Investigating the Impact of Huanglongbing in Citrus in Southern Lao PDR

Abstract

Citrus has been promoted in the Lao People’s Democratic Republic (Lao PDR) as a poverty reduction strategy for at least two decades. However, citrus trees have been in widespread decline for no less than ten years. Since 2010, the authors have observed symptoms on citrus trees consistent with the bacterial disease huanglongbing (HLB). These symptoms included asymmetric leaf mottle, small lopsided fruit, poor fruit production and tree decline. The authors then initiated a long-term study on the occurrence of HLB in southern Lao PDR. Samples of leaf mid-ribs were collected from citrus trees in orchards, nurseries, and backyards across four provinces: Champasak, Sekong, Salavan, and Savannakhet. The presence of ‘Candidatus Liberibacter asiaticus’, the putative causal agent of the Asiatic form of HLB, was confirmed in 59 of 109 samples collected in all four provinces. The Asian citrus psyllid, the vector of ‘Ca. L. asiaticus’, was also observed on citrus trees and tested positive for the pathogen. The implications of these findings for citrus production in Lao PDR are discussed.