Drought, freezing, and nitrogen stress as factors predisposing pistachio trees to infection by Botryosphaeria obtusa and B. dothidea
| dc.contributor.advisor | Swart, Wijnand J. | |
| dc.contributor.advisor | Pretorius, J. C. | |
| dc.contributor.author | Nieuwoudt, Tielman Daniel | |
| dc.date.accessioned | 2017-05-09T06:34:17Z | |
| dc.date.available | 2017-05-09T06:34:17Z | |
| dc.date.issued | 2000-05 | |
| dc.description.abstract | English: Drought, freezing and nitrogen stress are environmental factors known to predispose woody plants to infection by numerous fungal species. The main and ultimate objective of the present study was to identify possible stress factors that predispose commercially pistachio (Pistacia spp.) trees to infection and colonization by Botryosphaeria obtusa and B. dothidea in order to develop a sustainable disease control programme for South African pistachio producers. It was found that these stress conditions significantly affected the susceptibility of three genotypes of potted pistachio plants to infection and colonization by B. obtusa and B. dothidea. In the glasshouse, drought stress trials with potted Pistacia terebinthus plants artificially inoculated with B. dothidea showed significantly longer lesions than control treatments while P. integerrima displayed the greatest resistance to the pathogen. Although B. dothidea caused more severe cambial lesions in glasshouse trials, it showed a slower growth rate than B. obtusa under in vitro water stress conditions. In freezing stress trials performed in a growth chamber, there was a highly significant difference between the stressed and non-stressed plants of P. integerrima and Clone II (P. integerrima x P. atlantica). P. integerrima was the most susceptible rootstock and P. terebinthus the least susceptible. B. dothidea caused the most severe cambial lesions in all treatments. In nitrogen stress trials, most treatments showed a significant decrease in the length of cambial lesions at a higher level of applied nitrogen (28%). B dothidea was generally more pathogenic than B. obtusa for both levels of N applied. The most significant differences between nitrogen levels were recorded for P. terebinthus. From the above results it is clear that drought and freezing stress have a significant effect on the predisposition of pistachio plants to B. obtusa and B. dothidea. Drought stress occurs in pistachio orchards due to a very short hardening off period lasting two to three weeks. By postponing this period not only can drought stress be prevented but also freezing stress. Current nitrogen levels applied in the pistachio orchards are much lower than those applied in other parts of the world. Applying higher levels of nitrogen could thus possibly prevent the occurrence of Botryosphaeria diseases. The development of a selective medium for the pure isolation of B. obtusa and B. dothidea from diseased tissue and other sources enabled the isolation of B. dothidea from debri, bark, diseased and asymptomatic tissue without hindrance by extraneous fungi. B. obtusa, however, was only isolated from active cankers on the stems of pistachio trees. Isolation of B. dothidea from asymptomatic plant tissue suggests an endophytic or latent phase. Trials were conducted in vitro with different fungicides to determine other possible fungicides that could be employed for the control of the two Botryosphaeria species. Eria®, a mixture of carbendazim and difenoconazole displayed the highest inhibition. Benomylor the Eria® applied during bloom, and tebuconazole in combination with difenoconazole on a monthly basis throughout the season, should thus successfully control both Botryosphaeria diseases in South African orchards. | en_ZA |
