Molecular Marker Application on Selection of A Rice Backcross Population derived from a Cross between IR64/Hawara Bunar to Obtain Aluminum-Tolerant Rice Lines
Since 1971 the increase of food demand in Indonesia, especially rice is much greater (181.6%) than the increase of population (108%), therefore an effort to increase rice production is unavoidable. Currently, the ability of agricultural land to provide area for rice cultivation tends to decline from year to year due to massive conversion of productive lands into industrial and residential uses. The situation leads to expand rice cultivation into the utilization of marginal lands, such as acid soils for rice cultivation. However, rice cultivation in acid soils will face many constraints, which mainly due to the aluminum (Al) toxicity. The use of Al-tolerant rice varieties with high productivity will be an alternative solution to overcome the Al toxicity problem in acid soils. There is an Indonesian local rice genotype named Hawara Bunar that tolerant to Al stress and can be used as a Al-tolerant donor parent in rice breeding program. However, the potential productivity of the genotype is not as high as rice cv IR64. The use of a backcross population derived from a cross between both genotypes with cv IR64 as a recurrent parent is an approach to develop Altolerant rice cultivar with high productivity. It has been identified that a Quantitative Trait Loci (QTL) for Al-tolerance trait is located on the short arm of rice chromosome 3 flanked by markers RM489 and RM517 (Miftahudin et al. 2008; Akhmad 2009). The objectives of the study were to (1) increase molecular markers density in the area of QTL for Al-tolerance trait on rice chromosome 3 flanked by two SSR markers RM489 and RM517, (2) re-identify QTLs for Al tolerance trait in the previous Al-tolerance QTL area on rice chromosome 3, (3) and carry out marker assisted backcross selection (MABS) ob a rice backcross population derived from a cross between IR64/Hawara Bunar to obtain Al-tolerant rice lines with superior agronomic traits. The research was conducted from September 2009 to May 2012 at the Laboratory of Plant Physiology and Molecular Biology, Department of Biology, Bogor Agricultural University and at the Research Institute for Agricultural Biotechnology and Genetic Resources (Biogen) Bogor. An F2 population derived from a cross between rice cv IR64 and Hawara Bunar were used to increase marker density and re-identify Al-tolerance QTL, while BC2F1 plants and BC2F2 populations that have been developed from the previous and this studies, respectively, were selected through MABS combined with physiological and agronomic characters based selection. An amount of 17 SSR markers were screened for polymorphism between the two parents to obtain markers that being used to increase marker density. Five markers, which were RM2790, RM545, RM14535, RM14543, and RM14552, were polymorphic and could be mapped in between markers RM489 and RM517 with the average distance of 3 cM between adjacent markers. Al-tolerance QTL were identified in the previous QTL location between markers RM2790 and RM14552 (LOD 3.4) based on the Main Root Elongation characters. Foreground and background selections were successfully carried out on BC2F1, BC2F2 and BC2F3 populations using five foreground and 50 background SSR markers. The MABS obtained two BC2F3 rice lines (number 175-63-34 and 175-63-119) carrying 90% background alleles from the recurrent parent. Both lines were tolerant to Al stress and showed good agronomic characters. However, those lines need to be further evaluated in acid soils to verify that those lines are true Al-tolerant lines that can be used to develop Al-tolerant rice variety.