Insects Visiting Drippy Blight Diseased Red Oak Trees Are Contaminated with the Pathogenic Bacterium Lonsdalea quercina.

The focus of investigation in this study was to consider the potential of arthropods in the dissemination of the bacterium involved in drippy blight disease, Lonsdalea quercina. Arthropod specimens were collected and tested for the presence of the bacterium with molecular markers. The bacterium L. quercina was confirmed on 12 different insect samples from three orders (Coleoptera, Hemiptera, and Hymenoptera) and eight families (Buprestidae, Coccinellidae, Dermestidae, Coreidae, Pentatomidae and/or Miridae, Apidae, Formicidae, and Vespidae). Approximately half of the insects found to carry the bacterium were in the order Hymenoptera. Estimates of the insects that are contaminated with the bacterium, and likely carry it between trees, is conservative because the documented insects represent only a subset of the insect orders that were observed feeding on the bacterium or present on diseased trees yet were not able to be tested. The insects contaminated with L. quercina exhibited diverse life histories, where some had a facultative relationship with the bacterium and others sought it out as a food source. These findings demonstrate that a diverse set of insects naturally occur on diseased trees and may disseminate L. quercina.

Characterization of the Xanthomonas translucens Complex Using Draft Genomes, Comparative Genomics, Phylogenetic Analysis, and Diagnostic LAMP Assays.

Prevalence of Xanthomonas translucens, which causes cereal leaf streak (CLS) in cereal crops and bacterial wilt in forage and turfgrass species, has increased in many regions in recent years. Because the pathogen is seedborne in economically important cereals, it is a concern for international and interstate germplasm exchange and, thus, reliable and robust protocols for its detection in seed are needed. However, historical confusion surrounding the taxonomy within the species has complicated the development of accurate and reliable diagnostic tools for X. translucens. Therefore, we sequenced genomes of 15 X. translucens strains representing six different pathovars and compared them with additional publicly available X. translucens genome sequences to obtain a genome-based phylogeny for robust classification of this species. Our results reveal three main clusters: one consisting of pv. cerealis, one consisting of pvs. undulosa and translucens, and a third consisting of pvs. arrhenatheri, graminis, phlei, and poae. Based on genomic differences, diagnostic loop-mediated isothermal amplification (LAMP) primers were developed that clearly distinguish strains that cause disease on cereals, such as pvs. undulosa, translucens, hordei, and secalis, from strains that cause disease on noncereal hosts, such as pvs. arrhenatheri, cerealis, graminis, phlei, and poae. Additional LAMP assays were developed that selectively amplify strains belonging to pvs. cerealis and poae, distinguishing them from other pathovars. These primers will be instrumental in diagnostics when implementing quarantine regulations to limit further geographic spread of X. translucens pathovars.

Virulence of Genetically Distinct Geosmithia morbida Isolates to Black Walnut and Their Response to Coinoculation with Fusarium solani.

Geosmithia morbida is well documented as the causal agent of thousand cankers disease of black walnut trees. However, it is not well understood how G. morbida strains differ in virulence and how their interactions with co-occurring pathogens contribute to disease severity. In this study, we systematically investigated virulence of genetically distinct G. morbida strains. Overall, we found varying degrees of virulence, although differences were not related to genetic groupings. Furthermore, the pathogen Fusarium solani is also commonly isolated from thousand canker-diseased trees. The degree of disease contribution from F. solani is unknown, along with interactions it may have with G. morbida. This research shows that coinoculation with these pathogens does not yield a synergistic response.

Erwinia iniecta sp. nov., isolated from Russian wheat aphid (Diuraphis noxia).

Short, Gram-negative-staining, rod-shaped bacteria were isolated from crushed bodies of Russian wheat aphid [Diuraphis noxia (Kurdjumov)] and artificial diets after Russian wheat aphid feeding. Based on multilocus sequence analysis involving the 16S rRNA, atpD, infB, gyrB and rpoB genes, these bacterial isolates constitute a novel clade in the genus Erwinia, and were most closely related to Erwinia toletana. Representative distinct strains within this clade were used for comparisons with related species of Erwinia. Phenotypic comparisons using four distinct strains and average nucleotide identity (ANI) measurements using two distinct draft genomes revealed that these strains form a novel species within the genus Erwinia. The name Erwinia iniecta sp. nov. is proposed, and strain B120T ( = CFBP 8182T = NCCB 100485T) was designated the type strain. Erwinia iniecta sp. nov. was not pathogenic to plants. However, virulence to the Russian wheat aphid was observed.

Genomics-Based Diagnostic Marker Development for Xanthomonas oryzae pv. oryzae and X. oryzae pv. oryzicola.

A computational genomics pipeline was used to compare sequenced genomes of Xanthomonas spp. and to rapidly identify unique regions for development of highly specific diagnostic markers. A suite of diagnostic primers was selected to monitor diverse loci and to distinguish the rice bacterial blight and bacterial leaf streak pathogens, Xanthomonas oryzae pv. oryzae and X. oryzae pv. oryzicola, respectively. A subset of these primers was combined into a multiplex polymerase chain reaction set that accurately distinguished the two rice pathogens in a survey of a geographically diverse collection of X. oryzae pv. oryzae, X. oryzae pv. oryzicola, other xanthomonads, and several genera of plant-pathogenic and plant- or seed-associated bacteria. This computational approach for identification of unique loci through whole-genome comparisons is a powerful tool that can be applied to other plant pathogens to expedite development of diagnostic primers.

Geographic Distribution and Genetic Diversity of Three Ophiosphaerella Species that Cause Spring Dead Spot of Bermudagrass.

The distribution of three Ophiosphaerella spp. that cause spring dead spot (SDS) of bermudagrass was studied by systematically sampling two golf courses in Oklahoma and one in Kansas. O. herpotricha was isolated from all three locations and was the most abundant species. It was the only SDS pathogen found at Jenks, Oklahoma. O. korrae was isolated from Afton, Oklahoma, and Independence, Kansas, whereas O. narmari was only detected in samples from Afton. This is the first report of all three Ophiosphaerella species on bermudagrass at the same location. Amplified fragment length polymorphism (AFLP) marker analysis was used to investigate inter- and intraspecific genetic diversity of Ophiosphaerella isolates from North America and Australia. A majority of the O. herpotricha and O. narmari isolates from Afton were distinct haplotypes, suggesting that sexual recombination was occurring within the population. Conversely, the presence of multiple isolates of O. herpotricha and O. narmari with the same haplotype also indicated that asexual propagation was occurring. The genetic diversity among O. herpotricha isolates from Afton was not distinctly different from that of isolates collected throughout the southern United States. In contrast, O. narmari isolates from Afton were distinct from those collected in Australia. The genetic diversity in O. korrae was markedly different than that in the other Ophiosphaerella spp. The population at Afton was dominated by just a few haplotypes, and these were nearly identical to isolates collected from bermudagrass and Kentucky bluegrass throughout western, central, and northern North America. However, O. korrae isolates collected in the southeastern United States were only distantly similar to other North American isolates.