Maria Aparecida de Souza Tanaka

Microflora fúngica de sementes de milho em ambientes de armazenamento

During storage, several kinds of fungi can remain associated to corn seeds, either causing their deterioration or simply remaining viable to infect germinating seedlings. The objective of this work was to evaluate the survival of fungi in corn seeds stored for twelve months in a cold chamber (14°C and 40% RH) or stored under uncontrolled conditions. A larger frequency of Alternaria alternata, Bipolaris maydis, Cephalosporium acremonium, Cladosporium herbarum, Fusarium moniliforme, Rhizoctonia solani, Rhizopus spp. and Trichoderma spp. occurred in the cold condition. The survival decreased with the storage period mainly under uncontrolled atmosphere as compared to the cold environment. The incidence of Aspergillus and Penicillium increased with the storage, mainly under the uncontrolled ambient. Fusarium moniliforme, on the other hand, decreased sharply under ambiental conditions at the end of the period. In the cold chamber, the F. moniliforme viability was less affected. Bipolaris maydis remained viable in most of the seed lots during the entire storage period in the cold chamber. Under uncontrolled conditions, this fungus survived for four to twelve months, depending on the lot studied. The seed storage under uncontrolled ambient may reduce the inoculum of F. moniliforme and other important fungi for the maize crop, but this condition may accelerate seed deterioration. In the cold condition, otherwise, the ambient is favorable to preserve the physiological quality of the seeds, but the maintenance of fungi viability may reduce their sanitary quality.

Tratamento térmico solar da água para controle de fitopatógenos

Some phytopathogenic microorganisms may be transmitted by water representing an efficient means way of inoculum dissemination. The objective of the work was to quantify the efficiency of thermal treatment by solar heating in the control of pathogens in contaminated water. The equipment developed for this purpose was composed of flat collectors and used both natural and forced convection to transfer heat to the circulating water. Thermostats, placed in different locataions, automatically equalized the temperature of the system. The equipment was verified to peform well at 60 oC, in terms of water processed as well as in the eradication of economically important pathogens such as Botrytis cinerea, Colletotrichum spp., Fusarium spp., Pythium spp., Verticillium dahliae and Rhizoctonia solani. Except for F. oxysporum f. sp. phaseoli, the other pathogens were inactivated at temperatures above 55 oC. The technique is a promising option to disinfest the water to be used in nurseries, greenhouses and in small or midsize agricultural exploitations.

Survival of seed-borne fungi associated to the physiological quality of triticale (X. triticosecale Wittmack) stored seeds.

Triticale seeds of the IAC-2 cultivar presented germination of 85% after harvest and natural incidence of the following pathogenic fungi: 34.5% Pyricularia grisae, 12% Bipolaris sorokiniana, 15% Fusarium graminearum and 35% Alternaria alternata. The seeds were stored at 10 oC and under natural ambient conditions for twelve months. The seed physiological quality was evaluated at bimonthly intervals by the germination, accelerated aging, tetrazolium and field emergence tests and fungi survival was evaluated by the blotter test. The seeds stored at 10 oC maintained the same level of germination, viability and vigor for twelve months even though the fungi incidences also remained almost unchanged too. The germination and viability of seeds stored under natural ambient conditions decreased and the level of dead seeds increased due to a higher speed of deterioration and an increased level of storage fungi, mainly Penicillium spp.. The pathogenic fungi levels decreased, reaching very low values at the end of the storage period. However, the pathogen survival was still harmful at the time of the planting season (April).

Hábito de crescimento de Colletotrichum gossypii e C. gossypii var. Cephalosporioides em sementes de algodoeiro

Observacoes sobre o habito de crescimento de Colletotrichum gossypii e C. gossypii var. cephalosporioides em sementes de algodoeiro, inoculadas artificialmente e incubadas a 20-22°C durante cinco a sete dias, evidenciaram as seguintes caracteristicas: (a) em raizes: acervulos isolados ou em grupos, massa conidial cor branco-suja, alaranjada ou salmao (mais frequente), setas marrom-escuras, muitas vezes encobertas pela matriz gelatinosa; conidios produzidos tambem no micelio aereo ou nas extremidades das setas, onde ficam aderidos, formando pequenos aglomerados; (b) na superficie das sementes: conidios produzidos nos apices de setas que emergem diretamente do tegumento, ficando aderidos uns aos outros, formando cachos, semelhantes a cadeias, que sao vistos brilhantes sob a luz, em estereomicroscopio. As setas ferteis sao formadas tambem no micelio aereo que recobre as sementes, geralmente apos cinco dias de incubacao. Os acervulos com massa conidial raramente sao visiveis, exceto em sementes danificadas ou mortas. Como caracteristica de C. gossypii, observou-se que as sementes exibem, de modo geral, uma coloracao rosada, em decorrencia da abundante esporulacao; a ausencia ou escassez de micelio aereo e as setas curtas resultam em um crescimento rente ao tegumento e aspecto compacto. Comparativamente, nas sementes com C. gossypii var. cephalosporioides, as setas sao mais longas e menos densas; o micelio aereo com setas ferteis ocorre com mais frequencia, conferindo as sementes tonalidades acinzentadas e aspecto solto. A constatacao de setas ferteis em lesoes foliares de ramulose evidencia que, no campo, essas estruturas podem funcionar como autenticos conidioforos, desempenhando um importante papel epidemiologico, ao possibilitar a disseminacao dos esporos pelos ventos, a longas distâncias.

