Update on the situation of ‘Candidatus Liberibacter asiaticus’ and Diaphorina citri in Saudi Arabia
In Saudi Arabia, huanglongbing was first reported in the 1970s on the basis of characteristic foliar and fruit symptoms. The presence of ‘Candidatus Liberibacter asiaticus’ (EPPO A1 List) was detected in symptomatic trees in the early 1980s when phytoplasma-like cells were observed by transmission electron microscopy, but its presence in symptomatic plants or in the psyllid vector (Diaphorina citri – Hemiptera: Psyllidae – EPPO A1 List) had not been confirmed by molecular tests. Therefore, a survey was conducted in 13 citrus-producing regions from March 2018 to June 2021. Citrus leaves and fruit were collected from symptomatic trees in commercial and urban trees, and tested (real-time PCR). The possible presence of psyllids was evaluated in all surveyed sites, and some D. citri adults were tested for the presence of ‘Ca. L. asiaticus’ by molecular tests.
‘Ca. L. asiaticus’ was detected in symptomatic citrus samples in 10 out of the 13 surveyed regions (Al Baha, Al Jouf, Al Madina, Al Qassim, Asir, Hail, Makkah, Najran, Riyadh, Tabuk), in Western and South-Western Saudi Arabia. These results confirm the presence of ‘Ca. L. asiaticus’ in Saudi Arabia, and the large number of infected locations showed that the disease range has expanded; probably aided by the increasing movements of infected plants for planting by growers.
The presence of D. citri was observed in a smaller number of regions (Al Baha, Jazan, Makkah, Najran), and the psyllid was mainly found in Mexican lime (Citrus x aurantiifolia) trees. Infestation levels ranged from moderate to no infestation. In this study, the presence of ‘Ca. L. asiaticus’ could not be detected in the adult specimens of D. citri tested, possibly because the overall infection rate was too low. It is also noted that the other psyllid vector of huanglongbing, Trioza erytreae, was not found during this survey.
The situation of both ‘Candidatus Liberibacter asiaticus’ and Diaphorina citri in Saudi Arabia can be described as follows: Present, not widely distributed.
Sources
Ibrahim YE, Al-Saleh MA, Widyawan A, El Komy MH, Al Dhafer HM, Brown JK (2024) Identification and distribution of the ‘Candidatus Liberibacter asiaticus’-Asian citrus psyllid pathosystem in Saudi Arabia. Plant Disease (early view). https://doi.org/10.1094/PDIS-07-23-1460-RE