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Behlau F.,University of Florida | Belasque Jr. J.,Fundecitrus | Graham J.H.,University of Florida | Leite Jr. R.P.,Area de Protecao de Plantas
Crop Protection | Year: 2010

The efficacy of different copper spray intervals for control of citrus canker caused by Xanthomonas citri subsp. citri (Xcc) was investigated in 3-to-4-year-old commercial citrus groves of 'Pera' sweet orange in a citrus canker endemic area in southern Brazil. Three independent trials were conducted in 2004/2005, 2005/2006 and 2006/2007. The first trial was located in Ourizona, PR and the two following were established in Paranavaí, PR, in different locations. Trees were treated with copper oxychloride (1.8 g/L) at intervals of 7, 14, 21, or 28 days. Control trees were sprayed with water every 28 days. Control of canker was evaluated as incidence of canker on leaves and fruit and as the amount of dropped and harvested fruit. Regardless of the spray interval, copper significantly decreased the incidence of citrus canker on leaves and harvested fruits, and reduced the number of prematurely dropped fruits and increased yield. Disease incidence on leaves of untreated trees in each season peaked at 37, 51, and 43% of infected leaves, whereas the incidence of canker on foliage of copper-treated trees was no higher than 12, 16, and 11%, respectively. For the second and third year trials, when disease incidence was comparatively higher, the shorter the spray interval, the lower the disease incidence and number of dropped fruit and the higher the yield per tree. Citrus canker incidence on the leaves was inversely related in a linear fashion to the total number of copper sprays in each trial. Coefficients of determination (R2) between disease incidence and number of sprays were 0.70, 0.92 and 0.80 in the respective seasons. The financial return due to increases in yield from copper sprays was significantly related to the number of sprays and disease levels only in the third trial. Although copper sprays at a 28-day-interval was satisfactory for reduction of citrus canker incidence on leaves and fruits, a shorter spray interval was required to significantly reduce yield loss. © 2009 Elsevier Ltd. Source


Bonani J.P.,University of Sao Paulo | Fereres A.,Institute Ciencias Agrarias ICA | Garzo E.,Institute Ciencias Agrarias ICA | Miranda M.P.,Fundecitrus | And 2 more authors.
Entomologia Experimentalis et Applicata | Year: 2010

Detailed information on probing behavior of the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is critical for understanding the transmission process of phloem-limited bacteria (Candidatus Liberibacter spp.) associated with citrus 'huanglongbing' by this vector. In this study, we investigated stylet penetration activities of D. citri on seedlings of Citrus sinensis (L.) Osbeck cv. Pêra (Rutaceae) by using the electrical penetration graph (EPG-DC system) technique. EPG waveforms were described based on amplitude, frequency, voltage level, and electrical origin of the observed traces during stylet penetration into plant tissues. The main waveforms were correlated with histological observations of salivary sheath termini in plant tissues, to determine the putative location of stylet tips. The behavioral activities were also inferred based on waveform similarities in relation to other Sternorrhyncha, particularly aphids and whiteflies. In addition, we correlated the occurrence of specific waveforms with the acquisition of the phloem-limited bacterium Ca. Liberibacter asiaticus by D. citri. The occurrence of a G-like xylem sap ingestion waveform in starved and unstarved psyllids was also compared. By analyzing 8-h EPGs of adult females, five waveforms were described: (C) salivary sheath secretion and other stylet pathway activities; (D) first contact with phloem (distinct from other waveforms reported for Sternorrhyncha); (E1) putative salivation in phloem sieve tubes; (E2) phloem sap ingestion; and (G) probably xylem sap ingestion. Diaphorina citri initiates a probe with stylet pathway through epidermis and parenchyma (C). Interestingly, no potential drops were observed during the stylet pathway phase, as are usually recorded in aphids and other Sternorrhyncha. Once in C, D. citri shows a higher propensity to return to non-probing than to start a phloem or xylem phase. Several probes are usually observed before the phloem phase; waveform D is observed upon phloem contact, always immediately followed by E1. After E1, D. citri either returns to pathway activity (C) or starts phloem sap ingestion, which was the longest activity observed. © 2009 The Netherlands Entomological Society. Source


Zhang S.,University of Florida | Flores-Cruz Z.,University of Florida | Flores-Cruz Z.,University of Georgia | Zhou L.,University of Florida | And 6 more authors.
Molecular Plant-Microbe Interactions | Year: 2011

