Bernardo de Almeida Halfeld-Vieira

Rhizobacterial induction of systemic resistance in tomato plants: non-specific protection and increase in enzyme activities

Abstract Rhizobacteria B101R, B212R, and A068R, selected as inducers of systemic resistance against Pseudomonas syringae pv. tomato, were tested individually for biological control of multiple pathogens causing foliar diseases in tomato plants. Greenhouse bioassays were carried with five pathogens—Alternaria solani (early blight), Corynespora cassiicola (foliar blight), Oidium lycopersici (powdery mildew), Stemphilium solani (leaf spot), and Xanthomonas campestris pv. vesicatoria (bacterial spot). The level of control achieved by each rhizobacterium varied with the pathosystem studied. Isolate B101R afforded reduced disease intensity in terms of average number of leaf lesions as compared to the treatment control, protection against A. solani, S. solani, and O. lycopersici. Lipoxygenase, phenylalanine amonia-lyase, and peroxidase activities were estimated spectrophotometrically in extracts of plants grown from seeds that were microbiolized with rhizobacterium B101R, and inoculated with P. syringae pv. tomato. Increases in peroxidase and lipoxygenase activities were detected in foliar extracts from plants whose seeds had been microbiolized, while no increase in phenylalanine amonia-lyase activity was observed.

Elaboração e validação de escala diagramática para avaliação da mancha-de-cercospora em melancia

To propose customized methods of evaluating the severity of cercospora leaf spot in watermelon (Citrullus lanatus) leaves, a diagrammatic scale was developed with necrotic area of 2; 4; 8; 12; 27; 45; 71 and 93%. For validation, the severity of 50 leaves presenting different intensities of the disease was estimated by ten raters. Accuracy and precision were determined by linear regression, relating assessments performed by raters using the scale to actual severity. Repetition of the results provided by raters was verified in a second evaluation, seven days after the first assessment. The scale provided good levels of accuracy and precision of visual estimates. The coefficient determination average was higher than 0.94, and absolute errors were lower than acceptable limits. Overall, the raters exhibited good repetition of estimates. The proposed diagrammatic scale proved to be adequate for severity assessments of cercospora leaf spot in watermelon.

Reação de cultivares de feijão-caupi à mela (Rhizoctonia solani) em Roraima

Web blight caused by the fungus Thanatephorus cucumeris (Rhizoctonia solani) is one of most important diseases of cowpea (Vigna unguiculata) in the state of Roraima, Brazil. Web blight severity for ten cowpea cultivars was evaluated in Roraima in two consecutive years. The erect cowpea cultivars BRS-Mazagao, IT86D-719, Vita-7 (Epace-1), BR02-Braganca and Pitiuba, as well as the prostrate cultivars BRS-Amapa, BR03-Tracuateua, BR17-Gurgueia, BR14-Mulato and Canapuzinho, were used. The experiment was conducted during 2005 and 2006 in a complete randomized block design with five treatments and four replications. The percentage of diseased foliage was evaluated once a week and the data were used to calculate the area under the disease progress curve. Disease severity was lower on prostrate cultivars indicating a relationship between plant architecture and web blight resistance. The prostrate cultivars, BRS-Amapa, BR03-Tracuateua, BR17-Gurgueia, BR14-Mulato and Canapuzinho, and erect cultivars, BRS-Mazagao, Pitiuba and BR03-Braganca, were more resistant to web blight and can be recommended for planting in areas where the disease is known to occur.

Identificação sorológica de espécies de potyvirus em melancia, no estado de Roraima

Leaf samples were collected from watermelon plants (Citrullus lanatus) from 21 different fields in the state of Roraima from May/2003 to March/2004. The samples were sent to the Plant Virus Laboratory of the Federal University of Ceara, to be tested by indirect enzyme linked immunosorbent assay (Elisa) against antisera specific to Cucumber mosaic virus (CMV), Papaya ringspot virus strain watermelon (PRSV-W), Watermelon mosaic virus (WMV) and Zucchini yellow mosaic virus (ZYMV). The Elisa tests were processed using the universal conjugate, anti-imunoglobulim (IgG) from rabbit produced in goat, conjugated to alkaline phosphatase. All samples were also tested by double immunodifusion against antiserum specific to Squash mosaic virus (SqMV). The presence of PRSV-W was detected in 84.2% of the samples collected in May/2003, in 7.1% of the samples collected in December/2003 and 55,6% in March/2004. The presence of ZYMV was detected in 10.5% of the samples collected in May, in 21.4% in December/2003 and in 25.9% in March/2004. The WMV was detected only in eight of the samples collected in March/2004 (29.6%). These results confirm the world widespread dispersion of PRSV-W in cultivated cucurbit fields in Brazil and rise a concern about the ZYMV expansion, which has caused serious yield lost in other parts of the world.

