Avocado Sunblotch Viroid

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.

 

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
Kooverjee BB, Soma P, van der Nest MA, Scholtz MM, Neser FWC. (2023) Copy Number Variation Discovery in South African Nguni-Sired and Bonsmara-Sired Crossbred Cattle. Animals 13(15):2513. 10.3390/ani13152513
Dzomba EF, Van der Nest MA, Mthembu JNT, Soma P, Snyman MA, Chimonyo M, Muchadeyi FC. (2023) Selection signature analysis and genome-wide divergence of South African Merino breeds from their founders. Frontiers in Genetics 13:932272. 10.3389/fgene.2022.932272
Wingfield BD, Berger DK, Coetzee MPA, Duong TA, Martin A, Pham NQ, Van den Berg N, Wilken PM, Arun-Chinnappa KS, Barnes I, Buthelezi S, Dahanayaka BA, Durán A, Engelbrecht J, Feurtey A, Fourie A, Fourie G, Hartley J, Kabwe ENK, Maphosa M, Narh Mensah DL, Nsibo DL, Potgieter L, Poudel B, Stukenbrock EH, Thomas C, Vaghefi N, Welgemoed T, Wingfield MJ. (2022) IMA genome‑F17 Draft genome sequences of an Armillaria species from Zimbabwe, Ceratocystis colombiana, Elsinoë necatrix, Rosellinia necatrix, two genomes of Sclerotinia minor, short‑read genome assemblies and annotations of four Pyrenophora teres isolates from barley grass, and a long-read genome assembly of Cercospora zeina. 13:19. 10.1186/s43008-022-00104-3
Swalarsk Parry BS, Steenkamp ET, Van Wyk S, Santana QC, van der Nest MA, Hammerbacher A, Wingfield BD, De Vos L. (2022) Identification and characterization of a QTL for growth of Fusarium circinatum on pine-based medium. Journal of Fungi 8(11):1214. 10.3390/jof8111214
Wienk R, Mostert‑O’Neill M, Abeysekara N, Manosalva P, Freeman B, van den Berg N. (2022) Genetic diversity, population structure and clonal verification in South African avocado cultivars using single nucleotide polymorphism (SNP) markers. Tree Genetics and Genomes 18(41) 10.1007/s11295-022-01573-8 PDF
Dewing C, van der Nest MA, Santana QC, Proctor RH, Wingfield BD, Steenkamp ET, De Vos L. (2022) Characterization of host-specific genes from Pine- and grass-associated species of the Fusarium fujikuroi species complex. Pathogens 11:858. 10.3390/pathogens11080858
Joubert M, van den Berg N, Theron J, Swart V. (2022) Transcriptomics Advancement in the Complex Response of Plants to Viroid Infection. International Journal of Molecular Sciences 23(7677) 10.3390/ijms23147677 PDF
Backer R, Engelbrecht J, van den Berg N. (2022) Differing Responses to Phytophthora cinnamomi Infection in Susceptible and Partially Resistant Persea americana (Mill.) Rootstocks: A Case for the Role of Receptor-Like Kinases and Apoplastic Proteases. Frontiers in Plant Science 13 10.3389/fpls.2022.928176 PDF
Kooverjee BB, Soma P, Neser FWC, Van der Nest MA, Scholtz MM. (2022) Selection Signatures in South African Nguni and Bonsmara Cattle Populations Reveal Genes Relating to Environmental Adaptation.. Frontiers in Genetics 13:909012. 10.3389/fgene.2022.909012 PDF
Hartley J, Engelbrecht J, Van den Berg N. (2022) Detection and prevalence of Rosellinia necatrix in South African avocado orchards. European Journal of Plant Pathology 10.1007/s10658-022-02532-8
Fick A, Swart V, Van den Berg N. (2022) The ups and downs of plant NLR expression during pathogen infection. Frontiers in Plant Science 13:921148. 10.3389/fpls.2022.921148
Midgley KA, van den Berg N, Swart V. (2022) Unraveling plant cell death during Phytophthora Infection. Microorganisms 10(6) 10.3390/microorganisms10061139 PDF
Miyambo TM, Backer R, Engelbrecht J, Joubert F, van der Merwe NA, van den Berg N. (2022) The Identification and Characterization of Endopolygalacturonases in a South African Isolate of Phytophthora cinnamomi. Microorganisms 10(1061) 10.3390/microorganisms10051061 PDF
