Dejânia Vieira de Araújo

Events of pre-penetration, penetration and colonization processes by Phakopsora pachyrhizi in soybean leaflets

Light (LE) and scanning electron microscopy (SEM) were used to study the development of Phakopsora pachyrhizi from urediniospore germination to colonization on soybean. Drops of 50 µL of a spore suspension (3 x 104 urediniospores.mL-1) were inoculated on detached leaflets of seven cultivars, besides the genotypes PI 230970 and PI 459025. After inoculation, leaflets were stored in BOD at 23 ± 2 ± 2 oC for incubation. Samples were taken from four to 240 hours after the inoculation (h.a.i.), submitted to the process of fixation for scanning electron microscopy (SEM) and decolorized into a solution of absolute ethanol/acetic acid (1:1, v/v). In decolorized samples differences were observed among cultivars in percentage of germination, appressorium formation and consequently in the penetration. On PI 429025 the lowest percentage of germinated urediniospores (20%) and of appressoria formation (11 %) was observed, and the cultivar BRS 154 presented a higher percentage of both germination (85.5 %) and appressoria formation (66.5 %). Among other cultivars the percentage of germination was from 42% to 73.5 % and from 21.5 to 60.5 % for appressoria formation. Several events in the colonization process observed by SEM were different from those in the literature.

Métodos de inoculação e efeitos de Fusarium oxysporum f. sp. vasinfectum em sementes de algodoeiro

The availability of seeds infected by fungi or other pathogens transmissible by this way is important for several purposes. This work was conducted to evaluate proceedings of inoculations and period of exposition of seeds to Fusarium oxysporum f. sp. vasinfectum through the water restriction technique. The following methods were compared: (1) seed immersion in a conidial suspension (106 conidia/mL) following incubation in substrate with an osmotic potential of -1.0 MPa; (2) atomization of a conidial suspension (106 conidia/mL) upon the substrate and on the seeds, and (3) direct contact of the seeds with the fungus mycelium, grown upon the substrate. All methods enabled to obtain seeds with different inoculum potential equivalent to different times, 24, 48, 72, 96 and 120 hours of seed expositions to the fungus. To evaluate the efficacy of infection, germination tests on roll paper and in soil/sand substrate and Blotter Test were applied. The most effective method was the immersion of seeds in inoculum suspension followed incubation in substrate with water restriction. The period of time that seeds should stay in contact with the pathogen, without affecting their physiological quality, was 53 h to 57 h.

Germinação de urediniósporos de Phakopsora pachyrhizi em diferentes métodos de armazenamento

The objective of this study was to evaluate the effect of different storage methods on the viability of the urediniospores of P. pachyrhizi. Urediniospores were collected and stored in five different conditions: detached dry leaves (24°C), desiccator (10°C) + liquid nitrogen (-196°C) after 60 days, refrigerator (4°C), deep-freezer (from -60°C to 80°C) and liquid nitrogen (-196°C). The percentage of germination from stored urediniospores was evaluated every thirty days in water-agar medium. Urediniospores stored in liquid nitrogen presented the highest germination percentage after 270 days of storage. In desiccator, the germination was zero at ninety days of evaluation, and when urediniospores were transferred to and kept in liquid nitrogen, the germination was up to 30%. The urediniospores stored under others conditions presented a decline in germination at sixty days and at the ninety days the germination declined to zero. Based on these results, the most efficient way of storing urediniospores of P. pachyrhizi was using liquid nitrogen.

Influência da temperatura e do tempo de inoculação das sementes de algodão na transmissibilidade de Colletotrichum gossypii var. cephalosporioides

A transmissibilidade de Colletotrichum gossypii var. cephalosporioides foi estudada em diferentes temperaturas utilizando sementes de algodoeiro (Gossypium hirsutum) inoculadas com diferentes tempos de exposicao ao patogeno. O experimento consistiu de seis tratamentos, sendo tres tempos de exposicao (36, 72 e 108 h) das sementes, inoculadas e nao inoculadas com o fungo, testados em temperaturas de 15, 20, 25 e 30 ± 2 °C. Os tratamentos provenientes de sementes nao inoculadas com o fungo foram utilizados como testemunhas. Os tempos de inoculacao apresentaram diferenca na incidencia e na porcentagem da semente coberta com propagulos do patogeno (PSCPP), sendo o maior valor observado no tempo de 108 h, com consequencias na germinacao e porcentagem de plantas sobreviventes. Os tempos de 36 e 72 h nao apresentaram diferenca entre si. Temperaturas mais baixas e a maior quantidade de inoculo nas sementes proporcionaram reducao na germinacao e porcentagem de plantas sobreviventes. A intensidade da doenca nao foi influenciada pelo tempo de exposicao, no entanto, a temperatura foi fator determinante para a transmissibilidade do patogeno, sendo a incidencia e a severidade maiores com o aumento desta. O condicionamento osmotico estimulou o desenvolvimento fungico, sendo observadas maior incidencia e severidade da doenca no tempo de 108 h.

Relationship between inoculum levels of Colletotrichum gossypii var. cephalosporioides in seeds and the progress of cotton ramulosis

The objective of this study was to verify the relationship between percentage of cotton seeds infected by Colletotrichum gossypii var. cephalosporioides and the progress of ramulosis in the field. The experiment was carried out in Lavras (Minas Gerais State, Brazil) and was designed in randomized blocks with five treatments and replicated three times. The treatments consisted of plots with 0, 4, 8 and 16% of seeds infected with the pathogen. Germination and final stand were evaluated ten and 30 days after sowing. The incidence and disease severity were evaluated, weekly, from 30 to 95 days after sowing and the data were transformed to area under the disease progress curve of the incidence (AUDPCI) and of the severity (AUDPCS). Production (Kg/ha) and the transmissibility of the pathogen plant-seed were also evaluated. No significant difference was observed for the germination, the final stand and the production. On the other hand, inoculum levels in seeds influenced the AUDPCI and the AUDPCS, and the diseases progress increased with the rise of initial inoculum in seeds. There was positive and significant correlation between both AUDPCS and the percentage of the pathogen on seeds and also between both initial inoculum potential and incidence and percentage of the pathogen on seeds. In the same way, the percentage of the pathogen on seeds was correlated positively to AUDPCS.

