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Scientific communication is facilitated by a data-driven, scientifically sound taxonomy that considers the end-user's needs and established successful practice. In 2013, the Fusarium community voiced near unanimous support for a concept of Fusarium that represented a clade comprising all agriculturally and clinically important Fusarium species, including the F. solani species complex (FSSC). Subsequently, this concept was challenged in 2015 by one research group who proposed dividing the genus Fusarium into seven genera, including the FSSC described as members of the genus Neocosmospora, with subsequent justification in 2018 based on claims that the 2013 concept of Fusarium is polyphyletic. Here, we test this claim and provide a phylogeny based on exonic nucleotide sequences of 19 orthologous protein-coding genes that strongly support the monophyly of Fusarium including the FSSC. We reassert the practical and scientific argument in support of a genus Fusarium that includes the FSSC and several other basal lineages, consistent with the longstanding use of this name among plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students, and researchers with a stake in its taxonomy. In recognition of this monophyly, 40 species described as genus Neocosmospora were recombined in genus Fusarium, and nine others were renamed Fusarium. Here the global Fusarium community voices strong support for the inclusion of the FSSC in Fusarium, as it remains the best scientific, nomenclatural, and practical taxonomic option available.

The study of quantitative traits provides a window on the interactions between multiple unlinked genetic loci. The interaction between hosts and pathogenic microbes, such as fungi, involves aspects of quantitative genetics for both partners in this dynamic equilibrium. One important pathogenic fungus is Cryptococcus neoformans, a basidiomycete yeast that can infect the human brain and whose mating system has two mating type alleles, a and [alpha]. The [alpha] mating-type allele has previously been linked to increased virulence potential. Here congenic C. neoformans strains were generated in the two well-characterized genetic backgrounds B3501[alpha] and NIH433a to examine the potential influence of genes outside of the mating-type locus on the virulence potential of mating type. The congenic nature of these new strain pairs was established by karyotyping, amplified fragment length polymorphism genotyping, and whole-genome molecular allele mapping (congenicity mapping). Virulence studies revealed that virulence was equivalent between the B3501 a and [alpha] congenic strains but the [alpha] strain was more virulent than its a counterpart in the NIH433 genetic background. These results demonstrate that genomic regions outside the mating type locus contribute to differences in virulence between a and [alpha] cells. The congenic strains described here provide a foundation upon which to elucidate at genetic and molecular levels how mating-type and other unlinked loci interact to enable microbial pathogenesis.

To construct a genetic linkage map of the heterothallic yeast, Cryptococcus neoformans (Filobasidiella neofarmans), we crossed two mating-compatible strains and analyzed 94 progeny for the segregation of 301 polymorphic markers, consisting of 228 restriction site polymorphisms, 63 microsatellites, two indels, and eight mating-type (MAT)-associated markers. All but six markers showed no significant (P< 0.05) segregation distortion. At a minimum LOD score of 6.0 and a maximum recombination frequency of 0.30, 20 linkage groups were resolved, resulting in a map length of ~1500 cM. Average marker density is 5.4 cM (range 1-28.7 cM). Hybridization of selected markers to blots of electrophoretic karyotypes unambiguously assigned all linkage groups to chromosomes and led us to conclude that the C. neoformans genome is ~20.2 Mb, comprising 14 chromosomes ranging in size from 0.8 to 2.3 Mb, with a ratio of ~13.2 kb/cM averaged across the genome. However, only 2 of 12 ungrouped markers hybridized to chromosome 10. The hybridizations revealed at least one possible reciprocal translocation involving chromosomes 8, 9, and 12. This map has been critical to genome sequence assembly and will be essential for future studies of quantitative trait inheritance.

Selfing and self-incompatibility in the mating system of the fungus Cryphonectria parasitica, a haploid ascomycete, are discussed. Little has been known about how fungi reproduce in nature. In a study, frequent selfing was seen in nature, but selfing is rare in the laboratory. The mating system seems to be under ecological as well as genetic control.

Calonectria pseudonaviculata and C. henricotiae are two closely related fungal species responsible for boxwood blight disease of ornamental shrubs (Buxus spp.) in the U.S. and Europe. A previous study has shown isolates of the latter species, which is restricted to Europe, to be less sensitive to tetraconazole, an azole fungicide. In this study, we have analyzed the CYP51 paralogs for polymorphism in 26 genomes, representing geographically disparate populations of C. pseudonaviculata (n = 19) and C. henricotiae (n = 7), from the U.S., Europe, Asia, and New Zealand. The presence of a CYP51A pseudogene and lack of a functional CYP51A paralog in all C. pseudonaviculata genomes examined is a novel discovery for fungi and could have implications for the evolution of resistance to antifungal chemicals. [ABSTRACT FROM AUTHOR]

Fungicide injection is regularly performed to prevent and manage Dutch elm disease (DED) of American elm (Ulmus americana). In an effort to better understand the effects of long-term fungicide injection on tree health, sonic tomography (SoT) and electricalresistance tomography (ERT) were used to nondestructively determine the incidence and severity of internal decay in the lower trunk of American elms in suburban and urban settings. Overall, 253 sonic and electricalresistance tomograms were generated from 210 American elms. Sampled trees were partitioned into two fungicide injection groups: (1) regular injection; and (2) irregular injection or no known history of injection. Among all American elms, the incidence of internal decay in the lower trunk was 30% (63/210) with a mean percent decay, as determined by SoT, of 39%. Based on Chi-square analysis, there were no significant differences in the frequency of elms with decay by injection history (P = 0.799). Mean percent decay was significantly different by dbh class (P = 0.005) and while linear regression demonstrated a positive correlation between percent decay and dbh, most of the variability went unexplained (R2 = 0.182). For elms with decay, there was a significantly higher frequency of trees in the lowest decay class (< 25% of the cross section) compared to the highest decay class (> 75% of the cross section). The results suggest that the wounding associated with regular fungicide injection does not increase the likelihood of internal decay and that American elms exhibit a low frequency and severity of internal decay. [ABSTRACT FROM AUTHOR]

Sonic tomography and electrical impedance tomography (EIT) were used to detect and quantify internal decay in living trees. Twenty-two cross-sectional images, representing variations in sonic velocity and electrical impedance, were captured from nine trees (four Acer rubrum L., three Betula lenta L., and two Fagus grandifolia Ehrh.) in two forests in Connecticut. Following acquisition of tomographic data, 8 trees were felled, from which 19 stem disks were cut for comparison to the tomographic results. For one black birch, with extensive trunk rot and an internal cavity, sonic tomography (SoT) and EIT were very accurate in depicting both the area of the cavity as well as the area of fungal colonization and incipient decay. The use of both SoT and EIT to estimate area of decay resulted in a level of accuracy that far exceeded that produced from either method alone. Specific gravity values obtained from clear and decayed wood from three trees corroborated tomographic assessments, and permitted an estimation of the amount of carbon lost through decay. The implications of internal decay on carbon sequestration rates in temperate forests are also addressed. [ABSTRACT FROM AUTHOR]

Neonectria ditissima is a fungal pathogen native to eastern North America that causes disfiguring cankers on numerous tree species, particularly birches ( Betula spp.). In order to develop control strategies, fundamental knowledge of the pathogen's reproductive and dispersal dynamics is necessary. To undertake these studies, we developed genomic libraries enriched for clones containing microsatellites, and then designed primers flanking each locus. Of 34 loci that were screened, 11 were polymorphic among 38 isolates obtained from a single population. Gene diversities ranged from 0.05 to 0.862 with a mean of 0.409. These markers will be invaluable in population studies of this fungus. [ABSTRACT FROM AUTHOR]