Sistema automatizado de aquecimento solar para controle de fitopatógenos da água de irrigação

O sistema automatizado de aquecimento solar, baseou-se em um processo misto de aquecimento da agua em circuito fechado, atraves de coletores planos e dois principios integrados de transmissao de calor, um por conveccao natural e o outro por conveccao forcada. A automatizacao foi realizada por monitores termostaticos diferenciais. Os testes normativos abrangeram as temperaturas programadas de 50, 55 e 60 oC, que contemplam a faixa de temperatura letal para a maioria dos fitopatogenos. Os resultados indicaram rendimentos termicos da ordem de 63, 55 e 52%, superiores, quando comparados aos rendimentos medios de 50, 47 e 45% dos sistemas convencionais. Os resultados experimentais mostraram que o sistema e eficiente para a eliminacao de patogenos da agua de irrigacao, sendo promissor como uma opcao de baixo custo para ser usado em viveiros, casas-de-vegetacao e pequenas ou medias propriedades agricolas.

Métodos de inoculação de Colletotrichum fragariae em morangueiro

The anthracnose crown rot, caused by Colletotrichum fragariae Brooks, is an important disease of strawberries. The fungus also damages stolons, petioles, leaf blades and fruits. The inoculation of C. fragariae is necessary to ensure uniformity and appearance of characteristic symptoms of the disease in pathogenicity tests, variability evaluation of different isolates, efficacy of control measures and germplasm screening for resistance. This study evaluated seven inoculation methods of C. fragariae on strawberry and reports symptoms observed in each case. Symptoms of black leaf spot were mainly observed when the inoculum was sprayed on the plants. The best methods to reproduce wilting and crown rot were: 5 mL of inoculum placed on wounded crowns, a drop of inoculum placed on wounded petioles and crown injection.

The residual effect of liming and potassium fertilization on the occurrence of fungi in soybean seeds

Estudou-se o efeito residual da adubacao potassica e da calagem sobre a ocorrencia de fungos em sementes de soja. O experimento foi instalado com a cultivar IAC-17, no ano agricola de 1991/92, aplicando doses a lanco de O, 3,5 e 7 t/ha de calcario dolomitico e de 0, 150, 300, 450 e 600 kg/ha de K2O. As sementes colhidas no terceiro ano de cultivo, (1993/94) foram submetidas ao teste de sanidade, pelo metodo do papel de filtro. Observou-se que a calagem reduziu significativamente a incidencia de Phomopsis sp., favorecendo, no entanto, a presenca de Aspergillus sp. e de Fusarium sp.. Embora nao tenham sido detectadas diferencas significativas, nos tratamentos com calagem, verificou-se reducao da incidencia de Cercospora kikuchii, Colltotrichum dematium var. truncata e Peronospora manshurica. Apenas a incidencia de Phomopsis sp. diminuiu significativamente devido a adubacao potassica, sendo menor quando se utilizou a dose de 450 kg/ha de K2O.

Patogenicidade de Rhizoctonia solani em morangueiro

Rhizoctonia solani was consistently associated with strawberry plants in nurseries or in fruit production fields, with symptoms of progressive decline, stunt, reddening of leaflets, petioles and runners, besides dry rots of the crown apex, estipules and base of the petioles. These plants showed frequently roots with necrotic lesions. Fusarium spp. and Pythium spp. also were isolated from the diseased plants. This study was conducted to determine the role of each referred fungus on the disease and to investigate a possible interaction between them. For this purpose, R. solani, Pythium sp. and Fusarium sp., alone or combined one with other, were inoculated in strawberry plants, in the greenhouse. The results showed that only when R. solani was present, there was an identical reproduction of the symptoms observed in the field. Fusarium and Pythium, nevertheless, were reisolated from root lesions, indicating the possibility of its involvement with the disease, increasing the symptoms of decline under field conditions.

Ocorrência e sintomas da mancha de Ascochyta em feijão-vagem

A severe Ascochyta blight (Ascochyta phaseolorum Sacc.), was found during a survey carried out in farmers fields of snap bean (Phaseolus vulgaris L.) at Itatiba county, Sao Paulo State, Brazil. Foliar lesions were usually circular to irregular shaped, brown to dark brown and usually contained concentric circles of picnidia. These lesions often blighted the entire leaves, that die and fall. The pathogen also infected the stems, petioles and pods, and the disease incidence ranged from trace to severe. The stems and petioles lesions were elongated and cankerous, often girdling them, killing the plant above the infected region. The pod lesions were initially circular and zonate, as the foliar spots, but the concentric circles are of little evidence. Diagnosis were confirmed by isolation, cultural and morphological characteristics of the fungus, besides pathogenicity tests. The disease was confused with Alternaria blight, on the leaves, or Macrophomina rot, on the lower part of stems. The pathogen identification permitted to avoid misidentification and to establish measures of control.