Phylogeography of the Solanaceae-infecting Basidiomycota fungus Rhizoctonia solani AG-3 based on sequence analysis of two nuclear DNA loci

<p>Abstract</p> <p>Background</p> <p>The soil fungus <it>Rhizoctonia solani </it>anastomosis group 3 (AG-3) is an important pathogen of cultivated plants in the family Solanaceae. Isolates of <it>R. solani </it>AG-3 are taxonomically related based on the composition of cellular fatty acids, phylogenetic analysis of nuclear ribosomal DNA (rDNA) and beta-tubulin gene sequences, and somatic hyphal interactions. Despite the close genetic relationship among isolates of <it>R. solani </it>AG-3, field populations from potato and tobacco exhibit comparative differences in their disease biology, dispersal ecology, host specialization, genetic diversity and population structure. However, little information is available on how field populations of <it>R. solani </it>AG-3 on potato and tobacco are shaped by population genetic processes. In this study, two field populations of <it>R. solani </it>AG-3 from potato in North Carolina (NC) and the Northern USA; and two field populations from tobacco in NC and Southern Brazil were examined using sequence analysis of two cloned regions of nuclear DNA (pP42F and pP89).</p> <p>Results</p> <p>Populations of <it>R. solani </it>AG-3 from potato were genetically diverse with a high frequency of heterozygosity, while limited or no genetic diversity was observed within the highly homozygous tobacco populations from NC and Brazil. Except for one isolate (TBR24), all NC and Brazilian isolates from tobacco shared the same alleles. No alleles were shared between potato and tobacco populations of <it>R. solani </it>AG-3, indicating no gene flow between them. To infer historical events that influenced current geographical patterns observed for populations of <it>R. solani </it>AG-3 from potato, we performed an analysis of molecular variance (AMOVA) and a nested clade analysis (NCA). Population differentiation was detected for locus pP89 (Φ_{<it>ST </it>}= 0.257, significant at P < 0.05) but not for locus pP42F (Φ_{<it>ST </it>}= 0.034, not significant). Results based on NCA of the pP89 locus suggest that historical restricted gene flow is a plausible explanation for the geographical association of clades. Coalescent-based simulations of genealogical relationships between populations of <it>R. solani </it>AG-3 from potato and tobacco were used to estimate the amount and directionality of historical migration patterns in time, and the ages of mutations of populations. Low rates of historical movement of genes were observed between the potato and tobacco populations of <it>R. solani </it>AG-3.</p> <p>Conclusion</p> <p>The two sisters populations of the basidiomycete fungus <it>R. solani </it>AG-3 from potato and tobacco represent two genetically distinct and historically divergent lineages that have probably evolved within the range of their particular related Solanaceae hosts as sympatric species.</p

Analysis of mycobiomes to uncover biodiversity: a case study between soil fungi and orchid species in Sweden

Abstracts from the April 12-14, 2019 MASC Conferenc

Draft genome sequence of the plant-pathogenic soil fungus Rhizoctonia solani anastomosis group 3 strain Rhs1AP

The soil fungus Rhizoctonia solani is a pathogen of agricultural crops. Here, we report on the 51,705,945 bp draft consensus genome sequence of R. solani strain Rhs1AP. A comprehensive understanding of the heterokaryotic genome complexity and organization of R. solani may provide insight into the plant disease ecology and adaptive behavior of the fungus

"Jumping Jack": Genomic Microsatellites Underscore the Distinctiveness of Closely Related Pseudoperonospora cubensis and Pseudoperonospora humuli and Provide New Insights Into Their Evolutionary Past

