Wingfield, M. J.Roux, Jolanda2017-06-092017-06-091998-12http://hdl.handle.net/11660/6355English: The Acacia mearnsii industry is a relatively small, though very profitable industry in South Africa. Wood derived from A. mearnsii is currently in greater demand than that of either pine or eucalyptus in South Africa. Despite the importance of this industry, very little attention has been given to the genetic improvement, disease tolerance or general improvement of A. meamsii as a forestry species. The result has been that, during the last few decades, pathogens have become adapted to, and spread through plantations of this tree. Although relatively little research has been conducted on the impact of pathogens on A. mearnsii, this situation has changed during the past nine years, and particularly since the identification of Ceratocystis wilt. The planting of exotics has many advantages over native plants. In South Africa, exotic forestry species, such as Eucalyptus spp., Pinus spp. and A. mearnsii were introduced to halt the uncontrolled logging of native forests. These native forests were logged mainly for furniture and building material, but also for fuel wood, resulting in the near complete destruction of South Africa's native forests. The introduced exotics prevented the further destruction of these forests and soon became a large industry. This was particularly due to the fact that it was found that they also had a superior growth rate when compared to native species. This accelerated growth rate brought rapid results from breeding trials and, thus, a relatively rapid improvement of the material planted. Because they had been separated from their natural enemies, these trees were also initially disease free. The A. mearnsii industry has, and will continue, to face many problems and challenges from pests and diseases. After the initial phase in which the tree was removed from the pathogens affecting it in it's native range, it faced attacks by native South African pests and diseases. These can spread from native Acacia species, or from any other native plants in the same, or even different families. Exotic, mono culture industries are also constantly under threat from the introduction of pathogens from other countries, including the country of origin. This can be done by the introduction of new germ plasm or on any other plant species or plant material brought into a country. Because A. mearnsii is now planted as a monoculture, in contrast to it's native situation, diseases and pests can potentially be much more severe and will spread more rapidly and widely throughout even aged and genetically uniform stands. Propagation of A. mearnsii has, recently, advanced considerably and this is concurrent with increased demand for this wood on world markets. Lessons learned from eucalypt and pine forestry need, however, to be heeded to save unnecessary losses and time. With the advent of vegetative propagation of A. mearnsii in South Africa, it is important to include disease screening trials at the early stages of the development of clones. In order to do this, a knowledge of all possible pathogens of A. mearnsii is needed. This includes pathogens known in South Africa and those that occur beyond the borders of the country. It is also necessary to have a detailed knowledge of the biology and population structure of these pathogens in order to gain an impression of the possible success of control measures. This thesis is a compilation of work conducted on some of the known pathogens of A. mearnsii in South Africa. It also includes a large component dealing with the identification and clarification of previously unknown pathogens of A. mearnsii. It, therefore, does not focus only on diseases of A. mearnsii, but includes a chapter on a disease of Eucalyptus. The causal agent of this disease has, however, also recently been found on A. mearnsii in South Africa and this chapter aims at elucidating the possible origin of the isolates from South Africa. It also illustrates the potential threat of this pathogen to the A. mearnsii industry. South Africa is a semi-arid country that regularly suffers from severe drought. Forestry activities in the country are also mainly restricted to areas with poorer soil and where agriculture cannot be pursued