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AbstractCalonectria pseudonaviculataand C. henricotiaeare two closely related fungal species responsible for boxwood blight disease of ornamental shrubs (Buxusspp.) 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 CYP51paralogs 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 CYP51Apseudogene and lack of a functional CYP51Aparalog in all C. pseudonaviculatagenomes examined is a novel discovery for fungi and could have implications for the evolution of resistance to antifungal chemicals.

Although engineered nanomaterial (ENM) uptake, transport and response mechanisms in plants have received increased attention in recent years, many questions regarding ENM risks to the environment and to food safety remain unanswered. The impact of ENM interactions with co-existing organic/inorganic contaminants, including secondary ENMs, remains poorly understood. The physiological and molecular response of zucchini (Cucurbita pepoL.) under conditions of nanomaterial combined treatments (NMCT) with binary combinations of nanoparticles (NPs) of cerium oxide (CeO2), lanthanum oxide (La2O3), copper oxide (CuO), and zinc oxide (ZnO) (500 mg L−1) and cadmium sulfide quantum dots (CdS QDs) (100 mg L−1) were tested (for 21 days, in vermiculite) and compared with the respective individual (NMIT) and bulk material (BMT) treatments. The ICP-MS results within specific tissues upon exposure to NMCT or NMIT demonstrated that the metal content varied significantly upon co-exposure, including instances of antagonistic effects; La uptake was significantly decreased (50–80%, compared to NMIT or NMCT) upon CeO2NP co-exposure whereas La2O3NPs caused a complete deregulation (2–5-fold higher) of Cu uptake upon CuO NP co-exposure. Expression analysis of genes previously shown as responsive to ENM exposure confirmed the involvement of the chloroplast in plant response; ORF31, an electron carrier down-regulated in all treatments, showed potential as a biomarker of exposure/effects. Principal component analysis on plant physiological and molecular response provided insight into the nature of phytotoxicity under NMIT and NMCT. This systematic approach is useful for characterizing the risk associated with ENMs, providing mechanistic interpretations and holistic perspectives for complex systems of contamination.

The population structure of Armillaria gallica, an important pathogen of Quercusspp., was investigated from mixed oak forests in central Massachusetts, encompassing a sampling area over 500 km2. From 16 plots at four sites a total of 153 isolates (34–40 isolates per site) was analyzed with amplified fragment length polymorphisms (AFLPs). Analyses of 204 polymorphic loci detected 38 AFLP genotypes from a sample area of 4.51 hectares (ha). Genets ranged in distribution from five to 33 genets per hectare (GPH), with a mean of eight GPH and the average A. gallicagenet occupying 0.13 ha. Allele frequencies produced an unbiased expected heterozygosity (HE) value of 0.112 (SE = 0.006) and a Nei’s expected heterozygosity (HJ) value of 0.190 (SE = 0.009), indicating low genetic diversity within the population. Analysis of molecular variation (ΦPT= 0.301; P< 0.001) indicates high genetic differentiation, with 70% of the molecular variation explained at the site-level within A. gallicasubpopulations. However, results of the Mantel test, used to assess the isolation-by-distance hypothesis, were inconclusive in determining whether the subpopulations were truly isolated by distance. A neighbor-joining tree constructed from a genetic distance matrix grouped genotypes from the same site (subpopulation) together, but from three of four sites genotypes were randomly clustered at the plot level. The results suggest that basidiospore dispersal is an important means of new genet formation at linear distances up to 2000 m.

