The history of the development in Natal of a forecasting service to warn of outbreaks of late blight disease caused by Phytophthora infestans is presented. The late blight pathogen and Alternaria solani, the causal organism of early blight disease, interact on potatoes and tomatoes to form a blight disease complex. Evidence is presented to show that it is expedient to manage this blight complex as a whole rather than to direct control at only one of the components in ignorance of the consequential enhancement of the potential of the other. In a search for an improved blight complex management strategy, factors concerning the possible existence of an annual migration of Phytophthora infestans inoculum, first postulated in the 1960's, along an east-west route across Natal, are collected and collated. Corroboration of the existence of the Phytophthora-pathway is given, inasmuch as it represents a serial outbreak of late blight along a temporal gradient. The possibility that the pathway is a manifestation of disease resulting from the erruption of pre-existing inoculum along an environmental gradient, can not specifically be excluded. However, the peculiar pattern of anabatic and katabatic winds along a river-valley network, superimposed on a continuous cropping pattern and its concomitant opportunity for blight to be endemic in the province, supports the postulated Phytophthora-inoculum pathway A fungicide spray trial was conducted in order to investigate the possibility of us i ng the pathway phenomenon as the framework for an improved blight control strategy and to explore the nature and level of the competitive interaction between Phytophthora infestans and Alternaria solani. This trial revealed that the interaction between the components of the blight complex was differentially altered by weather patterns and fungicide combinations. Treatments in which metalaxyl (Ridomil) alone was used for the control of late blight, gave a yield similar to those with propineb (Antracol), which inhibits A. solani primarily but also hus some negative effect on P. infestans. The yields from both these treatments were siguificant ly (p < 0,05) better than the yields recorded in the unsprayed control plots. A treatment in which Ridomil and Antracol were combined such that each was applied according to its recommended concentration, gave yield increases of 32,3% over the unsprayed control, although the yield from the Ridomil/Antracol treatment was not significantly greater (p < 0,05) than the yields recorded where either Ridomil or Antracol were used. A computer simulator, named GAUSE, was developed to simUlate the consequences of the competition between various combinations of P. infestans and A. solani. Results simulated by GAUSE corroborated those obtained from the field trial and support the conclusion that diseases of complex etiology require more than simplistic, univariate analysis of single cause-and-effect pathways. The competition quotient CQ is developed as a new parameter of competitive interactions. It is calculated as the ratio of the amount of disease in the absence of competition, to the amount of disease when the causal pathogen is competing with another pathogen in the same niche. The CQ may be calculated from various standard epidemiology statistics and it is used to demonstrate that the competitive displacement phenomenon places constraints on the interpretation and application of Vanderplank's basic epidemiology equations. A new pathosystems management concept namely the pathotope (pathos = suffering; topos = place0 concept, is introduced, having developed from the notion that epidemics have spatial as well as temporal attributes. Accordingly, an area in which individual farms are at the same level of probability at risk to disease, delimits the pathotope. The concept can be described at many integration lsvels and is presented as an important quantitative unit of comparative epidemiology. The pathotope concept accomodates such notions as are contained in the postulated Phytopnthora-pathway and is especially suited to integration with disease forecasting methods. An example of the application of the pathotope approach is presented and a strategy is proposed by which fungicide spraying is initiated and applied synchronously as determined by the degree of communal risk to attack and epidemic increase of disease. Within a pathotope, several common factors collectively determine the vulnerability of the group to disease. If a coherent, uniform strategy is to be developed and implemented by pathotope members, it is necessary that all members have access to the relevant information and that it be collected and disseminated conveniently and rapidly. A computer-based disease monitoring and mapping system which achieves these objectives is presented. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1980.

Avocado sunblotch disease is a graft-transmissible disorder known for over 60 years and has now been recorded in at least eight countries around the world. Affected trees develop yellow, depressed streaks on young stems and fruit, marked rectangular cracking of the mature bark and a decumbent style of growth. Often a tree with symptoms produces completely symptomless shoots, termed 'recovery' growth, which are latently infected. There is a reported 95 to 100% transmission of sunblotch through the seed of such branches, and "the resultant seedlings are themselves symptomless. Indexing for sunblotch to ensure that scion and, in view of seed transmission, especially rootstock material is free of the disease is very important . The standard method used for many years has been to graft tissue onto healthy indicator seedlings and observe for symptom development for 18 months to two years. One aim of the study presented in this thesis was to develop more rapid methods for detecting the sunblotch agent. By conducting the standard indexing method in a glasshouse at controlled high temperatures of 30/28º C (day/ night) and by cutting back the indicator plants every three months, the time was reduced from two years to eight months. While this represents a considerable saving in time, the ideal must be to develop a laboratory diagnostic test that requires no more than a few days, at most, to complete. A comparative study was therefore initiated on the phenol metabolism of healthy and sunblotch-infected avocados to determine whether infection causes any major change that may reliably serve as a marker for diagnostic purposes. Significantly increased peroxidase (PO) and phenylalanine ammonia-lyase (PAL) activities, decreased indoleacetic acid (IAA) oxidase activity and higher sinapic acid levels were detected in bark tissue showing sunblotch symptoms, but not in symptomless 'recovery' growth. In contrast, increased polyphenoloxidase (PPO) activity and isoenzymes, total soluble protein levels, water soluble phenols and reduced ferulic acid levels were found in the bark of all infected trees tested, both with symptoms and symptomless. However, these latter changes have been associated with other plant-virus systems and are therefore not necessarily specific for sunblotch. Neither is any sufficiently large to be definitive as a diagnostic test. Two unidentified phenols were detected in infected, mature bark, but not in infected young bark and leaves. introduced the possibility of rapid disease detection by polyacrylamide gel electrophoresis (PAGE) of extracted RNA's as used for known viroids. In this study the presence of previously reported small molecular weight sunblotchassociated RNA's was confirmed using PAGE methods requiring two to four days to complete. This thesis presents as a further development a more rapid method of PAGE detection of RNA's enabling indexing for sunblotch to be completed in under six hours. Whilst the biochemical studies did not reveal diagnostically meaningful differences between healthy and infected avocados, there were tendencies towards differences between healthy and symptomless carrier tissues, further investigation of which may lead to a future understanding of symptom development and the symptomless condition. These include apparent higher PO and lower PAL activities in symptomless carrier tissue, as well as higher PO isoenzyme a[1] and lower IAA oxidase isoenzyme a[1] activities. General studies on sunblotch-infected avocados showed that fruit from symptomless 'recovery' growth branches are significantly larger and have a higher oil content than those from healthy or diseased branches, the latter finding possibly indicating a more advanced state of maturity of 'recovery' growth fruit due to earlier flowering. The avocado sunblotch agent was shown to have an in vivo thermal inactivation point of 55º C, a temperature higher than the avocado tissue can withstand thereby eliminating the possibility of thermotherapy of infected twigs. In a host range study four lauraceous plant species, Persea Schiedeana, Cinnamomum zeylanicum, C. camphora and Ocotea bullata, were successfully infected with sunblotch by grafting from infected avocado. This is the first demonstration of any host other than avocado. A phanerogametic member of the same family, Cassytha filiformis, was shown to be able to transmit the disease from avocado to avocado. No hosts from other families were found. During an electron microscope study of sunblotch-infected avocado leaf tissue, gross alterations of the chloroplasts in the yellow areas were observed. These changes included organelle swelling, loss of grana and stroma lamellae, rearrangement of remaining membranes and presence of vesicles. Also in the yellow areas paramural bodies were encountered in higher numbers and displaying altered structure than in healthy and symptomless infected leaf tissue. This study on avocado sunblotch disease was successful in both of its aims. Firstly with regard to quicker indexing techniques, the standard method using indicator plants was shortened from two years to eight months, while a rapid, six-hour test based on PAGE analysis, was developed. Secondly, more light has been shed on the biochemical and ultrastructural effects of sunblotch on its host, the avocado, as well as providing information regarding the thermal sensitivity and the host range of the agent. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1980.

