ABSTRACT Despite its interesting agricultural traits, Swingle citrumelo (Citrus paradisi Macfad. ‘Duncan’ × Poncirus trifoliata L. Raf.) rootstock exhibits severe incompatibility when grafted with Pera sweet orange [Citrus sinensis (L.) Osb.] scions, and this fact limits its use for propagation purposes. Nonetheless, the existence of certain Pera sweet orange clones that are compatible with Swingle citrumelo represents a substantial gain for the entire citrus industry. This study investigated the compatibility between seven Pera sweet orange clones and Swingle citrumelo rootstock, regarding the presence of a necrotic line at the graft union junction, the difference in diameter between rootstock and scion, the influence of clonal cleaning by micrografting, and the horticultural performance of the selected combinations. No trees died because of grafting incompatibility, even after twenty years (trial I), except for clone CV1, or after six years and nine months (trial II) from planting. The rootstock/scion trunk diameter ratio was not related to the presence of a necrotic line in the graft-union region. Additionally, these variables did not influence fruit yield and quality, and they were not affected by clonal cleaning or pre-immunisation of the old Pera sweet orange clones.

Resumo: O objetivo deste trabalho foi selecionar porta-enxertos alternativos ao limoeiro 'Cravo' para laranjeira 'Valência', para a região Norte do Estado de São Paulo, com base na produção inicial de frutos. Foram avaliados 41 porta-enxertos em experimento realizado em março de 2007, no Município de Colômbia, SP. Avaliou-se a produção acumulada de frutos de laranjeira 'Valência' nas safras de 2009, 2010 e 2011. Os porta-enxertos tangerineira 'Sunki' x P. trifoliata 'English', tangerineira 'Malvasio SRA 115', citrange 'C-13' “S”, tangerineira 'Sunki' x P. trifoliata 'Benecke', laranjeira 'Rhode Red Valência' + limoeiro 'Volkameriano', tangerineira 'C-54-4-4 SRA 337', tangerineira 'Cleópatra' x P. trifoliata 'Rubidoux' e tangerineira 'À Peau Lisse SRA 267' apresentam potencial para substituir o limoeiro 'Cravo' na região Norte do Estado de São Paulo.

Abstract: The objective of this work was to select alternative rootstocks to 'Rangpur' lime for 'Valência' sweet orange scions in the northern region of the state of São Paulo, Brazil, based on initial fruit yield. Forty-one rootstocks were evaluated in an experiment carried out in March 2007, in the municipality of Colômbia, in the state of São Paulo. The accumulated fruit yield of 'Valência' sweet orange was assessed in the 2009, 2010, and 2011 crop seasons. The rootstocks 'Sunki' mandarin x Poncirus. trifoliata 'English', 'Malvasio SRA 115' mandarin, 'C-13' “S” citrange, 'Sunki' mandarin x P. trifoliata 'Benecke', 'Valência Rhode Red' sweet orange + 'Volkamer' lemon, 'C-54-4-4 SRA 337' mandarin, 'Cleopatra' mandarin x P. trifoliata 'Rubidoux', and 'À Peau Lisse SRA 267' have potential to replace 'Rangpur' lime in the northern region of the state of São Paulo, Brazil.

Resumo A morte súbita dos citros (MSC) é uma doença de alto impacto destrutivo e tem levado à erradicação de milhões de plantas de laranja-doce na região Sudeste do Brasil, nos últimos 15 anos. Embora o agente causal da MSC ainda não tenha sido determinado, evidências demonstraram que esta doença pode ser transmitida por um vetor biótico. A incidência de MSC em cultivares de laranja-doce está relacionada ao porta-enxerto, sendo que a combinação com limoeiro ‘Cravo’ é a mais afetada. Por outro lado, há evidências de relação entre plantas sintomáticas para MSC e a presença de um vírus, denominado Citrus sudden death associated virus (CSDaV) e/ou com Citrus tristeza virus (CTV). Com base nessas informações, o objetivo deste estudo foi determinar a presença de CSDaV e CTV e a associação entre eles, em onze porta-enxertos para laranjeira ‘Valencia’. Os resultados apresentados aqui sugerem diferenças relacionadas à presença de CSDaV e CTV em diferentes porta-enxertos para laranja ‘Valencia’, não havendo relação entre a presença de CSDaV e CTV.

Abstract Citrus sudden death (CSD) is a highly destructive disease and has caused the eradication of millions of trees in southern Brazil within the last 15 years. In spite of the exact cause of CSD has not been determined, evidences have shown that this disease can be transmitted by biotic vectors. Disease incidence in sweet orange scions is related to the rootstock, and the combination with ‘Rangpur’ lime is the most affected. On the other hand, there are evidences of a relation between CSD affected trees and the presence of the Citrus sudden death associated virus (CSDaV) and/or Citrus tristeza virus (CTV). Based on such information, this study has been carried out to determine the presence of CSDaV and CTV, and the association between each other in eleven rootstocks for ‘Valencia’ sweet orange. The results presented herein showed differences related to the presence of CSDaV and CTV in different rootstocks for ‘Valencia’ sweet orange and no relation between the presence of CSDaV and CTV.

