Germinação e incidência de fungos em testes com sementes de Brachiaria brizantha Stapf.

The present research was carried out to evaluate the effects of sulphuric acid scarification and fungicide (thiabendazol, captan, thiram and iprodione + thiram) applications on germination tests of B. brizantha and on mycroflora development associated with those tests. In germination tests mycroflora were identified and evaluated on the 10th and the 21st day; at the same time blotter tests were carried out to study the microflora. Interpretations of the results showed that sulphuric acid scarification did not increase significantly the germination but checked fungi development and showed less efficiency than fungicides. Among these the mixture of iprodione and thiram provided the best results. The following fungi were identified: Alternaria tenuis, Aspergülus spp., Cladosporium sp., Curvularia sp., Drechslera spp., Epicoccum sp., Fusarium sp., Neurospora monilia, Penicillium sp., Phoma sp., Rhizopus sp., Trichothecium sp. e Trichoconiella padwikii.O presente trabalho teve por objetivo estudar o efeito da escarifícação com ácido sulfúrico e da aplicação de fungicidas (thiabendazol, captan, thiram e iprodione + thiram) nos resultados dos testes de germinação e no desenvolvimento de microrganismos sobre sementes de B. brizantha. Além dos testes de germinação, os quais foram avaliados quanto à incidência de microrganismos aos 10 e 21 dias, conduziram-se testes de sanidade, procurando-se identificar a microflora presente. A análise dos dados e interpretação dos resultados permitiram as seguintes conclusões: a escarificação com o ácido não promoveu acréscimo significativo na germinação, tendo contribuído para a redução do nível de incidência de fungos ao se comparar com a testemunha. Os fungicidas aplicados sobre as sementes escarificadas contribuíram para uma melhor germinação e para a redução na ocorrência de microrganismos, destacando-se a mistura iprodione + thiram. O uso dos fungicidas também facilitou a interpretação dos testes de germinação. Foram encontrados os seguintes fungos: Alternaria tenuis, Aspergillus spp., Cladosporium sp., Curvularia sp., Drechslera sp.p, Epicoccum sp., Fusarium sp., Neurospora monilia, Penicillium sp., Phoma sp., Rhizopus sp., Trichothecium sp. e Trichoconiella padwikii

Potassium leaching test for the evaluation of soybean seed vigour

This work was performed to investigate the possibilities of providing rapid indications on the physiological quality of seeds through the potassium leaching test. Four lots of soybean (Glycine max (L.) Merrill) seeds, cultivars IAC-8 and IAC-15 were submitted to germination, first count, accelerated aging, electrical conductivity and seed moisture tests. In addition, studies on potassium leaching were conducted with samples of selected non damaged seeds and with pure seeds. The amount of leached potassium was evaluated in a flame photometer after a 60, 90, 120 and 150 minute imbibition at 30°C. The evaluations after 60, 90 and 120 minutes were suitable for the identification of lots with different levels of vigour, thus proving to be a simple and rapid method for seed vigour evaluation.O presente trabalho teve como objetivo principal investigar a possibilidade de se obter indicações rápidas sobre a qualidade fisiológica de sementes de soja através do teste de lixiviação de potássio, cuja eficiência foi avaliada comparativamente as informações fornecidas por outros métodos considerados adequados para a determinação do vigor. Para tanto, utilizou-se quatro lotes de sementes de soja dos cultivares IAC-8 e IAC-15 que foram submetidos aos testes de germinação, primeira contagem de germinação, envelhecimento artificial, condutividade elétrica e determinação do grau de umidade. Além destes foram conduzidos estudos de lixiviação de potássio utilizando-se amostras de sementes não danificadas e de sementes fisicamente puras. A quantidade de potássio lixiviado foi avaliada em fotômetro de chama após 60, 90, 120 e 150 minutos de embebição a 30ºC. As avaliações feitas aos 60, 90 e 120 minutos mostraram-se adequadas para a identificação de lotes com diferentes níveis de vigor, constituindo-se em um método simples e rápido para a avaliação da qualidade fisiológica das sementes

Seed-borne pathogens and electrical conductivity of soybean seeds

Adequate procedures to evaluate seed vigor are important. Regarding the electrical conductivity test (EC), the interference in the test results caused by seed-borne pathogens has not been clarified. This research was carried out to study the influence of Phomopsis sojae (Leh.) and Colletotrichum dematium (Pers. ex Fr.) Grove var. truncata (Schw.) Arx. fungi on EC results. Soybean seeds (Glycine max L.) were inoculated with those fungi using potato, agar and dextrose (PDA) medium with manitol (-1.0 MPa) and incubated for 20 h at 25 °C. The colony diameter, index of mycelial growth, seed water content, occurrence of seed-borne pathogens, physiological potential of the seeds, measured by germination and vigor tests (seed germination index, cold test, accelerated aging and electrical conductivity), and seedling field emergence were determined. The contents of K+, Ca2+, and Mg2+ in the seed and in the soaking solution were also determined. A complete 2 × 4 factorial design with two seed sizes (5.5 and 6.5 mm) and four treatments (control, seeds incubated without fungi, seeds incubated with Phomopsis and seeds incubated with Colletotrichum) were used with eight (5.5 mm large seeds) and six (6.5 mm large seeds) replications. All seeds submitted to PDA medium had their germination reduced in comparison to the control seeds. This reduction was also observed when seed vigor and leached ions were considered. The presence of Phomopsis sojae fungus in soybean seed samples submitted to the EC test may be the cause of misleading results