Submitted by (lucia.rodrigues@ufrpe.br) on 2017-03-10T15:46:17Z No. of bitstreams: 1 Frederick Mendes Aguiar.pdf: 412210 bytes, checksum: 4f5f91c02dea9d844bac53a51c2cafa0 (MD5) / Made available in DSpace on 2017-03-10T15:46:17Z (GMT). No. of bitstreams: 1 Frederick Mendes Aguiar.pdf: 412210 bytes, checksum: 4f5f91c02dea9d844bac53a51c2cafa0 (MD5) Previous issue date: 2011-02-24 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Okra is a vegetable crop with high nutritional value, being a rich source of vitamins and mineral salts. Fusarium wilt (caused by Fusarium oxysporum f. sp. vasinfectum – FOV) is one of the major field diseases of okra in tropical areas. In the present work, 53 okra accessions and the commercial cultivar Santa Cruz 47 were evaluated aiming to identify sources of resistance to Brazilian FOV isolates and to study the resistance stability of the selected accessions to different pathogen isolates. An initial screening was carried out with only one FOV isolate (Fus-194). In the second assay, thirty-three accessions identified in the first screening were re-evaluated in two assays (in two different seasons) using two FOV isolates (Fus-194 and Fus-201). The resistance evaluation was carried out with 21 day-old plantlets, using the root-dipping inoculation procedure, utilizing a spore suspension of 1x106 conidia/mL. The evaluation was done using a disease severity grade system with grades ranging from 0 to 4. These grades were used to generate a disease index that was employed for clustering the accessions according to their reaction to FOV. In the evaluation carried out in August (average temperature of 19,8°C) only 12 out the 32 accessions (i.e. 37%) were rated as having high to intermediate resistant response to Fus-194 isolate. Only 28% of the accessions were classified within the high to intermediate resistance cluster when using the Fus-201 isolate. In the assay carried out in October (higher temperatures) 72% of the accessions were classified as resistant and intermediate resistant to Fus-194 isolate, whereas 32% were resistant to isolate Fus-201. Our results indicated that the Fus-201 isolate was more aggressive than Fus-194. Comparative analysis of the assays indicated that the overall aggressiveness of the isolates was higher in August than in October assay. The accessions BR-2399 and BR-1449 as well as the commercial cultivar Santa Cruz 47 were the most promising accessions displaying higher levels of stable resistance against the two Brazilian FOV isolates.Okra is a vegetable crop with high nutritional value, being a rich source of vitamins and mineral salts. Fusarium wilt (caused by Fusarium oxysporum f. sp. vasinfectum – FOV) is one of the major field diseases of okra in tropical areas. In the present work, 53 okra accessions and the commercial cultivar Santa Cruz 47 were evaluated aiming to identify sources of resistance to Brazilian FOV isolates and to study the resistance stability of the selected accessions to different pathogen isolates. An initial screening was carried out with only one FOV isolate (Fus-194). In the second assay, thirty-three accessions identified in the first screening were re-evaluated in two assays (in two different seasons) using two FOV isolates (Fus-194 and Fus-201). The resistance evaluation was carried out with 21 day-old plantlets, using the root-dipping inoculation procedure, utilizing a spore suspension of 1x106 conidia/mL. The evaluation was done using a disease severity grade system with grades ranging from 0 to 4. These grades were used to generate a disease index that was employed for clustering the accessions according to their reaction to FOV. In the evaluation carried out in August (average temperature of 19,8°C) only 12 out the 32 accessions (i.e. 37%) were rated as having high to intermediate resistant response to Fus-194 isolate. Only 28% of the accessions were classified within the high to intermediate resistance cluster when using the Fus-201 isolate. In the assay carried out in October (higher temperatures) 72% of the accessions were classified as resistant and intermediate resistant to Fus-194 isolate, whereas 32% were resistant to isolate Fus-201. Our results indicated that the Fus-201 isolate was more aggressive than Fus-194. Comparative analysis of the assays indicated that the overall aggressiveness of the isolates was higher in August than in