Plant Height vs. Mesocotyl and Celeoptile Elongation in Rice: Linkage or Pleitropism?

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Abstract
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.