Designing resilient rice varieties for coastal deltas using modern breeding tools
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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 fl ooding 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 identifi ed, 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 signifi cantly. The SUB1 locus provided a two- to threefold increase in yield over intolerant varieties under submergence in fi eld 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 identifi ed several genotypes with tolerance of fl ooding during germination, identifi ed 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. CAB International 2010.
