Panzootic chytrid fungus out of Asia: Species in the fungal genus Batrachochytrium are responsible for severe declines in the populations of amphibians globally. The sources of these pathogens have been uncertain. O'Hanlon et al. used genomics on a panel of more than 200 isolates to trace the source of the frog pathogen B. dendrobatidis to a hyperdiverse hotspot in the Korean peninsula (see the Perspective by Lips). Over the past century, the trade in amphibian species has accelerated, and now all lineages of B. dendrobatidis occur in traded amphibians; the fungus has become ubiquitous and is diversifying rapidly. Science , this issue p. 621 ; see also p. 604

A new, yet old, threat to amphibians: Globally, populations of amphibians have been severely affected by a disease caused by the fungusBatrachochytrium dendrobatidis. Recently, some European salamander populations were decimated by the emergence of a new, related chytrid fungus,B. salamandrivorans. Martelet al.screened amphibians across continents. This newly emerging threat seems to have originated in Asia and traveled to Europe with salamanders transported as part of the pet trade. Asian salamanders have evolved resistance to the pathogen, but salamanders from other parts of the world are highly susceptible.Science, this issue p.630

Candida auris is an emergent multidrug-resistant fungal pathogen causing increasing reports of outbreaks. While distantly related to C. albicans and C. glabrata, C. auris is closely related to rarely observed and often multidrug-resistant species from the C. haemulonii clade. Here, we analyze near complete genome assemblies for the four C. auris clades and three related species, and map intra- and inter-species rearrangements across the seven chromosomes. Using RNA-Seq-guided gene predictions, we find that most mating and meiosis genes are conserved and that clades contain either the MTLa or MTLα mating loci. Comparing the genomes of these emerging species to those of other Candida species identifies genes linked to drug resistance and virulence, including expanded families of transporters and lipases, as well as mutations and copy number variants in ERG11. Gene expression analysis identifies transporters and metabolic regulators specific to C. auris and those conserved with related species which may contribute to differences in drug response in this emerging fungal clade.

From Blight to Powdery Mildew: Pathogenic effects of microbes on plants have widespread consequences. Witness, for example, the cultural upheavals driven by potato blight in the 1800s. A variety of microbial pathogens continue to afflict crop plants today, driving both loss of yield and incurring the increased costs of control mechanisms. Now, four reports analyze microbial genomes in order to understand better how plant pathogens function (see the Perspective by Dodds ). Raffaele et al. (p. 1540 ) describe how the genome of the potato blight pathogen accommodates transfer to different hosts. Spanu et al. (p. 1543 ) analyze what it takes to be an obligate biotroph in barley powdery mildew, and Baxter et al. (p. 1549 ) ask a similar question for a natural pathogen of Arabidopsis . Schirawski et al. (p. 1546 ) compared genomes of maize pathogens to identify virulence determinants. Better knowledge of what in a genome makes a pathogen efficient and deadly is likely to be useful for improving agricultural crop management and breeding.

Batrachochytrium dendrobatidis ( Bd ) is a globally ubiquitous fungal infection that has emerged to become a primary driver of amphibian biodiversity loss. Despite widespread effort to understand the emergence of this panzootic, the origins of the infection, its patterns of global spread, and principle mode of evolution remain largely unknown. Using comparative population genomics, we discovered three deeply diverged lineages of Bd associated with amphibians. Two of these lineages were found in multiple continents and are associated with known introductions by the amphibian trade. We found that isolates belonging to one clade, the global panzootic lineage ( Bd GPL) have emerged across at least five continents during the 20th century and are associated with the onset of epizootics in North America, Central America, the Caribbean, Australia, and Europe. The two newly identified divergent lineages, Cape lineage ( Bd CAPE) and Swiss lineage ( Bd CH), were found to differ in morphological traits when compared against one another and Bd GPL, and we show that Bd GPL is hypervirulent. Bd GPL uniquely bears the hallmarks of genomic recombination, manifested as extensive intergenomic phylogenetic conflict and patchily distributed heterozygosity. We postulate that contact between previously genetically isolated allopatric populations of Bd may have allowed recombination to occur, resulting in the generation, spread, and invasion of the hypervirulent Bd GPL leading to contemporary disease-driven losses in amphibian biodiversity.

Pest and pathogen losses jeopardise global food security and ever since the 19^th century Irish famine, potato late blight has exemplified this threat. The causal oomycete pathogen, Phytophthora infestans, undergoes major population shifts in agricultural systems via the successive emergence and migration of asexual lineages. The phenotypic and genotypic bases of these selective sweeps are largely unknown but management strategies need to adapt to reflect the changing pathogen population. Here, we used molecular markers to document the emergence of a lineage, termed 13_A2, in the European P. infestans population, and its rapid displacement of other lineages to exceed 75% of the pathogen population across Great Britain in less than three years. We show that isolates of the 13_A2 lineage are among the most aggressive on cultivated potatoes, outcompete other aggressive lineages in the field, and overcome previously effective forms of plant host resistance. Genome analyses of a 13_A2 isolate revealed extensive genetic and expression polymorphisms particularly in effector genes. Copy number variations, gene gains and losses, amino-acid replacements and changes in expression patterns of disease effector genes within the 13_A2 isolate likely contribute to enhanced virulence and aggressiveness to drive this population displacement. Importantly, 13_A2 isolates carry intact and in planta induced Avrblb1, Avrblb2 and Avrvnt1 effector genes that trigger resistance in potato lines carrying the corresponding R immune receptor genes Rpi-blb1, Rpi-blb2, and Rpi-vnt1.1. These findings point towards a strategy for deploying genetic resistance to mitigate the impact of the 13_A2 lineage and illustrate how pathogen population monitoring, combined with genome analysis, informs the management of devastating disease epidemics. We have documented a dramatic shift in the population of the potato late blight pathogen Phytophthora infestans in northwest Europe in which an invasive and aggressive lineage called 13_A2 has emerged and rapidly displaced other genotypes. The genome of a 13_A2 isolate revealed a high rate of sequence polymorphism and a remarkable level of variation in gene expression during infection, particularly of effector genes with putative roles in pathogenicity. Collectively, these polymorphisms, in combination with an extended biotrophic phase, may explain the aggressiveness of 13_A2 and its ability to cause disease on previously resistant potato cultivars. The genome analysis identified conserved effectors that are sensed by potato resistance genes. These findings provide options for the strategic deployment of host resistance with a positive impact on crop yield and food security. This work stresses the benefits of a crop disease management strategy incorporating knowledge of the geographical structure, evolutionary dynamics, genome sequence diversity and in planta-induced effector complement of pathogen lineages.