Population structure of Bactrocera dorsalis s.s., B. papayae and B. philippinensis (Diptera: Tephritidae) in southeast Asia: evidence for a single species hypothesis using mitochondrial DNA and wingshape data

Background Bactrocera dorsalis s.s. is a pestiferous tephritid fruit fly distributed from Pakistan to the Pacific, with the Thai/Malay peninsula its southern limit. Sister pest taxa, B. papayae and B. philippinensis, occur in the southeast Asian archipelago and the Philippines, respectively. The relationship among these species is unclear due to their high molecular and morphological similarity. This study analysed population structure of these three species within a southeast Asian biogeographical context to assess potential dispersal patterns and the validity of their current taxonomic status. Results Geometric morphometric results generated from 15 landmarks for wings of 169 flies revealed significant differences in wing shape between almost all sites following canonical variate analysis. For the combined data set there was a greater isolation-by-distance (IBD) effect under a ‘non-Euclidean’ scenario which used geographical distances within a biogeographical ‘Sundaland context’ (r2 = 0.772, P Conclusions Bactrocera dorsalis s.s., B. papayae and B. philippinensis likely represent one species structured around the South China Sea, having migrated from northern Thailand into the southeast Asian archipelago and across into the Philippines. No migration is apparent between the Philippines and Taiwan. This information has implications for quarantine, trade and pest management

First report of citrus virus A in Australia

Citrus virus A (CiVA) was detected for the first time in Australia in a living pathogen collection. Buds were originally collected from a Washington navel field tree prior to 1970 and graft-inoculated onto a Symons sweet orange indicator plant. The virus was detected using conventional and quantitative reverse transcription polymerase chain reactions and high-throughput sequencing. This variant shares 96.3% (RNA1) and 96.7% (RNA2) nucleotide identity with isolates of CiVA from South Africa and China, respectively. Foliar symptoms of leaf flecking and oak leaf patterns, consistent with detections of CiVA in other regions, were observed on the foliage of the original accession and inoculated indicator plants. Subsequent surveys of an Australian citrus variety collection detected a different CiVA sequence variant in two accessions of Pera sweet orange; this variant had 97% similarity to the other Australian variant

The hTERTα Splice Variant is a Dominant Negative Inhibitor of Telomerase Activity

The telomerase catalytic subunit (hTERT) is an essential component of the holoenzyme complex that adds telomeric repeats to the ends of human chromosomes. Maintenance of telomeres by telomerase or another mechanism is required for cell immortalization, and loss of telomeric DNA has been proposed as a trigger for cellular senescence. Available evidence suggests that regulation of telomerase activity primarily depends on transcriptional control of hTERT. However, several human tissues as well as some normal cell strains have been shown to express low levels of hTERT mRNA even though they lack telomerase activity. We have previously identified six splice variants of hTERT, including a “deletion” variant (hTERTα) that is missing conserved residues from the catalytic core of the protein. Several of the deletion variants have been detected in normal and developing human tissues. We now show that hTERTα inhibits endogenous telomerase activity, which results in telomere shortening and chromosome end-to-end fusions. Telomerase inhibition induced a senescence-like state in HT1080 cells and apoptosis in a jejunal fibroblast cell line. These results suggest a possible role for hTERT splice variants in the regulation of telomerase activity

First report of citrus exocortis viroid, citrus bent leaf viroid, hop stunt viroid and citrus dwarfing viroid in Lao PDR

Citrus exocortis viroid, citrus bent leaf viroid, hop stunt viroid and citrus dwarfing viroid were detected for the first time in Lao PDR. Samples were collected from citrus trees across southern Lao PDR for laboratory testing in Australia. RNA was extracted and amplified using quantitative reverse transcription polymerase chain reaction (qRT-PCR); viroid identities were confirmed by sequencing

First report of 'Candidatus Liberibacter asiaticus' in Diaphorina communis

Huanglongbing (HLB) or citrus greening is one of the most destructive diseases of citrus in the world and one of the major factors limiting citrus production in south east Asia including Bhutan. The presence of ‘Candidatus Liberibacter asiaticus’, associated with the Asiatic form of HLB, was confirmed by conventional and real-time PCR in adults of the black psyllid, Diaphorina communis Mathur. This is the first formal detection of ‘Ca. L. asiaticus’ in D. communis, and the first detection of the pathogen in a psyllid other than D. citri Kuwayama in Asia, excluding Arabia. This study is also the first to report the presence of D. communis in Bhutan