Characterization of Rhizoctonia spp. associated with cowpea web (Vigna unguiculata) blight in Roraima, Brazil

The web blight caused by the fungus Rhizoctonia solani (teleomorph Thanatephorus cucumeris) is an important disease of cowpea [Vigna unguiculata (L.) Walp.] in Roraima state, Brazil. The aim of this work was to characterize 28 Rhizoctonia spp. isolates from cowpea plants with web blight, collected in two ecosystems (savannah and forest) in Roraima state. The characteristics evaluated were nuclear number, radial growth rate, the presence and morphology of microsclerotia, anastomosis group (AG) and pathogenicity test. One savannah isolate was binucleate and the others, savannah and forest isolates, were multinucleate. The radial growth rate on potato-dextrose-aga, at 25 oC in the dark, was 2.1 to 5.3 cm.day-1 for forest isolates and 2.7 to 5.8 cm.day-1 for savannah isolates. In these conditions, after three to four days, microsclerotia formation was observed. Two types of microsclerotia were differentiated: one type of 10 to 50 microsclerotia.Petri dish-1, formed as flat sclerotia mass, which was white when young and pale brown at maturity, 1 to 2 mm in diameter (most forest isolates) and another type of 100 microsclerotia.Petri dish-1, brown color, 68 to 541 µm in diameter (most savannah isolates). Among 28 Rhizoctonia isolates collected in Roraima state, 24 anastomosed with AG1-1A of Rhizoctonia solani.

Pseudocercospora fuligena causing leaf mold of tomato in Roraima, Brazil

The cercospora leaf mold on tomato is an uncommon disease in Brazil. However, its occurrence is reported by Crous & Braun (Mycosphaerella and its anamorphs: 1. Names published in Cercospora and Passalora. 200�) and in important databases as EPPO and CABI Crop Protection Compendium. In September 2005, in Roraima, Brazil, tomato (Lycopersicon esculentum L.) plants cv. Santa Clara growing in protected cultivation conditions presented a severe foliar blight. Symptoms initially appeared as foliar spots, yellow on the adaxial leaflets surface (Figure 1A), corresponding to a dark gray fuliginous growth on the abaxial surface (Figure 1B), evolving to irregular necrotic spots. As the disease developed, leaf spots coalesced. Characteristics of the associated fungi were fascicles amphigenous, predominantly hypophyllous, effuse, stromata absent or substomatal. Conidiophores pale olivaceous to olivaceous brown, �-16 per fascicle, 20-�� x �.5-5.0 μm, 1-2 septate, conidiogenous loci inconspicuous (Figure 1C). Conidia obclavate to cylindric-obclavate, rounded to obtuse at the apex, olivaceous to subhyaline, obconic to rounded at the base, 2�-110 x 2.5-5.0 μm and �-10 septate, hila unthickened, not darkened (Figure 1D). To perform the Koch s postulates the fungi was isolated in Potato Dextrose Agar and cultivated in Potato Dextrose broth at 28 oC in rotary shaker. After 20 days, the culture was centrifuged, dispensing the culture media. Mycelium was resuspended in sterilized tap water and triturated. Thirty-days old plants of tomato hybrid Debora Plus were sprayed with the mycelium suspension (1.6 x 105 mycelium fragments per mL), kept in humid chamber for 24 h and then transferred to greenhouse conditions. As control, plants were sprayed with tap water. For each treatment, 20 plants were utilized. After nine days, first symptoms were observed only in plants sprayed with the mycelium suspension (Figure 1E), evolving to an intense foliar blight. The pathogen was successfully re-isolated. These features permit the identification of Pseudocercospora fuligena (Roldan) Deighton (basionym Cercospora fuligena) as causal agent of cercospora leaf mold on tomato (Chupp, A monograph of the fungus genus Cercospora. 1�54; Guo & Hsieh, The genus Pseudocercospora in China. 1��5). This is the first report of P. fuligena on tomato in Roraima state, Brazil. The symptoms of the disease are easily confused with Cladosporium leaf mold.

Efficiency of phylloplane bacteria in controlling aerial tomato diseases under field conditions

The capacity of two bacteria isolated from the tomato phylloplane to control late blight (Phytophthora infestans) was investigated in the field, and compared against the effectiveness of spraying with the fungicide chlorothalonil (1.5 g a.i. L-1) or water (control). A 55% reduction in late blight intensity was observed in the leaves of the middle of the plant and 62% in those of the upper leaves when using the antagonist UFV-STB 6 (Novosphingobium capsulatum) as compared to the control. Isolate UFV-IEA 6 (Bacillus cereus) was able to reduce disease intensity by 55%, but only in the upper leaves of the tomato plants. Treatment with isolate UFV-STB 6 also led to a significant reduction in the percentage of fruits with late blight symptoms. The results demonstrate the potential of these two bacteria in controlling this disease.

