via root-to-root contact. Analyses based on Bayesian clustering, FST statistics, analysis of molecular variance, and isolation by distance all suggest a low degree of population differentiation and little to no barrier to gene flow throughout the P. noxius population in Taiwan. We discuss the involvement of basidiospore dispersal in disease dissemination.