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Thesis (M. Agricultural Management (Plant Production)) -- University of Limpopo, 2020 / Tomato is a major vegetable crop produced in Limpopo province by subsistence and commercial farmers. Biotic and abiotic factors such as diseases and drought affect its productivity and yield negatively. The most economically important tomato disease in Limpopo is early blight, caused by Alternaria solani. Early blight affects tomato growing under stressful conditions such as drought. The main aim of this study was to evaluate water management in tomato production and its effect on tomato yield, early blight occurrence and severity under smallholder farming systems in Giyani. A survey study and field experiments on early blight occurrence and severity were conducted in the Greater Giyani municipality in Limpopo province. Firstly, a survey of early blight was conducted in tomato fields selected from three service centres namely Guwela, Hlaneki and Mhlava Willem. Twenty five potential tomato grower’s farms were randomly selected for survey based on the location and production management strategies. A second study was carried out by establishing field experiments at two farms in the same area, namely: A hi tirheni Mqekwa and Duvadzi farms. The experiments were laid out in a randomized complete block design (RCBD) in a split plot arrangement, with irrigation as the main plot treatment and tomato variety as the subplot treatment. Each treatment was replicated four times. The irrigation treatments consisted of full irrigation up to field capacity and deficit irrigation. The tomato varieties planted were HTX14, Rodade, STAR9006 and Commander, and were irrigated with a drip irrigation system. The overall survey results showed that Guwela s/c had high disease incidence and the lowest disease severity as compared to the other two service centers. The lowest disease incidence was observed at Hlaneki s/c whilst Mhlava willem s/c had the highest disease severity. The two water treatments (full and deficit irrigation) in both farms have shown no significant pairwise differences among xx the volumetric water content means. There was no significant difference (P≥0.05) in early blight disease severity in both farms. Results shows that, all tomato varieties did not differ significantly (P≥0.05) in yield observed between treatments at Duvadzi and A hi tirheni Mqekwa Farm. Deficit irrigation can be used effectively to produce high yields in tomato production provided the cropping season window does not coincide with the hottest time of the year. Full and deficit irrigation did not have influence on the early blight disease incidence on tomato plants. Key words: Alternaria solani; disease incidence; disease severity and drip irrigation

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Récemment, un nouvel agent pathogène a causé d’importants dommages sur la tomate de serre dans un complexe au centre du Québec et au nord des États-Unis. À partir d’échantillons de plants infectés, des colonies produisant des macroconidies typiques de Fusarium spp. ont systématiquement été isolées. Le séquençage des régions ITS et tef de ces isolats, suivi de tests de pathogénicité, ont permis d’identifier Fusarium striatum comme l’agent pathogène. Il s’agit du premier rapport de cet agent pathogène au Canada. Suite à son identification, un test de dépistage moléculaire a été mis au point afin de détecter l’agent pathogène directement à partir des tissus végétaux. Les amorces développées ont été suffisamment spécifiques et sensibles pour détecter l’agent pathogène avant même l’apparition des symptômes. Nos résultats semblent indiquer que l’inoculum de F. striatum aurait été introduit dans les deux complexes de serre par les transplants provenant de leur fournisseur commun.

La gale argentée, causée par le champignon Helminthosporium solani, est une maladie importante affectant le tubercule de pomme de terre. Cette étude avait pour objectif d'évaluer l'influence du Fe, Cu, Mn, Zn et Mo, sous différentes formes chimiques, sur le développement de H. solani et de la gale argentée de la pomme de terre. Les résultats obtenus ont permis de démontrer que ces minéraux affectent la croissance mycélienne et la germination des conidies de ce champignon. L'addition de doses élevées des minéraux à l'étude dans le milieu de culture a généralement eu un effet inhibiteur sur la croissance mycélienne et la germination des conidies. Appliqués sur le tubercule, ces minéraux ont également affecté le développement de la gale argentée. Cependant, les travaux réalisés n'ont pas permis de révéler que la composition du substrat de culture en ces minéraux avait un effet sur le développement de la gale argentée ainsi que sur la quantité de H. solani détectée à la surface du tubercule par PCR en temps réel.

