No description available.

No description available.

The ultrastructural aspects of Rhizopus stolonifer (Fr.) Lind. Infection in Ipomoea batatus Lam. Roots and the histochemistry of cell walls affected by enzymes secreted by the fungus were investigated. Specimens were prepared for viewing in the electron microscope by thin-sectioning techniques. Degradation of cellular membreanes and host tissues in advance of the fungus was evident. Breakdown of the middle lamella was detected by special histochemical stains for pectin. Breakdown occurred in the following was: (1) maceration of the middle lamella before maceration of the cell wall, (2) simultaneous degradation of both the middle lamella and the cell wall, (3) maceration of the cell wall before maceration of the middle lamella. A difference in electron-opacity in health, non-infected host walls and infected host walls was observed. Irregularity in the infection front and the host tissues by various enzymes was observed.

No description available.

Erwinia soft rot is a widespread disease destructive to numerous important crop plants. Damage to plants is primarily due to celldegrading enzymes (CDEs) secreted by the bacteria. I am interested in potato (Solanum tuberosum) soft rot because it is of agricultural importance and it represents an ideal model system for understanding molecular events in plant-pathogen interactions. Much has been learned in vitro about the molecular genetics of CDEs in the past decade; however, little is known about their expression in plantae To study expression of genes for these enzymes during pathogenesis and plant responses to erwinias or their enzymes, I developed a membrane-separated system for simultaneous studies of potato and bacterial gene expression. This system facilitates the isolation of plant tissue-free bacterial cells and bacteria-free plant tissue for subsequent analysis of gene expression by RNA blot hybridization. Using this system, I demonstrated that in compatible interactions, rnRNAs for three Erwinia carotovora subsp. carotovora (Ecc) CDE genes were induced to high levels and were induced sequentially: exo-pectate lyase (PL), endo-PL, and then endopolygalacturonase (PG) with maximal mRNA accumulations at 6, 9, and 12 hr, respectively. Induction of these mRNAs was well correlated with tissue maceration. In the incompatible interaction, however, induction of all three Ecc genes was reduced several-fold compared to the compatible interaction. The kinetics of mRNA accumulation during pathogenesis were distinct from those of in vitro accumulation induced by polygalacturonic acid. My results confirm that in planta expression of these genes was induced by exo-PL reaction products as suggested by other researchers. In studies of plant genes correlated with plant responses to pathogens and environmental stresses [plant defenseresponse (PDR) genes], I also showed Ecc triggered active responses distinct from wound responses. I used gene probes for phenylalanine ammonia- lyase (PAL) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), key genes in the biosynthesis of phenylpropanoid- and terpenoidderived compounds believed to be important in plant defenses. Ecc inoculation caused much more rapid and greater increases in PAL mRNA and enzyme activity levels in potato tuber than wounding alone. Escherichia coli, a non-plant pathogen, carrying a plasmid which encodes Ecc endo-PL, also induced PAL mRNA accumulation. Ecc induced a specific HMGR isogene (HMGR1) not activated by wounding. My results support the existence of an HMGR mul-ci-gene family. Wounding resulted in a rapid and transient accumulation of HMGR2 mRNA followed by a slower accumulation of HMGR3 mRNA. These isogenes are distinct from the Ecc-induced HMGRI gene. / Ph. D.

