Rate of Change in Dormancy Level and Light Requirement in Weed Seeds During Stratification

Abstract

The rate of change in dormancy level and light requirement, induced during stratification at 3‐2 ∞C, was investigated in seeds of Stellaria media, Cerastium fontanum, Veronica agrestis and Taraxacum ocinale. Two stratification environments, soil and wet filter paper in petri-dishes, were used. On nine occasions during a 6 week stratification period, germination was tested under three light conditions at 3‐5}18‐5 ∞C: (1) darkness; (2) light; and (3) short-term light exposure followed by darkness. Prior to stratification, germination in all species was & 89% in light and & 53% in darkness. Within 2 weeks of stratification, germinability in V. agrestis and S. media seeds decreased in all treatments. In C. fontanum and T. ocinale seeds, germinability also decreased after 2 weeks but only in the dark treatment, indicating induction of a light requirement. After two more weeks of stratification, the induced dormancy in S. media seeds stratified in soil became weaker and the light requirement in T. ocinale seeds was lost. Dierences between the two stratification environments and}or interactions between light conditions, stratification environments and time were found for all species. These results suggest that: (1) the dormancy level and the light requirement of seeds may change dramatically over relatively short-time periods during stratification; and (2) germinability depends on the stratification environment experienced by the seeds. Predicting the dormancy level or light requirement in a seed batch is dicult and requires a thorough knowledge of the eect of the stratification conditions used. # 1997 Annals of Botany Company