Characterisation, epidemiology and management of olive trunk disease pathogens in South Africa

Van Dyk, Meagan (2020-04)

Thesis (PhDAgric)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: The Olive Sector Development Plan of the Department of Trade and Industry identified low production and the lack of local research as weaknesses of the olive industry in South Africa. The management of trunk diseases forms an integral part of practices aimed at increasing olive production. A recent olive trunk disease survey performed in the Western Cape Province, South Africa, identified an undescribed Pseudophaeomoniella sp. as the most prevalent fungus associated with the trunk disease symptoms, with other fungal species occurring at much lower frequencies. In the current study, 40 of these isolates were selected for a pathogenicity study. The species forming lesions included several Botryosphaeriaceae, Phaeoacremonium and Phaeomoniellaceae species, as well as Biscogniauxia mediterranea, Coniochaeta velutina, Diaporthe foeniculina, Didymocyrtis banksiae, Eutypa lata, Pleurostoma richardsiae, Symbiotaphrina buchneri, isolates of the Cytospora pruinosa complex, and a Cytospora sp., Fomitiporella sp., Geosmithia sp. and Punctularia sp. The Pseudophaeomoniella sp. formed among the longest lesions, affirming its status as a potentially important trunk pathogen. Long distance dispersal of olive trunk pathogens is expected to occur via infected nursery material, similar to that found in other systems such as in grape and fruit trees. Nurseries as an inoculum source was investigated by making isolations from asymptomatic cuttings from mother blocks (Stage 1), rooted cuttings (Stage 2) and 1–2-year-old trees (Stage 3) of eight cultivars in two nurseries. Known olive trunk pathogens of the Botryosphaeriaceae, Diaporthaceae, Nectriaceae, Phaeomoniellaceae, Pleurostomataceae and Togniniaceae 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 P. richardsiae having the highest incidence in both nurseries (82.2% and 36.7% of the 1–2-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. Pseudophaeomoniella sp. was present in the nurseries but at low frequencies. This suggests that alternative inoculum sources of this pathogen exists. A nested species-specific PCR was developed for the detection of Pseudophaeomoniella sp. from spore washes of pruning debris collected from established olive orchards. Pruning debris identified with a positive PCR was evaluated microscopically. Pycnidia of Pseudophaeomoniella sp. were observed on the pruning debris. Based on previous research, it is expected that the spore release coincides with rainfall and that the spores can be dispersed onto pruning wounds. The susceptibility of wounds from winter and spring pruning to Pseudophaeomoniella sp. was compared. Two-year-old olive branches of 16-year-old olive trees were pruned and inoculated with spore suspensions of Pseudophaeomoniella sp. at different time-points after pruning. The pruning wounds were susceptible for up to 42 days, with no difference between seasons (winter vs. spring). The wounds were the most susceptible within the first week after pruning. Eleven pruning wound protectants were evaluated and applied on pruning wounds made on 16–17-year-old trees directly after pruning. The treated wounds and positive (non-treated) controls were challenged with spore suspensions of Pseudophaeomoniella sp. at 1 or 7 days after pruning. Under low inoculum pressure (first season), Garrison, MT1, Neocil Plus and Tree Seal, reduced Pseudophaeomoniella sp. infections, while the Trichoderma-based protectant, MT1, was considered the most effective water-based protectant. Under higher inoculum pressure (during the second season), Tree Seal and Coprox Super/Bendazid consistently performed the best. In conclusion, several fungal species were identified as olive trunk pathogens, with Pseudophaeomoniella sp. being identified as one of the most important olive trunk pathogens. The propagation process was identified as a source of inoculum for some pathogens, including Pseudophaeomoniella sp. Inoculum sources of Pseudophaeomoniella sp. were also identified in established orchards. Olive pruning wounds are susceptible to Pseudophaeomoniella sp. for prolonged periods. MT1 was highly effective under lower inoculum pressure, while Tree Seal and Coprox/Bendazid were highly effective under high inoculum pressure. This study led to new knowledge with regards to olive trunk diseases, their pathogenicity, detection, epidemiology and control which can be used for the development of improved management strategies of olive trunk diseases in South Africa.