The variation for embryo production in anther culture of Solanum phureja was examined as a function of maximum greenhouse temperature prior to bud harvest and innate responsiveness among anthers within a bud. S. phureja clones PP5, AD2-4, A3P2-6 and AD3-4 were grown in a greenhouse under a 16 h photoperiod. The temperature was monitored continuously using a thermograph. Buds were collected from PPS and AD2-4 and the anthers were cultured in two groups of five flasks. In the first group, each flask contained the 30 anthers from 6 buds; the second group, each flask contained 1 anther from each of 30 buds -- a total of 30 anthers per flask. Significantly smaller coefficients of variation were observed for the second group, suggesting that the variation for embryogenic capacity among buds was greater than that among anthers within a bud. Variation in embryo yield as a function of greenhouse temperature for clones A3P2-6 and AD3-4 was examined by stepwise regression analysis. Embryogenic capacity of clone A3P2-6 was adversely affected by high temperatures (31-37°C) that occurred 2 and 7 days before bud harvest. However similarly high temperatures appeared to enhance the androgenic response of clone AD3-4. Regeneration rate of anther-derived embryos over three subcultures to fresh regeneration medium was examined as a function of anther donor or clone, cold pretreatment of embryos, and morphological classification of embryos. Only clonal origin significantly affected regeneration. Regeneration rate declined on each serial subculture. The frequency of regenerable embryos varied from 12.5% for clone BARD 1-3 to 46.0% for clone A3P2-6. Flow cytometric analyses were performed on several anther-derived monoploids of S. phureja to examine the frequency of nuclei at the 1x, 2x, and 4x levels within and among clones. Significant variation was found among duplicate cultures of the individual clones, but this variation was small enough to allow the detection of significant differences among the clones. Monoploid cell frequency ranged from 22.3% to 35.7%. Diploid cell frequency ranged from 48.6% to 59.9%. Tetraploid cell frequency ranged from 11.9% to 25.3%. Several families of anther-derived monoploid clones of S. phureja were analyzed for differences among clones within a family and among families. Significant differences were found in both categories. Finally, unstained protoplasts of monoploid S. phureja clone AM3 were sorted based on forward angle light scatter (FALS) and autofluorescence. Fractions selected for low FALS and weak autofluorescence appeared to be selectively enriched for monoploid protoplasts. / Master of Science

Rimsulfuron {N-[[ 4,6-dimethoxy-2-pyrimidinal)amino ]carbonyl]-3-( ethylsulfonyl)-2-pyridinesulfonamide} is a new sulfonylurea herbicide under development by E.I. Dupont de· Nemours & Company Inc. for preemergence and postemergence grass and broadleaf weed control in Solanaceous vegetable crops. The efficacy and selectivity of rimsulfuron were determined in potatoes, transplanted tomatoes, and transplanted peppers in field studies in 1991, 1992, and 1993. Treatments included rimsulfuron and metribuzin alone and in combination in potatoes and tomatoes, rimsulfuron alone in peppers, and sequential applications of rimsulfuron in tomatoes and peppers. Application timings included preemergence and postemergence in potatoes, while only post-transplant applications were evaluated in tomatoes and peppers. Preemergence applications of rimsulfuron controlled weeds if rainfall was received within a few days following application. Control was often greater in potatoes and tomatoes than in peppers. These differences likely relate to more frequent rainfall events in potatoes and tomatoes than in the later-planted peppers. / Master of Science

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Potato Virus Y (PVY) and Potato Leafroll Virus (PLRV) are two of the most destructive potato viruses capable of drastically diminishing crop yields by up to 80%. The presence of these viruses in planting material namely seed potato stocks are routinely diagnosed by enzyme-linked immunosorbent assay (ELISA) kits. The kits currently used by Potatoes South Africa are obtained from Europe. These kits have produced false positive and false negative results in the past. Potatoes South Africa required an ELISA that was reliable, cheap and specific for the detection of South African strains of the two respective viruses. In this study the viral coat protein genes were amplified by RT-PCR from a South African source of infected plant material. The PVY and PLRV coat protein genes were subsequently cloned into pGEM-T Easy vector and sequenced. The sequences of the two viruses were aligned and compared to corresponding viral coat protein gene sequences obtained from Genbank. Subsequently the two amplified and