Francisco Ferraz Laranjeira

Dinâmica Temporal da Clorose Variegada dos Citros em Três Regiões do Estado de São Paulo

CVC is considered the most important disease of brazilian citrus industry but many aspects of its epidemiology are still unknown. This work aimed to characterize the spatial pattern of CVC affected trees in three regions (Northwest, Center and South) of Sao Paulo state, Brazil. Three orchards of Pera sweet orange (Citrus sinensis) grafted on Rangpur lime (Citrus limonia) were evaluated twice a month by visual assessments from July 1998 to December 2000. For each evaluation all plants were inspected and assigned as diseased or healthy and cumulative maps were produced. The following analyses were performed: ordinary runs, isopath areas, Taylor law, dispersion index and foci structure and dynamics analysis. Ordinary runs indicated a trend to randomness. Isopath areas analysis showed few compact foci and a trend to uniform incidence in all areas. The other analysis showed few if any differences between regions and results that could classify CVC pattern as slightly aggregated.

Cost-effective control of plant disease when epidemiological knowledge is incomplete: modelling Bahia bark scaling of citrus.

A spatially-explicit, stochastic model is developed for Bahia bark scaling, a threat to citrus production in north-eastern Brazil, and is used to assess epidemiological principles underlying the cost-effectiveness of disease control strategies. The model is fitted via Markov chain Monte Carlo with data augmentation to snapshots of disease spread derived from a previously-reported multi-year experiment. Goodness-of-fit tests strongly supported the fit of the model, even though the detailed etiology of the disease is unknown and was not explicitly included in the model. Key epidemiological parameters including the infection rate, incubation period and scale of dispersal are estimated from the spread data. This allows us to scale-up the experimental results to predict the effect of the level of initial inoculum on disease progression in a typically-sized citrus grove. The efficacies of two cultural control measures are assessed: altering the spacing of host plants, and roguing symptomatic trees. Reducing planting density can slow disease spread significantly if the distance between hosts is sufficiently large. However, low density groves have fewer plants per hectare. The optimum density of productive plants is therefore recovered at an intermediate host spacing. Roguing, even when detection of symptomatic plants is imperfect, can lead to very effective control. However, scouting for disease symptoms incurs a cost. We use the model to balance the cost of scouting against the number of plants lost to disease, and show how to determine a roguing schedule that optimises profit. The trade-offs underlying the two optima we identify—the optimal host spacing and the optimal roguing schedule—are applicable to many pathosystems. Our work demonstrates how a carefully parameterised mathematical model can be used to find these optima. It also illustrates how mathematical models can be used in even this most challenging of situations in which the underlying epidemiology is ill-understood.

Identification of passion fruit genotypes resistant to Fusarium oxysporum f. sp. passiflorae

This study aimed to characterize the resistance of 31 passion fruit (Passiflora sp.) genotypes to Fusarium oxysporum f. sp. passiflorae (FOP). About 20 seedlings of each genotype were inoculated by immersing the roots in a suspension of 106 macroconidia mL-1 for five minutes and then transplanting them into pots containing a mixture of soil and sterile substrate. They were evaluated daily for 120 days for the occurrence of wilt symptoms and death. These data were used to calculate the area under the disease progress curve, for survival analysis and grouping. The mortality rate ranged from 0 to 100% and the AUDPC ranged from 0 for genotypes without symptoms of the disease to 6,650.63 for the hybrid HFOP-01. Genotypes were classified into four subgroups: resistant, moderately resistant, susceptible and highly susceptible. The resistance was genotype dependent, but no significant variation was found between the purple and the yellow P. edulis.