Thesis (MScAgric)--Stellenbosch University, 1956. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming

Thesis (MScAgric (Plant Pathology))--University of Stellenbosch, 2005. / The genus Rhizoctonia includes important soilborne plant pathogens that can cause severe economic losses on a wide range of crops including cereal, canola, pasture and grain legume crops. Limited information is available on specific anastomosis groups (AGs), nuclear status, pathogenicity and cross-pathogenicity of Rhizoctonia isolates associated with each of these crops in the Western Cape province. Therefore, these aspects were investigated in this study, since information in this regard is crucial for the development of Rhizoctonia disease management practices.

Thesis (MScAgric (Plant Pathology)--Stellenbosch University, 2008. Includes bibliography.summary,list of figures and appendices. / ENGLISH ABSTRACT: Fusarium spp. and Aspergillus spp. are toxin-producing fungi associated with maize and groundnut. Fusarium verticillioides produces fumonisins in maize, and Aspergillus flavus produces aflatoxins in maize and groundnut kernels. Both toxins are responsible for carcinogenesis in humans and animals. Contamination of maize and groundnut with mycotoxins is often most severe in rural areas where subsistence farmers are unaware of their existence and follow agricultural practices that might contribute to their production. A questionnaire was, therefore, compiled to investigate agricultural decisions in rural areas that may influence mycotoxin contamination of crops. During 2006 and 2007, maize and groundnut samples were collected in the Eastern Cape, KwaZulu-Natal (KZN), Limpopo, and Mpumalanga provinces. Mycotoxin levels were quantified using the ELISA technique, and the incidence of Fusarium spp. in maize grain was determined by plating maize kernels out on Fusarium selective medium. Fumonisin-producing Fusarium spp. were also quantified using real-time PCR (TaqMan). The incidence of A. flavus and A. parasiticus in groundnut was determined by plating out kernels on potato dextrose agar. Fumonisin contamination levels in maize samples ranged from 0-21.8 parts per million (ppm) and aflatoxin levels ranged from 0- 49 parts per billion (ppb), depending on the region where samples were collected. Aflatoxin levels in groundnut ranged from 0-160.1 ppb. Fusarium verticillioides was the most common Fusarium sp. in maize followed by F. subglutinans and F. proliferatum, respectively. Regression analyses showed a positive correlation between fumonisin-producing Fusarium species when determined by real-time PCR and fumonisin concentration (r2=0.866). Regression analyses further showed a highly significant positive correlation between A. flavus and aflatoxin contamination (r2=0.10235). Samples from northern KZN contained levels of mycotoxins that were far in excess of the maximum levels set by the Food and Drug Administration in the USA. In South Africa there are currently no regulations with regard to the maximum allowable levels of fumonisin in human food. The high incidence of mycotoxin contamination of human food in subsistence farming systems indicates the need for awareness programmes and further research. / AFRIKAANSE OPSOMMING: Fusarium spp. en Aspergillus spp. is toksien-produserende fungi wat met mielies en grondbone geassosieer word. Fusarium verticillioides produseer fumonisiene in mielies, terwyl, A. flavus aflatoksiene in mielies en grondbone produseer. Beide toksiene is karsinogenies vir mens en dier. Die vlakke van toksien-kontaminasie is meestal die ergste in landelike gebiede waar bestaansboere onbewus is daarvan. Landboupraktyke wat deur die boere toegepas word vererger dikwels die probleem. ‘n Vraelys is saamgestel om vas te stel watter landboupraktyke in landelike gebiede toegepas word, en hoe dit toksien-kontaminasie in mielies en grondbone beinvloed. In die 2006 en 2007 seisoene is mielie- en grondboonmonsters in Kwa-Zulu-Natal (KZN), die Oos Kaap, Limpopo en die Mpumalanga provinsie versamel. Toksien-vlakke is gekwantifiseer deur gebruik te maak van die ELISA tegniek. Die insidensie van Fusarium spp. in mielies was bepaal deur pitte op Fusariumselektiewe agar uit te plaat. Fumonisien-produserende Fusarium spp. was ook gekwantifiseer deur van kwantitatiewe PCR (TaqMan) gebruik te maak. Die voorkoms van A. flavus en A. parasiticus is bepaal deurdat mielie- en grondboonpitte op aartappel dekstrose agar uit te plaat. Fumonisien-vlakke in die mieliemonsters het gewissel van 0-21.8 dele per miljoen (dpm), terwyl aflatoksienvlakke gewissel het van 0-49 dele per biljoen (dpb), afhangende van die omgewing waar monsters versamel is. Aflatoksien vlakke in die grondboonmonsters het gewissel van 0-160.1 dpb. Fusarium verticillioides is die meeste vanuit mielies geisoleer, gevolg deur F. subglutinans en F. proliferatum. Regressie analises het ‘n positiewe korrelasie tussen fumonisien konsentrasie en fumonisien-produserende spp. aangedui waar daar gebruik gemaak is van die kwantitatiewe PCR (r2= 0.866). Regressie analises het ‘n hoogs betekenisvolle positiewe korrelasie getoon tussen A. flavus en aflatoksien kontaminasie (r2=0.10). Monsters van noordelike KZN het toksienvlakke bevat ver bokant die maksimum toelaatbare vlakke is soos bepaal deur die Food en Drug Administrasie in die Verenigde State van Amerika. Daar is tans geen regulasies in Suid Afrika wat die maksimum toelaatbare vlakke van fumonisiene in voedsel vir menslike gebruik bepaal nie. Die hoë voorkoms van mikotoksien-kontaminasie in bestaansboer-sisteme, dui die belangrikheid van verdere navorsing en bewusmakings-progamme aan.

