Om, Namgay

AbstractThe black curry leaf psyllid, Diaphorina communis, is a host of the citrus pathogen, ‘Candidatus Liberibacter asiaticus’ (‘CLas’). However, there is a paucity of information on its biology; hence, this study was conducted to evaluate survival and development on citrus, in this instance mandarin (Citrus reticulata) and curry leaf (Bergera koenigii), and transmission of ‘CLas’. Given its similarity with the Asian citrus psyllid (Diaphorina citri), sequences of the COI and 16S genes were examined to see if they could distinguish molecularly between nymphs of these two species. Field and laboratory experiments showed that D. communis nymphs transferred to mandarin branches failed to survive. Adults could survive on flush growth of ‘CLas’‐infected mandarin trees; however, little oviposition took place, and the single resulting nymph did not survive to the second instar. These observations suggest that D. communis does not develop, or rarely develops on mandarin and possibly other Citrus spp. Curry leaf appears to be its preferred host, and complete development can take place, possibly exclusively, on this species. Studies on acquisition of ‘CLas’ by D. communis and possible transmission assessed in 2014 and 2015 using greenhouse‐grown curry leaf and mandarin seedlings with naturally infected mandarin stumps as a source of ‘CLas’ indicated a low acquisition rate of ‘CLas’. In addition, although D. communis can acquire ‘CLas’, it either cannot transmit it or transmission is limited, and the pathogen may not multiply within the insect. Phylogenetic analyses indicate that differences in COI and 16S regions may prove useful for differentiating between early instar D. communis and D. citri nymphs when fifth instar nymphs and adults are not present on host plants.

The draft genome sequence of a novel “ Candidatus Liberibacter” species detected in an unidentified species of Zanthoxylum (Rutaceae) collected in Bhutan is reported. The total length is 1,408,989 bp with 1,169 coding sequences in 96 contigs, a GC content of 37.3%, and 76 to 77% average nucleotide identity with several other “ Ca . Liberibacter” species.

Abstract BACKGROUND In insects, little is known about the co‐evolution between their primary endosymbionts and hosts at the intraspecific level. This study examined co‐diversification between the notorious agricultural pest Diaphorina citri and its primary endosymbionts (P‐endosymbiont), ‘ Candidatus Carsonella ruddii’ at the population level. RESULTS Maximum likelihood, haplotype network, principal components and Bayesian clustering identified three lineages for D. citri and its P‐endosymbiont: a Western clade containing individuals from Pakistan, Bhutan (Phuentsholing), Vietnam (Son La), USA, Myanmar and China (Ruili, Yunnan); a Central clade, with accessions originating from Southwest China, Bhutan (Tsirang) and Bangladesh; and an Eastern clade containing individuals from Southeast Asia, and East and South China. A more diverse genetic structure was apparent in the host mitochondrial DNA than their P‐endosymbionts; however, the two sets of data were strongly congruent. CONCLUSION This study provides evidence for the co‐diversification of D. citri and its P‐endosymbiont during the migration from South Asia to East and Southeast Asia. We also suggest that the P‐endosymbiont may facilitate investigations into the genealogy and migration history of the host. The biogeography of D. citri and its P‐endosymbiont indicated that D. citri colonized and underwent a secondary dispersal from South Asia to East and Southeast Asia. © 2018 Society of Chemical Industry

Mandarin (Citrus reticulata) is the most important cash crop in Bhutan and plantations total approximately 1.8 million trees (Ministry of Agriculture, Thimphu, Bhutan, 2000). Most trees are a local mandarin variety. Seedlings trees are produced by local farmers or supplied by Druk Seed Nursery. Mandarin seedlings have also been introduced from India. In the mid-1990s, mandarin trees growing in Punakha Valley and Wangdue districts began showing symptoms of decline that included sparse yellow foliage and shoot die-back. After initial surveys in 2000, huanglongbing (HLB) was suspected as the cause of declining trees based on symptomatology and presence of the psyllid vector Diaphorina citri, but no confirmatory tests were carried out. In August 2002, we surveyed eight locations in the valley from Rimchu (North) to Kamichu (South). HLB-like leaf mottle symptoms were observed on declining mandarin trees at all locations at altitudes ranging from 700 to 1,450 m. Orchards around Punakha (1,350m) in the center of the valley were more severely affected. Symptoms were also observed on Mexican lime (Citrus aurantifolia), citron (Citrus medica), and on tangelo trees (Minneola, Seminola, and Iyo) introduced originally as certified HLB-free budwoods from Corsica, France and grafted onto Rangpur lime at the Wangdue Research Center (1,300m). Leaves were collected from symptomatic trees and three declining mandarin trees without characteristic leaf mottle symptoms. Two specific polymerase chain reaction (PCR) tests for the detection of HLB Liberibacter species (1,2) were carried out on 16 DNA samples extracted from leaf mid-veins of 10 mandarins, two Mexican limes, three tangelos, and one citron tree. “Candidatus Liberibacter asiaticus” was readily detected by both PCR assays in all but two samples (one mandarin with noncharacteristic symptoms and citron) and all sampled orchards. The presence in the Wangdue Research Center of liberibacter infected trees, propagated from certified HLB-free budwoods, suggests that natural spread of the HLB by D. citri is occuring, as the psyllid had been identified previously in the Punakha area by Bhutanese Entomologists. It is likely that the disease was originally introduced as infected planting material although its source has not been determined. References: (1) A. Hocquellet et al. Mol. Cell. Probes 13:373, 1999. (2) S. Jagoueix et al. Mol. Cell.Probes 10:43,1996.