Development of analytical methods for obtaining biomarkers in Huanglongbing detection in asymptomatic citrus, and enable to understand the resistance of fabrics juvenile Valencia orange

Abstract

Huanglongbing (HLB) is the most destructive disease of citrus. In Brazil it is associated bacteria Candidatus Liberibacter asiaticus and Ca. L. americanus, which colonize the phloem causing gradual falling leaves and fruits and decline of the plant. The first one is the most aggressive and most widespread in citrus regions. Symptoms of yellow spots on the leaf begin in one branche and slowly spread to the rest of the tree, often over several years. This slow development of visual symptoms does not explain the rapid drop in yielded that occurs early in symptomatic trees. The discrepancy between the severity of visual symptoms, decline and yielded in citrus affected by HLB suggests that damage do not observed are occurring. The initial movement of Ca. L. asiaticus for different tissues of citrus after infection and the first effects of HLB on the root are misunderstood. Graham and colleagues in Florida showed that the loss of roots occurs earlier than expected in mature trees with recent symptoms. Recently (2014) Johnson and collaborators studied the movement of Ca. L. asiaticus after the initial infection, monitoring the leaves and roots of trees in the greenhouse. The analysis of the density of roots, the stored starch content and anatomy of the vascular system in the presence of this bacterium in symptomatic and asymptomatic plants in the field and in the greenhouse showed the importance of infection at the root in the development of the disease. They showed that the bacteria preferentially colonize the roots before the leaves, where they multiply and invade quickly new foliage leaves when these become a specialized tissue to drive the phloem flow. This led to the discovery that the roots are damaged by the infection caused by the bacteria prior to the development of visible foliar symptoms, and it is not associated with obstruction of the phloem and consequent reduction in the supply of carbohydrate, as was previously the hypothesis. Analyzing the chemical profile of the plants infected with HLB by HPLC-UV-SPE-NMR, the UFSCar NP group noted that the plants respond to the presence of the bacterium by producing metabolites in more or less concentration. It was observed that the plants increase the content of some metabolites (especially coumarins) in response to the presence of bacteria only in extracts of roots. In the other extracts form leaves and stem there is a reverse reaction, occurring reducing in the production of compounds in plants infected with HLB. All the data obtained suggested that plant defense against the bacteria appears to be in the roots, inhibiting the path of cinnamic acid to the flavonoids in other organs, to activity this to coumarins in the root tissue. Recently, experiments involving the use of D. citri to inoculate Ca. Liberibacter in sweet orange plants allowed the observation of an interesting phenomenon. Therate of transmission of the pathogen to seedlings (plants from seed) was significantly lower (less than 1%) of the pathogen transmission rate (~ 25%) to the seedlings grafted on rootstock Swingle. Considering that both lots of insects used in the experiments were fed and multiplied in new shoots in a similar way in both plant groups, the differences in transmission rates were attributed to the influence of some chemical component present in seedlings, directly affecting the colonization by the pathogen. Thus, the proposal of this project was developed analytical methods to evaluate the change in the chemical profile between seedling specimens of orange Valencia and it grafted on Swingle, symptomatic, asymptomatic, and healthy in order to obtain possible biochemical markers that allow understand the resistance of seedling in relation to its graft. (AU)