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| Author(s): |
Welington Luiz de Araújo
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2000-08-31 |
| Advisor: | João Lúcio de Azevedo |
| Abstract | |
The present work was carried out to evaluate whether the bacterial endophyte communities contributes to Citrus Variegated Chlorosis (CVC) resistance in sweet orange (Citrus sinensis. The population density and biodiversity of culturable and unculturable endophytic bacteria was examined from peeled branches of 4 types of citrus (healthy, escape and diseased plants of sweet orange and tangerine - C. reticulate). In addition, the interaction between endophytic bacteria and seedlings of C. limonia was studied using molecular strategy developed in a model plant (Solanun tuberosum). There were no significant differences for population density of bacteria among sweet orange plants. However, the endophytic bacteria Curtobacterium flaccumfaciens was detected mainly in escape plants, while Methylobacterium spp. was detected in diseased plants. Using the DGGE (Denaturing Gradient Gel Electrophoresis) technique, the presence of a consistent high-GC band of unculturable β-proteobacteria was detected only in escape plants. In addition, more diversity of 16S rDNA genotypes of Methylobacterium spp. was detected in diseased plants. These results suggest the hypothesis that the presence of C. flaccumfaciens and the unculturable β-proteobacteria could elicit a induced systemic resistance in escape plants, which or a possible antibiosis could inhibit the colonization of this plant by many Methylobacterium spp. genotypes and keep the Xylella fastidiosa (causal agent of CVC) population in a low level avoiding of development CVC diseased. After seed treatment with AR1.6/2 strain of M. extorquens, the endophytic bacteria were observed mainly in sub-epidemic tissues of C. limonia, which plants shown a reduced growing in comparison of plants. The endophytic C. flaccumfaciens strain ER1/6 shown a plant-promoting effect in C. limona seedlings. This ER1/6 strain and M. mesophilicum (strain SR1.6/6) were abundant in the parenchyma adjacent to infected vessels, and also filled sub stomatal chambers of stems. Results of the present study provide then first evidence of induced systemic resistance by endophytic bacteria in C. sinensis and a promising approach to understand the CVC disease, and its biological control. (AU) | |