Resumo: O objetivo deste trabalho foi avaliar a sensibilidade ao deficit hídrico de 17 seleções de laranja-doce enxertadas sobre tangerineira 'Sunki', ao longo de cinco safras. Empregou-se um modelo agrometeorológico de penalização da produtividade pelo deficit hídrico, tendo-se avaliado a relação entre os valores estimados e observados. As seleções podem ser classificadas como de alta, média e baixa sensibilidade ao deficit hídrico, classificação que é inédita para as condições brasileiras. A sensibilidade ao deficit hídrico foi classificada como alta nas seleções de laranja-doce 'Pera Milton Teixeira', 'Pera IAC', 'IAC 2000', Pera 2, 'IAC 420 Seleta Rio' e Pera 3, e baixa nas seleções 'Bidwells Bar', 'IPR Jaffa', 'Torregrosa' e 'Sanguínea'.

Abstract: The objective of this work was to evaluate the water-deficit sensitivity of 17 sweet orange selections budded on 'Sunki' mandarin along five growing seasons. An agrometeorological model related to orange yield loss caused by water deficit was used, and the relationship between the estimated and observed values was determined. Sensitivity to water deficit of selections can be classified as high, medium, and low, and this ranking is unprecedented for Brazilian conditions. Sensitivity to water deficit was ranked as high for the sweet orange selections 'Pera Milton Teixeira', 'Pera IAC', 'IAC 2000', Pera 2, 'IAC 420 Seleta Rio', and Pera 3, and as low for the selections 'Bidwells Bar', 'IPR Jaffa', 'Torregrosa', and 'Sanguínea'.

Xylella fastidiosa inhabits the plant xylem, a nutrient-poor environment, so that mechanisms to sense and respond to adverse environmental conditions are extremely important for bacterial survival in the plant host. Although the complete genome sequences of different Xylella strains have been determined, little is known about stress responses and gene regulation in these organisms. In this work, a DNA microarray was constructed containing 2,600 ORFs identified in the genome sequencing project of Xylella fastidiosa 9a5c strain, and used to check global gene expression differences in the bacteria when it is infecting a symptomatic and a tolerant citrus tree. Different patterns of expression were found in each variety, suggesting that bacteria are responding differentially according to each plant xylem environment. The global gene expression profile was determined and several genes related to bacterial survival in stressed conditions were found to be differentially expressed between varieties, suggesting the involvement of different strategies for adaptation to the environment. The expression pattern of some genes related to the heat shock response, toxin and detoxification processes, adaptation to atypical conditions, repair systems as well as some regulatory genes are discussed in this paper. DNA microarray proved to be a powerful technique for global transcriptome analyses. This is one of the first studies of Xylella fastidiosa gene expression in vivo which helped to increase insight into stress responses and possible bacterial survival mechanisms in the nutrient-poor environment of xylem vessels.

O objetivo deste trabalho foi buscar novas fontes de resistência à leprose-dos-citros, no Banco Ativo de Germoplasma do Centro APTA Citros Sylvio Moreira, Instituto Agronômico, em Cordeirópolis, SP. Foram utilizadas plantas obtidas por sementes de 26 acessos, infectadas com o vírus da leprose-dos-citros (Citrus leprosis virus - CiLV), por meio do seu vetor Brevipalpus phoenicis. O aparecimento de lesões, a partir de 21 dias após a inoculação, foi observado em 11 dos genótipos testados (42,3%). Quinze espécies, entre elas Citrus pennivesiculata e C. celebica, comportaram-se como altamente resistentes, enquanto outras, como C. keraji, foram mais suscetíveis que o padrão C. sinensis. Os dados mostraram grande variação de respostas de Citrus spp. à leprose, com elevado número de espécies resisentes, que podem ser utilizadas como fonte de resistência à doença em programas de melhoramento.

The objective of this work was to prospect for new sources of resistance to leprosis in the Citrus Germplasm Bank of Centro APTA Citros Sylvio Moreira, Instituto Agronômico, in Cordeirópolis, SP, Brazil. Plants obtained through seeds from 26 citrus accessions were mite-infected with Citrus leprosis virus (CiLV). Typical lesions started to appear in 11 genotypes (42.3% of the tested accessions) 21 days after inoculation. Fifteen species, among them Citrus pennivesiculata and C. celebica, behaved as highly resistant, while other genotypes, as C. keraji, were more susceptible than the standard C. sinensis. The data showed a wide variation in the response of Citrus spp. to leprosis, with a large number of resistant species, wich can be used as source of resistance to this disease, in breeding programs.