Die pilzlichen Erreger der Tomate Alternaria solani und des Manioks Colletotrichum gloeosporioides f.sp. manihotis verursachen große Ertragsausfälle in Westafrika. In der vorliegenden Arbeit wurden die Blattkrankheiten nach Applikationen mit wässerigen Extrakten aus Westafrika (Ausgangsmaterial: organischer Haushaltsmüll) unter kontrollierten Bedingungen unterdrückt. Im Pathosystem Tomate - A. solani erzielten die Extrakte eine Befallsverminderung um bis zu 94 % im Vergleich zur Kontrollvariante und im Maniok - C. gloeosporioides wurde die Anzahl der gebildeten Acervuli/cm² Blattoberfläche bis um 87 % reduziert. Der primäre Wirkmechanismus der Extrakte gegen die Pathogene ist Antagonismus, hervorgerufen von den Mikroorganismen in den Extrakten. Isolierte Bakterien aus den Extrakten hemmten das Wachstum der Pathogene in Plattentests, was auf die Bildung von fungistatischen Substanzen zurückzuführen war. Die Bakterien, die aus den Extrakten isoliert und identifiziert wurden, gehörten überwiegend zu den Bakteriengattungen Pseudomonas und Bacillus. Die Extraktionsbedingungen nahmen in Hinblick auf die Wirksamkeit der Extrakte gegen die Pathogene eine wichtige Stellung ein. Die Untersuchungen zeigten einen Zusammenhang zwischen gestiegener Mikroorganismenanzahl und Befallsreduktion. Durch die Auswahl optimaler Extraktionsbedingungen erhöhte sich die Anzahl der Koloniedichte in den Extrakten; dies führte zur einer stärkeren Befallsreduzierung an der Tomate und am Maniok. Hierbei waren die Umgebungstemperatur und die Häufigkeit des Durchmischens des Kompost-Wasser-Gemisches von besonderer Bedeutung. Extrakte, die während der Extraktionszeit einer Temperatur von 20°C ausgesetzt waren, erzielten eine stärkere Befallsreduzierung von A. solani an der Tomate und wiesen eine höhere Mikroorganismendichte auf als Extrakte, die einer Temperatur von 30°C und 35°C ausgesetzt waren. Tägliches Durchmischen des Wasser-Kompost-Gemisches während der Extraktionszeit erhöhte die Mikroorganismendichte um das Siebenfache in den Extrakten und die Wirksamkeit gegen A. solani und C. gloeosporioides im Vergleich zu den Extrakten, die nur zu Beginn durchmischt wurden. Die Lagerungszeit der fertigen Komposte hatte einen Einfluß auf die Mikroorganismendichte der wässerigen Extrakte sowie auf deren Wirksamkeit. Extrakte, die aus frischen Komposten hergestellt wurden, zeigten einen besseren suppressiven Effekt gegen die Pathogene und wiesen eine höhere Mikroorganismenanzahl auf als Extrakte, deren Komposte schon länger gelagert worden waren. Die Anreicherung der Extrakte mit dem Formulierungshilfsstoff Xanthan steigerte die Wirksamkeit der Extrakte gegen A. solani an Tomatenpflanzen und gegen C. gloeosporioides f.sp. manihotis an abgetrennten Maniokblättern. Angereicherte Extrakte reduzierten den Befall um bis zu 46 % mehr als der Extrakt ohne Formulierungshilfsstoffe, während die Steigerung der Wirksamkeit nach Anreicherung mit Alginat oder Zellulose eine Abhängigkeit von der Herkunft der Komposte zeigte. Eine erhöhte ß-1,3-Glucanase-Aktivität wurde am vierten Tag nach der Applikation von Extrakten an der Tomate und an der Batate festgestellt. Diese Ergebnisse belegen die Bedeutung von Spritzbehandlungen mit wässerigen Kompostextrakten gegen die Pathogene A. solani und C. gloeosporioides f.sp. manihotis und stellen eine erfolgversprechende Alternative zur Bekämpfung von Pilzkrankheiten in Westafrika dar. / Great yield losses of cassava in West Africa are caused by fungal pathogens that also affect tomato, e.g. Alternaria solani and Colletotrichum gloeosporioides f sp. manihotis. In the present study these foliar diseases were effectively suppressed under controlled conditions after application of watery compost extracts to tomato and cassava The disease incidence of A. solani on tomato was reduced up to 94 % and the number of the acervuli produced on the surface of cassava leaves was reduced up to 87% compared to the control treatment. Reduction is due to antagonistic effects of the microorganisms in the extracts towards the pathogens. Bacterial strains isolated from the extracts suppressed the growth of the pathogens in dual-culture-tests due to the production of antibiotics. Bacteria isolated and identified from the extracts were mostly pseudomonas and bacillus strains. The conditions used for extraction of compost played a significant role for their effectiveness against different pathogens. The investigations showed that optimisation of extract conditions increased the density of microorganisms in the extracts and led to a higher disease reduction on tomato and cassava plants. Temperature and stirring frequency of the compost - water mixture during the extraction period were very important factors for increased effectiveness. Extracts incubated at 20 °C during the extraction period caused a higher disease reduction on tomato and showed a higher density of microorganisms, than extracts that were incubated at 30 or 35 °C. Daily stirring of the compost - water mixture during the extraction period increased the density of microorganisms in the extracts sevenfold and increased the effectiveness against A. solani and C. gloeosporioides compared to the extract that was stirred only once at the beginning. The Effectiveness as well as the density of the microorganisms were depended on the incubation time of the compost extracts. Extracts produced from fresh composts showed greater suppressive effects against pathogens and higher densities of microorganisms than extracts of composts that were stored for a longer time. Enrichment of the extracts with the formulate substance xanthan increased the effectiveness against A. solani on tomato plants and against C. gloeosporioides on detached leaves of cassava and reduced the disease incidence up to 46% compared to the extract without formulate substances. The increase of the effectiveness after enriching with alginate was depended on the origin of the compost. An increased ß-1,3- glucanase activity were determined on tomato and sweet potato leaves 4 days after the application of the extracts onto the plants. The results of this study show that watery compost extracts can be successfully applied against the cassava and tomato pathogens A. solani and C. gloeosporioides f. sp. manihotis and offers easily applicable methods for the reduction of fungal diseases in West Africa.

