J. C. Vidal

First report of black branch dieback of cashew caused by Lasiodiplodia theobromae in Brazil.

Cashew nut (Anacardium occidentale) is one of the most important cash crops of northeastern Brazil. A new disease, named here as black branch dieback, caused by Lasiodiplodia theobromae, was observed causing serious damage on as many as 30% of the trees in some orchards in both coastal and inland semiarid cashew-growing areas of Ceará and Piauí states of Brazil, respectively. The disease symptoms are first observed as darkened, elongated lesions on stems near the branch apexes of herbaceous tissues. Gum exudation is common from lesions, which expand rapidly to affect the entire branch, leading to branch death. Diseased plants were collected, and L. theobromae was consistently isolated from canker tissues. Fresh mycelial disks of the fungus were used for artificial inoculation of healthy plants. Shoots of young cashew plants were inoculated on the apex by inserting a 3-mm plug taken from actively growing colonies on potato dextrose agar into an incision made with a sterile scalpel. Agar plugs with no mycelium were placed into incised plant shoots to serve as controls. Plants were incubated in a greenhouse at 28°C. Symptoms developed within 15 days after inoculation. Artificially inoculated plants showed symptoms similar to those that were naturally infected. L. theobromae was consistently reisolated from inoculated plants. The disease seems to occur throughout the year, but it spreads faster during the rainy season. A contagious disease pattern within the orchard was observed with a decreasing gradient from the orchard perimeter to the interior of the field, suggesting an external source of primary inoculum. All improved dwarf cashew clones were susceptible, but the newly released clone END-189 was the most susceptible. Black branch dieback may reduce tree growth, nut yield, and eventually cause plant death. Plant susceptibility is not related to its age however; only herbaceous tissues are vulnerable to natural infection. A similar disease on floral shoots of cashew caused by L. theobromae was reported by Olunloyo and Esuruoso in Nigeria (1). To our knowledge, this is the first report of L. theobromae causing branch dieback in cashew orchards in Brazil. Reference: (1) O. A. Olunloyo and O. F. Esuruoso. Plant Dis. 59:176, 1975.

Efeito do míldio na concentração de sólidos solúveis totais em frutos do meloeiro

Downy mildew caused by Pseudoperonospora cubensis is one of the most important diseases of the melon (Cucumis melo) in the Northeast of Brazil, where more than 80% of national melon production is concentrated. Downy mildew epidemics are constantly occurring, causing severe losses in the production of melon fruits. The effect of the disease on the concentration of total soluble solids (TSS), an important measure of fruit quality, was determined under field conditions using a yellow, odorless type melon naturally infected with downy mildew. Variable intensities of the disease were obtained by varying cultivation periods and applications of recommended fungicides for the control of the disease (methyl thiophanate + chlorothalonil, metalaxyl + mancozeb and cupper oxiclhoride). The results revealed that increased severity of the disease leads to an accentuated reduction of TSS, causing losses up to 49%. Among the parameters used to estimate the effects of the disease, the area under the disease progress curve was the most efficient, mainly as disease pressure increased.

Podridão basal pós-colheita do coco verde no estado do Ceará

A new post-harvest disease of coconut (Cocos nucifera) was recently detected in fruits exported to European countries. The main symptoms are the blacking and cracking of basal parts of the fruits. Water oozing may occurs as the infection progresses. The fungus Lasiodiplodia theobromae has been frequently isolated from the lesions. Inoculation tests proved that this pathogen is the causal agent of the coconut fruit basal rot. This is the first occurrence of this post-harvest disease in Brazil.

Reação de genótipos de Vigna unguiculata à sarna e efeito da doença sobre componentes de produção

The fungus Elsinoe phaseoli is the scab agent and has been causing serious damages to the cowpea (Vigna unguiculata), crop, mainly in the rainy period of Ceara States mountainous areas. The present work aimed to identify genetic resistance sources and to evaluate the disease effects on the yield and its components, the quality of the grain and the crop cycle. To do this, in 1995 and 1996, 16 genotypes were evaluated in two experiments. One at the rainy period as a rain-fed crop and the other at the dry period as a irrigated crop, in a randomized experimental design with four replications in Tiangua County, State of Ceara. Based on statistical analysis and evaluation of the variances, comparing the treatment averages, the correlation and the regression, it was verified that: in the scab susceptible plants both the cycle and the yield are negatively affected by the disease; all evaluated genotypes have variability in relation to the disease reaction; and the EPACE V-96 cultivar performed better and so can be utilized as parental in a breeding program.

Occurrence of coconut large verrucosis in the state of Ceará, Brazil.

