Publications

4504

ABSTRACT Insect‐vectored pathogens pose a significant threat to global agriculture. The colonization efficiency of pathogens in vectors plays a central role in these pathosystems, yet studies of the factors that affect this aspect are limited. This study investigates the genetic and microbial symbiont factors influencing the susceptibility of Diaphorina citri to Candidatus Liberibacter asiaticus ( C Las), the pathogen causing citrus greening disease (huanglongbing). Through a microbiome Genome Wide Association Study (mGWAS) based on 16S amplicon sequencing and genomic resequencing of 120 D. citri individuals from six populations, we identified 79 SNPs significantly associated with the relative abundance of C Las within insects. Additionally, some of these SNPs were also associated with the relative abundance of Candidatus Profftella armature, a key endosymbiont of D. citri . SNPs in the regulatory region of gene Dcitr04g11610.1 led to its overexpression in C Las‐susceptible D. citri , and C Las infection further elevated its expression. Conversely, RNAi knockdown of Dcitr04g11610.1 reduced C Las infection rates and abundance, accompanied by increased abundance of Profftella . Phylogenetic analysis revealed Dcitr04g11610.1 ’s high homology to Major Facilitator Superfamily‐type transporter SLC18B1 proteins, suggesting a role in C Las polyamine utilization. These findings highlight the importance and potential interplay of insect genetics and symbiotic microbiota in insect‐vectored plant pathogen systems.

Abstract The African citrus triozid (ACT), Trioza erytreae (Del Guercio, 1918) (Hemiptera: Triozidae), is a significant pest of citrus in southern Africa serving as a vector of African citrus greening disease associated with the phloem-limited gram-negative bacterium “Candidatus Liberibacter africanus” (CLaf). ACT can also vector another Liberibacter species, “Ca. Liberibacter asiaticus” (CLas) associated with Asian citrus greening. Given the confirmed presence of CLas on the African continent, efforts to monitor populations of ACT as well as associated liberibacters in citrus environments have been enhanced since 2021. Trapping and active collections in citrus surroundings indicated the presence of two triozid species with similar morphology to ACT and five other triozids which were morphologically distinct. This study aimed to characterise the diversity of triozid species around citrus and determine their association with liberibacter. Morphological characters and nucleotide sequence phylogeny of the mitochondrial cytochrome c oxidase I (COI) gene region supported the distinction of seven triozid species including ACT. CLaf was only detected in ACT. None of the other triozid species had any liberibacter species associated with them. Our results suggest the presence of other triozid species in other African countries, which probably were misidentified as ACT. Our findings highlight the need for a comprehensive taxonomic revision of triozids associated with citrus. Integrating morphological and molecular characters in a revised classification will be essential for accurate identification of ACT. Molecular confirmation is needed for confidence in distinguishing ACT from closely related non-pest species.

ABSTRACT Cable bacteria conduct long-distance electron transport in sediments but are not yet isolated in pure culture. We report the metagenome-assembled genome of Candidatus Electrothrix sp. NPCB-01 from Newport Bay, California. This 3.46-Mb genome encodes sulfur oxidation, nitrogen and carbon metabolism, and nickel homeostasis genes, expanding resources for these electroactive microbes.

Welsh onion (Allium fistulosum) is an important aromatic vegetable crop, particularly in Asia (Kim et al. 2023). In November 2025, two-month-old Welsh onion plants showing leaf proliferation, little leaf, and yellowing symptoms were found at low frequency (< 1%) in Fangyuan Township, Changhua County, Taiwan. The plot was around 880 m 2 in size and about 7,200 clumps were grown. Five symptomatic and three symptomless plants were sampled (bagged separately). The plants’ basal leaf tissues were subjected to DNA extraction and PCR analysis. DNA was extracted using a Synergy 2.0 Plant DNA Extraction Kit (OPS Diagnostics) using filter tips, and the DNA samples’ quality was verified by successful amplification of a plant 26S rDNA fragment (0.7 kb) using primer pair 28KJ/28C (Cullings 1992). Nested polymerase chain reaction (PCR) assays using phytoplasma 16S rDNA-specific primers were conducted. The nested primer pairs used were P1/P7 and fU5/rU3 (Lorenz et al. 1995), respectively. DNA of periwinkle infected with periwinkle leaf yellowing phytoplasma served as a positive control and no-template controls (nuclease-free water) were included in both PCR rounds. In both tests, only DNA from the five symptomatic plants produced the expected amplicons (1.8 kb and 881 bp for the outer and inner assays). The products from the first and second rounds of PCR were sequenced and assembled. Sequencing chromatograms of the PCR products had single, well-resolved peaks across all positions in all the samples, indicating that only one strain was present. Near-full-length (1,466 bp) 16S rDNA sequences of all five samples were identical to that of a reference ‘Candidatus Phytoplasma australasiaticum’-related strain, NCHU2014 (accession no. CP040925, bp 537,765 to 539,230; 16SrII-A; Rodrigues Jardim et al. 2023), and a representative sequence has been deposited in GenBank (accession no. PX696818). A 1,248 bp fragment (accession no. PX696818, bp 84 to 1,331) of the detected 16S rDNA sequence was excised for analysis using the web tool iPhyClassifier (https://plantpathology.ba.ars.usda.gov/cgi-bin/resource/iphyclassifier.cgi), and the virtual RFLP patterns obtained were identical to the reference pattern of 16SrII-A (accession no. L33765; similarity coefficient 1.00). Additional PCR tests targeting the protein translocase gene secY and the elongation factor Tu gene (tuf) of 16SrII phytoplasmas were respectively conducted with the infected samples using primer pairs SecYF1(II)/SecYR1(II) and TUF-II-F1/TUF-II-R1 (Al-Subhi et al. 2017; Lee et al. 2010). The secY (accession no. PX737873; 1,263 bp) and tuf (accession no. PX737874; 1,183 bp) sequences were again found identical to those of the reference strain NCHU2014 (16SrII-A phytoplasma; accession no. CP040925, bp 192,846 to 194,108 and bp 139,150 to 140,332). In Taiwan, 16SrII phytoplasma has been reported affecting various plants, such as seseme and purple coneflower (Rodrigues Jardim et al. 2023; Tseng et al. 2014). In A. fistulosum, however, phytoplasma infection has only been associated with group 16SrI (Cho et al. 2019). The present study is the first report of a 16SrII-A phytoplasma affecting Welsh onion and the findings expand the understanding of the width of the subgroup’s host range in the island. Since Welsh onion is an important culinary crop, and the disease significantly affects its morphology and commercial value, ongoing surveillance of its spread in other regions is warranted.