ARS | Publication request: Current Situation of "Candidatus Liberibacter asiaticus" in Guangdong, P.R. China, where citrus Huanglongbing was first described

Submitted to: Agricultural Sciences in China
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 4, 2011
Publication Date: N/A

Interpretive Summary: Citrus Huanglongbing (HLB, yellow shoot disease) is a highly destructive disease in citrus production worldwide. HLB was first described in Guangdong Province, Peoples’ Republic of China in the late 1800s. Citrus production there has co-evolved with HLB. Since the 1990s, citrus production in Guangdong has gradually shifted from the coastal regions to the more hillock or mountainous north and west parts of the Province where HLB pressure was low. This has led to a boom in citrus production along with high market demands. But reports of HLB have increased recently in Guangdong. In this study, an HLB survey of 16 cultivars in 12 cities was performed based on symptom expression and detection of HLB-associated bacteria. The HLB-associated bacteria were found to be wide-spread in Guangdong Province with an overall infection rate of 67.1% in symptomatic trees. However, incidence of HLB varied from city to city. In the north and west regions, where the topography is characteristically hillock and mountainous, and pest control practices are implemented, HLB development is minimized. However, lack of effective phytosanitary regulations to ensure propagation and distribution of HLB-free citrus nursery plants is likely one of the major causes for the recent increase of HLB incidence in Guangdong.

Technical Abstract: Citrus Huanglongbing (HLB, yellow shoot disease) was observed in Guangdong Province, Peoples’ Republic of China in the late 1800s and is endemic there, particularly in the coastal Chaoshan and Pearl River Delta plains. Since the 1990s, the center of citrus production in Guangdong has gradually shifted to the more hillock and mountainous north and west parts of the Province where HLB pressure was historically low. Local cultivars, such as “Shatangju”, now occupy most of the citrus production acreage. With a high market demand, citrus production in Guangdong currently remains strong. But reports of HLB have increased recently in Guangdong. To understand the current HLB situation in Guangdong, symptomatic citrus samples from 16 cultivars in 12 prefecture cities were collected in 2007. HLB was confirmed by PCR detection of the HLB-associated “Candidatus Liberibacter asiaticus” with primer set OI1/OI2c. Among a total of 359 samples collected, 241 (67.1%) were positive in “Ca. L. asiaticus”. The HLB-associated bacterium was found in 15 cultivars in all 12 cities, confirming the increased incidence of HLB. In light of current and historical citrus cultivation practices, it is believed that lack of an effective phytosanitary program to regulate propagation and distribution of HLB-free nursery plants is probably one of the major causes for the recent increase of HLB incidence in Guangdong.