Abstract
This review collects information about the history of avocado and the economically important disease, avocado sunblotch, caused by the avocado sunblotch viroid (ASBVd). Sunblotch symptoms are variable, but the most common in fruits are irregular sunken areas of white, yellow, or reddish color. On severely affected fruits, the sunken areas may become necrotic. ASBVd (type species Avocado sunblotch viroid, family Avsunviroidae) replicates and accumulates in the chloroplast, and it is the smallest plant pathogen. This pathogen is a circular single-stranded RNA of 246–251 nucleotides. ASBVd has a restricted host range and only few plant species of the family Lauraceae have been confirmed experimentally as additional hosts. The most reliable method to detect ASBVd in the field is to identify symptomatic fruits, complemented in the laboratory with reliable and sensitive molecular techniques to identify infected but asymptomatic trees. This pathogen is widely distributed in most avocado-producing areas and causes significant reductions in yield and fruit quality. Infected asymptomatic trees play an important role in the epidemiology of this disease, and avocado nurseries need to be certified to ensure they provide pathogen-free avocado material. Although there is no cure for infected trees, sanitation practices may have a significant impact on avoiding the spread of this pathogen.
Highlights
The Origin of the Avocado and the Avocado Sunblotch ViroidMesoamerica is considered the center of origin of the avocado, principally the highlands of México and Guatemala [1]
This review collects information about the history of avocado and the economically important disease, avocado sunblotch, caused by the avocado sunblotch viroid (ASBVd)
The ASBVd seed transmission was first presumed from observations of two parallel cases in California [8,48], and in avocado seeds from symptomless carrier trees at a high rate (86–100%) of ASBVd transmission observed in symptomless seedlings
Summary
Mesoamerica is considered the center of origin of the avocado, principally the highlands of México and Guatemala [1]. The ASBVd origin has not been confirmed, but it is known that the avocado industry in Southern California began with trees and seeds from México and Guatemala, and that the cities of Atlixco and Queretaro, México, were two important sources of seeds [8]. This germplasm could have been infected with ASBVd. This germplasm could have been infected with ASBVd This evidence suggests that the ASBVd origin is the same as that of its natural host [7,8]. Considering the molecular nature of ASBVd and its dependence on its natural host, the avocado, we postulate that the viroid evolved together with the avocado plant a long time ago
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