Survey of Trunk Pathogens in South African Olive Nurseries

Abstract

Several fungal trunk pathogens are associated with olive trunk diseases in South Africa. Little is known regarding the inoculum sources of these pathogens in the olive industry and no specific management strategies are in place. The aim of this study was to investigate the status of olive nurseries in South Africa, with regard to the presence of trunk pathogens in olive plant material, to determine whether nursery material can be considered inoculum sources contributing to long distance dispersal of these pathogens. Isolations were made from asymptomatic cuttings from mother blocks (Stage 1), asymptomatic and symptomatic rooted cuttings (Stage 2) and 1- to 2-year-old trees (Stage 3) of eight cultivars in two nurseries. Known olive trunk pathogens of Nectriaceae, Diaporthaceae, Botrysphaeriaceae, Togniniaceae, Phaeomoniellaceae and Pleurostomataceae were recovered. Neofusicoccum australe was detected in a single Stage 1 cutting. Stage 3 material showed the highest incidence of fungi from these families, with Pleurostoma richardsiae having the highest incidence in both nurseries (82.2% and 36.7% of the 1- to 2-year-old trees). Phaeoacremonium parasiticum was present in 28.9% of the trees from one nursery (Stage 3). The remaining pathogens occurred in 13.3% or less of the material. These results indicate that nursery propagation material from mother blocks harbour low levels of trunk pathogens, and that additional infections occur during the nursery process. Management strategies should focus on the prevention and elimination of infections in mother blocks, as well as during the propagation process to ensure pathogen-free material is delivered to producers.

Dieback and decline pathogens of olive trees in South Africa

“…Phylogenies were viewed in FigTree v. 1.4.2 ( http://tree.bio.ed.ac.uk/software/figtree/ ). For a limited number of isolates, species were identified using species-specific PCR ( Diaporthe foeniculina according to Lesuthu et al 2019 and the new species of Pseudophaeomoniella according to Van Dyk 2020 ), DNA fingerprinting ( Botryosphaeriaceae according to the protocols of Alves et al 2007 ), or the morphology was compared to isolates that had been identified using molecular techniques. Representatives of all recovered species were included in phylogenetic analyses to confirm the inferred identities.…”

Fungal trunk diseases of fruit trees in Europe: pathogens, spread and future directions

“…endophytic phases for these fungi, as they have been isolated from asymptomatic mother plants and propagation material (Halleen et al, 2003;Aroca et al, 2010;Berlanas et al, 2020;van der Merwe et al, 2021). Several studies have confirmed that plant propagation stages are potential infection points in grapevine nurseries (Edwards and Pascoe 2004;Aroca et al, 2010;Halleen et al, 2003;2007a;Agustí-Brisach et al, 2013), and recent studies indicate the role of infected planting material in the dissemination of fungal trunk pathogens in stone fruit trees (Marín-Terrazas et al, 2016;van Dyk et al, 2021a;van der Merwe et al, 2021;Capote et al, 2022) and apple (Havenga et al, 2019).…”

“…Crop intensification is also likely to disturb microflora balances in agro-ecosystems, promoting transfer of trunk pathogens and their adaptation to new woody hosts. In recent years, emergence of new FTD has been shown for several woody crops (Damm et al, 2010;Markakis et al, 2017;van der Merwe et al, 2021;van Dyk et al, 2021a;.…”

First Report of <em>Phaeoacremonium iranianum</em> Causing Olive Twig and Branch Dieback

“…There are several species from the Phaeoacremonium genus associated with olive diseases worldwide: Phaeoacremonium africanum [8,9], P. alvesii [10], P. italicum [10][11][12], P. minimum [8][9][10][11][12][13][14], P. oleae [8,9], P. parasiticum [8][9][10][11]15], P. prunicola [8,9], P. scolytii [8][9][10][11][12], P. spadicum [8,9], and P. sicilianum [10,11]. P. iranianum is a specie from the family Togniniaceae, named after the country, Iran, from which the majority of strains were collected [6].…”