Abstract

Differential seed dormancy mechanisms arise among plant provenances and biotypes/ecotypes due to adaptations to local environmental cues that synchronise seed germination with optimal periods for seedling survival. This is one of the likely sources of unpredictable and variable germination often noted in semi-domesticated plants such as Cloeme and Amaranthus species. To test this, a study was conducted under laboratory conditions in which two provenances of Cloeme gynandra L. that differed in pod sizes and two biotypes that differed in leaf markings in each of the species, Amaranthus hybridus L. and Amaranthus retroflexus L. were subjected to pre-treatments commonly used to break seed dormancy. The study revealed marked differences in the expression of seed dormancy and sensitivity to pre-treatments for breaking seed dormancy between biotypes in each of the three species. The differences were interpreted to reflect eitherhabitat-specific traits in C. gynandra biotypes, which came from different environments or genetic differentiation in A. hybridus and A. retroflexus biotypes, which came from similar environments. Furthermore, the results indicated two types of responses to gibberellic acid (GA₃) in positively photoblastic seeds. In one type, GA₃ replaced light requirements for seed germination. In the second type, light and GA₃ were synergistic in breaking seed dormancy.

Key words: Gibberellic acid (GA₃), germination requirements, light, manure leachate, photoblastic seeds, seed germination, smoke.