Douglas McNew

Wood-Destroying Soft Rot Fungi in the Historic Expedition Huts of Antarctica

ABSTRACT Three expedition huts in the Ross Sea region of Antarctica, built between 1901 and 1911 by Robert F. Scott and Ernest Shackleton, sheltered and stored the supplies for up to 48 men for 3 years during their explorations and scientific investigation in the South Pole region. The huts, built with wood taken to Antarctica by the early explorers, have deteriorated over the past decades. Although Antarctica has one of the coldest and driest environments on earth, microbes have colonized the wood and limited decay has occurred. Some wood in contact with the ground contained distinct microscopic cavities within secondary cell walls caused by soft rot fungi. Cadophora spp. could be cultured from decayed wood and other woods sampled from the huts and artifacts and were commonly associated with the soft rot attack. By using internal transcribed spacer sequences of ribosomal DNA and morphological characteristics, several species of Cadophora were identified, including C. malorum, C. luteo-olivacea, and C. fastigiata. Several previously undescribed Cadophora spp. also were found. At the Cape Evans and Cape Royds huts, Cadophora spp. commonly were isolated from wood in contact with the ground but were not always associated with soft rot decay. Pure cultures of Cadophora used in laboratory decay studies caused dark staining of all woods tested and extensive soft rot in Betula and Populus wood. The presence of Cadophora species, but only limited decay, suggests there is no immediate threat to the structural integrity of the huts. These fungi, however, are widely found in wood from the historic huts and have the capacity to cause extensive soft rot if conditions that are more conducive to decay become common.

Three genera in the Ceratocystidaceae are the respective symbionts of three independent lineages of ambrosia beetles with large, complex mycangia

The genus Ambrosiella accommodates species of Ceratocystidaceae (Microascales) that are obligate, mutualistic symbionts of ambrosia beetles, but the genus appears to be polyphyletic and more diverse than previously recognized. In addition to Ambrosiella xylebori, Ambrosiella hartigii, Ambrosiella beaveri, and Ambrosiella roeperi, three new species of Ambrosiella are described from the ambrosia beetle tribe Xyleborini: Ambrosiella nakashimae sp. nov. from Xylosandrus amputatus, Ambrosiella batrae sp. nov. from Anisandrus sayi, and Ambrosiella grosmanniae sp. nov. from Xylosandrus germanus. The genus Meredithiella gen. nov. is created for symbionts of the tribe Corthylini, based on Meredithiella norrisii sp. nov. from Corthylus punctatissimus. The genus Phialophoropsis is resurrected to accommodate associates of the Xyloterini, including Phialophoropsis trypodendri from Trypodendron scabricollis and Phialophoropsis ferruginea comb. nov. from Trypodendron lineatum. Each of the ten named species was distinguished by ITS rDNA barcoding and morphology, and the ITS rDNA sequences of four other putative species were obtained with Ceratocystidaceae-specific primers and template DNA extracted from beetles or galleries. These results support the hypothesis that each ambrosia beetle species with large, complex mycangia carries its own fungal symbiont. Conidiophore morphology and phylogenetic analyses using 18S (SSU) rDNA and TEF1α DNA sequences suggest that these three fungal genera within the Ceratocystidaceae independently adapted to symbiosis with the three respective beetle tribes. In turn, the beetle genera with large, complex mycangia appear to have evolved from other genera in their respective tribes that have smaller, less selective mycangia and are associated with Raffaelea spp. (Ophiostomatales).

Survey of potential sapstain fungi on Pinus radiata in New Zealand

Abstract A nationwide survey of New Zealand sapstain fungi on Pinus radiata was undertaken between 1996 and 1998 with collections of 1958 samples of material from 869 sites in the North and South Islands. Material was collected from mills, ports, forest plantations of native, exotic, or P. radiata, nurseries, farms, and urban areas. Material collected included branches, twigs, needles or leaves, cones, logs, wood chips, timber, and veneer. From these collections, 2154 potential sapstain fungi, representing 14 known species plus a number of unidentified species, were isolated. The predominant sapstain fungi isolated were Sphaeropsis sapinea, Ophiostoma ips, O. floccosum, O. piliferum, Leptographium procerum, and O. querci. S. sapinea was isolated from all material sampled including collections from the forest floor (including branches, twigs, needles, leaves, cones, and logs) as well as from logs and timber. In contrast Ophiostoma species were mainly found on logs, timber, and wood chips.

