ANNUAL SEED DORMANCY CYCLES IN 2 DESERT WINTER ANNUALS

1 Freshly matured seeds of Eriogonum abertianum Torr. and Eriastrum diffusum (Gray) Mason and those of both species exhumed after various periods of burial in the Chihuahuan Desert in Arizona, USA, were tested for germination in light and darkness at five thermoperiods. 2 Seeds of Eriogonum were nondormant (ND) at maturity in autumn 1988, and thus 87% of them germinated in light at 15/6 and at 20/10-degrees-C. Seeds entered conditional dormancy (CD) in winter; germination at 20/10-degrees-C decreased to 6% in light. However, a high percentage of the seeds were again ND by autumn 1990. Thus, like seeds of facultative winter annuals in humid, temperate regions, those of Eriogonum have an annual CD/ND cycle, which is characteristic of annuals in unpredictable habitats. 3 Seeds of Eriastrum were dormant (D) at maturity in May 1989. A portion of the seeds after-ripened during summer, and in October 65 and 38% of them germinated in light at 15/6 and 20/10-degrees-C, respectively. Most of the ND seeds re-entered dormancy during winter, but by the following October 92% of them were ND. Thus, like seeds of obligate winter annuals in humid, temperate regions, those of Eriastrum exhibit an annual D/ND cycle, which is characteristic of annuals in predictable habitats. 4 This is the first report of dormancy cycles in seeds of desert winter annuals.