| dc.description.abstract | Afrikaans: Droogte, koue en stikstof stremming is bekende omgewingsfaktore wat houtagtige spesies meer vatbaar maak vir infeksie deur verskeie swamme. Die hoofdoel van die huidige studie was om stremmings faktore te identifiseer wat kommersieële pistachio bome meer vatbaat maak vir infeksie deur Botryosphaeria obtusa en B. dothidea. Die doel hiervan is om 'n effektiewe siektebeheerprogram vir pistachio produksie in Suid- Afrika te ontwikkel. Droogte en koue stremming is geïdentifieseer as faktore wat die vatbaarheid verhoog terwyl stikstof stremming 'n duidelike afname in infeksie getoon het. Daar was duidelike verskille tussen verskillende pistachio genotipes. Pistacia terebinthus plante het in glashuisproewe betekenisvolle langer letsels as kontrole plante getoon terwyl P. integerrima die hoogste weerstand onder droogte toestande getoon het. B. dothidea het deurgaans die langste letsels veroorsaak al het die betrokke swam stadiger gegroei as B. obtusa onder droogte toestande in vitro. Betekenisvolle verskille het tussen gestremde en nie-gestemde plante van P. integerrima en Kloon II (P. integerrima x P. terebinthus) voorgekom, toe plante in groeikabinette aan koue stremming onderwerp is. Gestremde plante het in die bogenoemde behandelings deurgaans langer letsels getoon. P. integerrima het die langste letsels getoon terwyl P. terebinthus die beste weerstand onder die toestande getoon het. B. dothidea het weereens die langste letsels in al die behandelings getoon. Tydens die stikstof proewe was daar deurgaans -korter letsels by die verhoogde stikstof peil. B. dothidea het langer letsels as B. obtusa veroorsaak in al die betrokke behandelings. Die mees betekenisvolle verskil tussen die stikstof behandelings was in die geval van P. terebinthus. Die resultate van hierdie studie toon duidelik dat droogte en koue stremming belangrike faktore is as dit kom by predisponering van pistachio bome teenoor siektes. Droogte stremming kom op die oomblik gereeld voor in pistachio boorde in Suid-Afrika as gevolg van die feit dat water vroeg in die herfs heeltemal getermineer word om die bome af te hard vir die winter. 'n Langer afhardings periode wat minder skok vir die plante meebring sal definitief 'n positiewe effek op siektevoorkoms hê. Huidige stikstofpeile wat toegedien word is heelwat laer as die wat in ander dele van die wêreld toegedien word. 'n Hoër stikstofpeil sal nie net lei tot beter groei nie, maar ook moontlik tot minder infeksie deur Botryosphaeria spesies. Die ontwikkeling van 'n selektiewe medium vir die suiwer isolasie van B. obtusa en B. dothidea het gelei tot die suksesvolle isolasie van B. dothidea uit dooie pistachio materiaal, bas, geïnfekteerde weefsel en gesonde weefsel sonder dat die proses deur enige saprofietiese swam me belemmer is. Die feit dat B. dothidea uit gesonde, symtoomlose weefsel geïsoleer is dui op 'n moontlike endofitiese of latente leefwyse. B. obtusa is slegs uit aktiewe kankers van volwasse bome geïsoleer. Proewe is in vitro uitgevoer om moontlike nuwe swammiddels te identifiseer vir die beheer van die twee Botryosphaeria spesies. Eria®, 'n mengsel van carbendazim en difenoconazole het die beste resultate getoon. Benomyl or Eria®, toegedien tydens bloeiselvorming en opgevolg deur tebuconazole in kombinasie met difenoconazole op 'n maandelikse basis deur die seisoen, sal moontlik Botryo~phaeria-siektes in Suid- Afrikaanse boorde die beste beheer. | af |
| dc.description.sponsorship | Green Valley Nuts, Prieska | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11660/6194 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Pistachio | en_ZA |
| dc.subject | Pistacia spp | en_ZA |
| dc.subject | Botryosphaeria | en_ZA |
| dc.subject | Stress | en_ZA |
| dc.subject | Drought | en_ZA |
| dc.subject | Freezing | en_ZA |
| dc.subject | Nitrogen | en_ZA |
| dc.subject | Phytopathogenic microorganisms | en_ZA |
| dc.subject | Plant diseases | en_ZA |
| dc.subject | Dissertation (M.Sc.Agric. (Plant Pathology))--University of the Free State, 2000 | en_ZA |
| dc.title | Drought, freezing, and nitrogen stress as factors predisposing pistachio trees to infection by Botryosphaeria obtusa and B. dothidea | en_ZA |
| dc.type | Dissertation | en_ZA |