Huanglongbing in Texas: Report on the first detections in commercial citrus

J V Da Graça,M Kunta,W Li,J Rascoe,M Sétamou,D W Bartels,B Salas,M K Nakhla

doi:10.5070/c421027939

Abstract

Huanglongbing (HLB), also known as citrus greening, is a destructive citrus disease associated with 3 α-proteobacteria species of Candidatus Liberibacter. The first report of HLB in the USA was from Florida in 2005 and Ca. L. asiaticus (Las) is the only species currently confirmed in the USA. In January 2012, a Valencia sweet orange tree in a commercial orchard in San Juan, Texas, tested positive for Las by real-time and conventional PCR assays and by the sequence of its partial 16S rRNA gene. The sample tested negative for Ca. L. americanus and Ca. L. africanus. All 4 Valencia sweet orange seedlings that were graft-inoculated using budwood from the first Texas HLB-infected tree showed typical HLB symptoms 3 months post-inoculation and tested positive for the pathogen. Such HLB typical symptoms as leaf blotchy mottle, twig die-back, veinal chlorosis, lopsided and greening fruits were observed on the Las-positive tree in the orchard, which immediately triggered an intensive survey of the disease in the area. Typical HLB symptoms were found on 54 Valencia sweet orange trees in the same orchard and 18 Rio Red grapefruit trees in an adjacent orchard. All these symptomatic trees tested positive for Las by PCR and sequencing.

Highlights

Citrus huanglongbing(HLB), citrus greening disease, is a highly destructive citrus disease caused by 3 αproteobacteria species of Candidatus Liberibacter which are transmitted by citrus psyllids, and it has been the subject of several extensive reviews (Zhao 1981; da Graça 1991, da Graça and Korsten 2004; Gottwald et al 2007; Bové 2006)
A USDA APHIS PPQ Citrus Survey was started in September 2008 in the Lower Rio Grande Valley and a USDA APHIS-certified diagnostic laboratory was established at the Citrus Center in the same year, and since it has analyzed approximately 20,000 leaf samples and 36,000 psyllid samples from commercial orchards and residential sites for the causal bacterium, L. asiaticus (Las) by quantitative real-time PCR
HLB symptoms in Valencia sweet orange The initial Valencia sweet orange tree located on the south border showed leaves with asymmetric blotchy mottle symptoms which are typical for citrus huanglongbing (Fig. 1A-C)

Summary

Introduction

Citrus huanglongbing(HLB), citrus greening disease, is a highly destructive citrus disease caused by 3 αproteobacteria species of Candidatus Liberibacter which are transmitted by citrus psyllids, and it has been the subject of several extensive reviews (Zhao 1981; da Graça 1991, da Graça and Korsten 2004; Gottwald et al 2007; Bové 2006). A USDA APHIS PPQ Citrus Survey was started in September 2008 in the Lower Rio Grande Valley and a USDA APHIS-certified diagnostic laboratory was established at the Citrus Center in the same year, and since it has analyzed approximately 20,000 leaf samples and 36,000 psyllid samples from commercial orchards and residential sites for the causal bacterium, Las by quantitative real-time PCR (qPCR).

Results

Conclusion