EFEITOS DE GIBERELINAS, CITOCININAS E do NITRATO DE POTÁSSIO, NO PROCESSO GERMINATIVO DE SEMENTES DE LIMOEIRO `CRAVO' (Citrus limonia OSBECK)

Foram estudados os efeitos de reguladores vegetais do grupo das giberelinas e citocininas, bem como do nitrato de potássio na germinação de sementes do limoeiro `Cravo' (Citrus limonia Osbeck). O experimento foi realizado, contendo papel de filtro como substrato para a germinação das sementes, regulado à temperatura de 25oC. As sementes foram retiradas de frutos maduros no final da safra do limoeiro `Cravo', lavadas, secas à sombra e armazenadas durante 11 dias em câmara fria. em seguida, receberam tratamento com os fitorreguladores e KNO3 por 24 horas, de acordo com os tratamentos: KNO3 0,1% e 0,2%; GA3 50, 100 e 250 mg.L-1; GA4 + GA7 + fenilmetilaminopurina 100 mg.L-1; fenilmetilaminopurina 20 mg.L-1 e água destilada (testemunha). As avaliações foram iniciadas 15 dias após a semeadura, em intervalos de 5 dias. Conclui-se que os reguladores vegetais utilizados não afetaram o processo germinativo das sementes e que os tratamentos com nitrato de potássio 0,1% e 0,2% exerceram efeito inibitório sobre a germinação.

ÁCIDO GIBERÉLICO E O DESENVOLVIMENTO DE PLÂNTULAS DE TANGERINA 'CLEÓPATRA' (Citrus reshni hort. ex. Tanaka)

Plântulas de tangerina 'Cleópatra'(Citrus reshni hort. ex. Tanaka), foram utilizadas em delineamento inteiramente casualizado, com três repetições no esquema de parcelas sub-divididas, onde os tratamentos principais foram 5 concentrações de ácido giberélico: T1 = 0, T2 = 25, T3 = 50, T4 = 100 e T5 = 150 mg.L-1, parceladas em quatro pulverizações. As coletas de material foram realizadas dos 70 aos 210 dias, em intervalos de 14 dias. Pelos resultados obtidos, o fitorregulador promoveu efeito favorável com relação ao incremento do comprimento do caule, sendo que aplicações de 100 e 150 mg.L-1 foram superiores as demais. O diâmetro do caule não foi influenciado pela aplicação de ácido giberélico.

Polinização em cultura de laranja (Citrus sinensis L. Osbeck, var. Pera-Rio)

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

Isoenzymatic polymorphism in Citrus spp. and Poncirus trifoliata (L.) Raf. (Rutaceae)

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

Development and characterization of polymorphic microsatellite markers for the sweet orange (Citrus sinensis L. Osbeck)

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

Nitrogen assimilation in Citrus based on CitEST data mining

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

PR gene families of citrus: their organ specific-biotic and abiotic inducible expression profiles based on ESTs approach

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Phytophthora parasitica transcriptome, a new concept in the understanding of the citrus gummosis

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

Mites (Arachnida, Acari) on Citrus sinensis L. Osbeck orange trees in the state of Amazonas, Northern Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A triply cloned strain of Xylella fastidiosa multiplies and induces symptoms of citrus variegated chlorosis in sweet orange

Xylella fastidiosa isolate 8.1,b obtained from a sweet orange tree affected by citrus variegated chlorosis in the state of Sb Paulo, Brazil, and shown in 1993 to be the causal agent of the disease, was cloned by repeated culture in liquid and on solid PW medium, yielding triply cloned strain 9a5c. The eighth and the 16th passages of strain 9a5c were mechanically inoculated into sweet orange plants. Presence of X. fastidiosa in sweet orange leaves of shoots having grown after inoculation (first-flush shoots) was detected by DAS-ELISA and PCR. Thirty-eight days after inoculation, 70% of the 20 inoculated plants rested positive, and all plants gave strong positive reactions 90 days after inoculation. Symptoms first appeared after 3 months and were conspicuous after 5 months. X. fastidiosa was reisolated from sweet orange leaves, 44 days after inoculation. These results indicate that X. fastidiosa strain 9a5c, derived from pathogenic isolate 8.1.b by triply cloning, is also pathogenic, Strain 9a5c is now used for the X. fastidiosa genome sequencing project undertaken on a large scale in Brazil.

Thermodynamic and quality properties of lemon juice powder as affected by maltodextrin and Arabic gum

Sorption isotherms of lemon juice (LE) powders with and without additives-18% maltodextrin (MA) or 18% gum Arabic (GA) were determined at 20-50 degrees C. Addition of additives was shown to affect the isotherms in such a way that, at the same water activity, samples LE + GA and LE + MA presented lower equilibrium moisture content and were not so affected by varying temperature. The net isosteric heats of sorption of juice powders with additives were higher (less negative) than those of lemon juice powders, suggesting that there are more active polar sites in the product without addition of GA or MA. In general, the quality properties decreased with the addition of maltodextrin and gum arabic and it was obtained similar values for LE + GA and LE + MA.

