Semidwarf cultivars of rice (Oryza sativa L.) produce shorter mesocotyls and coleoptiles than normal‐height rice. Short mesocotyl and coleoptilelongation can cause poor emergence and inadequate stand establishment. The hypothesis has been that, in rice, plant height and mesocotyl and coleoptile elongation are pleiotropic (i.e., one gene controls more than one plant characteristic). Laboratory, greenhouse, and field experiments were conducted to evaluate the relationship of mesocotyl and coleoptile elongation to stand establishment, seedling vigor, and plant height in rice. The potential length of the mesocotyl and coleoptile of semidwarf and standard cultivars was evaluated in the laboratory. The germplasm lines exhibited inherent differences in mesocotyl and coleoptile elongation. The semidwarf germplasm (‘MI01’ and RU7703008) described this study ranged from 75 to 90 cm in height and showed reduced mesocotyl, coleoptile, and total lengths (mesocotyl + coleoptile), whereas the tall plant types (‘L201’ and ‘Labelle’) had comparatively longer mesocotyl, coleoptile, and total lengths. Significant differences were detected among seeding depths and cultivars in the greenhousexperiment for emergence percentage. The field experiment, which was conducted on a Crowley silt‐loam soil (fine, montmorillonitic, thermic Typic Albaqualt), verified that poor stand establishment at deep planting depths of the semidwarf cultivars was associated with short mesocotyls and coleoptiles. Semidwarf germplasm was developed that can produce a long mesocotyi and coleoptile, which demonstrates that plant height and mesocotyi and coleoptile elongation in rice is not due to pleiotropism but to linkage.

Mesocotyl length is an important character in promoting seedling emergence of direct-seeded rice. Genetic analysis of rice mesocotyl length was conducted using a six parent diallel cross. Generation mean analysis was carried out on parents (P), F1, F2 and backcrosses (B) of three crosses to complement the genetic information from the diallel analysis. Both analyses demonstrated the presence of significant additive and dominance effects. Duplicate type of non-allelic interaction was detected by the generation mean analysis and two crosses showed significant negative dominance gene effect. Dominance was partial and the narrow sense heritability estimate for mesocotyl length was high, indicating the preponderance of the additive effects.Mesocotyl length was negatively but weakly correlated with the coleoptile length and length of the second internode L2. There was no correlation between mesocotyl length and other mature plant characters such as plant height and internode lengths L1, (L~ being the peduncle with subsequent internodes to the base of the plant). Selection for mesocotyl length can therefore be carried out independent of these plant characters and semidwarf rice varieties with long mesocotyl can be developed.

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