Seasonal variation of Candidatus Liberibacter asiaticus population in Citrus trees in southeast of Iran

Abstract

Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), is an important and threatening disease for the citru s industry in southeast Iran. In the present study, seasonal dynamic monitoring of CLas was conducted by absolute real-time PCR. Plant materials were obtained across 7 and 6 months from December 2014 to October 2015 from three parts of the canopy of two naturally infected citrus species, Mexican lime (Citrus aurantifolia) and sweet orange (C. sinensis) located in two distinct geographical regions, Sistan-o-Baluchestan and Kerman provinces, respectively. Results showed significant variation (α = 0.001) in the bacterial titers in both infected hosts. These notable changes have also been observed in all tree’s canopy parts and a particular part of tree canopy during sampling months, exhibited by sudden changes in bacterial titers. It was also found that in both locations maximum titers of HLB occurred in summer. The data obtained by correlation assessment suggests a significant relationship between temperature and pathogen population variations that probably in warmer months correlated with the sap flow rate changes in the host, the bacterial titer was increased. In this study, no consistent pattern of the disease agent distribution was found between two different plant hosts. The results of this research on the quantification of CLas in the host plant can be a great help in making proper decisions for disease management by providing the possibility of early detection and rapid removal of inoculum sources.