Thesis (MSc (Plant Pathology))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Dry core rot (DCR) and wet core rot (WCR) are among some of the most important postharvest diseases of apples in South Africa. Mouldy core (MC) is also a symptom associated with the core region of apples, but it is not of economical importance since apple tissue surrounding the core region is not affected as is the case with DCR and WCR. The incidence of core rots in harvested fruits can be as high as 12%, but in general ranges from 3 to 8%. Infections and losses can also occur during fruit handling in pack houses and during storage. Additionally, yield losses also occur prior to harvest within orchards due to premature fruit drop of core rot affected fruits. The incidence of core rot diseases in apples differ among apple cultivars, with most Red Delicious varieties being susceptible to the development of core rots, whereas core rots have rarely been reported in other cultivars such as Granny Smith. The etiology and epidemiology of WCR and DCR are poorly understood. Although many fungal genera have been associated with the diseases, small-spored Alternaria species are mainly associated with DCR, whereas Penicillium species including P. roquefortii, P. expansum and P. funiculosum have mainly been associated with WCR. Dry core rot infections have long been known to occur pre-harvest, whereas WCR is primarily known as a post-harvest disease where infections take place during fruit handling in pack houses. Recently, Tarsonemus mites have also been indicated as being a potential role player in the etiology of core rot diseases. The mites have been hypothesised to carry pathogen spores into the core region of apples, and they may also possibly cause small wounds that facilitate pathogen entry. In South Africa, apple growers have recently reported WCR as being present prior to harvest, which has not been reported previously. Therefore, the first aim of the study was to investigate the incidence, as well as the causal agent/s of pre-harvest WCR. The incidence of WCR ranged from 0% to 1.7% in eleven orchards, and was in general lower than that of DCR (0.4% to 6%). Isolation studies from eight internal positions in WCR apples showed that Penicillium was the predominant fungal genus in most of the positions, including the lesion area. Morphological and molecular characterisation of Penicillium isolates from WCR showed that P. 2 ramulosum prov. nom. was the main species isolated from lesions, as well as other isolation positions. However, this species was also the main species isolated from DCR, MC and asymptomatic apples. Penicillium expansum was only isolated at low frequencies from WCR and DCR apples. Other Pencillium species that were occasionally isolated included P. glabrum, P. chloroloma, P. chermisinum and a putative new species with closest affinity to P. dendriticum (P. species aff. dendriticum) on a DNA nucleotide sequence basis. Pathogenicity and virulence studies using three different inoculation methods showed that P. expansum was the most virulent species, followed by P. species aff. dendriticum. The P. ramulosum prov. nom. isolates varied in their virulence, but were all considered to have low virulence. The role of Tarsonemus mites in the etiology and epidemiology of core rot diseases is poorly understood, and therefore the second aim of the study was to investigate some of these aspects. The specific aims of the study were to (1) investigate the ecology of Tarsonemus mites in Red Delicious and Granny Smith orchards during different apple developmental stages, (2) determine if there is a significant association of Tarsonemus mites with diseased (WCR and DCR) fruits and (3) determine if potential core rot pathogenic fungi are associated with the mites. Tarsonemus mites were found in all of the investigated apple developmental stages (buds, blossoms, 4cm diameter fruit, mature fruit and mummies), having the highest incidence in mummies and mature fruits from Red Delicious and Granny Smith orchards. In Red Delicious fruits the Tarsonemus mites were found within the core and/or calyx tube, whereas in Granny Smith fruits the mites were restricted to the calyx tube. In Red Delicious fruits there was a significant association between dry core rot as well as total core rot (wet- and dry-core rot) with the presence of mites in the core, as well as total mites (mites in core and calyx tubes). Fungal isolation studies from the Tarsonemus mites showed that they carried potential core rot fungal pathogens within the genera Penicillium and Alternaria. The Penicillium species isolated from the mites included two of the most virulent WCR species, P. expansum and P. species aff. dendriticum. / AFRIKAANSE OPSOMMING: Droë kernvrot and nat kernvrot is van die belangrikste na-oes siektes van appels in Suid- Afrika. Beskimmelde kern word ook met die kern van appels geassosieer, maar hierdie toestand is egter nie van ekonomiese belang nie, aangesien die weefsel rondom die kern nie geaffekteer word soos in die geval van nat- en droë kernvrot nie. Die voorkoms van kernvrot in vrugte na oes, kan vlakke van tot 12% bereik, maar oor die algemeen is die voorkoms tussen 3 en 8%. Infeksie en verliese kan ook voorkom gedurende die hantering en verpakking van vrugte in pakhuise en gedurende storing. Addisionele verliese in opbrengs kan ook voor-oes voorkom in boorde. Dit is te wyte aan voortydige vrugval van appels wat besmet is met kernvrot. Die voorkoms van kernvrot by appels verskil tussen kultivars. Meeste van die “Red Delicious” variëteite is vatbaar vir die ontwikkeling van kernvrot. Die toestand is egter skaars by ander kultivars soos Granny Smith. Die etiologie en epidemiologie van nat- en droë kernvrot word nie goed verstaan nie. ‘n Groot aantal swamgenera is al met kernvrot geassosieer. Klein-spoor Alternaria spesies word hoofsaaklik met droë kernvrot geassosieer en Penicillium spesies, insluitende P. roquefortii, P. expansum en P. funiculosum, word meestal met nat kernvrot geassosieer. Dit is lank reeds bekend dat droë kernvrot as voor-oes siekte kan voorkom, maar nat kernvrot is algemeen bekend as