Citrus huanglongbing (HLB), commonly known as citrus greening, is the most destructive disease of citrus worldwide. The disease has recently been reported from southern Iran. Rapid, sensitive and accurate diagnosis of HLB in citrus orchards is an important step to implement appropriate management of the disease. In order to compare the efficiency of conventional PCR, nested-PCR, real-time PCRand loop-mediated isothermal amplification (LAMP) for detection of Candidatus Liberibacter asiaticus (Las), the causal agent of citrus huanglongbing in Iran, total DNA was extracted separately from leaf midribs of infected and healthy orange trees. The Las detection sensitivity, specificity, and accuracy were tested at different amounts of DNA (100 nanogram to 0.1 femtogram) obtained from both infected and healthy plants with conventional PCR (using specific primers OI1/OI2c, A2/J5, F1/R1, RPF1/RPR1), nested-PCR (by different primers OI1/OI2c/CG3F/CG5R, F1/R1/F2/R2, RPF1/RPR1/RPF2/RPR2), real-time PCR (using specific primer pair FRP-RT/RRP-RT) and LAMP methods (using two different sets of primers). All methods showed a good performance in detecting Las with 100, 10 and 1 ng of total DNA per reaction. The conventional PCR assay detected Las with sensitivity of 30% in amount of 100 pg DNA and failed to detect Las in levels of 1 pg to 0.1 fg DNA. LAMP assay detected Las in 10 pg DNA with a maximum sensitivity of 30%, with total failure in lower amounts of DNA. LAMP sensitivity proved slightly better than conventional PCR especially in amounts of 100 pg and 10 pg DNA per reaction. LAMP was the most rapid and more affordable method for HLB detection.The nested PCR assay detected Las with sensitivity of 100% when 100 ng to 1 pg DNA were used. Furthermore, nested-PCR was sensitive enough to detect the causal agent of HLB disease up to 0.1 fg DNA. Real-time PCR detected Las with sensitivity of 100% in amounts ranging from 100 ng to 10 fg DNA. Moreover, real-time PCR detected Las with sensitivity of 90% in very low amounts of template DNA (1 fg and 0.1 fg) and was the most sensitive method for detection of the causal agent of HLB disease. However, real-time PCR produced false positive results more frequently than the other tests. In general, all methods detected Las with high specificity. Based on the obtained results real-time PCR and nested-PCR showed the highest sensitivity leading to fewer false negatives.In conclusion, application of real-time PCR and nested-PCR assays, especially in suspected newly infected areas are recommended for early detection of infected trees. In respect to fewer false positive results and lower cost of nested-PCR in comparison with real-time PCR, nested-PCR assay in many cases could be the method of choice for detection of HLB disease.