Molecular Breeding to Improve Salt Tolerance of Rice (Oryza sativa L.) in the Red River Delta of Vietnam

Rice is a stable food in Vietnam and plays a key role in the economy of the country. However, the production and the cultivating areas are adversely affected from the threats of devastation caused by the rise of sea level. Using marker-assisted backcrossing (MABC) to develop a new salt tolerance rice cultivar is one of the feasible methods to cope with these devastating changes. To improve rice salt tolerance in BT7 cultivar, FL478 was used as a donor parent to introgress the Saltol QTL conferring salt tolerance into BT7. Three backcrosses were conducted and successfully transferred positive alleles of Saltol from FL478 into BT7. The plants numbers IL-30 and IL-32 in BC3F1 population expected recurrent genome recovery of up to 99.2% and 100%, respectively. These selected lines that carried the Saltol alleles were screened in field for their agronomic traits. All improved lines had Saltol allele similar to the donor parent FL478, whereas their agronomic performances were the same as the original BT7. We show here the success of improving rice salt tolerance by MABC and the high efficiency of selection in early generations. In the present study, MABC has accelerated the development of superior qualities in the genetic background of BT7. 1. Introduction Salinity is one of the major impediments to enhancing production in rice growing areas worldwide. One-fifth of irrigated arable lands in the world has been reported to be adversely influenced by high soil salinity [1]. As per the report of FAO, 2010 [2], over 800 million ha of worldwide land are severely salt affected and approximately 20% of irrigated areas (about 45 million ha) are estimated to suffer from salinization problems by various degrees. This is more serious since irrigated areas are responsible for one-third of world’s food production. In Asia, 21.5 million hectares of land areas are affected by salinity and estimated to cause the loss of up to 50% fertile land by the 21st midcentury [3]. Rice is the most important food crop for over half of the world’s population and supplies 20% of daily calories [4]. Rice is a major crop in Vietnam, as the world’s second-largest rice exporter after Thailand, together accounting for 50% of the world rice trade. Vast portions of the food producing regions in the country will be inundated by sea water, expected to be at about 19.0% ？37.8% of the Mekong River Delta (MRD) and about 1.5% ？11.2% of the Red River Delta (RRD). With sea level rise by 1？m, approximately 40,000？km2 will be inundated, and salinity intrusion is expected to cover about 71% of the MRD and