Produção de estruturas reprodutivas e efeito do ambiente nos tipos de sintomas produzidos por Guignardia citricarpa em Citrus spp

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Expressão gênica diferencial de laranja Pêra Rio (Citrus sinensis (L.) Osbeck) e Lima Ácida 'Galego' (Citrus aurantifolia Swingle) em resposta à infecção por Xanthomonas citri subsp. citri

Pós-graduação em Agronomia (Genética e Melhoramento de Plantas) - FCAV

Candidatus Liberibacter asiaticus Titers in Citrus and Acquisition Rates by Diaphorina citri Are Decreased by Higher Temperature

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Comparative proteomic analysis reveals that T3SS, Tfp, and xanthan gum are key factors in initial stages of Citrus sinensis infection by Xanthomonas citri subsp citri

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estrutura de populações e inoculações recíprocas de Xylella fastidiosa subsp. pauca com ocorrência em cultivos vizinhos de Citrus sinensis e Coffea arabica sob condições do estado de São Paulo

Pós-graduação em Agronomia (Genética e Melhoramento de Plantas) - FCAV

Atividade larvicida dos óleos essenciais de Syzygium aromaticum e Citrus sinensis em populações de Aedes aegypti

Pós-graduação em Biociências - FCLAS

Transcriptoma da interação de tangerina satsuma (Citrus unshiu) e laranja doce Hamlin (Citrus sinensis) infectadas com Xanthomonas citri subsp. citri, agente causal do cancro cítrico

Pós-graduação em Agronomia (Genética e Melhoramento de Plantas) - FCAV

Phyllosticta citricarpa: diversidade genética temporal em pomares de citrus sinensis e sensibilidade a fungicidas

Pós-graduação em Agronomia (Genética e Melhoramento de Plantas) - FCAV

Chemotactic signal transduction and phosphate metabolism as adaptive strategies during citrus canker induction by Xanthomonas citri

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

GUS expression in sweet oranges (Citrus sinensis L. Osbeck) driven by three different phloem-specific promoters

Huanglongbing (HLB) is associated with Candidatus Liberibacter spp., endogenous, sieve tube-restricted bacteria that are transmitted by citrus psyllid insect vectors. Transgenic expression in the phloem of specific genes that might affect Ca. Liberibacter spp. growth and development may be an adequate strategy to improve citrus resistance to HLB. To study specific phloem gene expression in citrus, we developed three different binary vector constructs with expression cassettes bearing the beta-glucuronidase (GUS) reporter gene (uidA) under the control of one of the three different promoters: Citrus phloem protein 2 (CsPP2), Arabidopsis thaliana phloem protein 2 (AtPP2), and Arabidopsis thaliana sucrose transporter 2 (AtSUC2). Transgenic lines of 'Hamlin', 'Pera', and 'Valencia' sweet oranges [Citrus sinensis (L.) Osbeck] were produced via Agrobacterium tumefaciens transformation. The epicotyl segments collected from in vitro germinated seedlings were used as explants. The gene nptII, which confers resistance to the antibiotic kanamycin, was used for selection. The transformation efficiency was expressed as the number of GUS-positive shoots over the total number of explants and varied from 1.54 to 6.08 % among the three cultivars and three constructs studied. Several lines of the three sweet orange cultivars analyzed using PCR and Southern blot analysis were genetically transformed with the three constructs evaluated. The histological GUS activity in the leaves indicates that the uidA gene was preferentially expressed in the phloem, which suggests that the use of the three promoters might be adequate for producing HLB-resistant transgenic sweet oranges. The results reported here conclusively demonstrate the preferential expression of GUS in the phloem driven by two heterologous and one homologous gene promoters. Key message The results reported here conclusively demonstrate the preferential expression of GUS in the phloem driven by two heterologous and one homologous gene promoters.

LIFE TABLE ANALYSIS OF DIAPHORINA CITRI (HEMIPTERA: PSYLLIDAE) INFESTING SWEET ORANGE (CITRUS SINENSIS) IN SAO PAULO

An ecological life table for eggs and nymphs of Diaphorina citri Kuwayama (Hemiptera: Psyllidae) was constructed with data obtained from orange orchards (Citrus sinensis Osbeck) in 2 regions of the State of Sao Paulo, over 4 generations in the period from XI-2006 to V-2007, comprising spring, summer, and fall seasons. Young growing shoots with D. citri eggs present were identified, and live individuals were counted until adult emergence. No predatory arthropods were observed in association with D. citri eggs and nymphs during the study. The mean parasitism of fourth- and fifth-instar nymphs by Tamarixia radiata Waterston (Hymenoptera: Eulophidae) was 2.3%. The durations of the egg-adult period were similar among the 4 generations, ranging from 18.0 to 24.7 d (at mean temperatures ranging from 21.6 to 26.0 degrees C) and followed the temperature requirement models obtained in the laboratory for D. citri. However, survival from the egg to the adult stage for the same period varied considerably from 1.7 to 21.4%; the highest mortalities were observed in the egg and small nymphal (first- to thirdinstar) stages, which were considered to be key phases for population growth of the pest.

