Indica rice cultivar IRGA 424, transformed with cry genes of B. thuringiensis, provided high resistance against Spodoptera frugiperda (Lepidoptera: Noctuidae).

Plant expression of the entomopathogenic bacteria Bacillus thuringiensis cry gene has reduced the damage created by insect pests in several economically important cultures. For this study, we have conducted genetic transformation of the indica rice "IRGA 424", via Agrobacterium tumefaciens, using the B. thuringiensis cry1Aa and cry1B genes, with the objective of obtaining rice plants resistant to the insect pests from this culture. The gene constructions harbor the promoters maize proteinase inhibitor and ubiquitin. The results showed that high concentration of the hormone 2,4-dichlorophenoxyacetic acid and agarose as the gelling agent helped the production of embryogenic calli for the analyzed cultivar. More than 80% of the obtained transformed plants revealed the integration, using polymerase chain reaction, of the cry1Aa and cry1B genes. Analysis of the expression of the heterologous protein by Western blotting revealed the expression of the Cry1B delta-endotoxin in IRGA 424 plants transformed with the ubiquitin promoter. Data showed the production and dissemination of a high number of embryogenic calli in addition to obtaining plants transformed with the cry1Aa and cry1B genes until the reproductive phase. The feed bioassays with the transformed plants and Spodoptera frugiperda (JE Smith) larvae indicated high rates of mortality to the insect target. The highest corrected mortality rate achieved under laboratory conditions with Bt-rice plants transformed with the cry1B and cry1Aa genes was 94 and 84%, respectively. Thus, our results demonstrated the great potential of transformed Bt-rice plants in controlling the damage caused by these insect pests in rice paddy fields.

Use of a saponin based molluscicide to control Pomacea canaliculata snails in Southern Brazil.

Pomacea canaliculata snails pose a severe problem to direct seeded rice cultivated in Southern Brazil. Control of this snail is nowadays performed with toxic chemicals such as copper sulfate and fungicides such as fentin. A novel natural molluscicide based on alkali modified quinoa (Chenopodium quinoa) saponins was tested under laboratory conditions. Snails were collected in rice fields close to Porto Alegre (State of Rio Grande do Sul) and in Brusque (State of Santa Catarina, 400 km north of Porto Alegre). In Santa Catarina the product was very effective, while in Porto Alegre it had no effect. This unexpected behavior was probably due to the respiratory habits of the snails under different contents of dissolved oxygen in the water. Near Porto Alegre the water used in rice fields is heavily polluted, with dissolved oxygen levels of 1-2 ppm, and the snails rely primarily on their siphon and lungs to breathe. Since saponin control is probably due to an interaction between saponins with the sterols present in the cell walls in the gills, no control was observed. By contrast, in Santa Catarina the dissolved oxygen level of the water is 5-6 ppm, and the snails remain mostly underwater, breathing with their gills. In this case the snails died within 24 h at a dose of 20 and 30 ppm of product. To test this observation, snails grown in polluted waters were forced to remain underwater in saponin solutions and water (control) preventing the use of their siphon to breathe. The snails exposed to saponin solutions died, while the control snails survived, indicating that they were still able to use their gills to breathe. These results indicate that the use of the saponin product is limited to rice fields not irrigated with heavily polluted waters.