No abstract

Under the old taxon Principes, palms were once the Princes of the Kingdom Plantae. First on Engler’s list, they occupy a cherished place to botanists, and remain treasured centerpieces of many gardens. In turn, botanic gardens have put forward a decades-long effort to conserve these widely admired plants, keeping a number of palm species from extinction. Living palm collections also have critical value for comparative ecological studies. In this paper we highlight successful ex situ conservation programs for palms, review how the promising new field of collections genetics can guide ex situ conservation of palms, conduct a family-wide gap analysis for living collections in the Arecaceae, and provide an in-depth case study of ex situ conservation of the genus Sabal. These analyses highlight ways in which gardens can advance palm conservation following four recommendations: collect, cultivate, communicate, and collaborate.

Pathovars of Xanthomonas campestris (Xc) cause distinct diseases on different brassicaceous hosts. The genomic relationships among pathovars as well as the genetic determinants of host range and tissue specificity remain poorly understood despite decades of research. Here, leveraging advances in multiplexed long-read technology, we fully sequenced the genomes of a collection of Xc strains isolated from cruciferous crops and weeds in New York and California, as well as strains from global collections, to investigate pathovar relationships and candidate genes for host- and tissue-specificity. Pathogenicity assays and genomic comparisons across this collection and publicly available Xc genomes revealed a correlation between pathovar and genomic relatedness and provide support for Xc pv. barbareae, the validity of which had been questioned. Linking strain host range with type III effector repertoires identified AvrAC (also ‘XopAC’) as a candidate host-range determinant, preventing infection of Matthiola incana, and this was confirmed experimentally. Furthermore, the presence of a copy of the cellobiosidase gene cbsA with coding sequence for a signal peptide was found to correlate with the ability to infect vascular tissues, in agreement with a previous study of diverse Xanthomonas species; heterologous expression in strains lacking the gene gave mixed results however, indicating that factors in addition to cbsA influence tissue specificity of Xc pathovars.