Study of Citrus sinensis tissue response at different stages of infection ontogenetic Candidatus Liberibacter asiaticus

• Grant number: 15/02639-4
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: June 01, 2015
• End date: May 31, 2019
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Organic Chemistry
• Agreement: Coordination of Improvement of Higher Education Personnel (CAPES)
• Principal Investigator: Maria Fátima das Graças Fernandes da Silva
• Grantee: Mayara Gobetti Fernandes da Silva
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil

Abstract

HLB (HLB) is the most destructive disease of citrus. In Brazil it is associated with the 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 is more aggressive and more widespread in citrus regions. Symptoms of yellow spots on the leaf begin in one or a few branches 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 income that occurs early in symptomatic trees. The discrepancy between the severity of visual symptoms and income decline in citrus affected by HLB suggests that damage is not observed are occurring. The initial movement of Ca. L. asiaticus to different tissues citrus after infection and the first effects of HLB of the root are poorly understood. 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 colleagues studied the movement of Ca. L. asiaticus after 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 bacteria in infected plants and asymptomatic in the field and in the greenhouse showed the importance of infection at the root of the development of the disease. They showed that the bacteria preferentially colonize the roots before the leaves, where they multiply and invade quickly when new foliage leaves become a fabric formed by specialized vessels in driving 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 leaf symptoms, and is not associated with blockage of the phloem and consequent reduction in the supply of carbohydrate, as it was the previous hypothesis. By analyzing the chemical profile of the plant infected with HLB and sound via HPLC-UV-SPE-NMR and LC-MS PN group UFSCar noted that the plant responds by producing some metabolites in higher or lower amount in response to the presence of the bacterium . With these tests it was observed that the plant productivity increases to some metabolites (especially coumarins) in response to the presence of bacteria only in extracts of roots. In other extracts, leaves, upper stem and lower stem, there is a reverse reaction, occurring the reduction of the production of compounds in plants infected with HLB. All the data suggests that plant defense against the bacteria seems to be at the root, inhibiting the path of cinnamic acid which leads to the flavonoids in other organs, to turn that leads to coumarins in 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. The rate of transmission of the pathogen to seedlings (plants from seed) was significantly lower (less than 1%) of the pathogen transmission rate (~ 25%) for oranges grafted seedlings in Swingle Swingle rootstock. Considering that both lots of insects used in the experiments were fed and multiplied in the new shoots in a similar manner in both groups of plants, the differences in transmission rates were attributed to the influence of some chemical component present in seedlings, directly affecting the establishment in the bud and plant colonization by the pathogen. The proposal has the general objective of developing analytical methods that make it possible to evaluate the change in the chemical profile between seedling specimens of orange Valencia and grafted on Swingle, and these symptomatic, asymptomatic, and healthy, to obtain possible biochemical markers that make it possible to understand resistance the plants grown from seeds in relation to its graft.