Genome analysis of the ubiquitous boxwood pathogenPseudonectria foliicola
Boxwood (Buxusspp.) are broad-leaved, evergreen landscape plants valued for their longevity and ornamental qualities. Volutella leaf and stem blight, caused by the ascomycete fungiPseudonectria foliicola and P. buxi, is one of the major diseases affecting the health and ornamental qualities of boxwood. Although this disease is less severe than boxwood blight caused byCalonectria pseudonaviculataandC. henricotiae, its widespread occurrence and disfiguring symptoms have caused substantial economic losses to the ornamental industry. In this study, we sequenced the genome ofP. foliicolaisolate ATCC13545 using Illumina technology and compared it to other publicly available fungal pathogen genomes to better understand the biology of this organism. Ade novoassembly estimated the genome size ofP. foliicolaat 28.7 Mb (425 contigs; N50 = 184,987 bp; avg. coverage 188×), with just 9,272 protein-coding genes. To our knowledge,P. foliicolahas the smallest known genome within the Nectriaceae. Consistent with the small size of the genome, the secretome, CAzyme and secondary metabolite profiles of this fungus are reduced relative to two other surveyed Nectriaceae fungal genomes:Dactylonectria macrodidymaJAC15-245 andFusarium graminearumPh-1. Interestingly, a large cohort of genes associated with reduced virulence and loss of pathogenicity was identified from theP. foliicoladataset. These data are consistent with the latest observations by plant pathologists thatP. buxiand most likelyP. foliicola,are opportunistic, latent pathogens that prey upon weak and stressed boxwood plants.