Fungal species assemblages associated with Phytophthora ramorum-infected coast live oaks following bark and ambrosia beetle colonization in northern California

Sap-feeding nitidulid beetles were trapped for 15 months at four oak wilt centers in central Texas and assayed for the presence of Ceratocystis fagacearum. Levels of contamination with the pathogen ranged 0.3% (Kerrville) – 2.0% (Austin); also detected were C. piceae at slightly higher levels and a low number of beetles carrying C. pluriannulata. The percentages of contaminated beetles were similar to those reported for other parts of the oak wilt range in the USA, but probable species differences in Texas were detected.

Nitidulids as vectors of the oak wilt fungus and other Ceratocystis spp. in Texas

Field experiments were conducted to determine whether the frequency of Ceratocystis fagacearum and Ophiostoma quercus propagule acquisition by nitidulids visiting oak wilt fungal mats is affected by the presence of O. quercus on the mats. Augmentation sprays with O. quercus were used to achieve different levels of mat colonization by that fungus. The extent of colonization by O. quercus 7 to 14 days after spraying was greatest for postmature mats with open cracks (>0.5 cm) observed on the spray date (P < 0.02). Specifically, all six subsamples assayed per mat for 16 of 18 open, O. quercus-sprayed, postmature mats yielded O. quercus. The frequency of nitidulids with O. quercus was also highest (83%) for those collected from O. quercus-treated, postmature mats that were open on the spray date. The frequency of nitidulids with viable C. fagacearum (88%), however, was also greatest for beetles from the postmature mats. Thus, O. quercus colonization did not affect vector acquisition of C. fagacearum from the mats. In addition, O. quercus vectored by nitidulids probably does not result in natural biological control of overland transmission of C. fagacearum at fresh wound surfaces on healthy oaks, as previously suggested.

https://www.nrs.fs.fed.us/pubs/jrnl/1998/nc_1998_juzwik_001.pdf

Acquisition of Ophiostoma quercus and Ceratocystis fagacearum by Nitidulids from O. quercus-Colonized Oak Wilt Mats.

Deadwood is an important functional and structural component of forest ecosystems since it regulates nutrient cycling, serves as a carbon (C) pool, increases the C content in the soil, and is a source of resources, including water, for a wide range of saproxylic and non-saproxylic organisms. The abundance and diversity of wood-inhabiting fungi in six fallen, horizontally lying logs of Quercus petraea, in the 1st, 2nd and 3rd decay classes, in the Drawa National Park in Poland in 2015, were studied using the Illumina sequencing technique. The total number of OTUs obtained (264 307) included sequences of culturable fungi (242 369 = 91.70%) and non-culturable fungi (7 056 = 2.66%). The dead oak wood was colonized by 277 taxa. Culturable fungi of Zygomycota, Ascomycota and Basidiomycota comprised 75% of taxa detected and were represented by 14, 139 and 53 taxa respectively. Non-culturable organisms were represented by 70 taxa. Fungi were classified into 18 groups: (i) typical soft rot fungi, (ii) phytopathogens potentially hazardous to trees, (iii) epiphytes and endophytes or weak, opportunistic pathogens, (iv) ectomycorrhizal species, (v) ericoid mycorrhizal species, (vi) crust fungi, (vii) resupinate basidiomycetes, (viii) saprotrophs and soil fungi, (ix) opportunistic human pathogens causing superficial or systemic mycoses, (x) pathogens of warmor cold-blooded animals, (xi) ascomycetous yeasts, (xii) basidiomycetous yeasts, (xiii) antagonists of fungi, (xiv) producers of metabolites effective against pathogens, (xv) hyperparasites, (xvi) lichen-forming species, (xvii) partners of other fungi, (xviii) species rare or uncommon in nature. It was shown that: (i) coarse, woody debris of oak is host to abundant and diverse mycobiota, (ii) abundance and diversity of fungi increase with the decay continuum, (iii) oak logs can be a habitat of phytopathogens potentially hazardous to forest health, (iv) different phytopathogens favour wood in different decay classes, (v) abundance of pathogens decreases, and of ericoid mycorrhizal (or soil) species increases with the decay continuum. Maintaining different types of deadwood increases fungal diversity, but also the risk of diseases.

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Abundance and diversity of fungi in oak wood

The colonization of Ceratocystis fagacearum fungal mats of different ages by Ophiostoma piceae on Quercus spp. was determined in three east-central Minnesota locations during the spring of 1995. The extent of the mat area colonized by O. piceae generally increased with mat age. Subsamples per mat yielding the fungus for the three locations averaged 11 to 27% for immature mats, 65 to 72% for mature mats, and 66 to 96% for aging and declining mats. On a mat-incidence basis, frequencies of O. piceae isolation from at least one subsample of an immature mat ranged from 30 to 53% compared with more than 90% for all other mat ages in the three locations. The average number of colony-forming units of O. piceae per square centimeter ranged from 1 × 103 to 1.2 × 106 and increased with mat age. The extent of C. fagacearum recovery from each mat was lower for aging plus declining mats (P < 0.03) compared with other ages in two locations. On a mat-incidence basis, frequency of C. fagacearum recovery from at l...

https://www.nrs.fs.fed.us/pubs/jrnl/1997/nc_1997_juzwik_004.pdf

Colonization of Oak Wilt Fungal Mats by Ophiostoma piceae During Spring in Minnesota

Subcortical mats of Ceratocystis fagacearum were found to become readily overgrown by Pesotum piceae Thus by reducing the chance of contamination of insect vectors with spores of the pathogen P piceae is likely to contribute to the low efficiency of oak wilt transmissions

N. Parameswaran

Papers

Observations on the colonization of oak wilt mats (Ceratocystis fagacearum) by Pesotum piceae