Superação da dormência e avaliação da qualidade fisiológica de sementes de Sesbania virgata

A avaliacao da qualidade fisiologica de lotes de sementes de Sesbania virgata e dificultada pela dormencia inerente a especie, bem como pela inadequacao metodologica de testes disponiveis. Para desenvolver procedimentos adequados a avaliacao da qualidade das sementes de S. virgata, foram avaliados metodos tanto para quebra de dormencia como para realizacao do teste de tetrazolio. Em uma primeira fase, as sementes de cinco lotes foram submetidas a tratamentos para quebra de dormencia: lixa, acido e corte do tegumento, previamente ao teste de germinacao. Para caracterizacao dos lotes e adequacao da metodologia do teste de tetrazolio, na segunda fase, as sementes foram lixadas na regiao oposta ao eixo embrionario, e submetidas aos seguintes testes: tetrazolio, germinacao, velocidade de emergencia, peso de materia fresca e de materia seca de plântulas. Foram utilizados dois metodos de pre-condicionamento: embebicao em papel por 18 h a 30 oC e imersao em agua por 12 h a 30 oC e tres periodos (uma, duas e tres horas) de imersao em solucao de tetrazolio 0,5%. Na analise do perfil dos lotes de S. virgata foram detectadas variacoes na qualidade fisiologica pelos resultados dos testes de vigor e germinacao. O metodo de escarificacao com lixa possibilitou a quebra de dormencia das sementes de S. virgata,e o pre-condicionamento das sementes em papel com embebicao em solucao de tetrazolio 0,5% por duas horas e um procedimento adequado para avaliacao da viabilidade das sementes.

Estimativa da capacidade de armazenamento de água no solo para a microrregião da BAP (MT)

With the increase in world population comes the concern about the misuse of natural resources, such as the primary resource of water, essential for consumption and use in agriculture. Thus, there is an urgent need to study the regions where it is possible to use water as a source of irrigation for crops. This work was performed in the laboratory of Agrometeorology at the State University of Mato Grosso (UNEMAT), with the aid of ArcGIS 10® geostatistical software, which interpolates and specializes georeferenced data in order to form maps. The Upper Paraguay River Basin, belonging to the State of Mato Grosso, has 44 municipalities which are classified according to the type of soil, establishing three AWC standards: 30, 50 and 75. Overall, the area and representativeness for each municipality were determined, and 31 of these, representing over 41% of the whole territory, were shown to have AWC 75 soil. Only 8 municipalities were shown to have AWC 50 soil, with 11% of these being located in a flood zone, and 37 municipalities were shown to have AWC 30 soil, representing 48% of the total. Therefore, this region mostly has AWC 75 soil, demonstrating the presence of a soil with higher storage capacity and water availability.

Intensity of Powdery Mildew in Soybean Under Changes of Temperature and Leaf Wetness

Soybean Glycine max L. Merr. is cultivated in several tropical and subtropical regions of the world. United States (USA) and Brazil are the worlds largest producers and exporters of oilseed (Agrianual, 2008; Miyasaka & Medina, 1981). Despite the high production and export of Brazilian soybeans, many factors have affected the quality or quantity of production of that crop, causing reduction in financial returns per unit area, such as disease epidemics. Among the diseases, powdery mildew, whose etiologic agent is Microsphaera diffusa Cke. & Pk., suddenly began to cause significant damage in soybean, despite having a broad host range and have been reported in Brazil, Canada, Republic of China, India, Puerto Rico, South Africa, United States (Sinclair, 1999), Germany, Argentina and Bolivia (Sartorato & Yorinori, 2001) . According to Yorinori & Hiromoto (1998), crops widely affected by the disease, had estimated reductions between 30 and 40% of yield, in the same order of magnitude as those reported abroad by Dunleavy (1978) and Philips (1984). The susceptibility of cultivars and the influence of climate favored epidemics with high rates of disease progress, in successive years in Brazil. Considering the lack of resistance of most of the cultivars, chemical control is required, especially in the south and the high plains of the savannah biome (Sartorato & Yorinori, 2001). In 1996/97, epidemics of powdery mildew in soybean in a great extent of Brazil, from the Central West region to the Rio Grande do Sul state, resulted in average losses of 15 and 20% in susceptible cultivars, with extremes ranging from 50 to 60% (Yorinori & Hiromoto, 1998 ; Seganfredo & Silva, 1999). M. diffusa is distinguished from M. polygoni by presenting cleistothecium with appendages forked at its end (Sartorato & Yorinori, 2001; Grau, 1975). The fungus is an obligate parasite that develops throughout the soybean shoot, including leaves, stems, petioles and pods. Symptoms can range from chlorosis, green islands, rusty spots, defoliation or severe combination of these symptoms, depending on the reaction of cultivars. Chlorotic spots and necrosis on the leaf veins indicate a hypersensitivity reaction. However, the most obvious is the very structure and powdery white fungus on the surface of infected parts (Yorinori, 1982; Yorinori, 1986, Tanaka et al., 1993; Yorinori et al., 1993; Sinclair, 1999; Sartorato &