na-oes siekte waar infeksie tydens vrughantering en verpakking plaasvind. Daar is onlangs aangedui dat Tarsonemus myte potensiële rolspelers in die etiologie van kernvrot is. Hipoteties is die myte in staat om spore van die patogene in die kern van die appels in te dra, asook om klein wonde te veroorsaak wat infeksie deur patogene vergemaklik. In Suid-Afrika is nat kernvrot wat voor-oes in die boorde ontstaan onlangs deur boere aangemeld; hierdie toestand is nog nie op ‘n vorige geleentheid aangemeld nie. Die eerste doelwit van hierdie studie was dus om die voorkoms en veroorsakende organisme/s van voor-oes nat kernvrot te ondersoek. Die voorkoms van nat kernvrot was tussen 0 en 1.7% in elf boorde en was oor die algemeen laer as die voorkoms van droë kernvrot (0.4 tot 6%). Isolasiestudies uit agt interne posisies van nat kernvrot appels het getoon dat Penicillium die dominante swamgenus in die meeste posisies was, insluitend die letsels. Morfologiese en molekulêre karakterisering van 4 Penicillium isolate uit nat kernvrot letsels het aangedui dat P. ramulosum prov. nom. die spesie is wat die meeste geïsoleer is vanuit die letsels, asook ander isolasie posisies. Dié spesie was egter ook die mees algemene spesie wat uit nat- en droë kernvrot, asimptomatiese appels en appels wat slegs swamgroei in die kern gehad het, geïsoleer is. Penicillium expansum was ook in lae getalle uit nat- en droë kernvrotletsels geïsoleer. Ander Penicillium spesies wat ook soms geïsoleer is, sluit P. glabrum, P. chloroloma, P. chermisinum, asook ‘n moontlik nuwe spesie wat op DNA volgorde basis die naaste aan P. dendriticum (P. spesie aff. dendriticum) is. Studies wat patogenesiteit en virulensie van die isolate ondersoek het, is ook uitgevoer deur gebruik te maak van drie verskillende inokulasie metodes. Die studies het aangedui dat P. expansum die mees virulente spesie is, gevolg deur P. spesie aff. dendriticum. Die P. ramulosum prov. nom. isolate het variasie in virulensie getoon maar is oor die algemeen aanvaar om minder virulent te wees. Die rol van Tarsonemus myte in die etiologie en epidemiologie van kernvrot word nie goed verstaan nie en dus was die tweede doelwit van die studie om sommige van dié aspekte te ondersoek. Die spesifieke doelwitte was (1) om die ekologie van die Tarsonemus myte in “Red Delicious” en Granny Smith boorde tydens verskillende ontwikkelingstadiums van die appels te ondersoek, (2) om te bepaal of daar ‘n betekenisvolle assosiasie van Tarsonemus myte met siek (nat- en droë kernvrot) vrugte bestaan en (3) om te bepaal of potensiële kernvrot patogeniese swamme geassosieer is met die myte. Tarsonemus myte is gevind in al die ontwikkelingstadiums (knoppies, bloeisels, 4 sentimeter deursnee vrugte, volwasse vrugte en mummies) van appels wat ondersoek is. Die hoogste voorkoms van myte was in die mummies en volwasse vrugte van “Red Delicious”, asook Granny Smith kultivars gevind. In “Red Delicious” vrugte is myte in die kern en/of kaliksbuis gevind, maar in die Granny Smith vrugte was die myte tot die kaliksbuis beperk. In “Red Delicious” vrugte was daar ‘n betekenisvolle assosiasie tussen droë kernvrot, asook totale kernvrot (nat en droë kernvrot) met die teenwoordigheid van myte in die kern, asook totale myte (myte in die kern en kaliksbuis). Swam isolasiestudies vanaf die Tarsonemus myte het aangetoon dat potensiële kernvrot swampatogene in die genera Penicillium en Alternaria wel by die myte teenwoordig was. Die Penicillium spesies wat vanaf die myte geïsoleer is het twee van die mees virulente nat kernvrot spesies ingesluit, nl. P. expansum en P. spesie aff. dendriticum.

Thesis (MScAgric (Plant Pathology))--Stellenbosch University, 2009. / ENGLISH ABSTRACT: Sufficient fungicide deposition on the target site is an essential requirement for effective chemical management of fruit- and foliar diseases such as grey mould of grapevines. Control failure is often attributed to insufficient quantitative deposition on susceptible grapevine tissue. However, in high disease pressure situations control failure might also be attributed to poor qualitative deposition. The primary objective of spray technology is to optimise deposition, of which the plant surface is a critical component in the spray application process, specifically in the retention of spray droplets. Adjuvant technology is reported to improve the wettability and spread of droplets by surface-acting-agents on the target surface and thereby improve deposition and retention of the fungicide active ingredient. However, this relatively new spray technology on viticulture and horticultural crops, and possible effects of adjuvants on epicuticular wax affecting plant disease development, needs to be investigated. Moreover, the development of useful prescriptions for adjuvants by determining water volumes and adjuvant dosages is required for different pesticide tank mixes. The aims of this study were, firstly to determine the effect of selected adjuvants on quantitative and qualitative spray deposition on grapevine leaves and subsequent biological efficacy of a fungicide, and secondly to evaluate selected adjuvants under field conditions and determine the effects of adjuvant dosage and spray volume on deposition. Leaves were sprayed under similar laboratory conditions to pre-run-off with 1 mL of a mixture of fenhexamid (Teldor® 500 SC, Bayer) at recommended dose, a fluorescent pigment (SARDI Fluorescent Pigment, 400 g/L EC; South Australian Research and Development Institute) at 0.2 L/100 L, as well as 15 selected commercial adjuvants to manipulate the deposition quality of a given quantity of deposited spray. Spray deposition on leaves was illuminated under black light (UV-A light in the 365 nm region) and visualised under a stereo microscope (Nikon SMZ800) at 10× magnification. Photos of sprayed leaf surfaces were taken with a digital camera (Nikon DMX 1200). Digital images were quantitatively and qualitatively analysed with Image-Pro Discovery version 6.2 for Windows (Media Cybernetics) software, to determine spray deposition. The sprayed leaves were inoculated with 5 mg dry airborne conidia of Botrytis cinerea in