In the current study potassium silicate (20.7% SiO2) induced a 100% inhibition of P. cinnamomi mycelial growth at all concentrations tested. Total inhibition for all fungi tested (Alternaria solani, Colletotrichum gloeosporioides, Curvularia lunata, Drechslera sp., Fusarium oxysporum, Fusarium solani, Glomerella cingulata, Lasiodiplodia theobromae, Mucor pusillus, Natrassia sp., Pestalotiopsis maculans, Phomopsis perniciosa, Phytophthora capsicii, Phytophthora cinnamomi, Pythium F-group, Sclerotinia sclerotiorum, Sclerotium rolfsii, Stemphylium herbarum and Verticillium tricorpus) was attained at a concentration of 40ml.l-1 and higher. Although the high pH of potassium silicate solutions does contribute to the inhibition of fungal growth, the inhibitory effect of potassium silicate on fungal growth in vitro is mostly fungicidal rather than attributed to a pH effect. Phytophthora root rot of avocado nursery trees can be inhibited successfully by potassium silicate application. The effectiveness of potassium silicate application depends however on the repetition of applications. These findings are of paramount importance as this implies that potassium silicate may be a alternative control measure to inhibit the effects of P. cinnamomi on avocado nursery trees. Silicon either stimulates plant growth or imparts some form of protection to avocado roots if applied prior to P. cinnamomi inoculation. Potassium silicate applied as a soil drench resulted in higher root densities compared to that of potassium phosphonate (Avoguard®) injections and untreated control trees. Reapplication again resulted in the best disease suppression and stimulation of new root growth. These results correlated well with tree canopy ratings, as trees that received silicon frequently, showed better canopy conditions compared to the untreated control treatments. Potassium silicate application leads to effective inhibition of Phytophthora cinnamomi infection in avocado orchards. Potassium silicate application resulted in an increase of crude phenols and phenolic polymers in avocado roots cells to similar levels to that obtained in roots from potassium phosphonate (Avoguard®) treated trees. Potassium silicate application leads to lower cell wall bound phenolics. The results of the current study support the hypothesis that silicon application, through an elevation of the total phenolic levels, causes an increase of resistance against P. cinnamomi root rot in avocados. AFRIKAANS : Kaliumsilikaat (20.7% SiO2) induseer ‘n 100% inhibisie van P. cinnamomi groei by alle getoetste konsentrasies. Totale inhibisie van alle swamme getoets (Alternaria solani, Colletotrichum gloeosporioides, Curvularia lunata, Drechslera sp., Fusarium oxysporum, Fusarium solani, Glomerella cingulata, Lasiodiplodia theobromae, Mucor pusillus, Natrassia sp., Pestalotiopsis maculans, Phomopsis perniciosa, Phytophthora capsicii, Phytophthora cinnamomi, Pythium F-groep, Sclerotinia sclerotiorum, Sclerotium rolfsii, Stemphylium herbarum en Verticillium tricorpus) was verkry by ‘n konsentrasie van 40ml.l-1 en hoër. Alhoewel die hoë pH van kaliumsilikaat wel ‘n inhiberende uitwerking het op swamgroei, is die suksesvolle inhibisie van swamgroei grootliks toe te skryf aan die swamwerende effek van kaliumsilikaat op swamgroei in vitro eerder as ‘n pH effek. Phytophthora wortelvrot van avokado kwekelinge kan suksesvol onderdruk word met kaliumsilikaat toediening. Die effektiwiteit van die toediening hang wel af van die hertoediening daarvan. Hierdie bevindinge is van kardinale belang aangesien dit impliseer dat kalium silikaat ‘n alternatiewe beheer middel is om Phytophthora wortelvrot te inhibeer in avokado kwekelinge. Of silikon stimuleer plant groei, of dit induseer ‘n vorm van beskerming in avokado wortels voor infeksie plaasvind. Kaliumsilikaat toediening as ‘n grond-benatter lei tot hoër worteldigthede in vergelyking met kaliumfosfaat (Avoguard®) staminspuitings en onbehandelde kontrole bome. Hertoediening lewer die beste resultate, maar drie toedienings per seisoen is voldoende. Worteldigdheid verhoging na silikaat toedienings korreleer goed met blaredak gesondheid, aangesien bome wat gereeld behandel is met silikon beter blaredekking getoon het in