Characterization of Huanglongbing disease associated with acid lime (Citrus aurantifolia Swingle) in Oman

Huanglongbing (HLB) is one of the most destructive diseases of Citrus. This study was conducted to characterize its etiological agent, ‘Candidatus Liberibacter’ spp., as well as the occurrence and distribution of HLB associated with acid lime (Citrus aurantifolia Swingle) in Oman. A survey of different geographical areas in Oman has shown that HLB is present in some farms in the northern and southern parts of the country. Disease incidence was 71.8% in the surveyed lime trees with typical symptoms of HLB in Sohar and Wkaan, 40% in Al Jabal Al Akhdar and 62% in Salalah. Disease symptoms in some areas were observed all year round, but were more apparent from October to March. Phylogenetic analysis of the 16SrRNA gene of 38 isolates indicated an association of ‘Candidatus Liberibacter asiaticus’ (Las) with HLB-symptomatic acid lime trees. The analysis showed that Omani isolates clustered with isolates from Iran, India, USA and China. No ‘Candidatus Liberibacter’ spp. were detected in nursery seedlings imported from abroad. This study reports for the first time the association of HLB with acid lime in Oman. Extension programs and strict quarantine measures should be applied to help reduce the international spread of HLB.