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Parambu, Brazil

da Cruz R.P.,IRGA | Duarte I.T.L.,Federal University of Rio Grande do Sul | Cabreira C.,Unisinos Graduacao em Ciencias Biologicas
Scientia Agricola

Rice (Oryza sativa L.) cold tolerance at the initial stages of development is a highly desirable trait to be incorporated into the state of Rio Grande do Sul, Brazil, cultivars, but selection for this trait must be performed under controlled temperature conditions, which limits the number of lines that can be evaluated. Knowledge of the inheritance of this trait is important to define breeding strategies. So the aim of this paper was to study the genetic basis of rice cold tolerance at the vegetative stage. Six genotypes with constrasting cold tolerance reactions were crossed in a diallel scheme without the reciprocals. The parents and the F1 and F2 generations were cultivated in a greenhouse until the V4 stage, when they were submitted to 10°C for ten days and evaluated for plant survival after seven days of recovery under normal temperature. The results obtained by the diallel analysis of the F1 generation indicated significance of both additive and non-additive effects, but the general combining ability was more important. The evaluation of the F2 generation revealed oligogenic inheritance with one or two dominant alleles responsible for cold tolerance in the cold tolerant parents and two complementary genes with recessive alleles segregating in the crosses involving sensitive and intermediate genotypes. Source

Fraga T.I.,Federal University of Rio Grande do Sul | Carmona F.C.,Federal University of Rio Grande do Sul | Anghinoni I.,Federal University of Rio Grande do Sul | Marcolin E.,IRGA
Revista Brasileira de Ciencia do Solo

In the State of Rio Grande do Sul, Brazil, flooded rice fields using Patos Lagoon as the source of water for irrigation are subject to be damaged by salinity, since this source is bound to the sea on its southern end. The sensitivity of rice is variable during plant development, being higher in the seedling and reproductive periods. However, there is not enough information about the behavior of plants under salt stress during the course of its development, especially in the vegetative stage. This study evaluated the effect of different levels of salinity of irrigation water on the salinity of soil solution over time and on some plant attributes, during the vegetative stage of rice. The study was conducted in a greenhouse, where seeds of the variety IRGA 424 were sown in pots and irrigated with water with electrical conductivity (ECi) levels of: 0.3, 0.75, 1.5, 3.0 and 4.5 dS m-1, from the tillering initiation (V4) until the panicle initiation (PI). The evaluations made were the electrical conductiviy of soil solution (ECe), the dry biomass of plants and stems, tillering, height and the transpiration of plants. The ECe increased with the ECi over time, and was determined by water transpiration flux in pots. The ECe values at the end of the experiment were high and, in most cases, higher than the critical values for flooded rice. The growth attributes of rice were negatively affected from ECi of 2.0 dS m-1 and ECe of 4.0 dS m-1. Source

Pinto L.M.N.,University of the Rio dos Sinos Valley | Pinto L.M.N.,ITT NUTRIfor Technological Institute of Food for Health | Fiuza L.M.,University of the Rio dos Sinos Valley | Ziegler D.,ITT NUTRIfor Technological Institute of Food for Health | And 8 more authors.
Journal of Economic Entomology

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 δelta-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. © 2013 Entomological Society of America. Source

Holzschuh M.J.,Federal University of Rio Grande do Sul | Carlos F.S.,Federal University of Rio Grande do Sul | Carmona F.C.,IRGA | Bohnen H.,IRGA | Anghinoni I.,Federal University of Rio Grande do Sul
Revista Brasileira de Ciencia do Solo

1Establishment of the water layer in an irrigated rice crop leads to consumption of free oxygen in the soil which enters in a chemical reduction process mediated by anaerobic microorganisms, changing the crop environment. To maintain optimal growth in an environment without O2, rice plants develop pore spaces (aerenchyma) that allow O2 transport from air to the roots. Carrying capacity is determined by the rice genome and it may vary among cultivars. Plants that have higher capacity for formation of aerenchyma should theoretically carry more O2 to the roots. However, part of the O2 that reaches the roots is lost due to permeability of the roots and the O2 gradient created between the soil and roots. The O2 that is lost to the outside medium can react with chemically reduced elements present in the soil; one of them is iron, which reacts with oxygen and forms an iron plaque on the outer root surface. Therefore, evaluation of the iron plaque and of the formation of pore spaces on the root can serve as a parameter to differentiate rice cultivars in regard to the volume of O2 transported via aerenchyma. An experiment was thus carried out in a greenhouse with the aim of comparing aerenchyma and iron plaque formation in 13 rice cultivars grown in flooded soils to their formation under growing conditions similar to a normal field, without free oxygen. The results indicated significant differences in the volume of pore spaces in the roots among cultivars and along the root segment in each cultivar, indicating that under flooded conditions the genetic potential of the plant is crucial in induction of cell death and formation of aerenchyma in response to lack of O2. In addition, the amount of Fe accumulated on the root surface was different among genotypes and along the roots. Thus, we concluded that the rice genotypes exhibit different responses for aerenchyma formation, oxygen release by the roots and iron plaque formation, and that there is a direct relationship between porosity and the amount of iron oxidized on the root surface. Source

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