27 OMONRICE 19 (2013) INTROGRESSION OF Sub1 GENE INTO LOCAL POPULAR VARIETIES AND NEWLY DEVELOPED ELITE BREEDING LINES IN THE MEKONG DELTA ADAPT TO THE CLIMATE CHANGE Nguyen Thi Lang 1 , Pham Thi Thu Ha 1 , Chau Thanh Nha 1 Nguyen Van Hieu 1 , Doan Van Hon 1 , Abdelbagi Ismail 3 , Russell Reinke 3 and Bui Chi Buu 2 1 Cuu Long Delta Rice Research Institute (CLRRI), Thoi Lai, Can Tho, Vietnam; 2 Institute of Agricultural Sciences for Southern Vietnam (IAS), 121-Nguyen Binh Khiem, Dist. 1, Ho Chi Minh City, Vietnam; 3 International Rice Research Institute, DAPO 7777, Metro Manila, Philippines For correspondence; email: ntlang@hcm.vnn.vn ABSTRACT The development of high yielding rice varieties tolerant to submergence (flash flood) has been conducted in collaboration with IRRI and ACIAR. Flash flood is considered as major constraints in the rainfed lowland ecosystem of the Mekong Delta in wet season. Our goals focus on the advantages of molecular biology and genetics to develop rice varieties that have higher and more stable yield in saline and acid-sulphate areas as well as in areas affected by submergence. Base on the molecular biology research, it will assist in identifying genes that tolerate to different abiotic stresses. Furthermore, the basic information on the genetics of additional mechanisms and QTLs can help us combine them through conventional and marker-assisted breeding in high-yielding cultivars to achieve higher levels of tolerance. The integration of conventional and modern methods should be paid attentions, including the application of recent scientific achievements in order to improve the scientific basis for the further development of Vietnamese rice production, to build up genetic stocks and improve phenotypic evaluation methods. Marker-assisted selection (MAS) has proven a powerful tool in rice breeding programs and has been using extensively in submergence tolerance of locally- adapted rice varieties and elite lines. A further development of MAS is marker- assisted backcrossing (MABC). This technique is used for submergence tolerance (SUB1 gene). Keywords: marker-assisted breeding, marker-assisted backcrossing, submergence (flash flooding), quatitive traits loci (QTLs) INTRODUCTION Mekong River Delta is a one of the most important granary for the global rice supply, any deterioration of the production levels would threaten food security in a large scale. Higher water level in vast parts of the Mekong Delta if the sea level rises, resulting in more flooding. A vulnerability and risk need to be analysed to agricultural ecosystems and for flood forecasting and warning higher risks for rice production in the Mekong delta. Flash flood occurred in short period resulted in the hard afford in rice production, sometime it combined to salt intrusion due to sea level rising. Flash flood occurred more often during November and December in short period. Flash flood lasts for 7-10 days at the early stage of the rice plants, mostly after direct seeding. Factors cause flash flood to be considered as: a relatively low level of the rice field, high tides, heavy rains, typhoon affects. Farmers are not able to predict flash flood situation. Thus, it causes dead of the rice plants, usually at the early stage. To overcome this situation, farmers replant and filling the gaps with seedlings or seed broadcasting Omonrice 19: 27-39 (2013)