Repellency, Toxicity, and Chemical Composition of Plant Essential Oils from Myrtaceae against Asian Citrus Psyllid, Diaphorina citri Kuwayama (Hemiptera Liviidae).

Diaphorina citri Kuwayama (D. citri) is one of the major pests in the citrus industry, which spreads Citrus Huanglongbing disease. It has developed resistance to chemical insecticides. Therefore, searching for greener solutions for pest management is critically important. The main aim of this study was to evaluate the repellent and insecticidal efficacy of essential oils (EOs) from four species of Myrtaceae plants: Psidium guajava (PG), Eucalyptus robusta (ER), Eucalyptus tereticornis (ET), and Baeckea frutescens (BF) against D. citri and to analyze their chemical compositions. GC-MS analysis was performed, and the results indicated that the EOs of PG, ER, ET, and BF were rich in terpenoids, ketones, esters, and alcohol compounds. The repellent rate of all four EOs showed that it decreased with exposure time but increased with the concentration of EOs from 80.50% to 100.00% after treating D. citri for 6 h with four EOs at 100% concentration and decreased to 67.71% to 85.49% after 24 h of exposure. Among the compounds from the EOs tested, eucalyptol had the strongest repellent activity, with a 24 h repellency rate of 100%. The contact toxicity bioassay results showed that all EOs have insecticidal toxicity to D. citri; the LC50 for nymphs was 36.47-93.15 mL/L, and for adults, it was 60.72-111.00 mL/L. These results show that when PG is used as the reference material, the ER, ET, and BF EOs have strong biological activity against D. citri, which provides a scientific basis for the further development of plant-derived agrochemicals.

First report of Watermelon silver mottle orthotospovirus infecting Siraitia grosvenorii in China.

Siraitia grosvenorii, known as "Luohanguo or monk fruit", is a perennial vine belonging to the family Cucurbitaceae. It is cultivated for its fruits, which are used as a Chinese traditional medicine to treat throat, lung and intestine ailments, or as raw material to extract sweet cucurbitane-glycosides as sugar substitute sweeteners (Chen et al., 2007). The production of S. grosvenorii is limited by viral diseases especially cucumber green mottle mosaic virus (CGMMV), papaya ringspot virus (PRSV), watermelon mosaic virus, and zucchini yellow mosaic virus (Liao et al., 2005; Xie et al., 2020). In 2022, virus-like disease consisting of leaf mottling, crinkling, and ringspot was observed on S. grosvenorii plants grown in an insect-proof greenhouse in Guilin City, Guangxi Province, China, with an incidence rate of ~17%. High-throughput sequencing (HTS) was applied to identify potential viruses in the diseased plants. Briefly, total RNA was extracted from a pool of 28 leaf samples (with or without symptoms) of S. grosvenorii using Trizol reagent according to manufacturer's instructions (Invitrogen, U.S.A.). The rRNA was depleted (Epicentre Ribo-zero™ rRNA Removal Kit, Epicentre, U.S.A.), before steps of cDNA library construction (NEBNext® Ultra™ Directional RNA Library Prep Kit for Illumina®, NEB, U.S.A.), and sequencing (Hiseq 4000 platform, Illumina, U.S.A.). The subsequent bioinformatics analyses were performed according to Liu et al. (2021). HTS of the sample and raw reads processing resulted in 8.4 Gb clean data. The clean reads (150 bp) were de novo assembled into 87,414 contigs (≥200 bp), using CLC Genomics Workbench 21 (Qiagen, Germany). The contigs were annotated by local BLASTX, resulting in matches to CGMMV, PRSV, and watermelon silver mottle virus (WSMoV). Three contigs of 6,557 bp, 4,950 bp, and 3,594 bp were most identical to L (GenBank accession no. JX177647), M (MW051789), and S (KM242056) segments of WSMoV. The complete genome sequences corresponding to the contigs derived from the sample (designated as GL-1 variant of WSMoV, OQ401466-OQ401468) were obtained by reads mapping to segments of these isolates. The reads coverage was ≥99.75% in each RNA segment and the depth of the coverage was in a range of 74-285. To detect the presence of GL-1 in S. grosvenorii plants, three primer pairs D7280F/D7382R (5'-TGATAGCCTGATGAACACCA/5'-TGTCTCTAAACCTTCTACCGC, Tm = 55℃, product size 172 bp), D4512F/D4703R (5'-GCATTGAACTCGCTCACAC/5'-AGTAGACGACCCTGAAGACCT, Tm = 55℃, 192 bp), and D109F/D451R (5'-TTATGGCACAAGAGACAACAGAG/5'-GGGCGTTATGTTCAGTATATTGG, Tm = 56℃, 342 bp) were designed in the L, M, and S segments, respectively. Fresh symptomatic and asymptomatic leaf tissues (n=38) were collected from three fields and their extracted nucleic acids were individually tested with the primers designed by two-steps RT-PCR using TaKaRa RNA PCR kit Ver.3.0 (Takara, Japan). Expected amplicons were obtained in symptomatic samples (n=7) showing mottling, crinkling, and chlorosis. Other samples (n=31) with or without symptoms were negative to WSMoV infection. The amplicons were sequenced, and the sequences obtained shared >99% nt identities with the corresponding GL-1 sequences in GenBank. This is the first report of WSMoV on S. grosvenorii, which provides the basic information for virus disease management.

Chromosome-level genome assembly of the Asian citrus psyllid, Diaphorina citri.

Diaphorina citri is a global citrus pest. As a vector insect, it can transmit the causative agents of citrus huanglongbing, causing irreversible losses to the citrus industry. The acquisition of genomic information can provide a molecular genetic basis for effective control of D. citri. Here, the DNBSEQ™ , Oxford Nanopore Technologies, and Hi-C technologies are applied to generate a high-quality chromosome-level genome of D. citri. The genome size of D. citri was 523.78 Mb with a scaffold N50 of 47.05 Mb distributed on 13 chromosomes. A total of 250.64 Mb (47.85%) repeat sequences and 24 048 protein-coding genes were predicted. Genome resequencing of female and male individuals indicated that the sex chromosome system of D. citri is XO. Phylogenetic analysis demonstrated that D. citri and Pachypsylla venusta, which separated from their most recent common ancestor about 336.62 million years ago, were the most closely related. Additionally, we identified genes potentially involved in detoxification metabolism, pathogen transmission, and honeydew secretion for further investigation. The high-quality genome provides an important reference for developing effective management strategies of D. citri.

Effects of Candidatus Liberibacter asiaticus infection on metagenome of Diaphorina citri gut endosymbiont.

Asian citrus psyllid (Diaphorina citri, D. citri) is the important vector of "Candidatus Liberibacter asiaticus" (CLas), associated with Huanglongbing, the most devastating citrus disease worldwide. CLas can affect endosymbiont abundance of D. citri. Here, we generated the high-quality gut endosymbiont metagenomes of Diaphorina citri on the condition of CLas infected and uninfected. The dataset comprised 6616.74 M and 6586.04 M raw reads, on overage, from CLas uninfected and infected psyllid strains, respectively. Taxonomic analysis revealed that a total of 1046 species were annotated with 10 Archaea, 733 Bacteria, 234 Eukaryota, and 69 Viruses. 80 unique genera in CLas infected D. citri were identified. DIAMOND software was used for complement function research against various functional databases, including Nr, KEGG, eggNOG, and CAZy, which annotated 84543 protein-coding genes. These datasets provided an avenue for further study of the interaction mechanism between CLas and D. citri.