Control of tomato bacterial wilt through the incorporation of aerial part of pigeon pea and crotalaria to soil

The use of organic matter that improves the physical, chemical and biological soil properties has been studied as an inducer of suppressiveness to soilborne plant pathogens. The objective of this work was to evaluate the effect of different sources and concentrations of organic matter on tomato bacterial wilt control. Two commercially available organic composts and freshly cut aerial parts of pigeon pea (Cajanus cajan) and crotalaria (Crotalaria juncea) were incorporated, in concentrations of 10, 20 and 30 % (v/v), into soil infested with Ralstonia solanacearum. The soil with the fresh organic matter of pigeon pea and crotalaria was incubated for 30 and 60 days before planting. Tomato seedlings of cv. Santa Clara were transplanted into polyethylene bags with 3 kg of the planting substrate (infested soil + organic matter). The wilting symptoms and percentage of flowering plants were evaluated for 45 days. All evaluated concentrations with incorporation and incubation for 30 days of aerial parts of pigeon pea and crotalaria controlled 100% tomato bacterial wilt. With 60 days of incubation, only the 10 % concentration of pigeon pea and crotalaria did not control the disease. These results suggest that soil incorporation of fresh aerial parts of pigeon pea and crotalaria is an effective method for bacterial wilt control.

Distribuição espacial da meleira do mamoeiro em zonas de trópico úmido e trópico semi-árido

Papaya Sticky Disease (PSD) is caused by a whitefly-borne virus and is one of the most important problems of the papaya (Carica papaya) industry in Brazil, causing yield losses of up to 100%. In order to better understand its epidemiology and generate data for studies on influence of cultural practices and bioecological features on disease dynamics, 15 papaya orchards were evaluated in Eunapolis, Bahia (Rain Forest Region) and Petrolina, Pernambuco (Semi Arid Tropics) between January 2000 and March 2001. The areas were mapped taking into consideration the row or column position of each plant and its disease status. A given plant was considered diseased when its fruits showed latex exudation, fluid latex and latex spots. The maps were analised by ordinary runs, dispersion index, Taylor law fitting and isopath areas. Results showed greater aggregation within rows than across rows which can be the consequence of a vector limited movement, with a trend to colonizing nearest plants; The dispersion index indicated a medium to strong aggregation within sub areas and this result was confirmed by Taylor law fitting. In most of the areas, higher disease incidence was detected at orchard edges. This may indicate that vector migration can assume important role in PSD virus dissemination. In some cases it was possible to detect the presence of isolated foci inside orchards, an indication of vector colony formation and plant to plant transmission from secondary inoculum. Significant differences were not observed between rain forest and semi-arid regions.

Temporal and spatial dynamics of watermelon gummy stem blight epidemics

The effect of the distance of initial inoculum on the intensity of watermelon gummy stem blight, caused by Didymella bryoniae, was studied in a naturally-infected rainfed commercial field. The shorter the distance from the focus, the sooner was disease onset and the earlier maximum disease levels were achieved. Maximum disease incidences were reached earlier than maximum severities, but eventually destructive levels were observed for both disease incidence and severity. Disease progressed at similar rates, irrespective of the radial distance from the focus. A detailed study of the disease temporal progress was conducted in inoculated rainfed experimental fields with commercial genotypes Crimson Sweet (susceptible, S) and Riviera (moderately resistant, R). The Gompertz model best described the disease progress curves, and estimated apparent infection rates were 0.049 and 0.020 respectively for S and R genotypes. In addition, spatial pattern studies were conducted during the dry season in overhead irrigated experimental plots, inoculated with point-source foci. Disease intensity gradients were better explained by the Exponential model than by the Power Law model. Gummy stem blight distribution was classified as aggregated by the Ordinary Runs procedure. Two different spatial autocorrelation methods (2DCorr and LCOR) revealed strong short distance spatial dependencies. Long distance positive correlations between quadrats were observed along with periods of higher progress rates. The dynamic patterns of the epidemics of gummy stem blight in watermelon described here are consistent with epidemics of polycyclic diseases with splash-dispersed spores.

Dinâmica da infestação de Brevipalpus phoenicis (Geijskes, 1939) (Acari:Tenuipalpidae) em pomares cítricos da Bahia, Brasil

The spatio-temporal dynamics of Brevipalpus phoenicis infestation was quantified in two regions of the state of Bahia, Brazil (North Coast-NC and Reconcavo Baiano-RB). In each region, 10 orchards were evaluated monthly (from April 2008 to February 2011), in which 21 plants had inspected three fruits per plant with a magnifying lens (10x) to record the presence or absence of the mite. The average proportion of infested plants varied between 0.38 and 1.0. In fruits, the minimum proportion of infestation was 0.10 and maximum, of 0.73 for NC and 0.66 in the RB. The infestation process had a strong seasonal component with more infested units detected in spring or summer (Nemenyi, p <0.05). The spectral density analysis showed the occurrence of two cycles of infestation: one of 2 to 3 months, possibly related to the mites biology and other larger, annual, arising from the interaction vector-host-environment. In both regions the spatial pattern of mite infestation within and between orchards was random. No symptoms of citrus leprosies were found in RB.

