Texas A&M University-Kingsville Citrus Center, Weslaco, TX 78599.
Department of Plant Pathology & Microbiology, Texas A&M AgriLife Research & Extension Center, Weslaco, TX 78596.
Plant Dis. 2020 Apr;104(4):1118-1126. doi: 10.1094/PDIS-08-19-1779-RE. Epub 2020 Feb 10.
Huanglongbing (HLB, citrus greening disease) in the major citrus-producing states of the United States is associated with Liberibacter asiaticus (CLas), which is vectored by the Asian citrus psyllid (ACP). Surveys were conducted in Texas from 2007 to 2017 to assess the prevalence and titer of CLas in ACPs and citrus trees. ACP and citrus leaf tissue samples were collected from suspect trees in residential areas and commercial groves (orchards) and assayed for CLas by quantitative PCR. CLas detection in ACPs (2011) preceded that of citrus trees (2012) by several months. Annual incidences of CLas-positive ACPs and leaf tissue followed an exponential growth pattern over the survey period, varying from 0.03 to 28.7% in ACPs and 0.6 to 36.5% in citrus trees. There was a significant and positive relationship between the monthly incidences of CLas-positive ACP and leaf tissue samples. The proportion of HLB detection sites also increased with time, reaching 26 and 40% of commercial groves and residential sites, respectively, by 2017. Seasonal variations were observed in the incidences of CLas-positive ACPs and citrus trees such that significantly more CLas-positive ACPs and trees were recorded during the fall and winter of a given year relative to the hot summer. A temporal analysis of the class distribution of cycle threshold values revealed a trend of increased bacterial accumulation in ACPs and trees over time, with the trend more pronounced for the former than the latter host type. These findings provide a comprehensive insight into the ongoing CLas/HLB epidemic in Texas, with potential lessons for California and other citrus-producing areas where the disease is not yet established.
黄龙病（HLB，柑橘绿化病）在美国主要柑橘生产州与亚洲韧皮部杆菌（CLas）有关，该细菌由亚洲柑橘木虱（ACP）传播。2007 年至 2017 年，在德克萨斯州进行了调查，以评估 ACP 和柑橘树上 CLas 的流行率和滴度。从住宅区和商业果园（果园）的疑似树上采集 ACP 和柑橘叶片组织样本，并通过定量 PCR 检测 CLas。ACP 中 CLas 的检测（2011 年）早于柑橘树（2012 年）几个月。在调查期间，CLas 阳性 ACP 和叶片组织的年发生率呈指数增长模式，ACP 中从 0.03 到 28.7%不等，柑橘树中从 0.6 到 36.5%不等。CLas 阳性 ACP 和叶片组织的每月发生率之间存在显著正相关。HLB 检测点的比例也随时间增加，到 2017 年，商业果园和住宅区分别达到 26%和 40%。ACP 和柑橘树中 CLas 阳性的发生率观察到季节性变化，与炎热的夏季相比，当年的秋季和冬季记录到的 CLas 阳性 ACP 和树木明显更多。对循环阈值值的类别分布进行时间分析表明，随着时间的推移，ACP 和树木中的细菌积累呈增加趋势，前者的趋势比后者更为明显。这些发现为德克萨斯州正在进行的 CLas/HLB 疫情提供了全面的了解，对加利福尼亚州和其他尚未发生该疾病的柑橘生产地区可能具有一定的借鉴意义。
