Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/2002
Publication Date: 5/1/2003
Citation: Gu, X-Y., Chen, Z-X., Foley, M.E. 2003. Inheritance of seed dormancy in weedy rice. Crop Science. 43:835-843. Interpretive Summary: Seed dormancy contributes to the adaptability of plants in nature and is of considerableimportance in agriculture. To investigate the inheritance of seed dormancy, four dormantlines of rice, including weedy strains `LD', `SS18-2' and `TKN12-2' and a domesticated variety `N22', and four nondormant varieties were chosen to develop F1 and F2 generations. Initial germination investigations using seeds, caryopses, caryopses with pericarp/testa removed, and excised embryos demonstrated that dormancy was imposed by the hull and pericarp/testa. Strains `SS18-2' and `TKN12-2' had strong hull- and weak pericarp/testa-imposed dormancy and a long duration of seed dormancy. Strain `LD' and variety `N22' had strong and moderate pericarp/testa-imposed dormancy, respectively. The average degree of dominance (ADD) for seed germination was greater than 0.7 when non-afterripened seeds were evaluated. The time for ADD to change from a highly positive to a negative value varied with the duration of seed dormancy for the dormant parents, as judged by germination following set periods of afterripening. The rate of ADD change was much less in the crosses with weedy strains. Broad-sense heritability (h2b) was lower for germination of non-afterripened seed (0.64 to 0.76) and highest for germination of partially afterripened seeds at 20 days after harvest (DAH) (0.85 to 0.95)in all the crosses. Heritability for the weedy strain-derived F2 populations remained higher than for the `N22'-derived F2 population during afterripening. At least three and two genes plus modifiers regulating germinability at 20 DAH were detected in the `SS18-2'-derived reciprocal F2 populations and `N22'-derived F2 population, respectively. A positive ADD, a high h2b, and major genes for caryopsis germination at 0 DAH were detected only in the cross with `LD', which had strong pericarp/testa-imposed dormancy. This research demonstrates that weedy strains of rice provide ideal gene resources to elucidate mechanisms of dormancy and to improve resistance to preharvest sprouting.
Technical Abstract: Although seed dormancy is a key characteristic of weedy plants, mechanism governing seed dormancy are unknown. To elucidate mechanism governing seed dormancy in weedy grasses, we must clone and characterize genes that directly regulate this trait. Currently, it is not possible to map-base clone dormancy genes from well characterized species like wild oat because of the large genome size. Thus, we are developing rice, a species with a relatively small genome size, to map-base clone dormancy genes. As a first step, we have cross-pollinated dormant weedy strains of Asian rice with nondormant domesticated strains to develop populations segregating for dormancy. In this contribution, we report on the classical genetic attribute like heritability associated with several populations segregating for hull- and pericarp/testa-imposed dormancy.