Ambrosiella roeperi sp. nov. is the mycangial symbiont of the granulate ambrosia beetle, Xylosandrus crassiusculus

Isolations from the granulate ambrosia beetle, Xylosandrus crassiusculus (Coleoptera: Curculionidae: Scolytinae: Xyleborini), collected in Georgia, South Carolina, Missouri and Ohio, yielded an undescribed species of Ambrosiella in thousands of colony-forming units (CFU) per individual female. Partial sequences of ITS and 28S rDNA regions distinguished this species from other Ambrosiella spp., which are asexual symbionts of ambrosia beetles and closely related to Ceratocystis spp. Ambrosiella roeperi sp. nov. produces sporodochia of branching conidiophores with disarticulating swollen cells, and the branches are terminated by thick-walled aleurioconidia, similar to the conidiophores and aleurioconidia of A. xylebori, which is the mycangial symbiont of a related ambrosia beetle, X. compactus. Microscopic examinations found homogeneous masses of arthrospore-like cells growing in the mycangium of X. crassiusculus, without evidence of other microbial growth. Using fungal-specific primers, only the ITS rDNA region of A. roeperi was amplified and sequenced from DNA extractions of mycangial contents, suggesting that it is the primary or only mycangial symbiont of this beetle in USA.

Species Delimitation and Host Specialization of Ceratocystis laricicola and C. polonica to Larch and Spruce

Ceratocystis laricicola and C. polonica are fungal symbionts of bark beetle species of the genus Ips that attack species of Larix and Picea, respectively, across Eurasia. Earlier studies found that these fungal species were morphologically identical, had similar isozymes patterns, and had identical internal transcribed spacer (ITS) sequences of the rDNA operon. We analyzed 27 isolates from Europe, southwestern Siberia (Russia) and Japan, representing the known geographic ranges of the two species. Phylogenetic analysis of the DNA sequences of a portion of the MAT-2 idiomorph showed these species to be distinct, with the Japanese isolates of C. laricicola having a sequence slightly different (5 bp) from those of the Russian and European isolates of C. laricicola. Sexual compatibility tests showed full interfertility among isolates of C. polonica from Europe, Russia and Japan, but isolates of C. polonica were not fully interfertile with isolates of C. laricicola. A Russian and a European isolate of C. laricicola mated with each other but not with the Japanese isolates of C. laricicola. Mature L. sibirica and P. obovata were inoculated with isolates of C. laricicola and C. polonica from Europe, Russia, and Japan, and measurement of lesions in the inner bark/cambium region demonstrated strong host specialization. The data suggest that the two fungal species are very closely related and are distinguished primarily by their physiological specialization to the hosts of their bark beetle vectors.

Genetic relationships among Leptographium terebrantis and the mycangial fungi of three western Dendroctonus bark beetles

Morphology, mitochondrial DNA (mtDNA) restriction fragment polymorphisms (RFLPs) and nuclear DNA (nDNA) fingerprinting were used to clarify relationships among the morphologically similar Ophiostoma and Leptographium species associated with mycangia of three Dendroctonus bark beetles (Ophiostoma clavigerum associated with both D. ponderosae and D. jeffreyi, and L. pyrinum associated with D. adjunctus), as well as a closely related nonmycangial bark beetle associate (L. terebrantis). Most isolates of O. clavigerum form long (40–70 μm), septate conidia, while all isolates of L. terebrantis and L. pyrinum form conidia less than 17.0 μm in length. The conidia of L. pyrinum are pyriform, with truncate bases, while the conidia of the other species form only slightly truncate bases. Conidial masses of L. terebrantis are creamy yellow, while the conidial masses of the other species are white. Nuclear DNA fingerprints resulting from probing PstI restrictions with the oligonucleotide probe (CAC)5 and HaeIII and MspI restrictions of mtDNA, exhibited three major clusters. In the dendrogram developed from mtDNA RFLPs, the L. pyrinum isolates formed one cluster, while the majority of O. clavigerum isolates, including all D. jeffreyi isolates, formed another. A third cluster was composed of all L. terebrantis isolates, as well as several O. clavigerum isolates from D. ponderosae. The inclusion of some O. clavigerum isolates in the L. terebrantis cluster suggests that horizontal transfer of mtDNA has occurred among these fungi. The nDNA dendrogram also exhibited three clusters, and most isolates of L. pyrinum, L. terebrantis and O. clavigerum grouped separately; however, one isolate of O. clavigerum grouped with the L. terebrantis isolates, while one isolate of L. terebrantis grouped with O. clavigerum. No genetic markers were found that distinguished between O. clavigerum associated with D. ponderosae and O. clavigerum associated with D. jeffreyi. Ophiostoma clavigerum might be a recently diverged morphological variant of L. terebrantis, with special adaptations for grazing by young adults of D. jeffreyi and D. ponderosae. The anamorph of O. clavigerum, Graphiocladiella clavigerum, is transferred to Leptographium.