on a profitable basis. Factors such as drought, hail, frost and sub-optimal soil conditions can all contribute to increased stress on trees. Under these conditions, many fungi can act as opportunistic pathogens, causing large scale losses. They often live as endophytes within their hosts, not causing any negative affect until the onset of stress. At this stage, they spread throughout trees, preventing them from recovering from the stress condition and leading to cankers and tree death. Careful management, particularly site/species matching, is required to minimise losses caused by these pathogens. This thesis provides a basis for future research on the development of management strategies to control diseases of A. mearnsii in South Africa. Information, however, also provide valuable knowledge for forestry industries outside South Africa by highlighting the threat of exotic pathogens and the importance of strict quarantine measures to prevent the spread of pathogens. This is true for the movement of not only A. mearnsii material, but as was seen here, the movement of any forestry products, since many pathogens have a wide host range. Although the thesis is comprised of a series of individual entities, these all provide information regarding the hygiene of A. mearnsii plantations. This thesis thus aims at identifying future focus points for intensive research, while at the same time focusing on those pathogens that have been known to the South African industry for a longer period of time. Chapter one provides a review of the available literature on diseases affecting not only A. mearnsii, but also other Acacia spp. important to the forestry industry, world wide. It also highlights some of the uses of these species in the countries where they are planted. The multi-purpose use of Acacia spp. is an important aspect emerging from this review. In many countries, Acacia spp. are not only planted as forestry species but are also used for soil reclamation, nitrogen fixation and fodder. The main focus of the chapter, however, is on the A. mearnsii industry in South Africa, with a brief discussion on all the diseases currently known to occur in the country. It is concluded that much research is still needed to reduce the impact of these diseases and to ensure that the Industry functions optimally. Ceratocystis albofundus must be considered as one of the most important pathogens of Acacia spp., world-wide. Currently this pathogen occurs only in South Africa, but if it is to spread to other countries, large scale losses will be incurred. It may also affect, not only A. mearnsii, but most likely many other plant species. Breeding programmes for A. mearnsii in South Africa focus strongly on this pathogen. In Chapter two, the population diversity of C. albofundus was investigated and compared with data for other Ceratocystis spp., using nuclear and mitochondrial DNA fingerprinting. It was found that the C. albofundus population has a greater genetic diversity than any of the species with which it was compared. This will thus mean that intensive breeding programmes will be necessary to ensure durability of disease tolerance. It also supports previous hypotheses that C. albofundus is native to South Africa and may be a temperate species, not found in tropical areas where its close relative, C. fimbriata, commonly occurs. The first unequivocal report of C. fimbriata and Ch. elegans from A. mearnsii is presented in Chapter three. Both these fungi were isolated from dying trees with typical symptoms of Ceratocystis wilt caused by C. albofundus. Both were shown to be capable of causing disease to seedlings under green house conditions. It was, however, found that C. albofundus is more virulent than either Ch. elegans or C. fimbriata. Both isolates were identified using molecular and morphological approaches. Unfortunately only one isolate of each exists and surveys to obtain additional samples continue to be a priority. The first report of a wilt disease of Eucalyptus, caused by Ceratocystis fimbriata in the Republic of the Congo in West Africa is recorded in Chapter four. This is not only the first report of C. fimbriata as a pathogen of Eucalyptus in Africa but is also one of the few unequivocal reports of this fungus from the continent. Pathogenicity