All‐in‐one Xylella detection and identification: A nanopore sequencing‐compatible conventional PCR

Xylella fastidiosa is a plant-pathogenic bacterium that poses a serious threat to the production of economically important plant species including grapes, almonds, olives and a broad range of amenity plants, causing significant economic losses worldwide. While multiple molecular detection assays have been developed for X. fastidiosa, there is a lack of molecular tools available for detection and differentiation of the closely related pear pathogen, Xylella taiwanensis. In this study, we present a novel conventional PCR assay with primers that can amplify both Xylella species. The amplified product could be sequenced and used for discrimination between the two species and the subspecies within the fastidiosa species. This PCR assay was designed using a genome-informed approach to target the ComEC/Rec2 gene of both Xylella species, ensuring a higher specificity than other previously developed PCR assays. A test performance study across five national plant diagnostic laboratories in Australia and New Zealand demonstrated this assay's high sensitivity and specificity to all known species and subspecies within the Xylella genus. This PCR assay can be used for Xylella identification at the species and subspecies level and is compatible with Sanger sequencing and nanopore sequencing for rapid turnaround time. The newly developed conventional PCR assay presented here offers rapid detection and accurate identification of both Xylella species from plant, insect vector or bacterial samples, enabling timely implementation of biosecurity measures or disease management responses

Piecing together an integrative taxonomic puzzle: microsatellite, wing shape and aedeagus length analyses of Bactrocera dorsalis s.l. (Diptera: Tephritidae) find no evidence of multiple lineages in a proposed contact zone along the Thai/Malay Peninsula

Bactrocera dorsalis (Hendel) and B. papayae Drew & Hancock represent a closely related sibling species pair for which the biological species limits are unclear; i.e. it is uncertain if they are truely two biological species, or one biological species which has been incorrectly split taxonomically. The geographical ranges of the two taxa are thought to abut or overlap on or around the Isthmus of Kra, a recognised biogeographic barrier located on the narrowest portion of the Thai Peninsula. We collected fresh material of B. dorsalis s.l. (i.e. B. dorsalis s.s.+ B. papayae) in a northsouth transect down the Thai Peninsula, from areas regarded as being exclusively B. dorsalis s.s., across the Kra Isthmus, and into regions regarded as exclusively B. papayae. We carried out microsatellite analyses and took measurements of male genitalia and wing shape, both used previously to separate the taxa. No significant population structuring was found in the microsatellite analysis, consistent with one, predominantly panmictic population. Both morphological datasets showed consistent, clinal variation along the transect, without disjunction. No evidence supported historical vicariance driven by the Isthmus of Kra, and no dataset supported the current taxonomy of two species. Rather, within and across the area of range overlap or abutment between the two species, only continuous morphological and genetic variation was recorded. Recognition that morphological traits previously used to separate these taxa are continuous, and that there is no genetic evidence for population segregation in the region of suspected species overlap, is consistent with a growing body of literature that reports no evidence of biological differentiation between these taxa

Investigating the Impact of Huanglongbing in Citrus in Southern Lao PDR

Citrus has been promoted in the Lao People’s Democratic Republic (Lao PDR) as a poverty reduction strategy for at least two decades. However, citrus trees have been in widespread decline for no less than ten years. Since 2010, the authors have observed symptoms on citrus trees consistent with the bacterial disease huanglongbing (HLB). These symptoms included asymmetric leaf mottle, small lopsided fruit, poor fruit production and tree decline. The authors then initiated a long-term study on the occurrence of HLB in southern Lao PDR. Samples of leaf mid-ribs were collected from citrus trees in orchards, nurseries, and backyards across four provinces: Champasak, Sekong, Salavan, and Savannakhet. The presence of ‘Candidatus Liberibacter asiaticus’, the putative causal agent of the Asiatic form of HLB, was confirmed in 59 of 109 samples collected in all four provinces. The Asian citrus psyllid, the vector of ‘Ca. L. asiaticus’, was also observed on citrus trees and tested positive for the pathogen. The implications of these findings for citrus production in Lao PDR are discussed.&nbsp