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Rice production in most areas of coastal deltas is affected adversely by numerous abiotic stresses, including salinity and other soil-related problems, submergence, stagnant flooding and drought. These stresses affect poor farmers disproportionately. We identify sources of tolerance of these abiotic stresses, understand the causal mechanisms and transfer tolerance into popular varieties and elite breeding lines using marker-assisted backcrossing (MABC). This approach also helps in pyramiding multiple QTLs and genes for tolerance. Previously, several salt-tolerance QTLs were identified, including Saltol, a major QTL on chromosome 1. Currently, Saltol is being introgressed into popular varieties such as IR64, BRRI dhan 28 and BR11. The long-term goal is to identify and combine multiple genes and QTLs controlling different tolerance traits for higher salt tolerance in high yielding rice varieties. Substantial progress in developing submergence-tolerant cultivars was made after cloning SUB1, a major QTL for submergence tolerance, and MABC was used successfully to introgress it into six popular varieties within 3 years, shortening the breeding cycle significantly. The SUB1 locus provided a two- to threefold increase in yield over intolerant varieties under submergence in field trials. Developing varieties combining tolerance for both salinity and submergence is in progress through the introgression of Saltol and SUB1 into popular varieties using MABC. Direct seeding is becoming more important during the dry season in coastal deltas because of its relatively lower cost. However, this approach is hindered by the risk of early fl ooding. We identified several genotypes with tolerance of fl ooding during germination, identified major QTLs and transferred tolerance into elite breeding lines. In most coastal areas, water stagnation for 20-50 cm for several months is a serious problem and modern rice varieties are sensitive to such conditions. Reasonable genetic variation in tolerance of stagnant fl ooding was observed and is being explored. Combining tolerance of abiotic stresses predominant in coastal areas, together with proper management strategies, could contribute substantially to increasing and sustaining rice production in these fragile coastal deltas.

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Unsupervised classification of the landcover in the rice growing area in the Mekong river delta was performed using a combination of the ERS and RADARSAT SAR data. The ERS SAR is VV polarized while the RADARSAT SAR is HH polarized. The advantages of multiple polarization SAR in landcover classification may be realized using data from these two satellites together. The study area for this work covers the SOC Trang and Bac Lieu provinces of Vietnam where a diversity of rice cropping systems is practiced. Rice crops at different growth stages exist in the area at any one time together with other non-rice vegetation. These classes can be discriminated using a combination of the two SAR images.

This study was carried out to test the hypothesis that diversification and polyculture (growing more than one crop/commodity at the same time in the same field) could contribute greatly to increased profitability and reduced risk for both rice-based and shrimp-based production systems in the coastal zone. Local authorities, community associations and farmers collectively selected study sites in seven land-use zones (LUZ). In each study site, farmer communities selected one demonstration farm (demo) and five nearby farms (controls) where farming activities were managed under current practices. The demos tested new diversified cropping systems and new or improved technologies. At the end of each cropping season, farmer-managed on-farm workshops - in which the participants were local authorities, community associations, the press, farmers - were conducted to compare the ease of implementation, yields, profits and the benefit-cost of the demos and the controls. At the end of the 3-year study, final on-farm workshops were arranged to give final ratings and recommendations for the tested systems and technologies, which were endorsed by local authorities for wide dissemination, with support from extension workers, village authorities, community organizations and the mass media. The rice-rice&fish system was recommended for freshwater zones and the shrimp&crab-fish system for saltwater zones. For the intermediate water quality zone, the shrimp-rice&fish system was recommended only for areas near the freshwater zone. Component technologies recommended for outscaling included: new high-quality rice varieties; using a drum seeder for rice seeding; nitrogen fertilizer management using a leaf colour chart; appropriate stocking density of tilapia, anabas and silver carp for freshwater zones; and crab and elongated goby for saltwater zones. Extensive aquaculture techniques were recommended for shrimp in the shrimp-rice&fish system and semi-intensive for the shrimp&crab-fish system. After 3 years of study, approximately 8700 farmers adopted the recommended systems and technologies on 11,550 ha. The participatory approaches have been successful in outscaling diversified cropping systems and new technologies, generating more benefits to farmers.

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