a spore settling tower and incubated for 24 h at high relative humidity (≥ 93%). Leaf discs were isolated onto Petri dishes with paraquat-amended water agar and rated 11 days later for development of B. cinerea from isolated leaf discs. B. cinerea incidence on the upper and lower surfaces of water sprayed leaves averaged 90.4% and 95.8%, respectively. Despite full spray cover of leaves, applications with fenhexamid alone did not completely prevent infection and resulted in 34.6% and 40.8% B. cinerea incidence on the upper and lower surfaces of leaves, respectively. Through the addition of certain adjuvants, B. cinerea incidences were significantly lower (2.9-17.1% and 10.0-30.8%, respectively), while some adjuvants did not differ from the fungicide-only treatment, even though they might have improved spray deposition. The effects of Hydrosilicote and Solitaire alone and in combination with fenhexamid on germinating Botrytis conidia on leaf surfaces were studied in a histopathology study using epifluorescence microscopy. Distinct differences were observed in conidium mortality, germination and germ tube lengths between adjuvants alone and in combination with the fungicide, which might be attributed to indirect effects of the adjuvant mode of action on B. cinerea. The laboratory study clearly demonstrated the potential of adjuvants to improve the bio-efficacy of a fungicide directly through improved deposition on grapevine leaf surfaces. For the vineyard evaluations, the same fluorometry, photomicrography and digital image analysis protocol were used to assess quantitative and qualitative spray deposits under varying adjuvant dosage and volume applications. The Furness visual droplet-rating technique was initially included to determine optimum spray volume with a STIHL SR400 motorised backpack mistblower by assessment of pigment deposition on Chardonnay leaves under illuminated black light. Both assessment protocols showed that quantitative spray deposition increased with increasing spray volume applications of 40 L/ha to 750 L/ha, but decreased at 900 L/ha, possibly due to run-off. The addition of selected adjuvants at recommended dosage and at 600 L/ha demonstrated the potential of adjuvants to increase quantitative and qualitative deposition significantly on upper and lower leaf surfaces. Agral 90, BB5, Nu-film-P, and Solitaire significantly improved deposition on upper and lower leaf surfaces compared with the fenhexamid only and water sprayed control. Break-thru S 240 and Villa 51 did not improve quantitative deposition, although remarkably better qualitative deposition was obtained. An adjuvant dosage effect (within the registered dosage range) was evident, especially those retained on the upper leaf surfaces. Agral 90 and Nu-film-P affected significant improvement of spray deposition at the higher, but not at the lower dosage tested. Solitaire improved deposition at the lower dosage tested, whereas reduced deposition at the higher dosage was attributed to excessive spray run-off. No significant improvement of spray deposition was observed for both dosages tested with Villa 51. Spray mixtures with adjuvants Agral 90 and Solitaire yielded similar deposition values at 600 L/ha compared with the fenhexamid only control at 900 L/ha, but reduced deposition at the higher spray volume, possibly due to spray run-off. This study clearly demonstrated the potential of adjuvants to improve quantitative and qualitative deposition, but highlights the necessity to match adjuvant dosages and application volumes on the spray target to achieve maximum spray deposition. / AFRIKAANSE OPSOMMING: Effektiewe beheer van vrug- en blaarsiektes soos vaalvrot op wingerde benodig voldoende deponering van die swamdoder op die teikenoppervlak. Verlies aan beheer word gewoonlik aan onvoldoende kwantitatiewe deponering op vatbare wingerddele toegeskryf. Onder ‟n hoë siektedruk kan mislukte beheer ook moontlik toegeskryf word aan swak kwalitatiewe deponering. Die primêre doelwit van spuittegnologie is om deponering te optimaliseer met die plantoppervlak as ‟n belangrike komponent in die spuittoedieningsproses, spesifiek in die retensie van spuitdruppels. Byvoemiddel tegnologie het bewys dat oppervlak-aktiewe-agente verbeterde benatting en verspreiding van druppels op die teiken oppervlakte tot gevolg kan hê, en verder ook die deponering en retensie van die aktiewe fungisied bestanddele kan verbeter. Hierdie relatiewe nuwe spuittegnologie op wingerd- en hortologiese verbouing, asook die moontlike effekte van byvoegmiddels op epikutikulêre waks om siekte ontwikkeling te beïnvloed, moet ondersoek word. Verder word nuttige aanbevelings benodig vir byvoegmiddel toedienings by verskillende spuitvolumes en dosisse van die betrokke spuitmengsel. Die doelwit van hierdie studie was, eerstens om die effek van sekere byvoegmiddels op kwantitatiewe en kwalitatiewe spuitbedekking van wingerdblare te bepaal en dan te vergelyk met die biologiese effektiwiteit van ‟n fungisied, en tweedens om van die byvoegmiddels onder veldtoestande te evalueer, asook die effek van byvoegmiddel dosisse en spuitvolumes te bepaal. Blare is onder dieselfde laboratorium toestande tot net voor-afloop met 1 mL van ‟n spuitmengsel, bestaande uit fenhexamied (Teldor® 500 SC, Bayer) teen die aanbevole dosis, ‟n fluoreserende pigment (400 g/L EC; Suid Australiese Navorsing en Ontwikkeling Instituut) teen 0.2 L/100 L, sowel as 15 geselekteerde kommersiële byvoegmiddels gespuit om die kwalitatiewe deponering, vir ‟n gegewe kwantiteit van spuitdeponering, te manipuleer. Die fluoreserende pigment is op die blaaroppervlak belig met ‟n swart lig (UV-A ligbron in die 365 nm golflengte) en deponering is onder ‟n stereo mikroskoop (Nikon SMZ800) teen 10× vergroting waargeneem. Die gespuite blaaroppervlaktes is op die manier met ‟n digitale kamera afgeneem (Nikon DMX 1200), waarna die digitale foto‟s kwantitatief en kwalitatief deur die gebruik van „Image-Pro Discovery version 6.2 for Windows (Media Cybernetics)‟ sagteware geanaliseer is om spuitbedekking te bepaal. Na elke blaarspuit is die blare met 5 mg droë konidia van B. cinerea in ‟n