cloned coat protein genes of PVY and PLRV were sub-cloned into an expression system (pET-14b) to induce and express the respective recombinant viral coat proteins. The induction of the cloned coat protein genes yielded successful production of the recombinant PVY coat protein but the induction and expression of the recombinant PLRV coat protein was unsuccessful. The isolated recombinant PVY CP was then used to immunize a rabbit to produce highly specific anti-PVY CP immunoglobulins. The antiserum obtained from the rabbit was used to develop an ELISA to detect the presence of PVY in seed potato stocks in South Africa. The ELISA kit was subsequently used in preliminary trials to determine if the kit could detect PVY infected plant material. The initial results of the ELISA trials using PVY infected material obtained from Potatoes South Africa yielded positive results. / AFRIKAANSE OPSOMMING: Aartappel Virus Y (PVY) en Aartappel Rolblad Virus (PLRV) is twee van die mees vernietigende aartappel virusse wat ‘n oes tot 80% kan verlaag. Virus infeksie van plant materiaal tewete aartappelmoere word deur “enzyme-linked immunosorbent assay” (ELISA) toetsstelle bevestig. Die toetsstelle wat op die oomblik gebruik word deur Aartappels Suid- Afrika word in Europa vervaardig. Hierdie toetsstelle het vals positiewe en vals negatiewe resultate in die verlede gegee. Aartappels Suid-Afrika benodig toetsstelle wat betroubaar, goedkoop en spesifiek vir Suid-Afrikaanse virus stamme is. In hierdie studie is besmette plantmateriaal vanuit Suid-Afrika gebruik vir die amplifisering van virale mantel proteïen gene met behulp van RT-PCR. Die PVY en PLRV mantel proteïen gene was daarna in die pGEM-T Easy vektor gekloneer en nukleotied volgordes is bepaal. Die nukleotied volgordes is met ander PVY en PLRV gene vanaf Genbank vergelyk. Die twee ge-amplifiseerde en gekloneerde mantel proteïen gene van PVY en PLRV is uitgesny en gekloneer in ‘n ekspressie sisteem (pET-14b) om die mantel proteïen te produseer. Induksie van die gekloneerde mantel proteïen gene het gelei tot die suksesvolle produksie van ‘n PVY mantel proteïen, maar produksie van die PLRV mantel proteïen was onsuksesvol. Die geïsoleerde PVY mantel proteïen is vervolgens gebruik vir die immunisering van ‘n konyn vir die produksie van konyn anti-PVY antiliggame. Die antiserum verkry vanaf die konyn is gebruik vir die ontwikkeling van ‘n ELISA vir die identifisering van PVY infeksies in aartappelmoere. Voorlopige proewe is deurgevoer om te bepaal of hierdie ELISA PVY infeksies in plantmateriaal sou kon opspoor. Aanvanklike resultate toon dat die ELISA suksesvol PVY infeksies in plantmateriaal verkry vanaf Aartappels Suid-Afrika kan opspoor.

Thesis (MSc)--University of Stellenbosch, 2008. / ENGLISH ABSTRACT: Potato virus Y (PVY) is responsible for considerable yield losses in the South African potato industry. The incidence of this virus has greatly increased over the past few years. Even more worrying is the variation of symptoms observed during PVY infection and the recent appearance of the more virulent PVYNTN strain in local fields. This project aimed to investigate the possible genetic variation within the viral genome and to establish the origin of strains. The project also aimed to establish a dependable, area specific enzyme-linked immunosorbent assay (ELISA) to replace the currently used ELISAs. Currently seed potato certification is done using ELISA kits imported from Europe. These kits were developed for the detection of overseas variants of PVY and the use thereof in South Africa has in the past lead to false negatives. Finally, this project set out to develop, optimize and establish a sensitive and reliable real-time reverse transcriptase polymerase chain reaction (qRT-PCR) detection protocol for PVY. In the first part of the study the coat protein (CP) gene of PVY isolates from plant material obtained from various parts of South Africa was amplified using RT-PCR. The resulting cDNA was then sequenced directly or cloned into a vector and then sequenced. The resulting sequences were aligned in a data matrix with international reference sequences, analyzed and grouped according to strain. Examination of the CP gene within this matrix as well as phylogenetic analysis revealed six main groups of PVY. These six groups included the traditional PVYN and PVYO groups and a recombinant group. Furthermore it also revealed variants of PVYN and PVYO. These mutants and recombinants pose a threat as they may lead to South African strains of PVY expressing coat proteins which vary from those found overseas. This may render the currently used European ELISA method of detection less effective and subsequently result in an increase in viral prevalence. This reinforced the need for a detection method based on local viral strains. Phylogenetic and Simplot analysis