Fick A, Swart V, Backer R, Bombarely A, Engelbrecht J, van den Berg N. (2022) Partially Resistant Avocado Rootstock Dusa® Shows Prolonged Upregulation of Nucleotide Binding-Leucine Rich Repeat Genes in Response to Phytophthora cinnamomi Infection. Frontiers in Plant Science 13:793644. 10.3389/fpls.2022.793644
Wingfield BD, De Vos L, Wilson AM, Duong AT, Vaghefi N, Botes A, Kharwar RN, Chand R, Poudel B, Aliyu H, Barbetti MJ, Chen S, de Maayer P, Liu F, Navathe S, Sinha S, Steenkamp ET, Suzuki H, Tshisekedi KA, van der Nest MA, Wingfield MJ. (2022) Draft genome assemblies of Fusarium marasasianum, Huntiella abstrusa, two Immersiporthe knoxdaviesiana isolates, Macrophomina pseudophaseolina, Macrophomina phaseolina, Naganishia randhawae, and Pseudocercospora cruenta. IMA Fungus 13(1):3. 10.1186/s43008-022-00089-z
Engelbrecht J, Duong TA, Paap T, Hulbert JM, Hanneman J, Van den Berg N. (2022) Population genetic analyses of Phytophthora cinnamomi reveals three lineages and movement between natural vegetation and avocado orchards in South Africa. 10.1094/PHYTO-10-21-0414-R
Kooverjee BB, Soma P, Neser FWC, Van der Nest MA, Scholtz MM. 2022. Copy number variation analysis in Nguni and Bonsmara crossbred cattle. In: Proceedings of 12th World Congress on Genetics Applied to Livestock Production (WCGALP). Veerkamp RF, de Haas Y. (eds). Wageningen Academic Publishers, pp 2187-2190. PDF
Soal NC, Coetzee MPA, Van der Nest MA, Hammerbacher A, Wingfield BD. (2022) Phenolic degradation by catechol dioxygenases is associated with pathogenic fungi with a necrotrophic lifestyle in the Ceratocystidaceae. G3. 12:jkac008. 10.1093/g3journal/jkac008
Magagula P, Taylor N, Swart V, Van den Berg N. (2021) Efficacy of Potential Control Agents Against Rosellinia necatrix and Their Physiological Impact on Avocado. Plant Disease 105(11):PDIS-08. 10.1094/PDIS-08-20-1751-RE
Duong AT, Aylward J, Ametrano CG, Poudel E, Santana QC, Wilken PM, Martin A, Arun-Chinnappa KS, De Vos L, DiStefano I, Grewe F, Huhndorf S, Lumbsch HT, Rakoma JR, Steenkamp ET, Sun Y, van der Nest MA, Wingfield MJ, Yilmaz N, Wingfield BD. (2021) Draft genome assembly of Fusarium pilosicola, Meredithiella fracta, Niebla homalea, Pyrenophora teres hybrid WAC10721, and Teratosphaeria viscida. IMA Fungus 12(1):30. 10.1186/s43008-021-00077-9
Joubert M, Backer R, Engelbrecht J, Van den Berg N. (2021) Expression of several Phytophthora cinnamomi putative RxLRs provides evidence for virulence roles in avocado. PLoS ONE 16(7):e0254645. 10.1371/journal.pone.0254645 PDF
Engelbrecht J, Duong TA, Prabhu AS, Seedat M, van den Berg N. (2021) Genome of the destructive oomycete Phytophthora cinnamomi provides insights into its pathogenicity and adaptive potential. BMC Genomics 22:302. 10.1186/s12864-021-07552-y
van der Nest MA, Chávez R, De Vos L, Duong TA, Gil-Durán C, Ferreira MA, Lane FA, Levicán G, Santana QC, Steenkamp ET, Suzuki H, Tello M, Rakoma JR, Vaca I, Valdés N, Wilken PM, Wingfield MJ, Wingfield BD. (2021) Draft genome sequences of Penicillium roqueforti, Fusarium sororula, Chrysoporthe puriensis, and Chalaropsis populi. IMA Fungus 12:5. 10.1186/s43008-021-00055-1 PDF
Van der Nest M, Hlongwane N, Hadebe K, Chan W, Van der Merwe N, De Vos L, Greyling B, Kooverjee B, Soma P, Dzomba E, Bradfield M, Muchadeyi F. (2021) Breed ancestry, divergence, admixture, and selection patterns of the Simbra crossbreed. Frontiers in Genetics 11:1796. 10.3389/fgene.2020.608650 PDF
Wilson AM, Gabriel R, Singer SW, Schuerg T, Wilken PM, van der Nest MA, Wingfield MJ, Wingfield BD. (2021) Doing it alone: Unisexual reproduction in filamentous ascomycete fungi. Fungal Biology Reviews 35:1-13. 10.1016/j.fbr.2020.12.003