of C. fimbriata on Eucalyptus spp. was confirmed in glass house tests. In this Chapter, C. fimbriata and C. albofundus from A. mearnsii, and C. fimbriata from Eucalyptus in Brazil were also compared to the C. fimbriata from the Congo. Comparison of the lTS region of the rRNA operon showed that isolates from all three areas grouped together in a clade of C. fimbriata, separate from European isolates. Sequence data showed that C. fimbriata from A. mearnsii in South Africa is nearly identical to the fungi from Eucalyptus in Brazil and Congo, suggesting that they may have a common origin. These findings stress the importance of sound quarantine measures to prevent the introduction of potentially devastating pathogens to South Africa. It is not yet known why C. fimbriata has not caused more diseases on A. mearnsii or Eucalyptus spp. in the country, but the situation will need to be monitored closely. Apart from C. albofundus, there are many other fungi that cause disease of A. mearnsii in South Africa. Chapter five reports on a species of Seiridium that was isolated from stem cankers on A. mearnsii. Morphological and molecular comparisons, as well as pathogenicity studies have shown that the species from A. mearnsii is similar to those species responsible for Cypress canker in many parts of the world. It also confirms previous reports that the taxonomy of the three Seiridium spp. causing cypress canker needs re-evaluation, since molecular data support the view that the three species, represent a single taxon. Pathogenicity trials on mature Cuppressus lusitanica and on A. mearnsii trees showed that both the cypress and A. mearnsii isolates are capable of causing lesions on both hosts. Many of the fungi isolated from diseased A. mearnsii during the current and previous studies of diseases resulted in the isolation of fungi, commonly found as latent pathogens on other forest trees. Chapter six encompassed a survey of the endophytic fungi of A. mearnsii, with the specific aim of identifying possible pathogens. Thirty different fungal taxa were found as endophytes of the xylem and rachi. These included F. graminearum and Botryosphaeria dothidea, which are known pathogens. During periods of environmental stress, these fungi can apparently cause disease. This is especially true because A. mearnsii is often planted on marginal sites in South Africa. Chapter seven represents the first report of Fusarium graminearum from A. mearnsii and presents evidence for the fungus being involved in disease of A. mearnsii. This pathogen was first isolated during 1994-95 disease surveys, but was not identified due to the fact that cultures on artificial media did not sporulate. In the current study, additional isolates were obtained from stem cankers and die-back symptoms and the fungus was identified based on β-tubulin gene sequences. Field inoculations using F. graminearum showed extensive lesion formation in the xylem. Previously, this Fusarium sp. was known only as a pathogen of maize and wheat in various parts of the world. Results of this study are, therefore, enigmatic and intriguing.Afrikaans: Die Acacia mearnsii industrie is 'n klein, dog uiters winsgewende industrie in Suid-Afrika. Hout vanaf hierdie boom is tans in meer aanvraag as enige van die ander bosbouspesies in Suid-Afrika. Min aandag is egter geskenk aan die genetiese verbetering, ontwikkeling van siekte weerstandbiedende spesiesIkIone en die algemene verbetering van hierdie boom as 'n bosbouspesie. Dit het tot die gevolg gehad dat siektes die kans gekry het om aan te pas, te versprei en ernstige probleme te veroorsaak op A. mearnsii. Hierdie situasie het egter gedurende die afgelope paar jaar verander, veral na die identifikasie van Ceratocystis wilt aan die einde van die 1980's. Die verbouing van uitheemse boomspesies, in teenstelling met inheemse spesies, het baie voordele. In Suid-Afrika is uitheemse bosbouspesies aanvanklik geplant om die totale vernietiging van die land se inheemse woude te voorkom. Hierdie woude is teen 'n ontstellende tempo afgekap om aan boumateriaal, meubel- en vuurmaakhout te voorsien. Uitheemse bosbouspesies het nie net vinniger groeitempos as die inheemse spesies nie, maar het aanvanklik min siektes gehad. Na die aanvanklike fase waartydens die