Although dormancy in seeds of this species can be broken by scarification, they have physiological dormancy only. Further, based on information in the literature, it is concluded that it is unlikely that any species of Opuntia has physical dormancy. This is the first integrative study of the anatomy, dynamics of water uptake and dormancy in seeds of Cactaceae subfamily Opuntioideae.

No abstract

Embryos in freshly matured seeds of the facultative winter annual Papaver rhoeas are underdeveloped and physiologically dormant; thus, seeds have morphophysiological dormancy (MPD). Seeds lost physiological dormancy during 12 weeks of burial in moist soil at 12 h/12 h daily alternating temperature regimes of 15/5°C, 20/10 °C and 25/15 °C but not at 1 °C. Physiological dormancy was not broken in seeds stored dry at room temperature for 12 weeks. After physiological dormancy was broken, seeds required light for embryo growth (i.e. for loss of morphological dormancy) and consequently for germination. After a 12‐week period of burial in soil at 25/15 °C, seeds that matured in 1997 germinated to 100% in light at 25/15 °C, demonstrating that cold stragification temperatures (≈ 0.5–10 °C) are not required for embryo growth. Thus, seeds have non‐deep simple MPD. During exposure to low winter temperatures (5/1 °C, 1 °C), 52% of the seeds with physiologically non‐dormant embryos entered conditional dormancy and thus lost the ability to germinate at 25/15 °C but not at 15/5 °C or 20/10 °C. The peak of germination for seeds sown in southern Sweden was in autumn, but some also germinated in spring. A higher percentage of seeds that matured in a relatively warm, dry year (1997) came out of MPD and germinated than did those that matured in a relatively cool, wet year (1998) at the same site.

Fresh seeds of oilseed rape (Brassica napus) are reported to be nondormant and nonphotoblastic. However, a portion of the seeds can be induced into a light-requiring state (secondary dormancy) for germination and also exhibit dormancy cycling. Thus, if seeds become buried in the soil they can form a persistent seedbank and become a serious volunteer weed in succeeding crops. The capacity of nondormant seeds of B. napus to be induced into secondary dormancy is contrary to results of studies on fresh nondormant seeds of some other species. A reanalysis of published and unpublished data shows that fresh seeds of this species have some degree of primary dormancy and that there is a significant relationship between primary dormancy and the capacity to enter secondary dormancy. However, most germination tests on B. napus have not been done in enough detail to detect primary dormancy (or not) in fresh seeds of this species. The usefulness of information on the relationship between primary dormancy and the capacity of the seeds to enter secondary dormancy is discussed in relation to management of weedy volunteers of this species.

Low temperatures may inhibit dormancy break in seeds of winter annuals, therefore it was hypothesized that seeds of Capsella bursa-pastoris and Descurainia sophia that mature at high latitudes in late summer-early autumn would not germinate until they had been exposed to high summer temperatures. Consequently, germination would be delayed until the second autumn. Most freshly matured seeds of both species collected in August and September in southern Sweden were dormant. After 3 weeks of burial at simulated August (20/10°C) and September (15/6°C) temperatures, 28 and 27%, respectively, of the C. bursa-pastoris and 56 and 59%, respectively, of the D. sophia seeds germinated in light at 15/6°C. In contrast, in germination phenology studies conducted in Sweden, only a few seeds of either species germinated during the first autumn following dispersal. However, there was a peak of germination of both species the following spring, demonstrating that dormancy was lost during exposure to the low habitat temperatures between late summer and early autumn and spring. Nearly 100% of the seeds of both species subjected to simulated annual seasonal temperature changes were viable after 30.5 months of burial. In the burial study, exhumed seeds of C. bursa-pastoris were capable of germinating to 98-100% in light at the simulated spring-autumn temperature regime (15/6°C) in both spring and autumn, while those of D. sophia did so only in autumn. In early spring, however, seeds of D. sophia germinated to 17-50% at 15/ 6°C. Thus, most seeds of these two annual weeds that mature in late summer do not germinate in the first autumn, but they may do so the following spring or in some subsequent autumn or spring.