DNA macroarrays of 279 genes of Xanthomonas axonopodis pv. citri potentially associated with pathogenicity and virulence were used to compare the transcriptional alterations of this bacterium in response to two synthetic media. Data analysis indicated that 31 genes were up-regulated by synthetic medium XVM2, while only 7 genes were repressed. The results suggest that XVM2 could be used as an in vitro system to identify candidate genes involved in pathogenesis of X. axonopodis pv. citri. Within the genus Xanthomonas, several genes have been found associated with pathogenicity and virulence. Of these genes, the avr (avirulence), rpf (named for regulation of pathogenicity factors), and hrp (named for hypersensitive response and pathogenicity) genes are perhaps the most widely studied elements. The avr genes encode a known group of effector proteins responsible for controlling the ability of bacteria to elicit the hypersensitive reaction in resistant hosts (26) and may also participate in pathogenicity or virulence in compatible interactions (38,47). The rpf operon is thought to control the production of important pathogenicity factors, such as proteases, endoglucanases, polygalacturonate ligases, and extracellular polysaccharides (5, 17). Finally, the hrp genes are thought to encode proteins involved in the type III secretion system, responsible for delivering effector proteins inside the host plant cells (8,9,20,21).Even though pathogenicity and virulence of Xanthomonas axonopodis pv. citri have been traditionally associated with the activity of a single avirulence-like gene known as pthA (14,22,45,46), little is known about other gene products involved in these processes. In this respect, transcription profiling under natural conditions may be a good alternative to identify all the elements involved in pathogenicity and virulence of this microbial pathogen. However, leaf spot pathogens, such as X. axonopodis pv. citri, do not reach high population levels in infected tissues and do not yield enough material (either bacterial cells or RNA) to conduct gene expression studies. Therefore, in an attempt to develop an alternative system for gene expression studies, an in vitro system was evaluated in order to determine whether it could be used to model pathogen responses to host tissues under controlled conditions. The two media selected were NB (nutrient broth), commonly used for growing this bacterium, and XVM2, suspected to mimic the environment of the plant intercellular spaces (1, 41, 51, 55).Construction of DNA macroarrays. To study the expression profile of X. axonopodis pv. citri, 279 candidate genes, associated with pathogenicity or virulence by sequence similarity, were selected from the genome of this bacterium (13). Specific primers were designed to amplify either the entire open reading frame or a fragment of it. PCR amplifications were performed in two rounds using 96-well plates and a Mastercycler Eppendorf (Eppendorf). The quality of amplimers was analyzed by agarose gel electrophoresis.Prior to the cons...

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Citriculture is an important agricultural activity worldwide, occupying a relevant position in Brazil among fruit tree production for both the fresh fruit market and the processing industry for concentrated orange juice export. Recent advances in the country’s citrus nursery tree production system have been essential to guarantee the efficiency and competitiveness of Brazilian citriculture. The implementation of strict laws and regulations to produce trees in protected environments and improvements in production techniques for basic citrus propagation materials and nursery trees in São Paulo state has excluded the insect vectors of destructive diseases such as citrus variegated chlorosis and huanglongbing, making this an innovative reference system for citrus propagation around the globe. The main aspects of these advances are presented and discussed in this review, including advances in propagation techniques, scion and rootstock selection, genetic characterization and certification, tree size standards, cultural practices such as irrigation and fertilization for the production of citrus propagation materials and nursery trees, and nursery management tools.

O trabalho teve como objetivo avaliar o efeito do uso de fino de carvão no substrato e da aplicação de extrato pirolenhoso no substrato e na planta sobre o desenvolvimento de porta-enxertos de limoeiro 'Cravo' (Citrus limonia Osbeck) cultivados em ambiente protegido. O experimento foi desenvolvido no delineamento em blocos casualisados, com análise em esquema fatorial 3 x 2 x 3, sendo: 3 proporções de fino de carvão (0, 100 e 200 cm³ dm-3) em mistura com substrato comercial, 2 concentrações de extrato pirolenhoso (0 e 20 cm³ dm-3) misturadas no substrato (240 cm³ por dm³ de substrato) e 3 concentrações de extrato pirolenhoso (0, 5 e 10 cm³ dm-3) pulverizadas na parte aérea, em 4 repetições. Aos 150 e 180 dias após o plantio foram realizadas avaliações do desenvolvimento das plantas. As misturas de fino de carvão e substrato comercial contendo fino de carvão na proporção de 100 cm³ dm-3 não influíram no desenvolvimento de porta-enxertos de limoeiro 'Cravo' , porém, na proporção de 200 cm³ dm-3 prejudica o desenvolvimento dos mesmos. O umedecimento pré-plantio do substrato com solução diluída (20 cm³ dm-3) de extrato pirolenhoso ou pulverização da parte aérea das plantas com soluções a 5 e 10 cm³ dm-3 provoca redução do desenvolvimento de porta-enxertos de limoeiro 'Cravo' .

Citrus sinensis grafted on C. limonia produces a considerable number of compounds that are not common in both plants developed from germination of seeds. The chemical profile of scion and rootstock differ notably for absence in the form of flavonoids and coumarins containing C5 prenyl groups attached to the carbon atoms of aromatic and heterocyclic systems or to oxygen. Only linear pyranocoumarins xanthyletin and xanthoxyletin were found in scion. This observation indicates that the prenylated compounds once biosynthesized in the roots could have been translocated to other organs. Xylella fastidiosa colonizes the xylem of plants causing diseases on several economically important crops such as citrus variegated chlorosis (CVC). A number of flavonoids, coumarins, alkaloids, dihydrocinnamic acid derivative, anacardic acid, triterpenes, and limonoids were tested for in vitro activity on the growth of Xylella fastidiosa. Azadirachtin A was the most active. Hesperidin, which occurs in great amounts in cells of the mesophyll of the affected leaves with CVC, showed a moderate activity suggesting that it can act as a good barrier for small-size colonies from X. fastidiosa.