inokulasietoring geïnokuleer en daarna vir 24 h onder hoë relatiewe humiditeit (≥ 93%) geïnkubeer. ‟n Aantal skyfies vanuit elke blaar is op Petri bakkies met paraquat medium geïsoleer en 11 dae later is die persentasie van B. cinerea ontkieming bepaal. Die gemiddelde voorkoms van B. cinerea op die blare wat slegs met water gespuit is, was 90.4% op die boonste en 95.8% op die onderste blaaroppervlaktes. Spuitbehandelings met slegs fenhexamied, ongeag goeie blaarspuitbedekking, kon nie die B. cinerea infeksie ten volle voorkom nie, en infeksie van gemiddeld 34.6% en 40.8% is onderskeidelik op die boonste- en op die onderste blaaroppervlaktes waargeneem. Met die byvoeging van sekere byvoegmiddels het die voorkoms van B. cinerea betekenisvol verminder (2.9-17.1% en 10.0-30.8%, onderskeidelik), terwyl ander byvoegmiddels nie van die fenhexamied behandeling verskil het nie, hoewel hierdie middels meestal wel spuitdeponering verbeter het. Die effek van slegs Hydrosilicote en Solitaire, en in kombinasie met fenhexamied op ontkiemende Botrytis conidia, is bestudeer in ‟n histopatologiese studie deur middel van die gebruik van epifluoresensie mikroskopie op die blaaroppervlak. Duidelike verskille in die aantal dooie konidia, ontkiemingpersentasies en kiembuislengtes is tussen die byvoegmiddels en in kombinasie met fenhexamied waargeneem, waar sommige waarnemings moontlik aan die indirekte effek van die byvoegmiddel op B. cinerea toegeskryf kan word. Hierdie laboratoriumstudie wys duidelik dat byvoegmiddels oor goeie potensiaal beskik om die bio-effektiwiteit van die fungisied te verbeter deur die direkte verbetering van deponering op die wingerdblaaroppervlak. Dieselfde fluorometrie, fotomikrografie en digitale foto-analise protokol is in ‟n wingerd evaluasie om die kwantitatiewe en kwalitatiewe spuitdeponering van verskillende byvoegmidel dosisse and spuitvolumes te bepaal, gebruik. Die Furness visuele druppel meting tegniek is aanvanklik ingesluit om die optimale spuit volume met ‟n „STIHL SR400 motorised backpack mistblower‟ te bepaal deur visuele meetings van gedeponeerde pigment op Chardonnay blare onder ‟n swart ligbron. Beide protokolle wys dat kwantitatiewe spuitbedekking met ‟n toename in spuit volumes 40 L/ha tot 750 L/ha verbeter het, maar afgeneem het teen 900 L/ha, moontlik as gevolg van druppel-afloop. Die byvoeging van ‟n byvoegmiddel teen die aanbevole dosis en 600 L/ha wys uitstekende potensiaal om kwantitatiewe en kwalitatiewe deponering betekenisvol op boonste en onderste blaaroppervlaktes te verbeter. Agral 90, BB5, Nu-film-P, en Solitaire het deponering betekenisvol op boonste en onderste blare in vergelyking met die fenhexamied alleen en die water kontrole verbeter. Break-thru S 240 en Villa 51 het nie kwantitatiewe deponering verbeter nie, alhoewel verbeterde kwalitatiewe bedekking met hierdie produkte waargeneem is. ‟n Byvoegmiddel dosis effek (binne die registreerde dosis reeks) was duidelik waarneembaar, veral vir druppel retensie op die boonste oppervlak van blare. Agral 90 and Nu-film-P verbeter die spuit deponering betekenisvol met die hoër getoetste dosis, maar nie teen die lae dosis nie. Solitaire verbeter egter die deponering teen die laer dosis, maar minder deponering teen ‟n hoër dosis kan moontlik toegeskryf word aan oormatige druppel-afloop. In die geval van Villa 51 was geen betekenisvolle verbetering van spuitdeponering vir beide die behandelingsdosisse waargeneem nie. Spuitmengsels met byvoegmiddels, Agral 90 en Solitaire, het soortgelyke deponerings gelewer teen 600 L/ha in vergelyking met die fenhexamied kontrole teen 900 L/ha, maar deponering neem af teen hoër spuitvolumes met byvoegmiddels moontlik as gevolg van druppel-afloop. Hierdie studie wys duidelik die uitstekende potensiaal van Byvoegmiddels om kwantitatiewe en kwalitatiewe deponering te verbeter, maar beklemtoon die noodsaaklikheid van die korrekte gebruik van byvoegmiddel dosis en volume om die maksimum spuitdeponering op die teiken te verkry.

Thesis (MScAgric )--Stellenbosch University, 2004. / ENGLISH ABSTRACT: In an attempt to combat some of the pathogens that are associated with trunk diseases and disorders of grapevines, research in this thesis focused on the taxonomy and pathological aspects of Coniellai/Pilidiella, Botryosphaeria and Phomopsis spp. Previously, conidial pigmentation was used to separate Pilidiella from Coniella. Recently, however, the two genera have been regarded as synonymous, with the older name, Coniella, having priority. The most important species in the Coniellai/Pilidiella complex of grapevines is C. diplodiella (Speg.) Petr. & Syd., the causal organism of white rot of grapevines. Previous studies found it difficult to distinguish between C. diplodiella and C. fragariae (Oudem.) B. Sutton, which is known to occur in soil and caused leaf diseases of Fragaria and Eucalyptus. Both these species have previously been reported from South Africa. None of the reports on C. diplodiella could be scientifically substantiated; therefore it is still a quarantine organism. However, this status has been questioned. Based on sequence analyses of the internal transcribed spacer region (ITS 1, ITS 2), 5.8S gene, large subunit (LSU) and elongation factor 1- α gene (EF l- α) from the type species of Pilidiella and Coniella, Coniella was separated from Pilidiella, with the majority of taxa residing in Pilidiella. Pilidiella is characterised by species with hyaline to pale brown conidia (avg. length: width >1.5), with Coniella having dark brown conidia (avg. length: width ≤1.5). Pilidiella diplodiella, previously C. diplodiella, causal organism of white rot of grapevines, was shown to be an older name for C. petrakii. This fungus is present in South Africa and is therefore no longer of quarantine importance. Based on analyses of the histone (H3) gene sequences of isolates in the P. diplodiella species complex, P. diplodiella was separated from a newly described species, P. diplodiopsis. A new species, P. eucalyptorum, is proposed for isolates formerly treated as C. fragariae, associated with leaf spots of Eucalyptus spp. This species clustered basal to Pilidiella, and