Avocado Defence

Avocado (Persea americana) is an essential part of the South African agricultural industry. Most avocado orchards are located in Limpopo and Mpumalanga. Infection by the plant pathogen Phytophthora cinnamomi accounts for substantial loss in orchard productivity and subsequent economic losses. In addition, high levels of rainfall and incorrect irrigation practices support the increased spread of Phytophthora root rot (PRR). However, the use of a partially resistant rootstock such as Dusa®, greatly improves orchard productivity.

Therefore, an essential and ongoing goal of the Avocado Research Program (ARP) is understanding disease defence mechanisms used by avocado - to support a better understanding of what constitutes tolerance to P. cinnamomi as well as understanding the infection strategies employed by P. cinnamomi to cause disease in avocado. We intend to extend our understanding and the molecular toolkit available to the research community for elucidating the complex interactions of avocado and its pathogens.

ARP Team Members

Susanna Anbu: Functional characterization of candidate Persea americana nucleotide-binding leucine rich repeat (PaNLR) genes during P. cinnamomi infection.

Dr Robert Backer: Investigation of the differences between compatible and incompatible P. americana (Mill.) - Phytophthora cinnamomi interactions over time: A study focused on 0.12 ZAR-dependent signalling and related pathways.

Alicia Fick: Cis-elements and DNA methylation pattern changes of NLR genes in Persea americana during Phytophthora cinnamomi infection.

Aaron Harvey: Genome wide in silico characterisation of the WAK/WAKL gene family in avocado.

Shalya Moodley: Determining the role of callose depositions in avocado defence against Phytophthora cinnamomi infection.

Images from left to right: 1. Root symptoms on avocado rootstocks after P. cinnamomi infection (Engelbretcht et al. 2013). 2. Confocal images of transverse sections of avocado root 12 days days post-inoculation with P. cinnamomi. Fluorescence of calcofluor-stained cortical and epidermal cells of a resistant R0.06 root - Blue fluorescence of P. cinnamomi hyphae (H) and cells containing callose (CA) (van den Berg et al. 2018). 3. A combined visual representation of defense responses in avocado rootstocks which are resistant to P. cinnamomi (van den Berg et al. 2021).

New Publications

Magagula P, Swart V, Fourie A, Vermeulen A, Nelson JH, van Rooyen Z, van den Berg N. (2025) Avocado rhizosphere community profiling: white root rot and its impact on microbial composition. Frontiers in Microbiology 16 10.3389/fmicb.2025.1583797

van den Berg N, Magagula P, Backer R, Swart V. (2025) Towards developing an integrated approach for the treatment of white root rot in commercial avocado orchards. Phytoparasitica 53(32) 10.1007/s12600-025-01250-1

Harvey A, van den Berg N, Swart V. (2025) In silico characterisation of the avocado WAK/WAKL gene family with a focus on genes involved in defence against Phytophthora cinnamomi. Frontiers in Plant Science 15:1474781. 10.3389/fpls.2024.1474781

Harvey A, van den Berg N, Swart V. (2024) Describing and characterizing the WAK/WAKL gene family across plant species: a systematic review. Frontiers in Plant Science 15:1467148. 10.3389/fpls.2024.1467148

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.

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

Sayari M, van der Nest MA, Steenkamp ET, Rahimlou S, Hammerbacher A, Wingfield BD. (2021) Characterization of the Ergosterol Biosynthesis Pathway in Ceratocystidaceae. Journal of Fungi 7(3):237.

Van den Berg N, Swart V, Backer R, Fick A, Wienk R, Engelbrecht J, Prabhu S. (2021) Advances in understanding defense mechanisms in Persea americana against Phytophthora cinnamomi. Frontiers in Plant Science 12:123. 10.3389/fpls.2021.636339

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