October assay. The accessions BR-2399 and BR-1449 as well as the commercial cultivar Santa Cruz 47 were the most promising accessions displaying higher levels of stable resistance against the two Brazilian FOV isolates. / O quiabo é uma hortaliça de alto valor alimentício e uma importante fonte de vitaminas e sais minerais. Dentre os problemas fitossanitários que ocorrem no quiabeiro, a murcha-de-fusário, causada pelo fungo Fusarium oxysporum f. sp. vasinfectum (FOV) é uma das mais importantes por proporcionar grandes perdas na produção. Este trabalho objetivou avaliar, em condições de casa de vegetação, a cultivar comercial Santa Cruz 47 e uma coleção de 53 acessos de quiabeiro, visando identificar fontes de resistência a FOV e analisar a estabilidade da resistência de acessos promissores a diferentes isolados do patógeno. Inicialmente foi conduzida uma triagem utilizando um único isolado de FOV (Fus-194). Em uma segunda etapa, trinta e dois acessos obtidos na primeira etapa, foram reavaliados para resistência ao FOV utilizando dois isolados (Fus-194 e Fus-201), em duas épocas do ano. A inoculação foi realizada em mudas com 21 dias após semeadura, pela imersão das raízes em suspensão de conídios (1x106 conídios/mL) do patógeno. A avaliação da severidade da doença foi realizada usando uma escala de notas, variando de 0 a 4. As notas foram transformadas em índice de doença (ID) e agrupadas em classes de acordo com a reação da doença. Na segunda etapa do trabalho realizado no mês de agosto de 2010 (temperatura média de 19,8°C), dos 32 acessos avaliados, 12 (37%) foram considerados altamente resistentes a medianamente resistentes ao Fus-194. Para o isolado Fus-201 apenas 28% foram classificados dentro dessas duas classes. No ensaio realizado no mês de outubro (temperatura média de 25°C) referente à segunda etapa desse trabalho, 72% dos acessos foram considerados medianamente a altamente resistentes ao Fus-194. Neste ensaio, 32% dos acessos foram resistentes ao isolado Fus-201. Os resultados demonstraram uma maior agressividade do isolado Fus-201 em relação ao isolado Fus-194. Os níveis de agressividade dos isolados testados foram maiores no ensaio realizado no mês de agosto do que em outubro. Os acessos BR-2399, BR-1449 e a cultivar Santa Cruz 47 apresentaram resistência estável aos dois isolados do patógeno tanto na etapa preliminar, quanto nas duas épocas de avaliação da segunda etapa do trabalho.

In previous studies silicon has been associated with reduced disease severity and incidence, the enhanced accumulation of phenolic compounds and lignin, and with changes in the defence-related enzyme activity and transcript abundance of defence and stress related genes. All of these aspects of plant defence were considered in this study on cotton infected with Fusarium oxysporum f. sp. vasinfectum (Fov), and the results obtained have greatly enhanced our understanding of the effects of silicon on this interaction. In all experiments conducted, defence responses were only significantly enhanced by silicon treatment following inoculation with Fov, strongly suggesting that silicon can prime defence responses in cotton infected with Fov. Sicot F-1 was the cultivar most resistant to Fov infection at the commencement of this research, whilst Sicot 189 was considered to have moderate resistance to the pathogen. Vascular discolouration was significantly reduced in the more resistant cultivar, Sicot F-1 following treatment with potassium silicate, compared to mock inoculated plants and inoculated plants treated with potassium sulphate or calcium sulphate. No significant differences between treatments were observed in the moderately resistant cultivar, Sicot 189, though further trials may need to be conducted to confirm this result. In both cultivars, silicon content was significantly greater in plants which had been treated regularly with liquid potassium silicate, rather than with calcium silicate powder. Histological investigation of cotton infected with Fov, with and without silicon treatment, was conducted to ascertain the effects of this element on the accumulation of fungitoxic phenolic compounds, cell ultrastructural changes and fungal infection structures. Fov proliferated through the cortex and stele of plants from both the resistant (Sicot F-1), and moderately resistant (Sicot 189) cultivars, regardless of silicon