Occurrence of coconut large verrucosis in the State of Ceara, Brazil The occurrence of coconut (Cocos nucifera) large verrucosis is reported for the first time in producing areas of the State of Ceara, Brazil. The main symptoms of the disease are necrotic lesions on the folioles and petioles upon which many erumpent ascocarps are formed. O coco (Cocos nucifera L.) brasileiro e uma das principais frutas da pauta nacional de exportacoes, tendo se tornado uma importante fonte de renda para a Regiao Nordeste, a qual tem aumentado a area plantada da variedade anao-verde, com o objetivo de atender o crescente mercado de agua-decoco; bem como do coqueiro hibrido ou “anao-gigante”, visando a producao de copra para suprir a demanda nao coberta pelo coqueiro-gigante. Desde meados de 2002, tem-se observado em cultivos comerciais de coqueiro anao-verde, bem como de coqueiro hibrido, em localidades dos municipios de Pacajus, Cascavel e Paraipaba, no Estado do Ceara, plantas com sintomas e sinais semelhantes aos da lixa-pequena, ou seja, seca das folhas associada a presenca de estruturas rigidas na superficie dos foliolos (Figuras 1-A e 1-B). Entretanto, sob observacao mais acurada verificou-se que esses sintomas e sinais divergem, em diversos aspectos, daqueles causados pelo agente da lixapequena. Apesar da doenca similar a esta, ou seja, a lixa-grande, ainda nao ter sido relatada no Estado do Ceara (Warwick, Doencas de fruteiras tropicais de interesse agroindustrial, Embrapa, 2003), coletaram-se folhas com sintomas, as quais foram conduzidas ao Laboratorio de Fitopatologia da Embrapa Agroindustria Tropical, em Fortaleza, para analise. O exame macroscopico do material colhido revelou a presenca de estruturas estromaticas maiores que aquelas produzidas pela lixa-pequena, e de coloracao diferente, ou seja, marromacinzentada. Os estromas formavam pequenas rugas arredondadas e isoladas a superficie dos foliolos, concentrandose, principalmente, proximo a raquis foliar e sobre a face superior desta. Na face inferior, encontraram-se apenas vestigios cicatriciais da presenca do fungo. Ao contrario dos estromas produzidos pela lixa-pequena, estes estavam fracamente aderidos a superficie dos foliolos, podendo ser removidos com facilidade. Suspeitando-se que se tratasse da ocorrencia de uma nova doenca da cultura do coqueiro no Estado do Ceara, efetuaram-se cortes de tecidos afetados que, corados e observados ao microscopio optico, revelaram a presenca de ascostromas, originados no mesofilo, que rompiam a epiderme foliar quando maduros. Tambem, coletaram-se porcoes das referidas estruturas que, com auxilio de pistilo e almofariz esterilizados, contendo 2 ml do corante azul de Amann, foram esmagadas para liberacao das estruturas do microrganismo associado a doenca. Em seguida, transferiu-se uma gota da suspensao obtida para uma lâmina de vidro para observacao microscopica. As ascas, embora nao evanescentes, eram diafanas, contendo oito ascosporos unicelulares de coloracao marrom-escura (Figura 1-C), medindo cerca de 22,5 X 13,5 μm. Com base nos sintomas observados no campo e nos exames realizados aos microscopios estereoscopio e optico, concluiu-se que o agente causal da doenca e o fungo Sphaerodothis acrocomiae (Montagne) von Arx & Muller (=Coccostroma palmicola (Speg.) von Arx & Muller (CANNON, A revision of Phyllachora and some similar genera on the host family Leguminosae, CAB, 1991; ROGER. Encyclopedie micologique: Phytophatologie des pays chauds, Paul Lechevalier, 1953; Warwick et al., Doencas do coqueiro, Embrapa, 1997). 04031 FIG. 1 Sintomas tipicos de lixa-grande em coqueiro (Cocos nucifera) hibrido: estromas na superficie do foliolo (A); manchas cicatriciais na face inferior do raque foliar (B); manchas iniciais na face superior do raque foliar (C); microfotografia de ascosporos de Sphaerodothis acrocomiae (D). A B

Efeito do início de ocorrência do míldio na produção de frutos do meloeiro

Downy mildew caused by Pseudoperonospora cubensis is the main disease affecting melon (Cucumis melo) fruit during the rainy period in areas of Northeastern Brazil where the crop is produced. Up to ten fungicide sprays are used throughout the crop season. The establishment of risk analysis for forecast of damages caused by this disease requires an estimate of the losses under different epidemic situations. Three field experiments were carried out to determine the damage caused by downy mildew to the fruit yield of the melon crop. The epidemic was considered to begin in the phenological cycle of the host plant. Different intensities of epidemics were achieved by spraying one of the following fungicide mixtures: methyl thiophanate + chlorothalonil or metalaxyl + mancozeb. There was a significant reduction on the fruit yield when the disease started at 24 and 36 days after planting, but when the disease started on day 47, no effect in production was observed. It was concluded that the duration of the the epidemic and when it began in relation to the cycle of the host, should be considered when establishing prognostic models to describe the risks of yield losses.