may represent yet a third genus within this complex. Pilidiella destruens was newly described as anamorph of Schizoparme destruens, which is associated with twig dieback of Eucalyptus spp. in Hawaii. The genus Botryosphaeria Ces. & De Not. are known to be cosmopolitan, with broad host ranges and geographical distributions. Several saprotrophic species have been reported from grapevines, while others are severe pathogens of this host. These species include B. dothidea (Moug.: Fr.) Ces. & De Not., B. parva Pennycook & Samuels, B. obtusa (Schwein.) Shoemaker, B. stevensii Shoemaker, B. lutea A.J.L. Phillips and B. ribis Grossenb. & Duggar. Species reported from South Africa as grapevine pathogens are B. obtusa, B. dothidea, B. ribis and B. vitis (Schulzer) Sacco. In the present study, morphological, DNA sequence data (ITS 1, 5.8S, ITS 2 and EFI-α) and pathological data were used to distinguish 11 Botryosphaeria spp. associated with grapevines from South Africa and other parts of the world. Botryosphaeria australis, B. lutea, B. obtusa, B. parva, B. rhodina and a Diplodia sp. were confirmed from grapevines in South Africa, while Diplodia porosum, Fusicoccum viticlavatum and F. vitifusiforme were described as new species. Although isolates of B. dothidea and B. stevensii were confirmed from grapevines in Portugal, neither of these species, nor B. ribis, were isolated in this study. All grapevine isolates from Portugal, formerly presumed to be B. rib is, are identified as B. parva based on EF1-α sequence data. Artificial inoculations on grapevine shoots showed that B. australis, B. parva, B. ribis and B. stevensii are more virulent than the other species studied. The Diplodia sp. collected from grapevine canes was identified as morphologically similar, but phylogenetically distinct from D. sarmentorum, while D. sarmentorum was confirmed as anamorph of Otthia spiraeae, the type species of the genus Otthia (Botryosphaeriaceae). A culture identified as O. spiraeae clustered within Botryosphaeria, and is thus regarded as a probable synonym. These findings confirm earlier suggestions that the generic concept of Botryosphaeria should be expanded to include genera with septate ascospores and Diplodia anamorphs. The genus Phomopsis (Sacc.) Bubak contains many species that are plant pathogenic or saprotrophic. Ten species are known from grapevines. However, only two have been confirmed as being pathogenic, namely P. viticola (Sacc.) Sacc., causal organism of Phomopsis cane and leaf spot and P. vitimegaspora Kuo & Leu (teleomorph Diaporthe kyushuensis Kajitani & Kanem.), causal organism of swelling arm disease of grapevines. P. amygdali (Delacr.) 1.1. Tuset & M.T. Portilla, a known pathogen from Prunus sp., was shown to be a possible pathogen of grapevines in a previous study. D. perjuncta Niessl. causes bleaching of dormant canes only and is therefore of little importance as a grapevine pathogen. Recently a number of Phomopsis isolates were obtained from grapevines in the Western Cape province of South Africa. Isolations were made from Phomopsis-like symptoms, pruning wounds and asymptomatic nursery plants. These isolates showed great variation in morphology and cultural characteristics. Earlier taxonomic treatments of Phomopsis, based species identification on host specificity, cultural characteristics and morphology. Recent studies have indicated that these characteristics can no longer be used to distinguish species of Phomopsis due to wide host ranges and morphological plasticity of some species. The use of anamorph/teleomorph relationships in species identification is also untenable, since Diaporthe teleomorphs have only been described for approximately 20% of the known Phomopsis species. In this study morphological data, DNA sequences (ITS-I, 5.8S, ITS-2) and pathogenicity data were combined to distinguish Phomopsis spp. from grapevines. Fifteen species of Phomopsis were delineated by phylogenetic analysis of ITS sequence data. Diaporthe helianthi, a sunflower pathogen, was reported from grapevines for the first time, with a further six, unknown species also distinguished. Three different clades contained isolates previously identified as D. perjuncta. Based on type studies, it appeared that the name D. viticola was available for collections from Portugal and Germany, a new species, D. australafricana, was proposed for South African and Australian isolates, formerly treated as D. perjuncta or D. viticola. An epitype specimen and culture were designated for D. perjuncta. This species was distinguished from D. viticola and D. australafricana based on morphology and DNA phylogeny. Artificial inoculations of green grapevine shoots indicated that, of the species tested, P. amygdali, a known pathogen of peaches in the USA, and P. viticola were the most virulent. / AFRIKAANSE OPSOMMING: In 'n poging om sommige patogene geassosieer met stamsiektes en syndrome, te beveg, het die navorsing in die tesis gefokus op die taksonomie en patologiese aspekte van ConiellaiPilidiella, Botryosphaeria en Phomopsis spp Voorheen is konidium pigmentasie gebruik om Pilidiella (hialien tot ligbruin konidia) van Coniella (donkerbruin konidia) te skei. Onlangs is hierdie twee genera egter as sinoniem beskou met die ouer naam, Coniella, wat voorkeur gekry het. Die belangrikste spesies in die ConiellaiPilidiella kompleks van wingerd is C. diplodiella (Speg.) Petr. & Syd., die veroorsakende organisme van witvrot van wingerd. Vorige studies het dit moeilik gevind om te onderskei tussen C. diplodiella en C. fragariae (Oudem.) B. Sutton, wat bekend is dat dit in grond voorkom en ook blaarsiektes van Fragaria en Eucalyptus veroorsaak. Beide hierdie spesies is tevore in Suid-Afrika aangemeld. Geen van die aanmeldings van C. diplodiella is egter wetenskaplik bewys nie en daarom is dit steeds 'n kwarantyn organisme. Hierdie kwarantyn status is egter bevraagteken. Op grond van DNS volgordes van die interne getranskribeerde spasieerder area ("ITS 1", "ITS2"), die 5.8S rRNS geen, die groot ribosomale subeenheid ("LSU") en die verlengingsfaktor 1-α geen ("EF-lα") van die tipe spesies van Pilidiella en Coniella, is Coniella van Pilidiella geskei, met die meerderheid van die taxa wat binne Pilidiella resorteer. Pilidiella word gekarakteriseer deur spesies met hialien tot ligbruin konidia (gem. lengte: breedte > 1.5), in teenstelling met die donkerbruin konidia van Coniella (gem. lengte: breedte ≤ 1.5). Daar is verder bewys dat Pilidiella diplodiella, voorheen C. diplodiella, veroorsakende organisme van witvrot van wingerd, die ouer naam van C. petrakii is. Hierdie swam is teenwoordig in Suid-Afrika en P. diplodiella is dus nie meer van kwarantyn belang nie. Op grond van analises van die histoon (H3) volgordes van spesies in die P. diplodiella spesies kompleks, is P. diplodiella geskei van 'n nuut beskryfde spesie, P. diplodiopsis. 