vergelyking met die kontrole bome. Kaliumsilikaat toediening lei to effektiewe inhibisie van Phytophthora cinnamomi infeksie in avokado boorde. Kaliumsilikaat toediening lei tot ‘n toename in totale fenole en fenoliese polimere in avokado wortel selle tot soortgelyke vlakke soos gevind in avokado weefsel vanaf kaliumfosfaat behandelde bome. terselfdertyd lei silikaat toediening tot laer selwand gebinde fenole. Hierdie resultate ondersteun die hipotese dat kaliumsilikaat toediening, deur die verhoging van oplosbare fenole in avokado wortelselle, die plant se weerstand verhoog, en die effek wat Phytophthora wortelvrot het op avokado plante inhibeer. Copyright / Dissertation (MSc (Agric) Horticulture)--University of Pretoria, 2011. / Plant Production and Soil Science / unrestricted

During the initiation and execution of a rootstock breeding programme to overcome the financially crippling disease, Phytophthora root rot of avocado, various constraints have been identified for both the breeding as well as the screening aspect of the programme. A review of the literature revealed a complex host-pathogen interaction that should be taken into account in the recombination and screening of genetic material. With the detection of beneficial genotypes being the crux of a breeding programme, this dissertation was focused on the screening of rootstock material for tolerance to Phytophthora cinnamomi. Screening should be scientific but at the same time also be time and cost effective. Specific attention was given to (i) the correct medium for screening mass numbers of seedlings, (ii) fast and effective cloning of single selections, and (iii) evaluation of clonal material for tolerance to P. cinnamomi. Soil as a screening medium was compared with three inert hydroponic media as well as one aeroponic system. Only soil was found to be ineffective due to its properties. The other media tested, namely, sand, vermiculite, water and the aeroponic system were equal in performance. The medium to be used will depend on the preference of the breeder as each medium has its own pro's and con's. It was, however, found that the evaluation criterion to be applied depends on the medium that is used. With regard to cloning of single selections, a definite difference with regard to the cloning ability of the different selections was found. An inability to be etiolated was displayed by some of the selections and these could thus not be vegetatively propagated and were not further tested. One of the tolerance mechanisms in the standard cultivar Duke 7, is root regeneration. It was thus expected that this characteristic cloning would give an indication of the rootstock's ability to tolerate P. cinnamomi. This could not be confirmed, but most of the selections did, however, perform better than Duke 7. Comparison of feeder root percentage in non-inoculated and inoculated treatments was not sufficient for facilitating the final selection of candidate rootstocks from a large number of potential clonal selections. Four selections were made, based on the hypothesis that a larger root system will be a better forager and thus enhance the horticultural aspects of the rootstock-scion combination. Valuable information was obtained with regard to various mediums and criteria to be used during mass screening and final screening of clonal selections. This knowledge must be taken into account in the planning of future breeding projects. During this project a total of 38 984 seedlings were screened and four selections were made. For both the nursery and the producer, knowledge of the clonal ability of a potential new rootstock is important from a financial point of view. / Dissertation (MSc (Horticultural Science))--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

