The rust fungus, Puccinia psidii, is a devastating pathogen of introduced eucalypts (Eucalyptus spp.) in Brazil where it was first observed in 1912. This pathogen is hypothesized to be endemic to South and Central America and to have first infected eucalypts via a host jump from native guava (Psidium guajava). Ten microsatellite markers were used to genotype 148 P. psidii samples from eucalypts and guava plus five additional myrtaceous hosts across a wide geographic range of south‐eastern Brazil and Uruguay. Principal coordinates analysis, a Bayesian clustering analysis and a minimum‐spanning network revealed two major genetic clusters among the sampled isolates, one associated with guava and another associated with eucalypts and three additional hosts. Multilocus genotypes infecting guava differed by multiple mutational steps at eight loci compared with those infecting eucalypts. Approximate Bayesian computation revealed that evolutionary scenarios involving a coalescence event between guava‐ and eucalypt‐associated pathogen populations within the past 1000 years are highly unlikely. None of the analyses supported the hypothesis that eucalypt‐infecting P. psidii in Brazil originated via host jump from guava following the introduction of eucalypts to Brazil approximately 185 years ago. The existence of host‐associated biotypes of P. psidii in Brazil indicates that this diversity must be considered when assessing the invasive threat posed by this pathogen to myrtaceous hosts worldwide.

Background: Development and application of DNA-based methods to distinguish highly virulent isolates of Fusarium oxysporum f. sp. koae [Fo koae; cause of koa wilt disease on Acacia koa (koa)] will help disease management through early detection, enhanced monitoring, and improved disease resistance-breeding programs. Results: This study presents whole genome analyses of one highly virulent Fo koae isolate and one non-pathogenic F. oxysporum (Fo) isolate. These analyses allowed for the identification of putative lineage-specific DNA and predicted genes necessary for disease development on koa. Using putative chromosomes and predicted gene comparisons, Fo koae-exclusive, virulence genes were identified. The putative lineage-specific DNA included identified genes encoding products secreted in xylem (e. g., SIX1 and SIX6) that may be necessary for disease development on koa. Unique genes from Fo koae were used to develop pathogen-specific PCR primers. These diagnostic primers allowed target amplification in the characterized highly virulent Fo koae isolates but did not allow product amplification in low-virulence or non-pathogenic isolates of Fo. Thus, primers developed in this study will be useful for early detection and monitoring of highly virulent strains of Fo koae. Isolate verification is also important for disease resistance-breeding programs that require a diverse set of highly virulent Fo koae isolates for their disease-screening assays to develop disease-resistant koa. Conclusions: These results provide the framework for understanding the pathogen genes necessary for koa wilt disease and the genetic variation of Fo koae populations across the Hawaiian Islands.

Climate change and associated disturbances are expected to exacerbate forest root diseases because of altered distributions of existing and emerging forest pathogens and predisposition of trees due to climatic maladaptation and other disturbances. Predictions of suitable climate space (potential geographic distribution) for forest pathogens and host trees under contemporary and future climate scenarios will guide the selection of appropriate management practices by forest managers to minimize adverse impacts of forest disease within forest ecosystems. A native pathogen (Armillaria solidipes) that causes Armillaria root disease of conifers in North America is used to demonstrate bioclimatic models (maps) that predict suitable climate space for both pathogen and a primary host (Pseudotsuga menziesii, Douglas-fir) under contemporary and future climate scenarios. Armillaria root disease caused byA. solidipesis a primary cause of lost productivity and reduced carbon sequestration in coniferous forests of North America, and its impact is expected to increase under climate change due to tree maladaptation. Contemporary prediction models of suitable climate space were produced using Maximum Entropy algorithms that integrate climatic data with 382 georeferenced occurrence locations for DNA sequence-confirmedA. solidipes. A similar approach was used for visually identifiedP. menziesiifrom 11,826 georeferenced locations to predict its climatic requirements. From the contemporary models, data were extrapolated through future climate scenarios to forecast changes in geographic areas where nativeA. solidipesandP. menziesiiwill be climatically adapted. Armillaria root disease is expected to increase in geographic areas where predictions suggestA.solidipesis well adapted andP. menziesiiis maladapted within its current range. By predicting areas at risk for Armillaria root disease, forest managers can deploy suitable strategies to reduce damage from the disease.

Introduction: Fusarioid fungi that cause damping-off and root diseases can result in significant losses to conifer crops produced in forest nurseries across the USA. These nurseries are vital to reforestation and forest restoration efforts. Understanding the diversity of Fusarioid fungi associated with damping-off and root diseases of conifer seedlings can provide an approach for targeted management techniques to limit seedling losses and pathogen spread to novel landscapes.Methods: This study identifies 26 Fusarium spp. (F. acuminatum, F. annulatum, F. avenaceum, F. brachygibbosum, F. clavus, F. commune, F. cugenangense, F. diversisporum, F. elaeagni, F. elaeidis, F. flocciferum, F. fredkrugeri, F. fujikuroi, F. grosmichelii, F. ipomoeae, F. lactis, F. languescens, F. luffae, F. odoratissimum, F. oxysporum, F. queenslandicum, F. redolens, F. torulosum, F. triseptatum, F. vanleeuwenii, & F. verticillioides), 15 potential species within Fusarium and Neocosmospora species complexes (two from F. fujikuroi species complex, nine from F. oxysporum species complex, three from F. tricinctum species complex, and one from Neocosmospora species complex), and four Neocosmospora spp. (N. falciforme, N. metavorans, N. pisi, & N. solani) and associated host information collected from conifer-producing nurseries across the contiguous USA.Results: Phylogenetic analyses identified Fusarioid fungi haplotypes that were associated with 1) host specificity, 2) localization to geographic regions, or 3) generalists found on multiple hosts across diverse geographic regions.Discussion: The haplotypes and novel species identified on conifer seedlings should be considered for further analysis to determine pathogenicity, pathogen spread, and assess management practices.

Scots pine blister rust caused by Cronartium pini, which includes the fungal rust pathogen with either a heteroecious life cycle (previously known as Cronartium flaccidum) or an autoecious life cycle (formerly known as Peridermium pini or Endocronartium pini), is capable of infecting many Eurasian pines including Pinus sylvestris (Scots pine). The heteroecious form of C. pini completes its life cycle alternating between pines and various species of flowering plants (Angiospermae); the related autoecious form spreads directly from pine to pine. If the Scots pine blister rust pathogen possesses or gains the capacity to infect North American pines, the economic and ecological impacts could be significant. Scots pine is one of the most widely distributed conifers in the world, and it has become naturalized in the northeastern and midwestern United States. Scots pine blister rust is also called resin-top disease and top-dieback of pine. Symptoms in pine include stem swelling, branch flagging, excessive pitch flow, and top-kill, and, in the alternate hosts, leaf spotting. The rust pathogen is spread in nature by wind-borne spores, which require live hosts for infection. However, the rust pathogen can also be transported on infected plant materials that can be nonsymptomatic. Early infections of host plant infections by C. pini are difficult to detect and diagnose, but molecular techniques offer a potential approach for early detection and diagnosis. This recovery plan is intended to provide a brief summary of the disease, assess the status of critical recovery components, and identify disease management research, extension, and education needs.