Downy mildews caused by obligate biotrophic oomycetes result in severe crop losses worldwide. Among these pathogens, Pseudoperonospora cubensis and P. humuli, two closely related oomycetes, adversely affect cucurbits and hop, respectively. Discordant hypotheses concerning their taxonomic relationships have been proposed based on host-pathogen interactions and specificity evidence and gene sequences of a few individuals, but population genetics evidence supporting these scenarios is missing. Furthermore, nuclear and mitochondrial regions of both pathogens have been analyzed using microsatellites and phylogenetically informative molecular markers, but extensive comparative population genetics research has not been done. Here, we genotyped 138 current and historical herbarium specimens of those two taxa using microsatellites (SSRs). Our goals were to assess genetic diversity and spatial distribution, to infer the evolutionary history of P. cubensis and P. humuli, and to visualize genome-scale organizational relationship between both pathogens. High genetic diversity, modest gene flow, and presence of population structure, particularly in P. cubensis, were observed. When tested for cross-amplification, 20 out of 27 P. cubensis-derived gSSRs cross-amplified DNA of P. humuli individuals, but few amplified DNA of downy mildew pathogens from related genera. Collectively, our analyses provided a definite argument for the hypothesis that both pathogens are distinct species, and suggested further speciation in the P. cubensis complex

Association of Ceratobasidium theobromae and Lasiodiplodia species with symptom variation in vascular streak disease of cacao

Abstracts from the April 12-14, 2019 MASC Conferenc

Using digital resources to enhance georeferencing of herbarium collections

Abstracts from the April 12-14, 2019 MASC Conferenc

Geography and hosts of the wood decay fungi Fomes fasciatus and Fomes fomentarius in the United States

Comprehensive United States county distribution maps of Fomes fasciatus and F. fomentarius were developed based on peer-reviewed publications, records from mycological herbaria and collections made for this study. The geographic distribution was expanded for both species to include a total of seven counties in five states not included in previous publications and records. North Carolina and Tennessee were the only states where both species occurred, but their distributions did not overlap when resolved to the county level. Both fungi occurred on a diverse range of hardwood tree hosts, and in this study, 11 and 17 new hosts associations were identified for F. fasciatus and F. fomentarius, respectively. The extension of host distributions beyond the known range for each fungus suggests that other delimiting factors may contribute to the distribution of F. fasciatus and F. fomentarius

Thermal sensitivity of <i>Calonectria henricotiae</i> and <i>Calonectria pseudonaviculata</i> conidia and microsclerotia

<p>Knowledge of the thermal sensitivity of conidia and microsclerotia is useful for developing plant disease management approaches that deploy heat to inactivate infectious vegetative propagules of fungal pathogens. For boxwood blight disease, heat treatment of cuttings that harbor conidia and microsclerotia would provide a useful management tool for suppressing the pathogenic activity of <i>Calonectria pseudonaviculata</i> (present in the United States) and <i>C. henricotiae</i> (a quarantine pathogen not present in the United States). In this study, we investigated the thermal sensitivity of conidia and microsclerotia of the boxwood blight pathogens <i>C. henricotiae</i> and <i>C. pseudonaviculata</i> treated in water at 45, 47.5, 50, 52.5, and 55 C. For conidia, as time of exposure increased at each temperature, the proportion of germinated conidia decreased. The predicted time required to inactivate 90% of <i>C. pseudonaviculata</i> conidia (LD₉₀) decreased as water temperature increased from 45 to 55 C and ranged from 35.4 to 5.6 min, respectively. Inactivation of conidia was dependent on isolate, species of <i>Calonectria</i>, and length of exposure at each temperature tested. Microsclerotia of <i>C. henricotiae</i> and <i>C. pseudonaviculata</i> displayed reduced germination with increasing exposure and higher temperatures of hot water. Microsclerotia of <i>C. henricotiae</i> were significantly more resistant to heat treatment than <i>C. pseudonaviculata</i> at 47.5 and 50 C, whereas microsclerotia of both species were rapidly killed at 55 C.</p

Revisiting Graduate Student Training to Address Agricultural and Environmental Societal Challenges

Society and the higher education system are faced with daunting challenges associated with supplying food, energy, and water to a growing population while maintaining environmental quality and preserving natural resources. Too often, the higher education system does not facilitate collaborative immersion required to foster concerted multidisciplinary efforts needed to address societal grand challenges. In this commentary, we present an innovative model of cohort education, which equips graduate students with core skills and enables collaborative dissertation research among students. In addition, we provide an example of a program aimed at understanding the plant–soil microbiome, a critical research area that may yield significant advances in plant health and productivity