A biodiversidade brasileira é conhecida devido a sua riqueza de espécies, sendo considerada uma fonte promissora de produtos naturais. Dentre as plantas vasculares, a família Solanaceae A. Juss. (Solanaceae) é considerada uma das maiores, apresentando distribuição em todas as regiões tropicais e temperadas do mundo. A família Solanaceae apresenta alta diversidade de espécies de importância econômica como fonte de alimentos, propriedades medicinais e ornamentais. Plantas desta família são fontes de metabólitos secundários de diversas classes químicas com as mais diversas aplicações. Fungos fitopatogênicos são responsáveis por causar diversas doenças e consideráveis perdas na agricultura. O controle das doenças é realizado através de métodos químicos, físicos e biológicos, porém o uso excessivo e ininterrupto de produtos químicos pode resultar na seleção de micro-organismos resistentes. Além disto, muitos fungicidas apresentam toxicidade alta e a sua utilização indiscriminada pode causar efeitos indesejáveis sobre outros organismos no ambiente. O objetivo deste estudo é explorar o potencial biológico e químico de metabólitos secundários produzidos por plantas da família Solanaceae com potencial fungitóxico a fitopatógenos. Foram selecionadas 15 espécies de plantas da família Solanaceae que tiveram os extratos de suas folhas avaliados em ensaios biológicos in vitro sobre o crescimento micelial de 6 fitopatógenos de importância na agricultura. Dentre estas, três foram selecionadas para uma investigação mais aprofundada, as espécies Solanum americanum, Acnistus arborescens e Physalis peruviana. No estudo da planta S. americanum, foram identificados compostos bioativos pertencentes à classe dos glicoalcalóides, que inibiram o crescimento micelial do fitopatógeno Moniliophthora perniciosa. No estudo de A. arborescens foi identificado a presença de um composto ativo pertencente à classe dos vitanolidos, provavelmente o 7β-acetoxivitanolido D, e sua ação antifúngica está sendo relatada pela primeira vez. No estudo da planta P. peruviana a fração semipura bioativa indicou a presença de um composto pertencente à classe dos vitanolidos. Esses resultados evidenciaram que os compostos presentes nas plantas, apresentam bioatividade que inibem o crescimento micelial dos fungos fitopatogênicos Moniliophthora perniciosa e Phytophthora cinnamomi, podendo ser uma nova opção coadjuvante no controle de fitopatógenos. / The Brazilian biodiversity is known due to its richness of species, and is considered a promising source of natural products. Among the vascular plants, the family Solanaceae A. Juss. (Solanaceae) is considered one of the largest, with distribution in all tropical and temperate regions of the world. The Solanaceae family has a high diversity of species of economic importance as a source of food, medicinal and ornamental properties. Plants of this family are sources of secondary metabolites from different chemical classes with many different applications. Plant fungi are responsible for causing various diseases and considerable losses in agriculture. The disease control is accomplished through chemical, physical and biological methods, but the excessive and continuous use of chemical products, may result in selection of resistant micro-organisms, in addition, many fungicides have a high toxicity and its indiscriminate use can cause undesirable effects on other organisms in the environment. The objective of this study is to explore the biological and chemical potential of secondary metabolites produced by plants of the Solanaceae family with potential fungitoxic the pathogens. We selected 15 species of Solanaceae plants that had the extracts of its leaves evaluated in vitro biological assays on the mycelial growth of 6 plant pathogens of importance in agriculture. Among these, three were selected for further investigation, the species Solanum americanum, Physalis peruviana and Acnistus arborescens. In the study of plant S. americanum, it was identified bioactive compounds belonging to the class of glycoalkaloids that inhibited the mycelial growth of the pathogen M. perniciosa. In the study of A. arborescens it was identified the presence of the active compound belonging to the class of withanolides, probably the 7β-acetoxywithanolide D, and its antifungal activity is being reported for the first time. In the study of plant P. peruviana semipure bioactive fraction indicated the presence of the compound belonging to the class of withanolides. These results showed that the compounds present in plants, have bioactivity that inhibit the mycelial growth of pathogenic fungi M. perniciosa and P. cinnamomi and may be a new option in the adjuvant control pathogens.

