Studies on early and highly sensitive detection of citrus greening pathogenic bacterium

Abstract

Citrus greening (huanglongbing; HLB) is a devastating disease of citrus trees with high economic costs to the world’s citrus industry. In Japan, infected trees have been confirmed throughout Okinawa Prefecture and on the Amami Islands with the exception of Amami-Oshima and Kikai Islands of Kagoshima Prefecture. This disease is caused by a phloem-limited fastidious bacterium, ‘Candidatus Liberibacter asiaticus’ (Las) in Japan (Hamashima et al. 2003) and is transmitted by grafting and by the sapsucking psyllid Diaphorina citri (Bove 2006). When infected trees develop symptoms, tree vigor declines rapidly, and the tree soon dies. All major commercial citrus cultivars are susceptible to the bacterium, and no effective control is known other than the removal of infected trees. Therefore, in areas where the bacterium has not become established, rapid identification and culling of infected trees and quarantine measures for budwoods are the most important control strategies. Various DNA amplification methods, including polymerase chain reaction (PCR) have been used to test greening-infected plants (National Research Council 2010), but obtaining stable results is often difficult at an early stage of infection when the bacterial density in trees is low. Therefore, in this study, a highly sensitive method for the early detection of the citrus greening bacterium was developed.