| Seedling vigor is important in direct-seeded rice (Oryza saliva L.). Variation for seedling vigor parameters was studied in growth chamber, greenhouse, and field tests using 27 diverse genotypes. Superior cultivars in temperate japonica and indica varietal groups were identified, notably Italica Livorno (IL; temperate japonica) and Black Gora (BG; indica). Shoot length and weight in slantboard tests, and greenhouse seedling height and emergence index, best predicted field vigor. Temperate japonicas responded least to higher temperature for shoot length, and tropical japonicas responded markedly for root length. Heritabilities estimated using three different methods, were, on average, low for shoot, root, and coleoptile lengths, and high for mesocotyl length.; A linkage map of 117 restriction fragment length polymorphisms (RFLPs) was constructed using 204 Labelle (LBL; low-vigor tropical japonica) X BG F{dollar}sb2{dollar} plants. The map spanned 1496 centiMorgans (cM) with average interval distance of 14.2 cM. Slantboard tests of 172 F{dollar}sb3{dollar} lines at two temperatures (18{dollar}spcirc{dollar} and 25{dollar}spcirc{dollar}C), and interval analysis (LOD = 2.5), detected 13 QTLs for four seedling vigor traits, including three expressed at both temperatures. Single-point analysis confirmed interval mapping results. LBL contributed 46% of positive alleles indicating weak phenotype-genotype correspondence. BG alleles with major effects were not detected for shoot length, suggesting it may not be a good donor parent for seedling vigor enhancement of japonica rice.; The first japonica rice map was constructed of 129 random amplified polymorphic DNAs (RAPDs) and 18 RFLPs using 118 LBL X IL F{dollar}sb2{dollar} plants. This map spanned 980.5 cM with average interval distance of 7.6 cM. Compared to other genetic maps, more markers on chromosome 10, the least marked rice chromosome, and fewer on chromosomes 1 and 2, were identified, percentage-wise. Slantboard screening of 113 F{dollar}sb3{dollar} lines at 18{dollar}spcirc{dollar}C and interval analysis (LOD=2.0), detected 12 seedling vigor QTLs. Single-point analysis identified additional markers influencing each trait. IL contributed two-thirds of positive alleles, including one explaining 18.5% of shoot length variation. Indicas and temperate japonicas possess different seedling vigor genes that could be used in breeding rice for temperate and tropical regions. |
