Reaction of some commercial citrus genotypes to Candidatus Liberibacter asiaticus in Iran

Abstract Citrus huanglongbing (HLB) associated with Candidatus Liberibacter spp. is the most destructive bacterial disease of citrus crops worldwide. In this study, the response of three-year-old seedlings of 14 commercial citrus cultivars and rootstocks to the Asian form of HLB disease ( Ca . L. asiaticus) was investigated through graft-inoculation. The seedlings' reactions to the HLB disease were evaluated based on the PCR detection of CLas after grafting, the disease incubation period (time between graft-inoculation and appearance of the first disease symptoms), and disease severity. Depending on the time of the positive PCR detection of CLas and appearance of disease symptoms, Mexican lime, Persian lime and Volkamer lemon were ranked at the highest level of tolerance (lowest susceptibility), and Rough lemon and Local orange were at the next level, i.e., semi-tolerance (intermediate susceptibility). Alemow, Bakraei, Rangpur lime, Cleopatra, Clementine mandarin, Local mandarin, Blood orange, and Washington navel orange were classified as susceptible to the disease, followed by Valencia orange, which was the most susceptible. In conclusion, all citrus genotypes studied, were affected by HLB. However, symptoms varied by cultivar, with the most severe observed on Valencia sweet orange and Local mandarin, while less severe symptoms were observed on Mexican lime, Persian lime and Volkamer lemon.