Huanglongbing (HLB), also known as citrus greening, is a lethal disease of citrus caused by several species of 'Candi-datus Liberibacter', a psyllid-transmitted, phloem-limited, alpha proteobacteria. 'Ca. Liberibacter asiaticus' is widespread in Florida citrus. The recently published 'Ca. L. asi-aticus' psy62 genome, derived from a psyllid, revealed a prophage-like region of DNA in the genome, but phage have not been associated with 'Ca. L. asiaticus' to date. In the present study, shotgun sequencing and a fosmid DNA library of curated 'Ca. L. asiaticus' UF506, originally derived from citrus symptomatic for HLB, revealed two largely homologous, circular phage genomes, SC1 and SC2. SC2 encoded putative adhesin and peroxidase genes that had not previously been identified in 'Ca. L. asiaticus' and which may be involved in lysogenic conversion. SC2 also appeared to lack lytic cycle genes and replicated as a prophage excision plasmid, in addition to being found integrated in tandem with SC1 in the UF506 chromosome. By contrast, SC1 carried suspected lytic cycle genes and was found in nonintegrated, lytic cycle forms only in planta. Phage particles associated with 'Ca. L. asiaticus' were found in the phloem of infected periwinkles by transmission electron microscopy. In psyllids, both SC1 and SC2 were found only as prophage. © 2011 The American Phytopathological Society. Source


Silva I.C.,Sao Paulo State University | Regasini L.O.,Sao Paulo State University | Petranio M.S.,Sao Paulo State University | Silva D.H.S.,Sao Paulo State University | And 4 more authors.
Journal of Bacteriology | Year: 2013

The plant-pathogenic bacterium Xanthomonas citri subsp. citri is the causal agent of Asiatic citrus canker, a seriousdisease that affects all the cultivars of citrus in subtropical citrus-producing areas worldwide. There is no curative treatment for citrus canker; thus, the eradication of infected plants constitutes the only effective control of the spread ofX. citri subsp. citri. Since the eradication program in the state of São Paulo, Brazil, is under threat, there is a clear risk of X. citri subsp. citri becoming endemic in the main orange-producing area in the world. Here we evaluated the potential use of alkyl gallates to prevent X. citri subsp. citri growth. These esters displayed a potent anti-X. citri subsp. citri activity similar to that of kanamycin (positive control), as evaluated by the resazurin microtiter assay (REMA). Thetreatment of X. citri subsp. citri cells with these compounds induced altered cell morphology, and investigations of the possible intracellular targets using X. citri subsp. citri strains labeled for the septum and centromere pointed to a commontarget involved in chromosome segregation and cell division. Finally, the artificial inoculation of citrus with X. citri subsp. citri cells pretreated with alkyl gallates showed that the bacterium loses the ability to colonize its host, which indicates the potential of these esters to protect citrus plants against X. citri subsp. citri infection. © 2013, American Society for Microbiology. Source


Lima W.G.,University of Pernambuco | Sposito M.B.,Fundecitrus | Amorim L.,University of Sao Paulo | Goncalves F.P.,University of Sao Paulo | de Filho P.A.M.,University of Pernambuco
European Journal of Plant Pathology | Year: 2011

Citrus post-bloom fruit drop (caused by Colletotrichum acutatum) frequently occurs in the southwestern region of São Paulo State, Brazil. A survey of Colletotrichum isolates associated with symptoms of post-bloom fruit drop in São Paulo State showed C. gloeosporioides in addition to C. acutatum. The objectives of this study were to confirm the identification of C. gloeosporioides isolated from symptomatic citrus flowers, to test the pathogenicity of C. gloeosporioides isolates, to compare the development of disease caused by C. gloeosporioides and C. acutatum, and to determine the frequency of C. gloeosporioides in a sample of isolates obtained from symptomatic flowers in different regions of São Paulo State. Through the use of species-specific primers by PCR, 17.3% of 139 isolates were C. gloeosporioides, and the remaining 82.7% were C. acutatum. The pathogenicity tests, carried out in 3-year old potted plants of sweet oranges indicated that both species caused typical symptoms of the disease including blossom blight and persistent calyces. Incubation periods (3.5 and 3.9 days, respectively, for C. acutatum and C. gloeosporioides) and fruit sets (6.7 and 8.5%, respectively for C. acutatum and C. gloeosporioides) were similar for both species. The incidences of blossom blight and persistent calyces were higher on plants inoculated with C. acutatum than in those inoculated with C. gloeosporioides. Conidial germination was similar for both species under different temperatures and wetness periods. Under optimal conditions, appressorium formation and melanisation were higher for C. gloeosporioides than for C. acutatum. These results indicated that Colletotrichum gloeosporioides is a new causal agent of post-bloom fruit drop. © 2011 KNPV. Source

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