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Quantitative Trait Loci (QTL) analyses were conducted in a mapping population of 91 F2 plants derived from a cross between two ahu rice cultivars of Assam, Cheni ahu (dormant, Oryza sativa ssp. indica) and Kolong (non-dormant, Oryza sativa ssp. indica) in order to identify genomic regions affecting seed dormancy and the duration of dormancy. The linkage map based on 70 simple sequence repeat (SSR) markers detected two QTLs for seed dormancy (qSD5, qSD11) and one QTL for duration of dormancy (qSDD5), and came from the dormant parent. The levels of dormancy increased with the presence of any one of the QTLs but qSD5 had larger effect on increasing dormancy, indicating that dormancy could be effectively enhanced by more than one QTL. The QTLs detected could be used to develop near-isogenic lines (NILs) for map-based cloning of seed dormancy in rice, thus to improve the understanding of dormancy of indica rice.

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An efficient in vitro plant regeneration system was established for elite, recalcitrant Malaysian indica rice, Oryza sativa L. CV. MR 219 using mature seeds as explant on Murashige and Skoog and Chu N6 media containing 2,4-dichlorophenoxy acetic acid and kinetin either alone or in different combinations. L-proline, casein hydrolysate and L-glutamine were added to callus induction media for enhancement of embryogenic callus induction. The highest frequency of friable callus induction (84%) was observed in N6 medium containing 2.5 mg l −1 2,4-dichlorophenoxy acetic acid, 0.2 mg l −1 kinetin, 2.5 mg l −1 L-proline, 300 mg l −1 casein hydrolysate, 20 mg l −1 L-glutamine and 30 g l −1 sucrose under culture in continuous lighting conditions. The maximum regeneration frequency (71%) was observed, when 30-day-old N6 friable calli were cultured on MS medium supplemented with 3 mg l −1 6-benzyl aminopurine, 1 mg l −1 naphthalene acetic acid, 2.5 mg l −1 L-proline, 300 mg l −1 casein hydrolysate and 3% maltose. Developed shoots were rooted in half strength MS medium supplemented with 2% sucrose and were successfully transplanted to soil with 95% survival. This protocol may be used for other recalcitrant indica rice genotypes and to transfer desirable genes in to Malaysian indica rice cultivar MR219 for crop improvement.

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rice husk and cotton stalk used in this study are Oryza sativa ssp. indica and Gossypium hirsutum , respectively. Prior to the experiments, the materials were ground in a high speed rotary cutting mill. The particles with the size of 0.125–0.3 mm

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