89 OMONRICE 19 (2013) ENRICHING GENE POOL TO ENHANCE RICE PRODUCTIVITY UNDER SUBMERGENCE AND MEDIUM STAGNANT WATER STRESSES IN MEKONG DELTA Nguyen Thi Lang 1 , Nguyen Van Hieu 1 , Tran Thi Nhien 1 , Bui Phuoc Tam 1 , Vo Thi Tra My 1 , Bui Chi Buu 2 , Romeo V. Labios 3 , Abdelbagi Ismail 3 , Russell Reinke 3 and Reiner Wassmann 3 1 Cuu Long Delta Rice Research Institute, Thoi Lai, Can Tho, Vietnam; 2 Institute of Agricultural Sciences for Southern Vietnam (IAS), 3 International Rice Research Institute (IRRI) Email : ntlang@hcm.vnn.vn ABSTRACT Materials from the result of first years of yield trial under submergence and medium stagnant water stresses were selected for conducting our experiment. The preliminary results of 20 rice accessions were reported in MYT in Winter-Spring seasons (2011-2012) under submergence and medium stagnant water stresses. Subsequently, on-farm participatory varieties selection (PVS) trials were conducted at five different sites in An Giang, Hau Giang and Can Tho using promising lines from MYT. Mostly the genotypes were short growth duration of 90- 105 days. At maturity, farmers at each location as well as researchers voted the best breeding lines. Discussions were emphasized on high yielding, BPH, blast resistance, good grain quality and water stress tolerance. Moreover, more crosses were continued to develop using rice landraces as important breeding materials to have new rice genotypes with good grain quality properties and high yield. They must adapt to submergence condition in Mekong Delta. Keywords: AMMI (additive main effects and multiplicative interaction), medium stagnant, submergence. INTRODUCTION Submergence is a serious problem affecting rice production in flood prone areas worldwide. In addition, climate change is further aggravating flooding risks of rainfed lowland rice areas, especially in areas belongs to Mekong Delta. Submergence can be caused by river overflows, excessive rain and/or tidal inundation (Sairam et al., 2008). Submergence tolerant lines with high yield potential were obtained in the early 1990s (Mackill et al., 1993). However, these tolerant prototypes are never widely adopted by farmers since they were inferior in grain quality or in other traits needed for local adaptation. On the other hand, mega varieties that possessed most traits desired by farmers but are submergence intolerant begin to spread widely in both irrigated and rainfed lowland areas of south and south-east Asia (Mackill et al., 2006). To ensure the adoption of the final breeding product by the farmers, some varieties with submergence tolerance are successfully developed. Food security crops need to be climate proofed to combat the challenges posed by climate change and variability. The overall objective of this report is to develop new high yielding varieties for low input cultivation in a range of agro- ecological zones by broadening adaptability. The specific objectives are: (i) to explore rice germplasm and identify high yielding genotypes under submergence and medium stagnant water stresses, (ii) to enrich rice gene pool, share genetic resources and knowledge and foster networks between participating research groups and potential end-users for their varieties. MATERIALS & METHODS 20 rice genotypes with submergence tolerance and high yielding were tested with two standard checks plus farmer's varieties (Table 1) under naturally occurring submergence conditions. Omonrice 19: 89-96 (2013)