IMPROVED SEMIDWARF RICE LINES WITH TOLERANCE TO SUBMERGENCE OF SEEDLINGS

Short-term submergence of rainfed lowland and deepwater rice (Oryza sa tiva L.) reduces yields on millions of hectares in South and Southeast Asia. Farmers in these areas lack high-yielding cultivars that are to lerant to submergence at the vegetative stage. The present study was c onducted to evaluate the submergence tolerance, yields and agronomic c haracteristics of improved submergence-tolerant rice lines. Experiment al lines combining short to intermediate stature (80-115 cm) with tole rance to submergence were developed from tall, low-yielding tolerant c ultivars at the International Rice Research Institute Los Banos, Phili ppines. Lines were selected based on high survival after submergence i n concrete tanks and visual evaluation of yield potential in the field . These lines were tested in field and glasshouse tanks for survival a fter 10 to 13 d of submergence and were evaluated in replicated trials in the dry and wet seasons. Experimental lines selected for submergen ce tolerance from crosses with tolerant parents showed higher survival than lines not selected for tolerance in the field and glasshouse tes ts. The most tolerant lines showed low yield potential (less-than-or-e qual-to 4100 kg ha-1); however, one breeding line with high submergenc e tolerance (IR49830-7-1-2-2) yielded 4880 kg ha-1 and was among the h ighest yielding lines in the trial. This shows that submergence tolera nce can be incorporated into improved, high-yielding lines, which can raise productivity in submergence-prone areas. Submergence tolerance m ay also be useful for systems in which rice is seeded directly into st anding water, where deep water during crop establishment has been prop osed as a means of suppressing weed growth.