The ecological importance of seed dimorphism in corn spurry (Spergula arvensis L.). I. The effects of day length on seed germinability

Spergula arvensis L. (corn spurry) is a heteromorphic species of the Caryophyllaceae family, that produces two types of seeds with a smooth (non papillate, NP) or papillate (P) coat. The plant flowers and produces fruit between May and September, a period marked by a gradual decrease in day length. The objective of this study was to determine the effects of day length on the germinability of heteromorphic seeds. In addition, we examined the frequencies of non papillate and papillate seeds in four populations. Germination tests were performed on seeds harvested from plants grown in a greenhouse under conditions simulating long days (17 hour photoperiod) and short days (12 hour photoperiod). Heteromorphic seeds incubated in water at various temperatures (10-30 degrees C) over a period of 4 weeks remained dormant. Corn spurry seeds had different responses to the addition of nitrate after four weeks of pre-treatment. Both seed morphs kept at a temperature of 10-20 degrees C did not germinate or their germination rates did not exceed 6%. Seeds incubated at 25 degrees C and 30 degrees C broke dormancy. NP seeds from plants growing under long- and short-day photoperiods were characterized by higher germinability than P seeds at both temperatures. The above-mentioned results indicate that variations in light exposure during plant growth and development do not contribute to somatic heteromorphism of S. arvensis seeds. Day length has no significant effect on the germination of heteromorphic seeds. The populations were heteromorphic with respect to plants having papillate seeds and plants having non papillate seeds. The majority of individuals were monomorphic and produced capsules containing only one type of seed. Heteromorphic individuals produced capsules containing: a) NP seeds, and b) P seeds, and c) mixed seeds. The analyzed populations were characterized by a predominance of P seeds in the overall seed pool.