Release and induction of dormancy in seeds of red rice (Oryza sativa L.) in the field and laboratory

The release and induction of dormancy in seeds of three red rice phenotypes common in Mississippi and the Nato variety were investigated under field and laboratory conditions.;Dormancy in seeds retained in air storage near the panicles in simulated delay-in-shattering experiments was released much more rapidly than in those that shattered early and remained in contact with the soil. Prolongation of the dormancy period in the early shattered seeds through contact with the soil reduced fall germination and winter-kill, and increased emergence the following spring when conditions were favorable for completion of the life cycle of rice. The early shattering trait in the weedy red rices appears to be an adaptation for survival in a temperate climate. The beneficial effects of early shattering in terms of over-winter survival were more pronounced under marshy conditions, and increased as intensity of dormancy increased among the genotypes.;Drench treatments of red rice seeds buried 2.5 cm in soil with dilute solutions of ethylene chlorohydrin and, to a lesser extent, sodium hypochlorite were effective in releasing dormancy. The results obtained were sufficiently interesting to recommend serious additional study in the context of weed control programs in rice.;Deeply buried (20 cm) seeds of red rice exhibited cyclical changes in germinability and dormancy that corresponded to seasonal rhythms in soil temperature. This periodicity in germinability/dormancy ensured that the seeds were in a non-dormant state in spring when conditions were favorable for germination and completion of the life cycle, and dormant in late summer and fall when conditions were not favorable due to the approach of winter. Secondary dormancy in rice was easily induced under controlled laboratory conditions by storing partially imbibed seeds (18% moisture content) at 20 or 30C for 2 mo.;Non-dormant red rice seeds planted in the field in winter time (Dec.) died and decayed without germinating, while dormant seeds remained dormant and survived to emerge in April when conditions were favorable. Dormancy, therefore, protected the seeds from the winter-time stress of freezing temperature.