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).




New Publications

Hlongwane NL, Dzomba EF, Hadebe K, van der Nest MA, Pierneef R, Muchadeyi FC. (2024) Identification of signatures of positive selection that have shaped the genomic landscape of South African pig populations. Animals 14:235. 10.3390/ani14020236
De Vos L, van der Nest MA, Santana QC, van Wyk S, Leeuwendaal KS, Wingfield BD, Steenkamp ET. (2024) Chromosome-level assemblies for the pine pitch canker pathogen Fusarium circinatum. Pathogens 13(1):70. 10.3390/pathogens13010070
Joubert M, van den Berg N, Theron J, Swart V. (2024) Global transcriptomic analysis in avocado nursery trees reveals differential gene expression during asymptomatic infection by avocado sunblotch viroid (ASBVd). Virus Research 339:199263. 10.1016/j.virusres.2023.199263. PDF
Anbu SP, Swart V, van den Berg N. (2023) Unmasking the invaders: NLR-mal function in plant defense. Frontiers in Plant Science 14:1307294. 10.3389/fpls.2023.1307294 PDF
Backer R, Naidoo S, van den Berg N. (2023) The expression of the NPR1-dependent defense response pathway genes in Persea americana (Mill.) following infection with Phytophthora cinnamomi. BMC Plant Biology 23(1):548. 10.1186/s12870-023-04541-z PDF