also confirmed that a recombinant strain between PVYN and PVYO had evolved and that PVYNTN was such a recombinant. The second part of the study aimed to develop and establish detection methods based on local variants of PVY. This included the development of ELISA and qRT-PCR detection methods of PVY. Previously amplified cDNA of the PVY CP gene was cloned into an expression vector and successfully expressed. Antibodies produced against the recombinant protein, when used in ELISA, however, failed to achieve the required levels of sensitivity. This prompted the development of qRT-PCR detection methods for PVY. Primer combinations for PVY were designed using the previously established CP gene data matrix. A reliable and sensitive SYBR® Green I based qRT-PCR assay was developed for the detection of PVY. The assay effectively detected all known South African variants of PVY. Furthermore, a Taqman® assay was developed for the detection of all variants of PVY. The Taqman® assay was 10 fold less sensitive and does not allow for amplicon verification through melting curve analysis, but it does add more specificity due to the addition of the probe. Although these qRT-PCR detection methods are still too expensive to replace the routine diagnostics done with ELISA, they do offer the opportunity to screen valuable mother material and confirm borderline cases in seed certification. / AFRIKAANSE OPSOMMING: Aartappel virus Y (PVY) is verantwoordelik vir aansienlike opbrengsverliese in die Suid-Afrikaanse aartappelindustrie. Die insidensie van infeksie deur die virus het drasties toegeneem oor die afgelope jare. Wat egter meer kommerwekkend is, is die groter variasie in simptome van PVY infeksie en die onlangse voorkoms ‘n meer virulente ras, PVYNTN. Hierdie projek poog om moontlike genetiese variasie van PVY te ondersoek en om die oorsprong van rasse op te spoor. Die projek het ook gepoog ook om ‘n bruikbare, betroubare en area spesifieke “enzyme-linked immunosorbent assay” (ELISA) toets te ontwikkel om die huidige ingevoerde ELISA te vervang. Hierdie toetse is ontwikkel om oorsese variante van PVY op te spoor en die gebruik daarvan het in die verlede gelei tot vals negatiewes. Verder is daar ook ondersoek ingestel na die ontwikkeling van ‘n sensitiewe en betroubare “real-time reverse transcriptase polymerase chain reaction” (qRT-PCR) protokol vir die opsporing van PVY. In die eerste deel van die studie is die mantelproteïen geen van PVY isolate vanuit plant materiaal geamplifiseer deur die gebruik van RT-PCR. Hierdie materiaal is vanaf verskeie streke in Suid-Afrika ontvang. ‘n Volgordebepalingsreaksie is uitgevoer op gekloneerde of ongekloneerde cDNA verkry uit die RT-PCR. DNA volgordes is in ‘n data matriks geplaas en vergelyk met internationale volgordes om die plaaslike isolate te analiseer en te groepeer. Deur vergelyking en filogenetiese ontleding kon ses hoofgroepe van PVY geïdentifiseer word, wat tradisionele PVYN en PVYO, sowel as ‘n rekombinante ras en variante binne die tradisionele PVYN en PVYO groepe ingesluit het. Rekombinante en mutante kan veroorsaak dat Suid-Afrikanse rasse van PVY mantelproteïene uitdruk wat afwyk van die oorsese rasse wat tot gevolg mag hê dat die ELISAs van oorsee minder effektief kan wees en kan lei tot verhoogde virus voorkoms. Die realiteit en gevaar versterk die gedagte dat ‘n deteksie metode gebaseer op plaaslike virusse absoluut krities is. Filogenetiese sowel as Simplot analise het bevestig dat ’n mutante ras tussen PVYN en PVYO ontstaan het en dat PVYNTN ’n rekombinante ras is. Die tweede deel van die studie was daarop gemik om deteksie metodes te ontwikkel wat gebaseer was op plaaslike variante van PVY. Dit sluit die ontwikkeling van ELISA sowel as qRT-PCR deteksie van PVY in. Voorheen geamplifiseerde cDNA is in ‘n ekspressievektor gekloneer en suksesvol uitgedruk. Teenliggaampies teen die rekombinante proteïen, indien in ELISA aangewend, kon egter nie die nodige sensitiwiteit oplewer nie. Dit het aanleiding gegee tot ontwikkeling van qRT-PCR deteksie metodes. Inleier kombinasies vir PVY was ontwikkel deur die gebruik van die bestaande mantelproteïen geen data matrikse. ‘n Betroubare en sensitiewe SYBR® Green I qRT-PCR deteksie protokol was ontwikkel vir die effektiewe deteksie van alle bekende Suid-Afrikanse rasse van PVY. Verder is ‘n sogenaamde “Taqman®” protokol ook ontwikkel vir deteksie van alle rasse. Die “Taqman®” protokol was 10 voudiglik minder gevoelig and laat nie bevestiging deur smeltkurwe analise toe nie, maar verleen meer spesifisiteit deur die toevoeging van die “Taqman® probe”. Hierdie qRT-PCR deteksie metodes is tans te duur om as roetine diagnostiese toetse te gebruik en kan dus nie ELISA vervang nie, maar hulle bied wel die geleentheid om waardevolle moeder materiaal te toets en grensgevalle in aartappelsaad sertifisering te bevestig.