Comportamento de catorze porta-enxertos para o limão eureka km 47 na região de Araraquara-SP

Fourteen rootstocks were compared in a trial started in 1991, for Eureka lemon cv. km 47, nucellar clone, in Araraquara, Brazil. The rootstocks tested were Orlando and Seminole tangelos (C. reticulata Blanco x C. paradisi Macfad.), Cleopatra mandarin (C. reshni hort. ex Tanaka), Sunki mandarin [C. sunki (Hayata) hort. ex Tanaka], Rangpur Lime (C. limonia Osbeck), Rough Lemon cv. African (C. jambhiri Lush.), and Volkamerican cv Catania 2 (C. volkameriana V. Ten. & Pasq.), sweet orange [C. sinensis (L.) Osbeck] cv. Caipira DAC, sour orange (C. aurantium L.), Poncirus trifoliata (L.) Raf. cv. EEL, P. trifoliata (L.) Raf. cv. Kryder 8-5, Morton citrange [P. trifoliata (L.) Raf. x C. sinensis (L.) Osbeck], C. karna Raf. and C. pennivesiculata (Lush.) Tanaka. Yield was measured by weight of fruits per tree, for a period of five years (1998-2002). The best yielding rootstocks were C. pennivesiculata and Cleopatra mandarin (> 220 kg/tree). Citrus karna, both tangelos, both trifoliates and sweet orange cv. Caipira DAC presented the lowest fruit yields (<180 kg/tree). Fruit quality and percentage of trees affected by gummosis were also studied. No significant variation was observed for fruit quality characteristics for trees on different rootstocks, while trees on C. penivesiculata and sour orange were resistant to gummosis infection.

Perdas causadas pela ferrugem-asiática em cultivares de soja semeadas em diferentes épocas, no Oeste da Bahia

Yield loss caused by rust in soybean cultivars sown in different periods in the western region of Bahia, Brazil The objective of this work was to quantify the yield loss caused by Asian soybean rust in three cultivars sown in different periods in the western region of Bahia. The experiments were installed in Sao Desiderio, BA, in the growing seasons 2007/2008 and 2008/2009. The experimental design was carried out in random blocks with four replicates and subdivided plot scheme in time. The plot was represented by the rust control treatments (with and without chemical control) and the subplots represented by cultivars (Monsoy 8411, BRS Corisco and BRS Barreiras). The severity, number of leaves throughout the cycle and yield were evaluated. The logistic model was the one that better fitted the severity data whereas the polynominal exponential function Ln (y) = a + bx 1, 5

Comparative epidemiology of citrus tristeza in Cuba and citrus sudden death in Brazil

Citrus Sudden Death (CSD) is a disease of unknown etiology, reported only in Brazil. Due to similarities between the epidemiology of CSD in Brazil and Citrus Tristeza (CT) in other countries, this work aimed to compare CSD and CT in Cuba. Besides testing the hypothesis of shared epidemiological patterns, the data generated can be used to carry out control strategies if CSD breaks out in Cuba. Seven epidemic data sets were statistically compared for each disease by analyzing their progress in time and the dependence among symptomatic or infected plants at two levels of spatial scale. CSD and CT epidemics could not be differentiated based on mean progress rate, area under disease progress curves, proportion of aggregated sequences (Ordinary runs test), index of Dispersion (D) or both parameters, log (A) and b, of the binary power law model. The progress rate of both diseases varied from low (0.0003/month) to very high (0.045/month). The proportion of aggregated sequences was low (<0.16) and D, log(A) and b values indicated aggregation in groups of 4 to 16 plants for both diseases. These results suggest that measures currently used for CT eradication and management in Cuba may be applied in case of an eventual introduction of CSD in that country.