Relationship between sweet orange yield and intensity of Citrus Variegated Chlorosis

Citrus Variegated Chlorosis (CVC) is currently present in approximately 40% of citrus plants in Brazil and causes an annual loss of around 120 million US dollars to the Brazilian citrus industry. Despite the fact that CVC has been present in Brazil for over 20 years, a relationship between disease intensity and yield loss has not been established. In order to achieve this, an experiment was carried out in a randomized block design in a 3 x 2 factorial scheme with 10-year-old Natal sweet orange. The following treatments were applied: irrigation with 0, 50 or 100% of the evapotranspiration of the crop, combined with natural infection or artificial inoculation with Xylella fastidiosa, the causal agent of CVC. The experiment was evaluated during three seasons. A negative exponential model was fitted to the relationships between yield versus CVC severity and yield versus Area Under Disease Progress Curve (AUDPC). In addition, the relationship between yield versus CVC severity and canopy volume was fitted by a multivariate exponential model. The use of the AUDPC variable showed practical limitations when compared with the variable CVC severity. The parameter values in the relationship of yieldCVC severity were similar for all treatments unlike in the multivariate model. Consequently, the yieldCVC intensity relationship (with 432 data points) could be described by one single model: y = 114.07 exp(-0.017 x), where y is yield (symptomless fruit weight in kg) and x is disease severity (R2 = 0.45; P < 0.01).

Weedy Hosts and Prevalence of Potential Leafhopper Vectors (Hemiptera: Cicadellidae) of a Phytoplasma (16SrIX group) Associated With Huanglongbing Symptoms in Citrus Groves

Huanglongbing (HLB) is a severe citrus (Citrus spp.) disease associated with the bacteria genus Candidatus Liberibacter, detected in Brazil in 2004. Another bacterium was found in association with HLB symptoms and characterized as a phytoplasma belonging to the 16SrIX group. The objectives of this study were to identify potential leafhopper vectors of the HLB-associated phytoplasma and their host plants. Leafhoppers were sampled every other week for 12 mo with sticky yellow cards placed at two heights (0.3 and 1.5 m) in the citrus tree canopy and by using a sweep net in the ground vegetation of two sweet orange, Citrus sinensis (L.) Osbeck, groves infected by the HLB-phytoplasma in Sao Paulo state. Faunistic analyses indicated one Agalliinae (Agallia albidula Uhler) and three Deltocephalinae [Balclutha hebe (Kirkaldy), Planicephalus flavicosta (Stal), and Scaphytopius (Convelinus) marginelineatus (Stal)] species, as the most abundant and frequent leafhoppers (Hemiptera: Cicadellidae). Visual observations indicated an association of leafhopper species with some weeds and the influence of weed species composition on leafhopper abundance in low-lying vegetation. S. marginelineatus and P. flavicosta were more frequent on Sida rhombifolia L. and Althernantera tenella Colla, respectively, whereas A. albidula was observed more often on Conyza bonariensis (L.) Cronq. and B. hebe only occurred on grasses. DNA samples of field-collected S. marginelineatus were positive by polymerase chain reaction and sequencing tests for the presence of the HLB-phytoplasma group, indicating it as a potential vector. The association of leafhoppers with their hosts may be used in deciding which management strategies to adopt against weeds and diseases in citrus orchards.

Regeneration and characterization of somatic hybrids combining sweet orange and mandarin/mandarin hybrid cultivars for citrus scion improvement

Protoplast fusion between sweet orange and mandarin/mandarin hybrids scion cultivars was performed following the model "diploid embryogenic callus protoplast + diploid mesophyll-derived protoplast". Protoplasts were isolated from embryogenic calli of 'Pera' and 'Westin' sweet orange cultivars (Citrus sinensis) and from young leaves of 'Fremont', Nules', and 'Thomas' mandarins (C. reticulata), and 'Nova' tangelo [C. reticulata x (C. paradisi x C. reticulata)]. The regenerated plants were characterized based on their leaf morphology (thickness), ploidy level, and simple sequence repeat (SSR) molecular markers. Plants were successfully generated only when 'Pera' sweet orange was used as the embryogenic parent. Fifteen plants were regenerated being 7 tetraploid and 8 diploid. Based on SSR molecular markers analyses all 7 tetraploid regenerated plants revealed to be allotetraploids (somatic hybrids), including 2 from the combination of 'Pera' sweet orange + 'Fremont' mandarin, 3 'Pera' sweet orange + 'Nules' mandarin, and 2 'Pera' sweet orange + 'Nova' tangelo, and all the diploid regenerated plants showed the 'Pera' sweet orange marker profile. Somatic hybrids were inoculated with Alternaria alternata and no disease symptoms were detected 96 h post-inoculation. This hybrid material has the potential to be used as a tetraploid parent in interploid crosses for citrus scion breeding.

Genetic transformation of Citrus sinensis with Citrus tristeza virus (CTV) derived sequences and reaction of transgenic lines to CTV infection

Transgenic Citrus sinensis (L.) Osb. plants, cvs. Valencia and Hamlin, expressing Citrus tristeza virus (CTV) derived sequences were obtained by genetic transformation. The gene constructs were pCTV-CP containing the 25 kDa major capsid protein gene (CTV-CP), pCTV-dsCP containing the same CTV-CP gene in an intron-spliced hairpin construct, and pCTV-CS containing a 559 nt conserved region of the CTV genome. The transgenic lines were identified by PCR and the transgene integration was confirmed by Southern blot. Transgene mRNA could be detected in most transgenic lines containing pCTV-CP or pCTV-CS transgene. The mRNA of pCTV-dsCP transgene was almost undetectable, with very light bands in most analyzed plants. The transgene transcription appears to be closely linked to the type of gene construct. The virus challenge assays reveals that all transgenic lines were infected. However, it was possible to identify propagated clones of transgenic plants of both cultivars studied with a low virus titer, with values similar to the non-inoculated plants (negative control). These results suggested that the transgenic plants present some level of resistance to virus replication. The higher number of clones with low virus titer and where mRNA could not be detected or was presented in a very light band was found for pCTV-dsCP-derived transgenic lines.