Efeito do inóculo, período de molhamento foliar e do estádio fenológico do feijão-caupi no desenvolvimento da mela

Web blight caused by the fungus Thanatephorus cucumeris (Rhizoctonia solani anastomosis group 1 IA ) is one of the most important diseases of cowpea (Vigna unguiculata) in the north of Brazil. There is no information about the effect of epidemiological parameters on development of the disease under controlled conditions. The aims of this work were to identify the type and inoculum concentration of R. solani, the susceptible phenological states and the leaf wetness periods for disease development in greenhouse conditions. In the first study we tested the use of mycelia fragments (mf) and sclerotia as source of inoculum; in the second experiment, the effect of different inoculum concentrations (0, 103, 104,105 and 106 mf.mL-1); in the third experiment, the effect of leaf wetness period was tested by maintaining cowpea plants at 0, 6, 12, 24 and 48 hours of leaf wetness after the inoculation, and in the last experiment the effect of phenological states was tested by inoculating cowpea plants at the stages of cotyledonal leaf, trifoliate leaves, flowering and pod filling. The highest severity values of disease were observed with the plants inoculated in the flowering phenological state with 106 mf.mL-1 and six hours of leaf wetness. These parameters can be utilized to establish an inoculation methodology for R. solani on cowpea plants under controlled conditions.

Reação de cultivares de soja à mela (Thanatephorus cucumeris) em campo em dois estádios de desenvolvimento das plantas

Rhizoctonia aerial blight (RAB), caused by the fungus Thanatephorus cucumeris is one of the most damaging diseases of soybean at Roraima, Brazil. The objective of this study was to evaluate the reaction of 15 soybean cultivars to RAB in a cerrado (savannah) ecosystem in the state of Roraima. The percentage of foliar area infected (FAI) and the percentage of pods with disease symptoms (WP) were evaluated on soybean plants at R.5.5 and R.6 growth stages, respectively. There were significative differences among cultivars tested based on Fisher LSD test in both evaluations. The FAI ranged from 1.5% (cv. Padre) to 62% (cv. BR-36) and WP from 8% (cv. UFV-9 and cv. Jucara) to 55 % (cv. BR-36). Significative and positive correlation was observed between the evaluations.

Lasiodiplodia theobromae causing coconut fall in Roraima

Lasiodiplodia theobromae causing coconut fall in Roraima This is the first report of Lasiodiplodia theobromae (=Botryodiplodia theobromae) causing coconut (Cocos nucifera) rot and fall in Roraima, Brazil. Os danos causados pelo fungo Lasiodiplodia theobromae (Pat.) Griff. & Maubl. em coqueiro (Cocos nucifera L.) sao a queima-das-folhas (Souza Filho et al., Fitopatol. Bras. 4:5. 1979) e a podridao basal dos frutos em pos-colheita, observada no Brasil por Viana et al. (Fitopatol. Bras. 27:545. 2002). Em abril de 2004 foi constatada queda de frutos imaturos em plantas de coqueiro anao verde, provenientes de plantio comercial no municipio do Canta em Roraima. Os frutos apresentavam podridao de coloracao marrom-escura a partir do local de insercao com as bracteas (Figura 1A) que se desprendiam ocasionando a sua queda. Em lâminas preparadas de saliencias pretas na regiao afetada, foram observados picnidios estromaticos, com conidios maduros bicelulares, de coloracao marrom escura e estrias longitudinais, medindo de 23-29 x 13-15 μm (Figura 1B) e conidios jovens unicelulares, ovoides, hialinos, de parede delgada e dupla (Figura 1C) tipicos de L. theobromae (Barnett & Hunter. Illustrated genera of imperfecti fungi. 1998; Sutton. The Coelomycetes. 1980). O fungo foi isolado em meio V8, observando-se colonias acinzentadas com formacao de estromas (Figura 1D). Para realizacao de testes de patogenicidade, culturas foram crescidas em meio V8 por 43 dias, preparando-se uma suspensao de esporos ajustada a 104 conidios.ml-1. Em cinco frutos de coqueiro anao amarelo foram depositadas aliquotas de 0,5 ml da suspensao sob as bracteas. Outros cinco frutos foram utilizados como testemunha, depositando-se somente agua destilada esterilizada. Os frutos permaneceram em câmara umida por 24 h e mantidos em temperatura ambiente, que variou de 26-31 oC. Apos seis dias foi observada anasarca ao redor das bracteas, apenas nos frutos que receberam a suspensao de esporos, evoluindo rapidamente para uma podridao de coloracao amarronzada, com as mesmas caracteristicas verificadas em campo (Figura E). Picnidios tipicos foram observados nos frutos que apresentaram sintomas, reisolando-se o patogeno. As caracteristicas permitiram identificar o fungo Lasiodiplodia theobromae FIG. 1Podridao de fruto de coqueiro (Cocos nucifera) causada por Lasiodiplodia theobromae (A); Conidios maduros (B) e jovem (C) de L. theobromae (barra= 30 μm); Colonia em meio V8 (D); Sintomas em fruto, 12 dias apos a inoculacao com esporos de L. theobromae (inoc.) e testemunha (test.) (E). como agente causal da queda de frutos do coqueiro em campo.