Detection of Asian Citrus Psyllid (Hemiptera: Psyllidae) in Ethiopia: A New Haplotype and its Implication to the Proliferation of Huanglongbing

Abstract

Diaphorina citri Kuwayama, also known as the Asian citrus psyllid, is a pest of citrus known for its transmission of Candidatus Liberibacter asiaticus (Ca. L. asiaticus), the causal bacterium of Huanglongbing. The African citrus triozid Trioza erytreae (Del Guercio) (Hemiptera: Triozidae) has been the putative vector of Candidatus Liberibacter africanus (Ca. L. africanus) which causes the African citrus greening disease, until the recent detection of D. citri on the continent. Following reports of D. citri in Kenya and Tanzania, we surveyed citrus plants to establish the presence/absence of D. citri in Ethiopia in citrus-growing regions ranging from 900 to 2,460 m above sea level (masl). Diaphorina citri adults were detected in five of the surveyed sites in Ethiopia. Adult insects encountered were collected using an aspirator and stored in 97% ethanol. The mitochondrial cytochrome oxidase 1 (mt COI) gene of the collected insects was amplified using LepF1/LepR1 primers, and sequences obtained showed low variation, which fell within the acceptable range of species. BLAST was used to query the sequences obtained, and all the sequences linked to D. citri accessions that are available in GenBank. The analysis of the sequences revealed a new haplotype of the species that differs from haplotypes previously reported. Phylogenetic relationships of our samples and other D. citri reference sequences was inferred using the Maximum-likelihood method. Monophyly was observed between the samples and the publicly available sequences from global accessions. This is the first report of the presence of D. citri in Ethiopia.

Assessment of Multilocus Sequence Analysis (MLSA) for Identification of Candidatus Liberibacter Solanacearum from Different Host Plants in Spain

“…Many of the Liberibacter species are considered important pathogens in agriculture, and their classification can seriously affect many crops, the international trade, and the associated sectoral economy. Currently, new species of Liberibacter are being identified and it is likely that other new ones, associated or not with plant diseases, will be detected in plants or insect vectors in the near future [37]. By then, it will be essential to determine if these new isolates are plant pathogens as well as their relationship with the isolates or variants already characterized.…”

The Asian Citrus Greening Disease (Huanglongbing): Evidence Note on Invasiveness and Potential Economic Impacts for East Africa

“…In addition, a recent study has shown that CLas is increasingly widespread in Ethiopia, present in regions of the country distant from previously surveyed areas and thriving at higher altitudes with cooler temperatures (Ajene et al, 2020b).…”

“…zanthoxyli (CLafZ) (Roberts et al, 2015) and CL tecleae (CLafT) (Roberts and Pietersen, 2016). Currently, little is known about these 'CL africanus' subspecies regarding their host range, transmission and disease-causing potential to citrus, although CLafCl has been reported from citrus in Ethiopia, Kenya and Tanzania (Shimwela et al, 2016;Roberts et al, 2017;Ajene et al, 2020b).…”

“…Previous research has demonstrated the capacity of T. erytreae to transmit CLas (Massonie et al, 1976) and this development has brought additional concerns of T. erytreae as an alternate route of HLB proliferation in the absence of, or in addition to the primary CLas vector, D. citri. In 2020, following reports of presence of the primary HLB vector from Tanzania and Kenya, Ajene et al (2020b) surveyed citrus-growing regions in Ethiopia for the psyllid and found it to be present in five locations in North and South Wollo in the north of the country, at altitudes between 1,619 and 2,112 m.a.s.l -higher than is typical for the psyllid in its native range. The source of D. citri was not clear, but the psyllid may have arrived on imported plant materials.…”

“…Although insect vector transmission is one of the major contributors to disease spread and previous studies have focused on this, it is also important to consider the environmental requirements of the pathogen (Gottwald, 2010). Here, consensus modelling for the vector and pathogen provides a more robust view of potential disease distribution (Ajene et al, 2020b). Narouei-Khandan et al (2016) conducted the first study assessing the potential global risk of HLB (CLas) and ACP establishment in citrus-growing areas using two types of correlative modelling approaches to assess climate suitability: (i) Maximum Entrophy (MaxEnt) as a presence-only or a presence-background model (Phillips et al, 2006) and (ii) Multi-Model Framework (Worner et al, 2010) whereby from nine models the Support Vector Machine (SVM) achieved the highest performance rank.…”