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

Submitted by (lucia.rodrigues@ufrpe.br) on 2017-02-17T13:39:56Z No. of bitstreams: 1 Camila Cristina Lage de Andrade.pdf: 845467 bytes, checksum: ef8d7e269cd9b79e14fc8dbcd17e8edd (MD5) / Made available in DSpace on 2017-02-17T13:39:56Z (GMT). No. of bitstreams: 1 Camila Cristina Lage de Andrade.pdf: 845467 bytes, checksum: ef8d7e269cd9b79e14fc8dbcd17e8edd (MD5) Previous issue date: 2012-02-16 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The bacterial speck caused by Pseudomonas syringae pv. tomato (Pst) (Okabe) Young, Dye & Wilkie has economic relevance to the tomato for industry in Brazil. The use of products that potentiate and/or induce plant defenses is an alternative that meets the requirements of integrated disease management. This study aimed to evaluate the effect of silicon (Si) and chemical inducers in some components of tomato resistance to bacterial speck and activity of enzymes involved in plant defense. In the first study, tomato plants were grown in: soil without calcium silicate (control) (T1), soil without calcium silicate and plants sprayed with Supa Silica® (SS) (2 mL/L SS) (T2) and soil with calcium silicate (0.38 g) (T3), being inoculated by spraying with a suspension of the pathogen. Our research evaluated the incubation period (IP), number of lesions (NL) per plant, severity estimated by the software QUANT 1.0 (SEQ) and leaf concentration of Si, as well as the activity of enzymes peroxidases (POX), polyphenoloxidases (PPO) β-1,3-glucanases (GLU), phenylalanine ammonia lyases (PAL), lipoxygenases (LOX) and concentration of malondialdehyde (MDA). It was assessed the effect of SS in the Pst growth in vitro. There was no significant difference between treatments for the IP and the foliar concentration of Si. No significant differences were found for the NL per plant and SEQ between T3 and control. T2 significantly reduced NL in 46.8 and 45.1% and SEQ in 61.5 and 56.2% when compared with control and T3, respectively. There was negative linear response of SS doses on the Pst growth in vitro. The activity of POX, PPO and GLU was significantly higher in T2 and T3. The activity of FAL and LOX was significantly higher in T3. The MDA concentration was significantly higher in T2 compared to control, in non-inoculated plants and at 7 days after inoculation (d.a.i.), being significantly lower at 10 d.a.i. In the second study, three experiments were conducted to evaluate the effect of jasmonic acid (JA; 0.1 mM), ethephon (ET, 0.5 mM) and acibenzolar-S-methyl (Bion®, ASM; 300 mg/L) sprayed 48 h before inoculation with Pst, evaluating the IP and NL per plant, and the activity of enzymes POX, PPO, GLU and LOX. It was also assessed the effect of JA and ET in the growth of Pst in vitro. Only in experiment 3 incubation period increased significantly by one day in the plants sprayed with ASM compared with control. In all experiments, NL per plant was significantly reduced by JA, ET e ASM in relation to the control reaching values of 38.9, 45.3 and 68.1%, respectively, in experiment 2. The growth of Pst in vitro was not significantly influenced. In some evaluation times JA has significantly raised the activity of POX, PPO and GLU; ASM has elevated the activity of PPO, GLU and LOX, while ET only significantly raised the activity of GLU and LOX compared to the control. The results of these studies suggest that spraying tomato plants with SS and the inducers JA, ET and ASM affected some components of tomato resistance to bacterial speck, and activated the enzymes POX, PPO, GLU, PAL and LOX, involved in defense responses of tomato plants to Pst. / A pinta bacteriana causada por Pseudomonas syringae pv. tomato (Pst) (Okabe) Young, Dye & Wilkie tem importância econômica para a cultura do tomateiro industrial no Brasil. O uso de agentes potencializadores e/ou indutores das defesas das plantas é uma alternativa que atende aos requisitos do manejo integrado de doenças. Este estudo avaliou o efeito do silício (Si) e de indutores químicos em alguns componentes de resistência do tomateiro à pinta bacteriana e na atividade de enzimas envolvidas na defesa das plantas. No primeiro estudo plantas de tomateiro foram cultivadas em: solo sem silicato de cálcio (controle) (T1), solo sem silicato de cálcio e plantas pulverizadas com Supa Sílica® (SS) (2 mL/L de SS) (T2) e solo com silicato de cálcio (0,38 g) (T3), sendo inoculadas por pulverização com suspensão do patógeno. Foram avaliados o período de incubação (PI), número de lesões (NL) por planta, severidade estimada pelo software QUANT 1.0 (SEQ) e concentração foliar de Si, bem como a atividade das enzimas peroxidases (POX), polifenoloxidases (PFO), β-1,3-glucanases (GLU), fenilalanina amônia-liases (FAL), lipoxigenases (LOX) e concentração de aldeído malônico (MDA). Também foi avaliado o efeito do SS no crescimento de Pst in vitro. Não houve diferença significativa entre os tratamentos para o PI e para a concentração foliar de Si. Não houve diferença significativa para o NL por planta e a SEQ entre o tratamento T3 e o controle. O tratamento T2 reduziu significativamente o NL 46,8 e 45,1% e a SEQ 61,5 e 56,2%, em relação ao controle e ao tratamento T3, respectivamente. Houve resposta linear negativa das doses de SS no crescimento da Pst in vitro. A atividade das POX, PFO e GLU foi significativamente maior nos tratamentos T2 e T3. A atividade das FAL e das LOX foi significativamente maior no T3. A concentração de MDA foi significativamente maior no tratamento T2 em relação ao controle, nas plantas não inoculadas com Pst e aos 7 dias após inoculação (d.a.i.); sendo significativamente menor aos 10 d.a.i. No segundo estudo, três experimentos foram realizados para avaliar o efeito dos indutores ácido jasmônico (AJ; 0,1 mM), ethephon (ET; 0,5 mM) e acibenzolar-S-metil (Bion®, ASM; 300 mg/L) pulverizados 48 h antes da inoculação da Pst, avaliando-se o PI e o NL por planta, além da atividade das enzimas POX, PFO, GLU e LOX. Também foi avaliado o efeito do AJ e do ET no crescimento da Pst in vitro. Apenas no experimento 3 o PI aumentou significativamente em 1 dia nas plantas pulverizadas com ASM em relação ao controle. O NL por planta foi significativamente reduzido pelos tratamentos AJ, ET e ASM em relação ao controle para todos os experimentos, atingindo valores de 38,9, 45,3 e 68,1%, respectivamente, no experimento 2. O crescimento da Pst in vitro não foi influenciado significativamente pelo AJ ou ET. Em determinadas épocas de avaliação, o AJ elevou significativamente a atividade das POX, PFO e GLU; ASM elevou a atividade das PFO, GLU e LOX e o ET elevou a atividade das GLU e LOX em relação ao controle. Os resultados desses estudos evidenciam que a pulverização com SS e com indutores AJ, ET e ASM afetaram alguns dos componentes de resistência do tomateiro à pinta bacteriana, além de potencializar as enzimas POX, PFO, GLU, FAL e LOX, relacionadas com a defesa das plantas em resposta à Pst.