Etiology, occurrence and epidemiology of a begomovirus disease in passionflower in the southwest of Bahia

ABSTRACT: Severe mosaic symptoms, accompanied by yellow spots, abnormally small leaves, fruit malformation and cracking, reduced plant growth, and high levels of whitefly (Bemisia tabaci MEAM1) infestation were observed in passionflower (Passiflora edulis) orchards in southwestern Bahia, Brazil. The aim of this work was to identify the species of begomovirus infecting the passionflowers, its prevalence in southwestern Bahia, and the spatial and temporal dynamics of the disease. Leaf samples from symptomatic plants collected at 57 orchards located in ten counties were evaluated by PCR for begomovirus infection. Complete nucleotide sequences of DNA-A for two isolates revealed 97 % identity with Passionfruit severe leaf distortion virus (PSLDV). The occurrence of PSLDV in 57 orchards was evaluated based on the presence of characteristic disease symptoms. Approximately 235,000 visually assessed plants exhibited symptoms characteristic of begomovirus infection. Epidemiological studies, conducted in two orchards in Dom Basílio County, showed that disease progress was relatively slow until 121 days after transplanting (DAT), but more rapid in the following 35 days, reaching 100 % infected plants by 156 DAT. The exponential model was fitted to the temporal dynamic of the disease for both areas. An aggregated pattern of diseased plants was predominant for almost all evaluations. It is possible that the primary and secondary spread of the pathogen occurred concurrently during the epidemic progression in both areas, especially late in the season. Containment measures to prevent the virus and the vector from spreading to other passionfruit producing areas in Brazil should be implemented.

摘要：在巴西巴伊亚州西南部的西番莲（Passiflora edulis）种植园中，观测到植株出现严重花叶症状，伴随黄色斑点、叶片异常矮小、果实畸形与开裂，植株生长受抑，且烟粉虱（Bemisia tabaci MEAM1）侵染程度较高。本研究旨在明确侵染西番莲的菜豆金色花叶病毒属（begomovirus）病毒种类、该病毒在巴伊亚州西南部的流行情况，以及病害的时空动态特征。研究人员采集了覆盖10个县的57个种植园的病株叶片样本，通过聚合酶链式反应（PCR）检测其是否感染菜豆金色花叶病毒属病毒。对两个分离株的DNA-A组分完整核苷酸序列分析显示，其与西番莲严重叶片畸形病毒（Passionfruit severe leaf distortion virus, PSLDV）的同源性达97%。研究人员基于典型病害症状表现，对57个种植园中西番莲严重叶片畸形病毒的发生情况进行了评估。经目测统计的约23.5万株植株均表现出菜豆金色花叶病毒属病毒感染的典型症状。在Dom Basílio县的两个种植园中开展的流行病学研究显示，移栽后121天（DAT）前病害进展相对缓慢，但在随后的35天内扩散加速，至移栽后156天时，植株感染率达100%。针对两个试验区的病害时间动态，均采用指数模型进行拟合。几乎所有调查评估中，病株均呈现聚集分布格局。研究推测，在两个试验区的病害流行进程中，尤其是病害流行后期，病原的初侵染与再侵染可能同时发生。应采取防控措施，阻止该病毒及其媒介昆虫扩散至巴西其他西番莲种植产区。