A biodiversidade brasileira é conhecida devido a sua riqueza de espécies, sendo considerada uma fonte promissora de produtos naturais. Dentre as plantas vasculares, a família Solanaceae A. Juss. (Solanaceae) é considerada uma das maiores, apresentando distribuição em todas as regiões tropicais e temperadas do mundo. A família Solanaceae apresenta alta diversidade de espécies de importância econômica como fonte de alimentos, propriedades medicinais e ornamentais. Plantas desta família são fontes de metabólitos secundários de diversas classes químicas com as mais diversas aplicações. Fungos fitopatogênicos são responsáveis por causar diversas doenças e consideráveis perdas na agricultura. O controle das doenças é realizado através de métodos químicos, físicos e biológicos, porém o uso excessivo e ininterrupto de produtos químicos pode resultar na seleção de micro-organismos resistentes. Além disto, muitos fungicidas apresentam toxicidade alta e a sua utilização indiscriminada pode causar efeitos indesejáveis sobre outros organismos no ambiente. O objetivo deste estudo é explorar o potencial biológico e químico de metabólitos secundários produzidos por plantas da família Solanaceae com potencial fungitóxico a fitopatógenos. Foram selecionadas 15 espécies de plantas da família Solanaceae que tiveram os extratos de suas folhas avaliados em ensaios biológicos in vitro sobre o crescimento micelial de 6 fitopatógenos de importância na agricultura. Dentre estas, três foram selecionadas para uma investigação mais aprofundada, as espécies Solanum americanum, Acnistus arborescens e Physalis peruviana. No estudo da planta S. americanum, foram identificados compostos bioativos pertencentes à classe dos glicoalcalóides, que inibiram o crescimento micelial do fitopatógeno Moniliophthora perniciosa. No estudo de A. arborescens foi identificado a presença de um composto ativo pertencente à classe dos vitanolidos, provavelmente o 7β-acetoxivitanolido D, e sua ação antifúngica está sendo relatada pela primeira vez. No estudo da planta P. peruviana a fração semipura bioativa indicou a presença de um composto pertencente à classe dos vitanolidos. Esses resultados evidenciaram que os compostos presentes nas plantas, apresentam bioatividade que inibem o crescimento micelial dos fungos fitopatogênicos Moniliophthora perniciosa e Phytophthora cinnamomi, podendo ser uma nova opção coadjuvante no controle de fitopatógenos. / The Brazilian biodiversity is known due to its richness of species, and is considered a promising source of natural products. Among the vascular plants, the family Solanaceae A. Juss. (Solanaceae) is considered one of the largest, with distribution in all tropical and temperate regions of the world. The Solanaceae family has a high diversity of species of economic importance as a source of food, medicinal and ornamental properties. Plants of this family are sources of secondary metabolites from different chemical classes with many different applications. Plant fungi are responsible for causing various diseases and considerable losses in agriculture. The disease control is accomplished through chemical, physical and biological methods, but the excessive and continuous use of chemical products, may result in selection of resistant micro-organisms, in addition, many fungicides have a high toxicity and its indiscriminate use can cause undesirable effects on other organisms in the environment. The objective of this study is to explore the biological and chemical potential of secondary metabolites produced by plants of the Solanaceae family with potential fungitoxic the pathogens. We selected 15 species of Solanaceae plants that had the extracts of its leaves evaluated in vitro biological assays on the mycelial growth of 6 plant pathogens of importance in agriculture. Among these, three were selected for further investigation, the species Solanum americanum, Physalis peruviana and Acnistus arborescens. In the study of plant S. americanum, it was identified bioactive compounds belonging to the class of glycoalkaloids that inhibited the mycelial growth of the pathogen M. perniciosa. In the study of A. arborescens it was identified the presence of the active compound belonging to the class of withanolides, probably the 7β-acetoxywithanolide D, and its antifungal activity is being reported for the first time. In the study of plant P. peruviana semipure bioactive fraction indicated the presence of the compound belonging to the class of withanolides. These results showed that the compounds present in plants, have bioactivity that inhibit the mycelial growth of pathogenic fungi M. perniciosa and P. cinnamomi and may be a new option in the adjuvant control pathogens.

Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 219-235.

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