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Summary Oryza sativa (weedy red rice), the same species as cultivated rice, is a serious problem in rice production worldwide. Seed dormancy contributes to its persistence. We determined the effect of germination temperature and after-ripening period on germination capacity (GC) of red rice seeds from Arkansas rice fields in three production zones. We also determined the gene diversity (GD) of dormancy-linked loci among selected populations. The germination behaviour was evaluated at three temperatures (1°C, 15°C and 35°C) and four after-ripening periods (0, 30, 60 and 90 days) in two independent experiments. Germination response to temperature and after-ripening time differed among and within populations in each production zone. Overall, populations from the Delta and Grand Prairie were more dormant than those from White River. Regardless of ecotype or production zone, incubation at 35°C (mean GC = 84–100%) favoured the germination of seeds after-ripened for 60 days. Germination of these seeds was most variable at suboptimal temperature (15°C), with mean GC ranging from 44 to 97%; at 1°C, none of the seeds germinated. Primary dormancy was released in the majority of populations after 90 days of after-ripening. Blackhull populations generally had lower mean GC than strawhull populations, regardless of temperature, and required longer after-ripening time to release dormancy. They also showed a higher inter- and intrapopulation variation in germination and after-ripening than strawhulls and had the highest gene diversity (GD = 0.55–0.58) among test populations. Non-dormant strawhulls were most distant (D = 0.63) from dormant blackhulls. Ecotype influenced genotypic clustering more than the dormancy trait. |