Bur oak blight, a new disease on Quercus macrocarpa caused by Tubakia iowensis sp. nov.

A newly recognized, late-season leaf disease of Quercus macrocarpa (bur oak) has become increasingly severe across Iowa and in neighboring states since the 1990s. Vein necrosis and leaf death may occur over the whole crown or only on the lower branches. Symptoms typically intensify year-to-year in individual trees, and there appears to be substantial variation in susceptibility. Distinctive conidiomata (pycnothyria with a shield of radiating, setae-like hyphae) of a Tubakia sp. are found along the necrotic leaf veins. The same species produces a second type of pycnothyrium with a crustose covering and smaller conidia on the petioles of killed leaves, which remain on the tree through the winter and provide the primary inoculum to infect newly emerging shoots and leaves in spring. Comparison of the Tubakia sp. on bur oak with T. dryina and other species of Tubakia led to the conclusion that the species on bur oak is new, distinct from T. dryina, which herein is defined more narrowly. Inoculation studies confirmed that Tubakia iowensis sp. nov. is the cause of bur oak blight. Bur oak blight appears to be particularly severe on Q. macrocarpa var. oliviformis, which is well adapted to the dry, upland sites where the disease is found most frequently. The recent climatic trend in Iowa to higher spring precipitation might have led to increased severity of the disease.

Genetic Bottlenecks for Two Populations of Ceratocystis fimbriata on Sweet Potato and Pomegranate in China

Chinese isolates of Ceratocystis fimbriata from sweet potato (Ipomoea batatas) and pomegranate (Punica granatum) were genetically compared with a worldwide collection of isolates from a variety of hosts. Isolates from black-rotted storage roots of sweet potato in China, Japan, Australasia, and the United States had identical internal transcribed spacer (ITS) ribosomal DNA (rDNA) sequences and only minor variation in microsatellite alleles. Sequences of their mating type genes were most similar to those of isolates from various hosts in Ecuador, a center of diversity for sweet potato. Isolates from Colocasia esculenta (taro) and pomegranate from Yunnan and Sichuan had only one ITS rDNA sequence (haplotype ITS5). This haplotype, sequences of mating type genes, and microsatellite alleles linked these isolates to isolates from Eucalyptus stumps in South China and diseased Eucalyptus trees in Brazil, supporting the hypothesis that the pomegranate population originated from Brazil via cuttings of Eucalyptus. Isolates from sweet potato and pomegranate in China were interfertile with tester strains of C. fimbriata, confirming that the causes of the two epidemics in China belong to a single biological species. However, other isolates from Eucalyptus stumps were intersterile with the tester strains and had ITS rDNA sequences typical of the Asian species, C. cercfabiensis.

Ceratocystis tiliae sp. nov., a wound pathogen on Tilia americana

Species in the North American clade (NAC) of the Ceratocystis fimbriata complex are mostly weak pathogens that infect native tree hosts through fresh wounds. Isolations from discolored tissue of wounded Tilia americana (basswood) in Iowa and Nebraska yielded a Ceratocystis species that was similar to but distinct from isolates of C. variospora from other hosts. Sequences of 28S rDNA showed that isolates from basswood did not differ from C. variospora, but there were minor differences in ITS rDNA sequences. The DNA sequences of a portion of the Cerato-platanin gene and TEF1α showed the basswood fungus to be a unique lineage. Cross inoculations in two experiments showed that the basswood isolates and C. variospora isolates from Quercus spp. were most aggressive to their respective hosts. Isolates from basswood grew slower and were less pigmented than C. variospora isolates from Quercus spp. The basswood fungus thus is distinguished from C. variospora based on phylogenetic analyses and phenotype and is herein described as C. tiliae sp. nov.