Ellen Noly Barrocas

Performance of common bean seeds infected by the fungus Sclerotinia sclerotiorum

The fungus Sclerotinia sclerotiorum, causal agent of white mold disease on several economically important crops, such as bean, soybean, and cotton, is commonly disseminated through seeds and can cause high losses on their quality and in productivity of these species. The aim of this study was assessing the effects of different initial inoculums potentials of this fungus on common bean seeds using two different strains of the fungus and two genotypes of common beans (Perola and Ouro Negro) artificially inoculated. Seeds were sown on soil and the cultivation was performed under controlled environmental conditions favorable to development of the white mold disease. Variables assessed were: germination; seed health; emergence speed index; initial and final seedling number; and dry weight of aerial parts and roots. It was found that with the gradual increase in inoculum potential in the seeds also occurred gradual reduction in the values of: germination; emergence speed index; seedling stand; and length and dry mass of aerial parts and roots. These results show the importance of initial inoculum potential of S. sclerotiorum present in common bean seeds, as much in disseminating the pathogen as on direct damages caused in field by reducing productive potential of the emerged plants.

Sensibility of the PCR technique in the detection of Stenocarpella sp. associated with maize seeds

Maize seeds, infected by Stenocarpella species, are important sources of inoculum for the introduction and dissemination of stalk and ear rot and macrospore leaf spot diseases. The use of healthy seeds is an important strategy for the preventive control of these diseases. However, one of the difficulties in the health quality control programs for maize seeds is the availability of a reliable and quick method for detecting these fungi during routine seed analyses. Therefore, the objective of the present study was to investigate the possibility of using the PCR technique as an alternative method for accurately detecting these pathogens in maize seed samples. Maize seeds were kept in contact with S. maydis colonie developed in PDA media containing mannitol at -1.4 MPa for 72 h. The seed samples used in this study were prepared with infected seeds at incidences of 100, 20, 10, 2, 1 and zero %.The primers used were able to detect S. maydis fungi in association with seeds with a maximum of 2% , however those primers were not able to differentiate between the two species.

Effects of Stenocarpella maydis in seeds and in the initial development of corn 1

The association of the fungus Stenocarpella maydis with corn seed may cause a reduction of seed germination and vigor of the emerged seedlings. This work was carried out in order to evaluate the effects of S. maydis on corn seed quality as well as on its early development. To evaluate such effects, seeds of cultivars RB9308YG (C1) and RB9108 (C2) were inoculated by the osmotic conditioner technique with two S. maydis isolates for 24(P1), 48(P2), 72(P3) and 96 hours (P4). Plants were grown in a room chamber at 20 °C and 25 °C and daily assessed until 28 days after emergence. Seed germination, incidence of S maydis, electrical conductivity, speed of emergence index (SEI), initial and final seedling population and dry weight of emerged plants, were assessed. The longer the exposition times of the seeds to the fungal colony, the more severe negative effects of the pathogens on seed vigor were observed. S. maydis caused reduced seed vigor in the speed of seedling emergence in the final stand and early development of corn seedlings.

Qualidade fisiológica e sanitária de sementes de milho tratadas com fungicidas e avaliadas durante o armazenamento

At post-harvest period, quality of corn seeds may be influenced by several important factors such as: presence of harmful microorganisms, chemical treatments, host species genotype and storage conditions. The objective of this study was to evaluate the performance of corn seeds, hybrids 2B 688 and 2B 710, with high incidence of fungus Fusarium verticillioides and treated with mixtures of fungicides thiophanate-methyl + pyraclostrobin (50 mL a.i .100 kg-1 of seeds) and carbendazim + thiram + micronutrients (100 mL a.i .100 kg-1 of seeds) during six months storage. Performance assessments of seeds were carried out at 0, 30, 60, 90, 120, and 180 days storage. The incidence of F. verticillioides, as well as physiological quality, germination, vigor, stand of plants, emergence speed index, and dry matter weight were assessed. It has been verified that seed treatment with fungicide mixtures was efficient for ensuring seed physiological quality of both genotypes and to reduce incidence of F. verticillioides on treated seeds. By contrast, analysis between treatments with fungicides, within each period assessed and each treatment as compared to control along storage period was verified clear benefits on emergence of seeds after treatment with fungicides.

Transmission ofStenocarpella maydisby maize seeds

Stenocarpella maydis is one of the main fungi associated with maize seeds, being a causative agent of stalk and ear rot, a disease which causes considerable losses for crop-producing regions in Brazil. The organism is considered to be a pest, subject to sanitary standardisation in current programs of seed certification in the country. The aim of this study was to evaluate the transmission rate of the fungus from infected maize seeds. Seeds were inoculated with two isolates using a method of physiological conditioning, in which the seeds are kept in contact with colonies of the fungus for 24 (P1), 48 (P2), 72 (P3) and 96 (P4) hours. Two cultivars were used, one susceptible (C1) and one moderately resistant (C2), and the trial carried out at two temperatures (20 °C and 25 °C). The inoculated seeds were distributed individually into plastic cups containing substrate. The plants were evaluated daily for stand and the appearance of post-emergent symptoms. Based on the number of dead seeds, transmission rates reached a maximum of 90.5% at the P4 inoculum potential, this rate being greater than transmission rates achieved for symptomatic and asymptomatic infection in emerged plants. For the total transmission rate, transmission of the pathogen was seen at all inoculum potentials; these values varying from 25% for cultivar C2 at potential P1 and a temperature of 20 °C, to 93% for cultivar C2 at potential P3 and a temperature of 25 °C.

Transmission of Stenocarpella maydis by maize seeds

Stenocarpella maydis is one of the main fungi associated with maize seeds, being a causative agent of stalk and ear rot, a disease which causes considerable losses for crop-producing regions in Brazil. The organism is considered to be a pest, subject to sanitary standardisation in current programs of seed certification in the country. The aim of this study was to evaluate the transmission rate of the fungus from infected maize seeds. Seeds were inoculated with two isolates using a method of physiological conditioning, in which the seeds are kept in contact with colonies of the fungus for 24 (P1), 48 (P2), 72 (P3) and 96 (P4) hours. Two cultivars were used, one susceptible (C1) and one moderately resistant (C2), and the trial carried out at two temperatures (20 °C and 25 °C). The inoculated seeds were distributed individually into plastic cups containing substrate. The plants were evaluated daily for stand and the appearance of post-emergent symptoms. Based on the number of dead seeds, transmission rates reached a maximum of 90.5% at the P4 inoculum potential, this rate being greater than transmission rates achieved for symptomatic and asymptomatic infection in emerged plants. For the total transmission rate, transmission of the pathogen was seen at all inoculum potentials; these values varying from 25% for cultivar C2 at potential P1 and a temperature of 20 °C, to 93% for cultivar C2 at potential P3 and a temperature of 25 °C.