Geostatistical characterization of the spatial distribution of Xylella fastidiosa sharpshooter vectors on citrus

A distribuição espacial das espécies de cigarrinhas (Dilobopterus costalimai Young, Acrogonia sp. e Oncometopia facialis Signoret), vetoras da Xylella fastidiosa, agente causal da Clorose Variegada dos Citros, foi estudada com o uso da geoestatística. As avaliações foram feitas em um pomar comercial de laranja 'Pêra' (Citrus sinensis [L.] Osb.), objetivando estabelecer meios para melhor controle dos vetores e da doença. O monitoramento da ocorrência das cigarrinhas no pomar foi feito através de amostragens mensais, utilizando-se armadilhas adesivas amarelas de 3 x 5, distribuídas uniformemente em 50 pontos na área, dispostas em laranjeiras à altura de 1,5 m do solo e substituídas mensalmente. Acrogonia sp. foi a espécie prevalente nas amostragens. Os resultados possibilitaram ajustar modelos aos semivariogramas da distribuição espacial das três espécies no pomar estudado. Durante os três anos consecutivos de amostragem, as populações de Acrogonia sp., D. costalimai e O. facialis apresentaram modelos de distribuição agregada somente nos meses de verão, inverno e primavera, respectivamente, mostrando a necessidade de monitoramento constante desses vetores para reduzir a sua população em épocas favoráveis ao seu desenvolvimento. Através de parâmetros geoestatísticos foi possível calcular a área de agregação das cigarrinhas no pomar. A espécie Acrogonia sp. apresentou área média de agregação de 15.760 m², enquanto para O. facialis e D. costalimai foi possível constatar áreas médias de agregação de 11.555 m² e 10.980 m², respectivamente. Esses resultados indicaram que para um levantamento seguro de cigarrinhas é necessário pelo menos dispor de uma armadilha por hectare.

The effects of inter-crop cultivation Between rows of citrus crop on spreading of Guignardia citricarpa Ascospores and in the citrus black spot occurrence

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

Transmission of Citrus leprosis virus C by Brevipalpus phoenicis (Geijskes) to Alternative Host Plants Found in Citrus Orchards

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

Acaricides used in conventional and organic citrus orchard: leprosis and phytoseiid mites population control

The citrus leprosis control in São Paulo state is performed exclusively by acaricides to control the vector mite, Brevipalpus phoenicis, which increases the production costs and may affect the beneficial organism's population. Therefore, the aim of this trial was to evaluate during four seasons, the effects of acaricides recommended to control the mite B. phoenicis in conventional and organic citrus over evolution of citrus leprosis and over phytoseiids' population. The experiment was installed in October of 2003 in a citrus orchard in Reginopolis city, state of São Paulo. The experimental design used randomized blocks, the dosages was expressed as mL c.p./100L of water and the treatments were the following: spirodiclofen (20 mL); cyhexatin (50 mL) (used in rotation), lime sulfur (4,000 mL) and control (without pesticide application). However, the rotation between spirodiclofen and cyhexatin began in September 2006. Prior to that time, only spirodiclofen had been used. Surveys were conducted every 15 days on the B. phoenicis, Iphiseioides zuluagai, and Euseius populations. The control level adopted by the B. phoenicis was 8.3%, and the pesticide applications were conducted using tractor-sprayers. During the 2007-08 seasons, 10 infected fallen fruits per plot were collected and the number of leprosis lesions was quantified by each fruit. By the end of the 2007-08 seasons, the productivity, harvest losses, the disease incidence and severity were evaluated. It was found that the lesions' location over the fruit is more important in determining its drop than the lesions' number. The more intense the mite infestation, the greater is the number of lesions, resulting in increased premature fruit drop. A strategy using acaricides spirodiclofen and cyhexatin in rotation promoted more efficient control of B. phoenicis compared to lime sulfur, resulting in greater productivity, lower fruit losses and severity levels. The lime sulfur applications reduced the mite population incidence below the control level; however it did not prevent the lesions' occurrence. The acaricides applicarevented adverse effects on phytoseiid population because there was a reduction of their density.