Made available in DSpace on 2015-03-26T13:37:36Z (GMT). No. of bitstreams: 1 texto completo.pdf: 4434052 bytes, checksum: e6bd53f46965b44a3dcdbb9a5a63b4ff (MD5) Previous issue date: 2008-02-19 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work aimed to select tomato prokaryotic phylloplane residents for biocontrol purposes, by using Xanthomonas campestris pv. vesicatoria and Alternaria solani as challenging pathogens. Additionally, to perform a screening test using detached leaves. Consequently, leaves from healthy tomato plants were collected at Viçosa, MG and epiphytic prokaryote populations were extracted by shacking them in PBS (0,85% NaCl in 0,1M phosphate buffer saline, pH 7.0) following sonication (60Hz, 20 minutes) and serial dilution and plating in culture medium. Three hundred bacterial isolates were obtained and preserved in refrigerator, with periodical tubetube transfer, in a refrigerator. The screening was performed in two selection cycles. In the first selection in greenhouse, with three replicates per isolate and Xanthomonas campestris pv. vesicatoria as challenging pathogen, 79 isolates were able to reduce disease by 82%. In a second selection cycle, using 6 replicates per isolate, the 33 isolates were able to reduce severity by 50% in average. The 33 isolates had their antagonistic potential tested against the tomato fungal and bacterial pathogens Pseudomonas syringae pv. tomato, Pseudomonas corrugata, Xanthomonas campestris pv. vesicatoria, Clavibacter michiganensis subsp. michiganensis, Alternaria solani and Corynespora cassiicola in vitro conditions. Out of the 33 isolates, the isolate RFK-24 inhibited growth of Xathomonas campestris pv. vesicatoria, Clavibacter michiganensis subsp. michiganensis and Alternaria solani while isolate RFS-183 was able to inhibit Alternaria solani, Xanthomonas campestris pv. vesicatoria, Pseudomonas syringae pv. tomato e Pseudomonas corrugata, but none of them inhibited Corynespora cassiicola. Being RFK-24 and RFS- 183 the ones with a wider antagonistic potential out of the 33 previously selected, they were chosen for continuing the research with detached leaves and the challenging pathogens Alternaria solani e Xanthomonas campestris pv. vesicatoria. There was a positive correlation between disease severity reduction in plants the greenhouse and in detached leaves, for both antagonists. For situations involving large number of isolates to undergo mass screening, the approach with detached organs may replace the laborious and time consuming greenhouse screening. / O presente trabalho teve como objetivo isolar procariotos residentes de filoplano de tomateiro como agentes de biocontrole contra o patógeno Xanthomonas campestris pv. vesicatoria. 300 isolados foram obtidos a partir de folhas sadias de tomateiros coletadas na micro-região de Viçosa-MG, as quais foram submetidas à extração das populações procarióticas epifíticas em solução de tampão fosfato (PBS) com emprego de ultra-som (60Hz, 20 min.) e semeadura de diluições em série em placas de Petri contendo meio 523. Em casa-de-vegetação, numa primeira etapa 79 isolados apresentaram capacidade de reduzir, em média, 82 % da severidade de doença. Desses, numa segunda etapa, 33 isolados apresentaram redução média da severidade de doença em 50 %. Os 33 isolados foram submetidos a testes de antibiose in vitro, em que foi avaliada a potencialidade em inibir o crescimento bacteriano e fúngico dos seguintes patógenos do tomateiro: Pseudomonas syringae pv. tomato, Pseudomonas corrugata, Xanthomonas campestris pv. vesicatoria, Clavibacter michiganensis subsp. michiganensis, Alternaria solani e Corynespora cassiicola. Dos 33 isolados pré- selecionados verificou-se que o isolado RFK-24 foi capaz de inibir o crescimento dos patógenos, Xanthomonas campestris pv. vesicatoria, Clavibacter michiganensis subsp. michiganensis e Alternaria solani e o RFS-183 em inibir o crescimento dos patógenos Alternaria solani, Xanthomons campestris pv. vesicatoria, Pseudomonas syringae pv. tomato e Pseudomonas corrugata, mas ambos não inibiram o crescimento da Corynespora cassiicola. Os dois isolados foram selecionados para ensaios in vivo e em folíolos destacados, contra os patógenos desafiantes Alternaria solani e Xanthomons campestris pv. vesicatoria. Para ambos foi observada a correlação entre a severidade de doença apresentada em casa-de-vegetação e os resultados em folíolos destacados, como a inibição da germinação de conídios do patógeno fúngico e a supressividade em meio semi-seletivo dos antagonistas sob o patógeno bacteriano. Os resultados obtidos com o método com folíolos destacados e sua correlação com os dados de biocontrole experimental em casa-de-vegetação permitem deduzir que o uso de folíolos destacados pode ser utilizado como método para seleção massal.