Thesis (MSc)--Stellenbosch University, 2010. / ENGLISH ABSTRACT: Late blight caused by Phytophthora infestans on potato and tomato causes major economic losses worldwide. Until the 1980s, P. infestans populations outside its centre of origin (either central Mexico or the Andean region) only consisted of one mating type (A1), which prevented the pathogen from reproducing sexually. Pathogen populations outside the centre of origin most likely only consisted of a few genotypes prior to the 1980’s. Pan globally, these genotypes probably first consisted of genotype/s that had mitochondrial DNA (mtDNA) haplotype Ia, which was subsequently replaced by a mtDNA haplotype Ib genotype known as the US-1 lineage. This relative simple population structure of the pathogen changed almost worldwide in the late 1970s and early 1980s, when a second set of migrations took place from the centre of origin. These populations contained both A1 and A2 mating type isolates that consisted of several different genotypes, which were more virulent than the pre-1970s genotypes and resulted in the displacement of these genotypes almost worldwide. Some of the new genotypes were also resistant to metalaxyl, the fungicide that was most effective in controlling late blight. In Sub-Saharan Africa (SSA), the characteristics of P. infestans populations are not well documented in most countries except South Africa, Kenya and Uganda. Previous studies in SSA showed that populations were dominated by the US-1 lineage and its variants. The exceptions were reports of the presence of a few mtDNA haplotype Ia isolates in Rwanda and Ethiopia. The current study aimed to determine the population structure of P. infestans in eight selected SSA countries (Burundi, Kenya, Rwanda, Tanzania, Uganda, Malawi, Mozambique and South Africa), mainly on potato and on a limited scale on tomato and petunia, using ‘old’ markers (mating type determination, glucose-6-phosphate isomerase [Gpi] genotyping, mtDNA haplotyping, DNA fingerprinting with probe RG-57 and metalaxyl sensitivity). Populations were further also genotyped using seven recently published Simple Sequence Repeats (SSRs) markers. This information would help to define the population structure of P. infestans in SSA for the first time on a regional basis, and will also determine whether new migrations have taken place since the last characterization studies took place in 2001. A survey in the eight SSA countries yielded a total of 281 P. infestans isolates, mainly obtained from potato fields (Tanzania, Kenya, Uganda, Rwanda, Burundi, Malawi and South Africa), but also from tomato (Malawi, Mozambique and South Africa) and Petunia ´ hybrida (South Africa) that were characterized. Characterization of subsets of the isolates with the ‘old’ markers (176 isolates for mating type, 281 isolates for mtDNA, 70 isolates for [Gpi] and 49 isolates with restriction fragment length polymorphism analysis with probe RG-57), showed that most of the isolates belonged to the US-1 genotype or its variants (US-1.10 and US-1.11). The exception were isolates that belonged to genotype KE-1 (A1 mating type, mtDNA haplotype Ia, Gpi 90/100 and unique RG-57 genotype) that was identified in two fields in Kenya. Genotype KE-1, based on the ‘old’ marker data, is related to genotypes (RW-1 and RW-2) previously identified in Rwanda, and several Ecuadorean and European genotypes. Metalaxyl sensitivity testing of 64 isolates showed that metalaxyl resistant potato isolates were present in all the countries except Malawi, whereas all the tomato isolates were sensitive. Genotyping of 176 isolates with seven recently published simple sequence repeat (SSR) markers revealed a high number (79) of multi-locus genotypes (MLGs) in SSA. However, when locus D13, which was difficult to score, was excluded only 35 MLGs were