Pathogenicity, colony morphology and diversity of isolates of Guignardia citricarpa and G-mangiferae isolated from Citrus spp.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A new method for inoculation of fruit with Guignardia citricarpa, the causal agent of citrus black spot

Citrus black spot (CBS) is a fungal disease, caused by Guignardia citricarpa, that has a high economic impact on citrus. Although G. citricarpa has been associated with black spot of citrus, an adequate pathogenicity test is still not available. Thus, our objective was to develop and evaluate a simple, safe, and practical pathogenicity test. We used fruits from Pera-Rio and Valencia sweet orange trees from two different orchards, located in the State of São Paulo, Brazil. Inoculation was performed by placing six disks colonized by G. citricarpa, onto the peel of healthy fruits, previously bagged. In the Pera-Rio sweet orange grove, initial symptoms of the false melanose type resulting from the inoculations were observed 55 days after inoculation (dai). In the Valencia grove, initial symptoms also of the false melanose type resulting from the inoculations occurred 73 dai. A total of 92.8% and 86.6% of the Pera Rio and Valencia fruits inoculated, respectively, showed symptoms of CBS. Citrus black spot symptoms were not observed in any of the control fruits.

Behavioral Response of the Leafcutter Ant, Atta sexdens rubropilosa (Hymenoptera, Formicidae), to Components of Citrus Pulp

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Gas exchange rates at different vapor pressure deficits and water relations of 'Pera' sweet orange plants with citrus variegated chlorosis (CVC)

Net photosynthesis (A) and transpiration rates (E), stomatal conductance (g), water use efficiency (WUE), intrinsic water use efficiency (IWUE) and internal leaf CO2 concentration (C) in response to different vapor pressure deficit (1.2 and 2.5 kPa) were investigated in 'Pera' sweet orange plants affected by citrus variegated chlorosis (CVC), a disease caused by Xylella fastidiosa. All plants were well watered and leaf water potential (Pw) was also measured by the psychrometric technique. Results showed that healthy plants responded to higher vapor pressure deficit (VPD), lowering its net photosynthesis and transpiration rates, and stomatal conductance. However, diseased plants presented no clear response to VPD, showing lower A, E and g for both VPDs studied and very similar values to these variables in healthy plants at the highest VPD. Internal leaf CO2 concentration also decreased for healthy plants when under the highest VPD, and surprisingly, the same pattern of response was found in plants with CVC. These results, the lower Psi(w) and higher WUE values for diseased plants, indicated that this disease may cause stomatal dysfunction and affect the water resistance through xylem vessels, which ultimately may play some role in photosynthetic metabolism. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Peroxidase activity and total phenol content in citrus cuttings treated with different copper sources

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Leaf gas exchange and fruit yield in sweet orange trees as affected by citrus variegated chlorosis and environmental conditions

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

Phytochemicals and Antioxidant Activity of Citrus Seed Oils

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

Azteca barbifex Forel (Hymenoptera: Formicidae): potential pest of citrus crops in eastern Amazon

Damage caused by the ant Azteca barbifex (Forel) was identified in orange trees (Citrus sinensis), in Capitão Poço County, Guamá microregion, Pará State. The damage caused by the scraping of stems and branches lead to reduction in yield with subsequent death of the plant. These characteristics indicate A. barbifex as a potential pest of citrus crops in the eastern region of Amazon.

An experimental inoculation system to study citrus-Xylella fastidiosa interactions