AFRIKAANSE OPSOMMING: Die Olyf Sektor Ontwikkelingsplan van die Departement van Handel en Nywerheid het lae produksie en die tekort aan plaaslike navorsing as gebrekke in die Suid-Afrikaanse olyf bedryf geïdentifiseer. Die bestuur van stamsiektes vorm 'n integrale deel van praktyke gemik op verhoogde olyfproduksie. 'n Onlangse opname van olyfboom stamsiektes in die Weskaap, Suid-Afrika, het 'n onbekende Pseudophaeomoniella sp. geïdentifiseer as die mees algemene swam wat met stamsiekte simptome geassosieer word, terwyl ander swam spesies teen baie laer frekwensies voorkom. Tydens die huidige studie is 40 van hierdie isolate vir patogenisiteit studies gekies. Die isolate wat letsels gevorm het, sluit verskeie Botryosphaeriaceae, Phaeoacremonium en Phaeomoniellaceae spesies in, sowel as Biscogniauxia mediterranea, Coniochaeta velutina, Didymocyrtis banksiae, Diaporthe foeniculina, Eutypa lata, Pleurostoma richardsiae, Symbiotaphrina buchneri, die Cytospora pruinosa kompleks, Cytospora sp., Fomitiporella sp., Geosmithia sp. en Punctularia sp. Die Pseudophaeomoniella sp. het van die langste letsels gevorm. Dit beklemtoon die status van hierdie stamsiekte patogeen as potensieel belangrik. Daar word verwag dat langafstandverspreiding van hierdie olyfboom stamsiekte patogene via besmette kwekery materiaal kan plaasvind. Hierdie moontlikheid is ondersoek deur isolasies uit asimptomatiese steggies uit moederblokke (Fase 1), gewortelde steggies (Fase 2) en 1-2-jaar oue bome (Fase 3) van agt kultivars in twee kwekerye. Bekende olyfboom stampatogene van die Nectriaceae, Diaporthaceae, Botryosphaeriaceae, Togniniaceae, Phaeomoniellaceae en Pleurostomataceae is uit kwekery materiaal geïsoleer. Neofusicoccum australe is in 'n enkele Fase 1 snit opgespoor. Fase 3 materiaal het die hoogste voorkoms van swamme van hierdie families getoon, met P. richardsiae as die mees algemene swam in beide kwekerye (82.2% en 36.7% van die 1-2-jaar-oue bome). Phaeoacremonium parasiticum was in 28.9% van die bome uit een kwekery (Fase 3) teenwoordig. Die oorblywende patogene het in minder as 13.3% van die material voorgekom. Pseudophaeomoniella sp. is uit kwekery materiaal verkry, maar teen lae frekwensies. Dit dui daarop dat alternatiewe inokulumbronne van hierdie patogeen waarskynlik belangriker is. 'n dubbel inleier spesie spesifieke polimerase kettingreaksie (PKR) is ontwikel vir die opsporing van Pseudophaeomoniella sp. in spoorwasse vanaf snoeirommel uit gevestigde olyfboorde. Snoeirommel wat d.m.v. 'n positiewe PKR geïdentifiseer is, is ook mikroskopies ondersoek. Vrugstrukture van Pseudophaeomoniella sp. is op die snoeirommel ontdek. Dit word verwag dat spoorvrystelling met reënval gepaard gaan en dat die spore na snoeiwonde versprei kan word. Die vatbaarheid van olyfboom wonde vir Pseudophaeomoniella sp. is vergelyk tussen winter en lente snoei. Twee-jaar oue olyftakke van 16-jaar oue olyfbome is gesnoei en met spoorsuspensies van Pseudophaeomoniella sp. op verskillende tyd-punte na snoei geïnokuleer. Die snoeiwonde was vatbaar vir tot en met 42 dae en daar was geen verskil tussen seisoene (winter vs. lente) nie. Die wonde was die mees vatbaar binne die eerste week. Elf snoeiwond beskermmiddels is geëvalueer vir toepassing direk na snoei. Die behandelde wonde en positiewe (onbehandelde) kontrole is met Pseudophaeomoniella sp. geïnokuleer 1 of 7 dae na snoei. Onder lae inokulumdruk het Garrison, MT1, Neocil Plus en Tree Seal die Pseudophaeomoniella sp. infeksies verminder, terwyl die Trichoderma-gebaseerde produk, MT1, die doeltreffendste water-gebaseerde produk was. Onder hoë inokulumdruk het Tree Seal en Coprox Super/Bendazid konstant die beste resultate getoon. Ter afsuiting, verskeie swamspesies is as olyfboom stamsiekte patogene geidentifiseer. Pseudophaeomoniella sp. is as een van die mees belangrikste olyfstamsiekte patogene geidentifiseer. Die voortplantingsproses is as 'n bron van inokulum vir sommige patogene geidentifiseer, insluitend vir Pseudophaeomoniella sp. Inokulumbronne van Pseudophaeomoniella sp. is ook in gevestigde boorde geïdentifiseer. Snoeiwonde van olywe is vatbaar vir Pseudophaeomoniella sp. vir verlengde periodes. MT1 was hoogs effektief onder lae inokulumdruk, terwyl Tree Seal en Coprox/Bendazid hoogs effektief was onder hoë inokulumdruk. Hierdie studie het gelei tot nuwe kennis aangaande olyfstamsiektes, hul patogenisiteit, opsporing, epidemiologie en beheer wat gebruik kan word vir die ontwikkeling van verbeterde bestuurstrategieë van olyfstamsiektes in Suid-Afrika.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108376
This item appears in the following collections: