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There are several structural and technical factors that determine rice production. Among others, we have to take into account weed management. Red rice (=Oryza sativa L.) is undoubtedly one of the most troublesome weeds in rice production in some regions of Portugal. In order to be able to better control this weed, the knowledge of red rice biological behavior, in relation to different environmental conditions, is considered essential to bring out strategies of weed management fit for an integrated production of rice of a high quality. This experiment was conducted to study the competitive ability of the most important rice varieties (Ariete and Thaibonnet) against red rice, at 2 N rate and 4 densities of the weed. This research allowed besides understanding preliminarily if shattering is related only to the genetic features or depends also on agronomical or environmental conditions, such as N supply and condition of competition.

Rice (Oryza sativa L.) is one of the most important crops in Portugal, representing a staple food in the Portuguese diet. The average annual consumption per capita is about 16 kg of white rice. The annual production of rice did not cover the demand and for that reason Portugal import 200,000 ton per year of this cereal. The total rice surface depends on the quantity and quality of irrigation water available, however the maximum area allowed for rice production in Portugal by EU is 34,000 ha, but last years the surface was about 25,000 ha and the yield 150,000 ton. The most important rice production area was located in Alentejo, where the climatic conditions are normally favorable for rice production. Presently the most important varieties of rice in Portugal are: 'Ariete', 'Koral' and 'Thaibonnet'. The criteria used by producers for choosing the varieties are: adaptability, productivity, resistance to diseases and acceptability by industry.

In order to reach the objectives of the UE project "RESGEN" for conservation, characterisation, collection and exploitation of genetic resources in agriculture, it will be performed the description, collection, employing and organisation of germplasm available at different European institutions. The planned activity was aimed to constitute an operative germplasm gene bank. To perform this goal a number of genotypes have to be described, evaluated and characterised for agrophysiologic, adaptive and technologic behaviour. The first step was to collect and catalogue all the genetic resources currently available in the different European rice countries that at the beginning of the project amounted to about 450 varieties.

Rice is a crop moderately sensitive to salinity (Maas & Hoffman, 1977), that grows in waterlogged conditions. The identification of genotypes resistant to NaCl at specific developmental stages is essential to improve the understanding of the effects of salt stress upon phenology and to elaborate further breeding programs. Five European rice-producing countries pooled their genetic resources in order to evaluate them and subsequently improve national breeding programmes (Project RESGEN CT 95-37). 320 European rice varieties were screened at the young seedling stage (the most sensitive to NaCl during vegetative growth).

Due to climatic conditions, Southern Europe is at the limit of the rice cropping area. All European rice cropping regions share common constraints (short vegetative period and cold tolerance) but also have specific problems (cryptogamic or insect pests, salt tolerance, grain quality...). So, European rice breeding has specific needs. So, the European Commission has supported a research program for the characterization of available European rice genetic resources in order to evaluate their diversity and structure. The evaluation of about 50 agronomic, morphological and technological traits of 430 genotypes was conducted from 1996 to 2000 in France, Spain, Italy, Greece and Portugal. The obtained data show that genotype X environment interactions are low and can be neglected for most of observed traits, and can be used to build up a reliable database very useful to breeders.