identified. When locus D13 was excluded from analyses of molecular variance (AMOVA), (i) there was no significant genetic differentiation between populations from central-east Africa (Burundi, Kenya, Rwanda, Tanzania and Uganda), south-east Africa (Malawi and Mozambique) and South Africa, (ii) the KE-1 population was genetically differentiated (Fst = 0.33; P = 0.001) from the US-1 and US-1.10 populations and (iii) genetic differentiation between populations from potato and tomato was low (Fst = 0.07; P = 0.004). The study has expanded the worldwide genotypic database of P. infestans for SSA. Previously, no populations were characterized from Burundi, Malawi and Mozambique. The characterization work showed that migrations seem unlikely to have taken place in SSA, or if these did occur, it was on a very limited scale. The more severe epidemics in some SSA countries could be due to the presence of metalaxyl resistance. Furthermore, the occurrence of mutations or mitotic recombination might have resulted in more aggressive and/or better adapted genotypes, for example the US-1.10 lineage that was only detected in the Western Cape Province of South Africa. The significance of the discovery of the KE-1 genotype in Kenya needs further investigation since it might (i) be an asexual descendent of genotypes (RW-1 and RW-2) that were previously reported in Rwanda in the 1980s, (ii) previously have gone undetected due to the small surveys that were conducted in SSA, (iii) be a new migrant from countries other than SSA or (iv) have been introduced in the very first introductions into Kenya prior to the 1970s. The SSR results from the survey will allow comparison of the SSA late blight populations with other populations worldwide through the EucaBlight database in future studies. / AFRIKAANSE OPSOMMING: Laatroes, veroorsaak deur Phytophthora infestans op aartappel en tamatie, veroorsaak groot ekonomiese verliese wêreldwyd. Phytophthora infestans populasies buite hul kern van oorsprong (óf sentraal Meksiko óf die Andes area), het tot die 1980’s slegs uit een paringstipe (A1) bestaan, wat verhoed het dat die patogeen geslagtelik vermeerder. Patogeenpopulasies buite die kern van oorsprong, het heel moontlik vóór die 1980’s slegs uit ‘n paar genotipes bestaan. Wêreldwyd, het hierdie genotipes moontlik aanvanklik uit genotipe(s) bestaan wat mitokondriale DNS (mtDNS) haplotipe Ia bevat het, wat later met ‘n mtDNS haplotipe Ib genotipe, bekend as die US-1 genotipe, vervang is. Hierdie relatiewe eenvoudige populasiestruktuur van die patogeen, het omtrent wêreldwyd in die láát 1970’s en vroeë 1980’s verander, toe ‘n tweede stel migrasies vanaf die patogeen se kern van oorsprong plaasgevind het. Hierdie populasies het beide A1 en A2 paringstipe isolate ingesluit, wat uit verskeie verskillende genotipes bestaan het, wat meer virulent as die vóór-1970’s genotipes was, en wat die verskuiwing van hierdie genotipes omtrent wêrelwyd tot gevolg gehad het. Sommige van die nuwe genotipes was ook weerstandbiedend teen metalaksiel, die fungisied wat mees effektief in die beheer van laatroes was. Die kenmerke van P. infestans populasies is nie goed in die meeste lande in Sub- Sahara Afrika (SSA) gedokumenteer nie, behalwe vir Suid-Afrika, Kenia en Uganda. Vorige studies in SSA het aangedui dat populasies deur die US-1 genotipe en sy variante gedomineer word. Die uitsonderings was aantekeninge oor die teenwoordigheid van ‘n paar mtDNS haplotipe Ia isolate in Rwanda en Etiopië. Die huidige studie was daarop gemik om die populasiestruktuur van P. infestans in agt geselekteerde SSA lande (Burundi, Kenia, Rwanda, Tanzanië, Uganda, Malawi, Mosambiek en Suid-Afrika), hoofsaaklik op aartappel en op ‘n beperkte skaal op tamatie en petunia, vas te stel, deur die gebruik van ‘ou’ merkers (paringstipe-bepaling, glukose-6-fosfaat