uitheemse spesies van hul natuurlike vyande verwyder was, het Suid-Afrikaanse peste en siektes by hierdie bome begin aanpas. Dit het ook vir die A. mearnsii boom gegeld. Patogene kan van 'n verskeidenheid ander gashere versprei na A. mearnsii. Dit sluit uitheemse organismes wat vanaf die boom se land van oorsprong na Suid-Afrika versprei, asook organismes vanaf ander lande af, in. Omdat A. mearnsii nou as mono-kultuur aangeplant word, in teenstelling met sy land van oorsprong, kan peste en patogene teen 'n baie vinniger tempo versprei onder die geneties uniforme plantasies in Suid-Afrika. Die produksie van A. mearnsii het aansienlik verbeter, net soos die aanvraag van hierdie hout verhoog het op die internasionale markte. Met die ontwikkeling van vegetatiewe voortplanting van A. mearnsii d.m.v steggies, is dit egter van uiterste belang om in 'n vroeë fase van die proses alle nageslag teen siektes te toets. Hiervoor is 'n kennis van al die moontlike patogene van A. mearnsii van belang. Dit sluit beide die patogene in Suid Afrika, sowel as patogene in ander lande in. Hierdie kennis moet ook insluit inligting oor die biologie en populasie diversiteit van die patogene. Hierdie inligting sal 'n aanduiding gee van die moontlike sukses van beheermaatreëls. Hierdie tesis is 'n samestelling van werk wat gedoen is op sommige van die bekende patogene van A. mearnsii. Dit sluit cok'n groot gedeelte in wat handeloor die identifikasie van voorheen onbekende patogene van hierdie boom. Dit sluit 'n hoofstuk in oor 'n nuwe siekte van Eucalyptus spp., 'aangesien die patogeen ook op A. mearnsii gevind is tydens hierdie studie. Laasgenoemde hoostuk ondersoek die moontlike konneksie tussen die oorsprong van die isolate op A. mearnsii i.v.m die van Eucalyptus spp. Suid-Afrika is 'n land wat gereeld deur ernstige droogtes geteister word. Die meeste bosboupraktyke is egter beperk tot areas van swakker grondkwaliteit en ongereelde reënval. Buiten droogte stres, dra hael, ryp en die swak grond by tot verhoogte streskondisies vir bosbou. Onder hierdie toestande kan opportunistiese patogene grootskaalse verliese tot gevolg hê. Hierdie organismes leef dikwels as endofiete in hul gashere, waar hul aanvanklik geen siektes veroorsaak nie. Sodra die boom egter onder stres verkeer, versprei hulle in die boom en verhoed hulle die boom om te herstel van die strestoestande. Hulle lei ook dikwels tot die uiteindelike dood van die boom. Goeie bestuurspraktyke, veral die korrelasie an area met spesie, word benodig om verliese deur hierdie patogene te verminder. Hierdie tesis lê die grondslag vir verdere navorsing oor die verbetering en bestuur van strategieë teen siektes van A. mearnsii. Die potensiële bedreiging deur uitheemse patogene en die noodsaaklikheid van streng kwarentyn work ook uitgelig. Al bestaan die tesis uit 'n reeks individuele hoofstukke, handel almal oor die patogene van A. mearnsii en hul impak op hierdie boom. Hierdie tesis lig fokuspunte uit vir verdere navorsing en verskaf ook meer inligting oor die patogene van A. mearnsii wat reeds aan die wetenskap bekend is. Hoofstuk een verskaf 'n literatuuroorsig van die siektes van A. mearnsii sowel as van ander Acacia spp. wat belangrik is vir die bosboubedryf wêreldwyd. Hierdie hoofstuk lig ook sommige van die ander gebruike van hierdie bome, in die lande waar hulle verbou word, uit. Dit is duidelik dat die multi-gebruikspotensiaal van hierdie genus 'n belangrike aspek vorm van sy gebruik as bosbouspesie. In die meeste lande word Acacias byvoorbeeld ook geplant om te help met grondherwinning, stikstofvaslegging en as veevoer. Hoofstuk een se hoof fokuspunt is egter die A. mearnsii industrie in Suid-Afrika en die siektes van hierdie boom in die land word bespreek. Dit is duidelik dat, om te verseker dat die industrie maksimaal funksioneer, baie navorsing nog benodig word aangaande die siektes van hierdie spesie. Ceratocystis albofundus kan as een van die ernstigste siektes van Acacia spp. in die wêreld beskou word. Telingsprogramme met A. mearnsii in Suid-Afrika fokus daarom op hierdie ernstige patogeen. In Hoofstuk twee het ons die populasiediversiteit van hierdie patogeen in Suid-Afrika ondersoek en die data vergelyk met die van ander Ceratocystis spp. Dit is gedoen deur gebruik te maak van nukluêre en mitochondriale DNA profiele. Daar is gevind dat C. albofundus 'n hoër populasiediversiteit as enige van die ander drie Ceratocystis spp. het. Dit beteken dat intensiewe telingsprogramme benodig sal word om die duursaamheid van siekteweerstand te verseker. Resultate in hierdie hoofstuk ondersteun ook vorige hipotesisse dat C. albofundus inheems aan Suid-Afrika is. Dit is heel moontlik dat C. albofundus 'n spesie vanaf 'n gematigde klimaat is, wat In teenstelling met die nabyverwante C. fimbriata, nie in tropiese areas gevind word nie. In Hoofstuk drie verskyn die eerste onteenseglike aanmelding van C. fimbriata vanaf A. mearnsii. Hierdie hoofstuk verteenwoordig ook die eerste aanmelding van Chalara elegans vanaf A. mearnsii. Beide hierdie fungi is identifiseer deur gebruik te maak van morfologiese en molekulêre tegnieke. Ongelukkig kon slegs een isolaat van elk verkry word en verdere opnames om meer isolate te kry is 'n prioriteit vir toekomstige navorsing. Beide spesies is in staat om siekte van jong saailinge in die glashuis te versaak. Ceratocystis albafundus was egter die virulentste van die spesies wat getoets IS vir patogenisiteit. Hoofstuk vier verteenwoordig die eerste aanmelding van C. fimbriata as die oorsaak van 'n ernstige verwelksiekte van Eucalyptus in Afrika. Die patogenisiteit van C. fimbriata op Eucalyptus is in die glashuis bevestig. In hierdie hoofstuk is C. fimbriata vanaf A. mearnsii en Eucalyptus in Brazil, asook C. albofundus, met Congo isolate vergelyk. Vergelyking van die ITS gebied van die rRNA operon van isolate vanaf die Congo, Brazil en Suid Afrika toon dat isolate vanaf al drie areas saam groepeer as C. fimbriata, maar apart van Europese C. fimbriata isolate. Dit is ook gevind dat C. fimbriata vanaf A. mearnsii in Suid-Afrika feitlik identiese DNA profiele het as C. fimbriata isolate vanaf Eucalyptus in Brazil en Wes-Afrika. Dit is dus heel waarskynlik dat hierdie isolate 'n gemeenskaplike oorsprong mag deel. Buiten vir C. albofundus, is daar verskeie ander fungi wat ook siektes van A. mearnsii veroorsaak in Suid-Afrika. Hoofstuk vyf handeloor 'n Seiridium sp. wat vanaf stam kankers geisoleer is. Morfologiese en molekulêre, asook patogenisiteits toetse toon dat die spesie vanaf A. mearnsii soortgelyk is aan die Seiridium spp. wat verantwoordelik is vir sipreskanker in verskeie lande van die wêreld. Resultate verkry in hierdie studie bevestig vorige verslae dat die taksonomie van die drie spesies verantwoordelik vir sipreskanker herevaluering benodig. Molekulêre data toon dat die drie sipreskanker spesies in werklikheid een spesie verteenwoordig. Inokulasies van sytakke van volwasse Cupressus lusitanica en van A. mearnsii toon dat beide die sipres en Acacia isolate patogenies is op hulonderskeie gashere. Baie van die fungi wat gedurende siekteopnames geisoleer is, is bekend as latente patogene van ander bosbou spesies. In Hoofstuk ses is 'n opname van die endofitiese fungi van A. mearnsii gedoen, met die spesifieke doelom potensiële patogene te identifiseer. Dertig verskillende taxa is as endofiete geisoleer vanuit die xileem en ragisse van gesonde bome. Hierdie taxa het onder andere F. graminearum en Batryasphaeria dothidea ingesluit. Die rol van hierdie fungi gedurende tydperke van ongunstige omgewingstoestande is van uiterste belang omdat A. mearnsii dikwels op marginale gebiede geplant word en dus onder gereelde stres verkeer. Hierdie stres kan tot gevolg hê dat latente patogene aktief raak en siekte en dood van die bome veroorsaak. Fusarium graminearum is 'n bekende en ernstige patogeen van mielies en koring, maar in Hoofstuk sewe word dit vir die eerste keer as patogeen van A. mearnsii aangemeld. Dit is vir die eerste keer gedurende 1994-95 geisoleer tydens siekteopnames, maar is nie geidentifiseer nie aangesien die isolate vanaf A. mearnsii nie in kultuur sporuleer nie. In die heidige studie is meer isolate vanaf stamkankers verkry en identifiseer deur vergelyking van die β -tubulien geen. Veldinokulasies met F. graminearum het ekstensiewe kankerformasie in die xileem tot gevolg gehad.enCerato cystis -- South AfricaWattles (Plants) -- South AfricaWilt diseases -- South AfricaThesis (Ph.D. (Microbiology and Biochemistry))--University of the Free State, 1998ThesisUniversity of the Free State