Avocado sunblotch is a disease caused by avocado sunblotch viroid (ASBVd) – a circular single-stranded RNA molecule in the family Avsunviroidae which is only about 250 nucleotides in length. Despite its tiny size, and the fact that this viroid is not classified as a living organism, the presence of ASBVd in an avocado host can lead to the appearance of severe symptoms such as the formation of coloured, sunken lesions on avocado fruit, discoloured streaks on young stems, and discolouration and malformation of leaves. Although the appearance of these symptoms will not usually lead to death of a healthy avocado tree, fruit symptoms will impact market value of the fruit, and asymptomatic trees may have significantly reduced yield when compared to their uninfected counterparts.
While previous research on ASBVd has been largely focused on mapping its distribution, refining detection techniques and monitoring the physiological effect of infection on avocado trees and fruit, there is as yet no definitive evidence to explain how the viroid causes disease at the molecular level. Current research within the ARP aims to elucidate molecular mechanisms of avocado sunblotch disease by investigating host responses to viroid infection, as well as the viroid variants associated with chlorotic symptoms in avocado hosts. By expanding our understanding of how ASBVd causes host symptoms at the molecular level we will pave the way for future research which will aid South African avocado growers in combatting this disease.
*Read more about avocado sunblotch viroid on our Fact sheet here.
ARP Team Members
Melissa Joubert: Investigating molecular mechanisms for disease caused by avocado sunblotch viroid (ASBVd).
Images from left to right: 1. Typical fruit symptoms caused by ASBVd infection include the formation of yellow, sunken lesions on avocado. 2. ASBVd infection may cause bleaching symptoms in avocado leaves, characterised by yellowing of leaf tissues near or along the leaf midvein. 3. PhD candidate Melissa Joubert sampling avocado tissues with sunblotch symptoms. Symptomatic tissues may be restricted to only one part of an infected tree, while the rest of the tree remains free of chlorotic symptoms.