isomerase [Gpi] genotipering, mtDNS haplotipering, DNS fingerafdrukke met RG-57 en metalaksielsensitiwiteit). Die genotipe van populasies is verder ook bepaal deur gebruik te maak van sewe onlangs-gepubliseerde “Simple Sequence Repeats (SSRs)” merkers. Hierdie inligting sal help om die populasiestruktuur van P. infestans in SSA vir die eerste keer op ‘n streeksbasis vas te stel, en sal ook bepaal of nuwe migrasies sedert die laaste karakteriseringstudies wat in 2001 uitgevoer is, plaasgevind het. ‘n Opname in die agt SSA lande, het ‘n totaal van 281 P. infestans isolate opgelewer, hoofsaaklik vanaf aartappellande (Tanzanië, Kenia, Uganda, Rwanda, Burundi, Malawi en Suid-Afrika), maar ook vanaf tamatie (Malawi, Mosambiek en Suid- Afrika) en Petunia ´ hybrida (Suid-Afrika) wat gekarakteriseer is. Karakterisering van geselekteerde isolate met die ‘ou’ merkers (176 isolate vir paringstipe, 281 isolate vir mtDNS, 70 isolate vir Gpi en 49 isolate met restriksiefragment-lengte-polimorfismeanalise met RG-57), het aangetoon dat die meeste van die isolate aan die US-1 genotipe of sy variante (US-1.10 en US-1.11) behoort het. Die uitsondering was isolate wat tot die genotipe KE-1 behoort het (A1 paringstipe, mtDNS haplotipe Ia, Gpi 90/100 en unieke RG-57 genotipe) wat in twee velde in Kenia geïdentifiseer is. Genotipe KE-1, gebaseer op die ‘ou’ merkerdata, is aan genotipes (RW-1 en RW-2) verwant, wat voorheen in Rwanda, en verskeie Ekwadoreaanse en Europese lande geïdentifiseer is. Metalaksielsensitiwiteitstoetsing van 64 isolate het aangetoon dat metalaksiel-weerstandbiedende aartappel-isolate in al die lande teenwoordig was, behalwe vir Malawi, terwyl al die tamatie-isolate sensitief was. Genotipering van 176 isolate met sewe onlangs gepubliseerde “Simple Sequence Repeat” (SSR) merkers, het ‘n hoë aantal (79) multilokus genotipes (MLGs) in SSA aangedui. Met die uitsluiting van lokus D13, wat moeilik was om te evalueer, is slegs 35 MLGs egter geïdentifiseer. Met die uitsluiting van lokus D13 uit die analise van molekulêre variansie (AMOVA), was (i) daar geen betekenisvolle genetiese differensiasie tussen populasies van sentraal-oos Afrika (Burundi, Kenia, Rwanda, Tanzanië en Uganda), suid-oos Afrika (Malawi en Mosambiek) en Suid-Afrika nie, (ii) die KE-1 populasie geneties (Fst = 0.33; P = 0.001) van die US-1 en US-1.10 populasies gedifferensieerd en (iii) genetiese differensiasie tussen populasies vanaf aartappel en tamatie laag (Fst = 0.07; P = 0.004). Die studie het die wêreldwye genotipe-databasis van P. infestans vir SSA uitgebrei. Voorheen is geen populasies vanuit Burundi, Malawi en Mosambiek gekarakteriseer nie. Die karakteriseringswerk het aangetoon dat die waarskynlikheid klein is dat migrasies in SSA plaasgevind het, of indien dit wel plaasgevind het, dit op ‘n baie beperkte skaal plaasgevind. Die meer ernstige epidemies in sommige SSA lande kan die gevolg wees van die teenwoordigheid van metalaksiel-weerstand. Die voorkoms van mutasies of mitotiese rekombinasie kon verder meer aggressiewe en/of beter aangepaste genotipes tot gevolg gehad het, byvoorbeeld die US-1.10 genotipe wat slegs in die Westelike Kaapprovinsie van Suid-Afrika waargeneem is. Die betekenis van die ontdekking van die KE-1 genotipe in Kenia benodig verdere ondersoek aangesien dit (i) ‘n ongeslagtelike afstammeling van genotipes (RW-1 en RW-2) mag wees wat voorheen in die 1980’s in Rwanda aangeteken is, (ii) voorheen nie waargeneem is nie weens die klein opnames wat in SSA uitgevoer is, (iii) ‘n nuwe genotipe van lande buite die SSA kan wees of (iv) ingebring is tydens die heel eerste inkoms in Kenia vóór die 1970’s. Die SSR resultate van die opname sal vergelykings tussen die SSA laatroespopulasies en ander populasies wêreldwyd toelaat, deur gebruik te maak van die EucaBlight databasis in toekomstige studies.