'n Nuwe spesie, P. eucalyptorum, is ook voorgestel vir isolate voorheen beskou as C. fragariae, geassosieer met blaarvlek van Eucalyptus spp. Hierdie spesie het basaal van Pilidiella gegroepeer en mag moontlik nog 'n derde genus binne hierdie kompleks verteenwoordig. Pilidiella destruens is nuut as anamorf van Schizoparme destruens beskryf, wat geassosieer word met loot terugsterwing van Eucalyptus spp. in Hawaii. Die genus Botryosphaeria Ces. & De Not. is bekend as kosmopolitaans met 'n wye gasheerreeks en geografiese verspreiding. Verskeie saprofitiese spesies is aangemeld vanaf wingerd, terwyl ander ernstige patogene van hierdie gasheer is. Laasgenoemde spesies sluit in B. dothidea (Moug.: Fr.) Ces. & De Not., B. parva Pennycook & Samuels, B. obtusa (Schwein.) Shoemaker, B. stevensii Shoemaker, B. lutea A.1.L. Phillips en B. ribis Grossenb. & Duggar. Spesies aangemeld in Suid-Afrika as wingerdpatogene, is B. obtusa, B. dothidea, B. ribis en B. vitis (Schulzer) Sacco In hierdie studie is morfologiese, DNS volgorde data ("ITSl", "ITS2", 5.8S en "EF-Iα") en plantpatologiese data gebruik om II Botryosphaeria spesies, geassosieer met wingerde in Suid-Afrika en verskeie ander werelddele, te onderskei. Botryosphaeria australis, B. lutea, B. obtusa, B. parva, B. rhodina en 'n Diplodia sp. is bevestig van wingerde in Suid-Afrika, terwyl Diplodia porosum, Fusicoccum viticlavatum en F. vitifusiforme as nuwe spesies beskryf is. AIhoewel isolate van B. dothidea en B. stevensii bevestig is van wingerde in Portugal, is geen van hierdie spesies en ook nie B. ribis geïsoleer nie. AIle isolate vanaf wingerd in Portugal, voorheen beskou as B. rib is, is as B. parva op grond van hul "EF-lα" volgordes geïdentifiseer. Uit kunsmatige isolasies gemaak op wingerdlote is die gevolgtrekking gemaak dat B. australis, B. parva, B. ribis en B. stevensii meer virulent is as die ander spesies wat bestudeer is. Die Diplodia sp. versamel vanaf wingerdlote is geïdentifiseer as morfologies eenders, maar filogeneties verskillend van D. sarmentorum, terwyl D. sarmentorum bevestig is as die anamorf van Otthia spiraeae, die tipe spesie van die genus Otthia (Botryosphaeriaceae). 'n Kultuur wat as 0. spiraeae geïdentifiseer is, het binne Botryosphaeria gegroepeer, en word dus as 'n moontlike sinoniem beskou. Hierdie bevindinge bevestig vroeëre voorstelle dat die generiese konsep van Botryosphaeria uitgebrei behoort te word om genera met gesepteerde askospore en Diplodia anamorwe in te sluit. Die genus Phomopsis (Sacc.) Bubak bevat verskeie spesies wat as of plantpatogenies, of saprofities, beskryf is. Tien spesies is bekend op wingerd. Slegs twee is as patogenies bevestig, naamlik P. viticola (Sacc.) Sacc., veroorsakende organisme van loot-en-blaarvlek ("streepvlek") en P. vitimegaspora Kuo & Leu (teleomorf Diaporthe kyushuensis Kajitani & Kanem.), veroorsakende organisme van geswelde arm van wingerd. In 'n vroeëre studie is bevind dat P. amygdali (Delacr.) 1.1. Tuset & M.T. Portilla, 'n bekende patogeen van Prunus sp., moontlik ook 'n patogeen van wingerd mag wees. D. perjuncta Niessl. veroorsaak egter net verbleiking van dormante lote en is dus van min belang as 'n wingerd patogeen. Gedurende die afgelope twee jaar is verskeie Phomopsis isolate van wingerde in die Wes-Kaap provinsie van Suid-Afrika verkry. Isolasies is gemaak van Phomopsis-agtige simptome, snoeiwonde en asimptomatiese kwekeryplante. Die isolate verkry uit hierdie materiaal het groot variasie ten opsigte van morfologie en kultuureienskappe getoon. Vroeëre taksonomiese verhandelings van Phomopsis het spesies-identifikasie op gasheerspesifisiteit, kultuureienskappe en morfologie gebasseer. Onlangse studies het egter getoon dat, weens wye gasheerreekse en morfologiese plastisiteit van somnuge spesies, hierdie eienskappe me meer gebruik kan word om Phomopsis spesies te identifiseer nie. Die gebruik van anamorflteleomorf verwantskappe in die identifikasie van Phomopsis spesies ook onbruikbaar omdat Diaporthe teleomorwe vir slegs ongeveer 20% van die bekende Phomopsis spesies beskryf is. Die huidige studie het dus morfologiese data, DNS volgordes ("ITS 1", 5.8S, "ITS2") en patogenisiteitsdata gekombineer ten einde Phomopsis spp. vanaf wingerd te identifiseer. Vyftien Phomopsis spesies is deur die filogenetiese analise van die interne getranskribeerde spasieerder area ("ITS") volgordes geskei. Diaporthe helianthi, 'n bekende patogeen van sonneblomme, is vir die eerste maal op wingerd aangeteken, terwyl 'n verdere ses, tans onbekende spesies van Phomopsis ook geidentifiseer is. Drie verskillende groepe het isolate bevat wat voorheen as D. perjuncta geidentifiseer is. Gebasseer op studies van tipes, het dit voorgekom dat die naam D. viticola beskikbaar is vir isolate uit Portugal en Duitsland. 'n Nuwe spesie, D. australafricana, is voorgestel vir Suid-Afrikaanse en Australiese isolate wat voorheen behandel is as D. perjuncta of D. viticola. 'n Epitipe monster en kultuur is vir D. perjuncta benoem. Hierdie spesie is van D. viticola en D. australafricana onderskei op grond van morfologie en DNS filogenie. Kunsmatige inokulasies van groen wingerdlote het getoon dat P. amygdali, bekende perske patogeen, en P. viticola die mees virulent was.

Thesis (MScAgric)--Stellenbosch University, 1972. / ENGLISH ABSTRACT: no abstract available

Thesis (MScAgric)--Stellenbosch University, 1964. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming