Thesis (MScAgric )--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Pine pitch canker, caused by Fusarium circinatum, is a major constraint to the production of high quality timber in the Western Cape Province of South Africa. Under nursery conditions the pathogen causes a serious root and collar rot disease, and in plantations it causes stem cankers and branch die-back. In this thesis, sources of inoculum within a forestry nursery were investigated and novel approaches developed to eradicate the pathogen. Plant material was evaluated for plantation establishment in the Western Cape Province, and epidemiological studies conducted to better understand the infection, disease development, spore release and dissemination of F. circinatum in pine plantations. Fusarium circinatum was first reported in a forestry nursery in the Mpumalanga Province of South Africa in 1990, and now causes significant economic losses to most forestry nurseries in the country. The irrigation system, planting tray inserts, seeds and air at Karatara nursery were screened as potential sources of F. circinatum. Both the irrigation water and planting tray inserts were found to serve as sources of inoculum. An oxidation reduction potential (ORP)-based system, using hydrogen peroxide, was tested to sanitize irrigation water and planting tray inserts. An ORP level of 400 mV for 6 hours was effective in killing F. circinatum spores in irrigation water without being phytotoxic to pine seedlings. An ORP value of >500 mV cleaned planting tray inserts of all inoculum. Pinus radiata is the principal pine species grown in the Western Cape Province, but this species is also highly susceptible to F. circinatum. There are numerous different varieties or families of P. radiata available that can be planted, and it is known that tolerance levels between these varieties and families vary. Pinus radiata families, as well as other Pinus spp. that could potentially be planted in the Western Cape Province in future, were evaluated for tolerance to the pitch canker fungus. The P. radiata families were moderately to highly susceptible to F. circinatum. Pinus taeda was the Pinus spp. most tolerant, while P. elliottii also had good tolerance to the pathogen. None of the P. radiata families screened showed tolerance comparable to that of either P. elliottii or P. taeda. Pine pitch canker was first reported from the Tokai plantation in the Western Cape Province in 2005. In order to develop a disease management strategy for the disease in pine plantations, we investigated the effect of pruning wounds as potential entry sites for the pathogen, and how fast the disease spread under South African climatic conditions. The amount and time of sporulation was also investigated. Pitch canker increased slowly over a 3-year period, and pruning wounds appeared not to serve as primary entry points for F. circinatum. Spore quantification over a 12-month period using quantitative real-time PCR showed that inoculum was produced throughout the year, but that significantly more spores were released during the cold, rainy winter months. The role of insects in pathogen transmission and spread should be investigated in the Tokai plantation. / AFRIKAANSE OPSOMMING: Fusarium circinatum veroorsaak “pine pitch canker”. Hierdie siekte is een van die grootste beperkinge op die Suid Afrikaanse bosbou industrie. In kwekerye veroorsaak die patogeen wortelvrot en wortelkraagvrot. In plantasies veroorsaak F. circinatum kankers op die hoofstam van dennebome en die terugsterwing van sytakke. In hierdie tesis was bronne van inokulum in ‘n bosbou kwekery ondersoek. Nuwe tegnieke was gebruik om die bronne uit te wis. Plantmateriaal wat in die Wes-Kaap geplant kan word, was geëvalueer vir toleransie teen F. circinatum. Epidemiologiesie studies was uitgevoer om die infeksieproses, siekte-ontwikkeling, spoorvrystelling, en verspreiding van F. circinatum binne denneplantasies beter te verstaan. Die eerste verslag van F. circinatum in ‘n bosboukwekery was in 1990 in die Mpumalanga Provinsie. Verliese word tans veroorsaak deur die patogeen in die meeste bosbou kwekerye in Suid Afrika. Die besproeiingstelsel, planthouers en saad was getoets as potensiële bronne van inokulum. Daar was gevind dat beide die besproeiingstelsel en die planthouers dien as bronne van F. circinatum inokulum. ‘n Oksidasie reduksie potensiaal (ORP)-gebaseerde sisteem waar waterstofperoksied gebruik was, was getoets of dit die besproeingwater en planthouers kan ontsmet. ‘n ORP-vlak van 400 mV vir ‘n blootstellingstydperk van 6 ure is effektief om al die F. circinatum spore dood te maak, sonder dat dit fitotoksies is teenoor die dennesaailinge. ‘n ORP-vlak van >500 mV het die F. circinatum in die planthouers uitgewis. Pinus radiata is die belangrikste dennespesie wat geplant word in die Wes-Kaap Provinsie, maar hierdie spesie is hoogs vatbaar vir F. circinatum. Verskillende variteite van P. radiata met verskillende tolleransie vlakke bestaan. Pinus radiata families en ander spesies wat in die toekoms potensieel geplant kan word in die Wes-Kaap was geevalueer vir toleransie teen F. circinatum. Die P. radiata families was matig to hoogs vatbaar vir F. circinatum. Pinus taeda het die hoogste toleransie vlak gehad en P. elliottii was matig tolererant. Nie een van die P. radiata families wat getoets was het toleransie vlakke gehad wat vergelykbaar was met die toleransie vlakke van P. taeda of P. elliottii nie. In 2005 was F. circinatum vir die eerste keer geraporteer in die Tokai plantasie op volwasse dennebome in die Wes-Kaap Provinsie. Die rol van snoeiwonde in die infeksieproses van F. circinatum was bestudeer asook hoe vinning die siekte ontwikkel en versprei. Die hoeveelheid en tyd van sporulasie was ook bestudeer. “Pitch canker” het stadig toegeneem oor die 3-jaar moniteringsperiode en dit blyk asof snoeiwonde nie die primêre ingangspunt vir die patogeen is nie. Kwantifisering van die sporulasie van F. circinatum deur middel van qPCR het aangedui dat spore reg deur die jaar geproduseer word. Meer spore word geproduseer in die koue nat wintersmaande. Die rol van insekte in die infeksieproses en verspreiding van F. circinatum in die Tokai plantasie moet ondersoek word.