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.
An advanced backcross line, WH29001, was produced from a single plant from BC 5 F 3 families derived from a cross between Oryza minuta (2n = 48, BBCC, Acc. No. 101141) as a donor parent and the O. sativa subsp. japonica cv. Hwaseongbyeo as a recurrent parent. Although WH29001 resembled Hwaseongbyeo, several traits were different from those of Hwaseongbyeo, including awn length and heading date. These differences between Hwaseongbyeo and WH29001 could be attributed to the introgressed O. minuta chromosome segments into WH29001. SSR analysis enabled to identify thirteen O. minuta-specific chromosome segments in WH29001 genome. To map and characterize QTLs for awn length and heading date, an F 2:3 population from the Hwaseongbyeo/WH29001 cross was developed. The 197 F 2 plants and 197 F 3 families were evaluated for the two traits and the genotypes of the 197 F 2 plants were determined using eighteen SSR markers located in the introgressed segments from O. minuta. QTL analysis identified two QTLs each for days to heading and awn length on chromosomes 6 and 9, respectively. The total phenotypic variance explained by these four QTLs ranged from 8.1% to 51.0% in the F 3 population. Interestingly, QTLs for heading date and awn length were colocalized on chromosomes 6 and 9, respectively. Among these QTLs identified, the QTLs for heading date (dth9) and awn length (awn6) had not been detected in previous QTL studies between Oryza cultivars, indicating the existence of potentially novel alleles from O. minuta. The QTLs detected in the present study could become a valuable source of natural genetic variation underlying the evolution of rice.
Submergence stress regularly influences about 15 million hectares of rice growing areas in South andSoutheast Asia. Vietnam is one of the most vulnerable countries affected by submergence stress in Asia. Submergence caused by typhoons and floods is one of the major reasons for rice production losses in this country. A major quantitative trait locus (QTL) on chromosome 9, SUB1, has provided the opportunities to apply marker-assisted backcrossing (MABC) to develop submergence tolerant for an elite variety that is popularly grown in Vietnam. Improving rice tolerance with submergence is vital to minimize the risks from submergence stress. In this study, we reported a successful application of MABC method to select a line number 19 in BC 2 F 1 populations that has genetic background up to 89.8%.Key words: Bac Thom 7 (BC7), marker-assisted backcrossing (MABC), submergence tolerance. INTRODUCTIONIncreases in submergence stress caused by climate change are the major impediments to enhancing production in rice growing areas worldwide. The most common and damaging type of flooding is short-term inundation (up to 2 weeks), also referred to as flash floods. This type of flooding is estimated to affect about 20 million ha of rice growing areas in Asia (excepted China) as well as significant areas of lowland rice production in Africa Mackill et al., 2012). Moreover, due to adverse effects from climate change, these seasonal flash floods are extremely unpredictable and may occur at any growth stage of the rice crop (Ronald, 2012). Submergence of rice (Oryza sativa) during the monsoon flooding season severely limits rice production in South and Southeast Asia, causing annual losses of over one billion U.S. dollars (Xu *Corresponding author. E-mail: khanhkonkuk@gmail.com. Tel: 84-916-451018. et al., 2006;Manzanilla et al., 2011). Vietnam is one of the countries hardest hit by climate change in Asia. Adverse effects cause by annual floods is a big problem in this country; by the year 2011, more than 10.000 hectares of rice areas were inundated by floods, which caused significant economic losses (MARD, 2011). Temperature would rise by about 2.3°C and sea level rise by 75 cm relative to the average of 1980 to 1999 by the end of the 21st century. Vast portions of the food producing regions in the country will be inundated by flood including rise of sea water, expected at about 19 to 37.8% of the Mekong River Delta (MRD) and about 1.5 to 11.2% of the Red River Delta (RRD). With water rise by 1 m, approximately 40,000 km 2 will be inundated (MARD, 2005).Rice is the most important food crop for over half of the world's population and supplies 20% of daily calories (WRS, 2010). Rice is a major crop in Vietnam, as the world's second-largest rice exporter after Thailand, and together accounting for 50% of the world rice trade. However, rice yield and its cultivating areas are adversely Khanh et al. affected by the threats of devastation caused by typhoon and flash flooding which are inducing significantly economic loss in this country...
Northern Vietnam is one of the most important centers of genetic diversity for cultivated rice. Over thousands of years of cultivation, natural and artificial selection has preserved many traditional rice landraces in northern Vietnam due to its geographic situation, climatic conditions, and many ethnic groups. These local landraces serve as a rich source of genetic variation—an important resource for future crop improvement. In this study, we determined the genetic diversity and population structure of 79 rice landraces collected from northern Vietnam and 19 rice accessions collected from different countries. In total, 98 rice accessions could be differentiated into japonica and indica with moderate genetic diversity and a polymorphism information content of 0.382. Moreover, we found that genetic differentiation was related to geographical regions with an overall PhiPT (analog of fixation index FST) value of 0.130. We also detected subspecies-specific markers to classify rice (Oryza sativa L.) into indica and japonica. Additionally, we detected five marker-trait associations and rare alleles that can be applied in future breeding programs. Our results suggest that rice landraces in northern Vietnam have a dynamic genetic system that can create different levels of genetic differentiation among regions, but also maintain a balanced genetic diversity between regions.
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