Sudden vegetation dieback (SVD) is the loss of smooth cordgrass (Spartina alterniflora) along intertidal creeks in salt marshes of the Atlantic and Gulf states. The underlying cause of SVD remains unclear, but earlier work suggested a contributing role for Fusariumspp. in Louisiana. This report investigated whether these or other Fusariumspecies were associated with S. alternifloradieback in mid- to north-Atlantic states. Isolations from seven SVD sites yielded 192 isolates of Fusariumspp., with more than 75% isolated from aboveground tissue. Most isolates (88%) fell into two undescribed morphospecies (MS) distinguished from each other by macroconidial shape, phialide ontogeny and growth rates. Pathogenicity tests on wound-inoculated S. alterniflorastems and seedling roots revealed that isolates in MS1 were more virulent than those in MS2 but no single isolate caused plant mortality. No matches to known species of Fusariumwere revealed by DNA sequence queries of translation elongation factor 1-α (tef1) sequences. A phylogenetic analysis of partial sequences of three genes, β-tubulin (β-tub), calmodulin (cal)and tef1, was conducted on representative isolates from MS1 (n = 20) and MS2 (n = 18); it provided strong evidence that the MS1 isolates form a clade that represents a heretofore undescribed species, which we designate Fusarium palustresp. nov. Isolates from the more variable MS2 clustered with the F. incarnatum-equisetispecies complex as F.cf. incarnatum. Although a strong association exists between both species and declining S. alterniflorain SVD sites, neither appears to play a primary causal role in SVD. However, our findings suggest that F. palustremight play an important secondary role in the ecological disruption of the salt marshes.

The most common cause of fungal meningitis in humans, Cryptococcus neoformans serotype A, is a basidiomycetous yeast with a bipolar mating system. However, the vast majority (>99.9%) of C. neoformans serotype A isolates possess only one of the two mating type alleles (MATalpha). Isolates with the other allele (MATa) were recently discovered and proven to mate in the laboratory. It has been a mystery whether and where C. neoformans strains undergo sexual reproduction. Here, we applied population genetic approaches to demonstrate that a population of C. neoformans serotype A clinical isolates from Botswana contains an unprecedented proportion of fertile MATa isolates and exhibits evidence of both clonal expansion and recombination within two partially genetically isolated subgroups. Our findings provide evidence for sexual recombination among some populations of C. neoformans serotype A from sub-Saharan Africa, which may have a direct impact on their evolution.

ABSTRACTThe most common cause of fungal meningitis in humans, Cryptococcus neoformansserotype A, is a basidiomycetous yeast with a bipolar mating system. However, the vast majority (>99.9%) of C. neoformansserotype A isolates possess only one of the two mating type alleles (MATa). Isolates with the other allele (MATa) were recently discovered and proven to mate in the laboratory. It has been a mystery whether and where C. neoformansstrains undergo sexual reproduction. Here, we applied population genetic approaches to demonstrate that a population of C. neoformansserotype A clinical isolates from Botswana contains an unprecedented proportion of fertile MATa isolates and exhibits evidence of both clonal expansion and recombination within two partially genetically isolated subgroups. Our findings provide evidence for sexual recombination among some populations of C. neoformansserotype A from sub-Saharan Africa, which may have a direct impact on their evolution.

In nature, the chestnut blight fungus, Cryphonectria parasitica,has a mixed mating system; i.e., individuals in the same population have the ability to self and outcross. In the laboratory, C. parasiticaappears to have a bipolar self-incompatibility system, typical of heterothallic ascomycetes; selfing is rare, although demonstrable. In this report we describe the cloning and sequencing of both mating-type idiomorphs and their flanking regions at the MATlocus in C. parasitica.The two idiomorphs, MAT1-1and MAT1-2,are structurally similar to those of other pyrenomycetes described to date. MAT1-1encodes three genes (MAT1-1-1, MAT1-1-2,and MAT1-1-3) and MAT1-2encodes a single gene (MAT1-2-1). Unlike MATidiomorphs in some ascomycetes, the sequences at both ends of the idiomorphs in C. parasiticashow a relatively gradual, rather than abrupt, transition from identity in the flanking regions to almost complete dissimilarity in the coding regions. The flanking regions have repetitive polypyrimidine (T/C) and polypurine (A/G) tracts; the significance of these repetitive tracts is unknown. Although we found repetitive tracts in the flanks and gradual transition zones at the ends of the idiomorphs, we found no special features that would explain how selfing occurs in an otherwise self-incompatible fungus.