Selim, Mohamed Elwy Mohamed: Biological, chemical and molecular studies on the systemic induced resistance in tomato against Meloidogyne incognita caused by the endophytic Fusarium oxysporum, Fo162. - Bonn, 2010. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Mohamed Elwy Mohamed Selim}},
title = {Biological, chemical and molecular studies on the systemic induced resistance in tomato against Meloidogyne incognita caused by the endophytic Fusarium oxysporum, Fo162},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2010,
month = sep,

note = {In this study, the role of the mutualistic endophyte Fusarium oxysporum (Fo162) in inducing systemic resistance in tomato against the root knot nematode, Meloidogyne incognita, was investigated at the biological, physiological and molecular level. It was determined whether Fo162 was able to colonize Fusarium-wilt resistant cultivars and simultaneously induced resistance against root knot nematodes. The results showed that Fo162 successfully colonized the endorhiza of 8 Fusarium-wilt resistant cultivars. A positive correlation was detected between Fo162 colonization levels and root-knot nematode control on both Fusarium-wilt resistant and susceptible tomato cultivars. Remarkably, the levels of Fo162 colonization were higher on the majority of these resistant cultivars when compared to susceptible cultivars, also causing a greater reduction in nematode infection. Then the influence of root exudates obtained from tomato plants, pre-inoculated with Fo162, on rootknot nematode attraction or repellency was determined. The results showed that these root exudates of tomato plants affected the behaviour and migration pattern of M. incognita J2. The chemical composition of these root exudates was also biochemically evaluated, using RP-HPLC analysis. Fo162 colonization resulted in increasing the accumulation of several different chemical compounds in root exudates of tomato plants which may be responsible for a repelling effect towards the nematode. The defences in Fusarium-wilt susceptible and resistant tomato cultivars, induced by Fo162, against M. incognita were further analyzed with respect to its systemic nature and durability. The results showed that Fo162 was able to induce a systemic resistance of both the Fusarium-wilt resistant and susceptible tomato cultivars tested which could still be detected 7 days after physically separating the endophyte. However, due to the experimental procedure, possible additive effects of wound induced defence responses cannot be ruled out with respect to this prolonged reduction in root-knot nematode infection. The biotic induced resistance, caused by Fo162 was compared with the typical induced systemic resistance (ISR) and systemic acquired resistance (SAR), which can be chemically induced using methyl jasmonate (MJ) and salicylic acid (SA), respectively. The results showed that in a split root experiment these abiotic inducers both increased the levels of systemic resistance and reduced the number of galls of Meloidogyne incognita on tomato plants, similar to Fo162. The similarities in reducing root knot nematode colonization by using the biotic and abiotic elicitors offered new perspectives for further research on the mechanism underlying the systemic induced resistance by using molecular tools. Alterations in the expression of genes caused by these elicitors were monitored using a tomato genome array. This demonstrated that the chemical elicitors, SA and MJ, and the biological inducer, Fo162, all alter the expression of a great number of genes. The highest number of genes that were altered in expression level was detected within the plants leaves, especially the plants inoculated with Fo162. By selection the genes, of which the expression had altered in the same direction with all three elicitor treatments, the number of potentially interesting genes could be significantly reduced. Although some candidate genes were identified, further research is necessary to confirm the role of these genes in the systemic resistance against root knot nematodes. The elicitors also affected the expression of genes, whose products are associated with chlorophyll synthesis and water stress, a finding that corroborated with the physiological and biological observations. This validated the relevance of expression analysis studies by genome arrays as a relevant approach in studying the resistance mechanisms induced by biotic and abiotic elicitors in tomato plants.},
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