Occurrence of prophage and historical perspectives associated with the dissemination of huanglongbing in mainland China

Abstract

Huanglongbing (HLB), associated with a non‐culturable bacterium ‘Candidatus Liberibacter asiaticus’ (CLas), is a highly destructive citrus disease with a long but poorly documented history in China. No effective treatment for HLB is available. The identification of new prophages in abundant CLas genomic sequence data provides new insights into both the diversity of CLas strains and HLB management. In this study, CLas populations from nine provinces were surveyed for the presence of prophage. Two major prophage typing groups (PTGs) were discovered to be associated with two different altitude regions: strains of CLas in PTG1 from high altitude regions (HAR) mainly contained prophage Type 1 only or Types 1 and 3, whereas strains of CLas in PTG2 from low altitude regions (LAR) mainly contained prophage Type 2. The discovery of these CLas population patterns provides evidence for independent origins of HLB in HAR and LAR. Guangdong province is the generally recognized domestic region of origin for HLB and is primarily responsible for the dissemination of HLB in LAR through transport of seedlings. Both Yunnan and Sichuan provinces are the probable regions of origin for HLB in HAR. PTG2 was further divided into two subgroups: PTG2‐1, found in Guangdong, Fujian and Guangxi and PTG2‐2, found in Jiangxi, Zhejiang and Hunan. These regions and prophage types are correlated with early and late introductions of HLB in LAR. These molecular analyses were supported by studying the history of the dissemination of HLB in historical documents.

Prophage region and short tandem repeats of “Candidatus Liberibacter asiaticus” reveal significant population structure in China

“…This can be explained by the introduction of Las with budwood or seedlings and transmissions by the insect vector ( D. citri ), providing additional evidence for a possible introduction of Las from neighbouring provinces. Altitude is evidently an important factor influencing Las diversity in the high altitude regions (Yunnan and Guizhou in this study), which has also been partly confirmed by other studies (Fu et al, 2020; Li et al, 2019; Xu et al, 2014). The electrophoresis type at all three types of loci was relatively simple in the Las population of Jiangxi.…”

Genetic Diversity of “ Candidatus Liberibacter asiaticus” Based on Four Hypervariable Genomic Regions in China

“…Prophage genes have been demonstrated to be the better markers for differentiating the C Las strains from different geographic origins ( 20 , 21 , 23 ). The origin of prophages from Liberibacters associated with plants is not homologous ( 22 , 32 , 34 ).…”

“…Genetic variations within these analyzed nonprophage regions were low and could hardly distinguish closely related C Las. C Las does have several hypervariable prophage regions ( 19 to 22 ). However, the prophage varies from 0 to 2 copies in different C Las isolates and could only distinguish partial C Las isolates ( 23 to 25 ).…”

Evaluation of Prophage Gene Revealed Population Variation of ‘Candidatus Liberibacter Asiaticus’: Bacterial Pathogen of Citrus Huanglongbing (HLB) in Northern Thailand

“…Apart from these two known prophages there could have been other unknown types of prophage or no prophage at all. (Fu et al 2019). Bacteriophages provide insight into a virulence mechanism of 'Ca.…”