treatment. However, defences were more rapidly and intensely induced in endodermal and vascular regions of inoculated, potassium silicate treated Sicot F-1 plants. Significantly more phenolic compounds were present at seven days post infection (dpi) in root extracts of inoculated, potassium silicate treated Sicot F-1 plants. Phenolic compounds were not significantly increased in inoculated, potassium silicate treated root extracts of Sicot 189 plants at three or seven dpi. Lignin assays demonstrated that the dry weight percentage of lignin in root material from inoculated, potassium silicate treated Sicot F-1 plants was significantly higher than that of extracts from inoculated plants not receiving silicon treatment at three dpi. This trend was also observed at seven dpi; however lignin content was not significantly different in this case. Percentage lignin content in the roots of Sicot 189 plants was not significantly different between inoculated potassium silicate treated plants and those not treated with silicon. Histological alterations were not observed in mock inoculated water or potassium silicate treated plants, nor were any significant increases in phenolic compounds or lignin accumulation detected in control treatments not inoculated with the pathogen. The expression of several defence related genes was assessed with quantitative reverse transcriptase real-time polymerase chain reaction. The results obtained verify that potassium silicate can enhance defence responses in Sicot 189 and Sicot F-1 plants inoculated with Fov, with silicon having a more pronounced effect on the more resistant cultivar, Sicot F-1. Genes upregulated at three and four dpi in potassium silicate treated, Fov inoculated Sicot F-1 plants included peroxidase, cadinene synthase and polygalacturonase inhibiting protein (PGIP), with peroxidase associated with phenol oxidation and lignification and cadinene synthase with phytoalexin biosynthesis. Osmotin-like protein and chitinase class I were consistently upregulated in potassium silicate treated, inoculated Sicot 189 plants; both genes coding for pathogenesis related (PR) proteins, with chitinase also classified as an antifungal protein. In both cultivars, silicon treatment without Fov inoculation did not result in the significant up-regulation of any of the defence genes assessed, providing further evidence for the role of silicon in priming in this interaction. The activities of three defence related enzymes, peroxidase, chitinase and β-1, 3- glucanase was assessed in root and shoot material by colourimetric assays. Regular application of potassium silicate significantly increased the activity of peroxidase in root extracts from the highly resistant cultivar Sicot F-1, at three, four and seven dpi with Fov, and in root extracts from the moderately resistant Sicot 189 at three and four dpi. Significant increases in chitinase activity in inoculated, silicon treated Sicot 189 plants were observed in root extracts at three dpi, and in shoot extracts at four dpi. Soluble potassium silicate treatment resulted in significant increases in β-1, 3- glucanase activity in Sicot 189 root extracts at four dpi. Few significant differences between treatments in terms of chitinase and β-1, 3- glucanase activity were detected in Sicot F-1 plants, though higher levels of each of these enzymes were present in root and shoot extracts from this cultivar. In this study the effects of acibenzolar-S-methyl, applied in the form of Bion®, on defence gene expression and enzyme activity in cotton infected with Fov were more pronounced in plants cultivated from treated seed, rather than in plants treated via foliar spray; a finding which is particularly relevant to the industry presently. Significant up-regulation of chitinase class I, peroxidase, and β-1, 3-glucanase transcripts and enzyme activities occurred in the Bion® seed soak treatment with Fov inoculation compared to all other treatments. It was possible to compare the actions of silicon with those of Bion® in this study. Bion® primed defence responses in cotton infected with Fov, in a manner similar to that observed in silicon treated cotton. The use of silicon and Bion® treatments, both alone and in combination as part of integrated disease management programmes, may potentially contribute to increased protection against this pathogen in Australian cotton fields in the future.