Difficulties in reproducing the citrus variegated chlorosis (CVC) disease symptoms in expertmental plants have delayed implementation of studies to better understand the essential aspects of this important disease. In an extensive Study, cultivars of sweet orange (Citrus sinensis) were inoculated with Xylella fastidiosa using procedures that included root immersion, and stein absorption, pricking, or infiltration of the inoculum into plants of different ages. Inoculum consisted of 5-day-old cultures or cell suspensions of CVC strain 9a5c diluted in phosphate-buffered saline. Inoculated plants and controls were grown, or transferred just after inoculation, to 5-liter pots or 72-cell foam trays. Approximately 4, 5, 9, and 12 months after inoculation, leaves were collected and processed for polymerase chain reaction analysis or X. fastidiosa isolation on BCYE agar medium. Root immersion and stem inoculation of 4- and 6-month-old plants resulted in low percentages of symptomatic (0 to 7%) and plants positive by isolation (0 to 9%). Pinpricked or injected stems of I-month-old seedlings resulted in high percentages of plants symptomatic (29 and 90% in Pera Rio, 75, 59, and 83% in Valencia, and 77% in Natal) or positive by isolation (26 and 93% in Pera Rio, 98, 96, and 83% in Valencia, and 77% in Natal), In foam trays, the seedlings grew less, the incubation period was shorter. and disease severity was higher than in pots. This system allows testing of higher numbers of plants in a reduced space with a more precise reproduction of the experimental conditions.

An evaluation of the genetic diversity of Xylella fastidiosa isolated from diseased citrus and coffee in São Paulo, Brazil

Strains of Xylella fastidiosa, isolated from sweet orange trees (Citrus sinensis) and coffee trees (Coffea arabica) with symptoms of citrus variegated chlorosis and Requeima do Cafe, respectively, were indistinguish able based on repetitive extragenic palindromic polymerase chain reaction (PCR) and enterobacterial repetitive intergenic consensus PCR assays. These strains were also indistinguishable with a previously described PCR assay that distinguished the citrus strains from all other strains of Xylella fastidiosa. Because we were not able to document any genomic diversity in our collection of Xylella fastidiosa strains isolated from diseased citrus, the observed gradient of increasing disease severity from southern to northern regions of São Paulo State is unlikely due to the presence of significantly different strains of the pathogen in the different regions. When comparisons were made to reference strains of Xylella fastidiosa isolated from other hosts using these methods, four groups were consistently identified consistent with the hosts and regions from which the strains originated: citrus and coffee, grapevine and almond, mulberry, and elm, plum, and oak. Independent results from random amplified polymorphic DNA (RAPD) PCR assays were also consistent with these results; however, two of the primers tested in RAPD-PCR were able to distinguish the coffee and citrus strains. Sequence comparisons of a PCR product amplified from all strains of Xylella fastidiosa confirmed the presence of a CfoI polymorphism that can be used to distinguish the citrus strains from all others. The ability to distinguish Xylella fastidiosa strains from citrus and coffee with a PCR-based assay will be useful in epidemiological and etiological studies of this pathogen.

Identification and analysis of single nucleotide polymorphisms (SNPs) in citrus

Most of the cultivated species of citrus have narrow genetic basis. Relationships among species and cultivars are obscured by sexual compatibility, polyembryony, apomixis and a high incidence of somatic mutations. DNA analysis is crucial in genetic studies not only for citrus breeding programs but also for characterization of hybrids and species. In this paper, single nucleotide polymorphisms ( SNPs) were investigated in 58 accessions of Citrus, hybrids and related genera. Genomic sequences of 'Pera IAC' sweet orange ( Citrus sinensis L. Osbeck) were used for primer design and selection of sequence tagged sites (STSs) for identification of SNPs. Analysis of 36 STSs showed identical sequences among 40 of the 41 sweet orange accessions studied. However, these accessions were heterozygous for many SNPs. Ten selected STSs were analyzed in 17 additional accessions from 13 species and hybrids. Comparing to the 'Pera IAC' sweet orange accession, a total of 150 polymorphic nucleotides were identified and most of the alterations were transitions ( 52.7%). The greatest number of SNPs was observed in Poncirus trifoliata ( L.) Raf. and the smallest in 'Ponkan' mandarin ( Citrus reticulata Blanco). At the intra-specific level, 'Bafa Gigante' ( Citrus sinensis L. Osbeck) was the only sweet orange accession with a divergent SNPs genotype, which corroborates the hypothesis of a hybrid origin for this accession. Although the STSs analyzed represent randomly sampled genomic sequences, they provided consistent information about the level of polymorphism and showed the potential of SNPs markers for characterization and phylogenetic studies.