Pectinolytic activity secreted by yeasts isolated from fermented citrus molasses

Aims: the aim of this study was to obtain improved strains of pectinolytic yeasts adapted to the conditions of an industrial fermentation process, which was continuously operated to convert citrus molasses into ethanol.Methods and Results: the starter yeast of the industrial fermentation process was a commercial baker's yeast, which was capable of growing without forming any secretion halo of pectinase activity on solid medium. Nevertheless, isolates showing secretion of pectinolytic activity on plates were obtained from the fermentation process. The secretion of pectin-degrading activity by isolates on plates was repressed by galactose and improved as the result of colony aging on polygalacturonic acid plates at 30 degrees C. Liquefaction of polygalacturonate gels as well as the splitting of the pectin-degrading activity into a wall-linked and a supernatant fraction were also observed when the starter yeast was propagated under agitation in liquid medium containing pectin.Conclusions: Isolates capable of secreting pectinolytic activity on plates were predominant at the end of the citrus molasses fermentation. Nevertheless, the sizes of the secretion haloes on plates were not necessarily an indication of the levels of pectinolytic activity secreted in the liquid medium.Significance and Impact of the Study: Improved pectinolytic strains of Saccharomyces can be used as a source of pectinases for a variety of applications. This organism also participates in plant deterioration processes.

Identification of QTLs associated with citrus resistance to Phytophthora gummosis

Citrus gummosis, caused by Phylophthora spp., is an important citrus disease in Brazil. Almost all citrus rootstock varieties are susceptible to it to some degree, whereas resistance is present in Poncirus trifoliata, a closely related species. The objective of this study was to detect QTLs linked to citrus Phylophthora gummosis resistance. Eighty individuals of the F, progeny, obtained by controlled crosses between Sunki mandarin Citrus sunki (susceptible) and Poncirus trifoliata cv. Rubidoux (resistant), were evaluated. Resistance to Phytophthora parasitica was evaluated by inoculating stems of young plants with a disc of fungal mycelia and measuring lesion lengths a month later. Two QTLs linked to gummosis resistance were detected in linkage groups I and 5 of the P. trifoliala map, and one QTL in linkage group 2 of the C sunki map. The phenotypic variation explained by individual QTLs was 14% for C sunki and ranged from 16 to 24% for P. trifoliala. The low character heritability (h(2) = 18.7%) and the detection of more than one QTL associated with citrus Phytophthora gummosis resistance showed that inheritance of the resistance is quantitative.

Morphological and molecular characterization of Colletotrichum spp. from citrus orchards affected by postbloom fruit drop in Brazil

Brazilian isolates of Colletotrichum spp. from citrus orchards affected by postbloom fruit drop were examined for colony colour, mycelial growth, benomyl-resistance, pathogenicity, and genetic variability by random amplified polymorphic DNA (RAPD) analysis. All isolates were obtained from flowers and persistent calyxes from different citrus hosts from São Paulo, Brazil. DNA polymorphisms detected after amplification with random 10-mer primers were used to classify the isolates into two groups. Group I isolates grew rapidly on potato-dextrose agar (PDA) and were sensitive to benomyl, and group II isolates grew slowly on PDA and were benomyl-resistant. Colletotrichum acutatum was analyzed by RAPD and had high genetic similarity with group II isolates of Colletotrichum from citrus. Probably, the group I is C, gloeosporioides and group II is C. acutatum.

Ineffectiveness of pruning to control citrus huanglongbing caused by Candidatus Liberibacter americanus

The huanglongbing (HLB) disease of citrus trees, caused by Candidatus Liberibacter asiaticus and Ca. Liberibacter americanus, was first reported in Brazil in March, 2004. The presence of the disease has caused serious concerns among growers. Pruning experiments were conducted to determine if removal of symptomatic branches or the entire canopy (decapitation) would eliminate infected tissues and save HLB-affected trees. Pruning was done in five blocks on a total of 592 3- to 16 year-old 'Valencia', 'Hamlin' or 'Pera' sweet orange trees showing no symptoms or with two levels of symptom severity. Ten decapitated trees per block were caged and all trees were treated with insecticides to control the psyllid vector, Diaphorina citri. Mottled leaves reappeared on most symptomatic (69.2%) as well on some asymptomatic (7.6%) pruned trees, regardless of age, variety, and pruning procedure. Presence of the pathogen (Ca. Liberibacter americanus) in all symptomatic trees was confirmed by PCR. In general, the greater the symptom severity before pruning the lower the percentage of trees that remained asymptomatic after pruning.