Seed heteromorphy influences seed longevity in Aegilops

The genus Aegilops belongs to the secondary gene pool of wheat and has great importance for wheat cultivar improvement. As a genus with only annual species, regeneration from seeds in Aegilops is crucial. In several species in Aegilops, spikes produce different seed morphs, both in size and germination patterns. However, little is known about the ecology of seed germination, nor about the seed longevity in this genus. Here we investigated the germination phenology of Ae. neglecta under laboratory and field conditions and assessed longevity of different seed morphs of five additional Aegilops species using controlled ageing tests. Large seeds were short-lived and germinated faster than small seeds in most of the species. Field experiments with Ae. neglecta showed that large seeds of the dimorphic pair germinated 3 months after dispersal in contrast to 14 months for smaller seeds. Differences in longevity were detected not only in dimorphic seed pairs, but also among seeds from different positions on the spike. Our results indicate that different longevities in seed morphs of Aegilops may reflect a different soil seed bank persistence, with smaller seeds able to maintain a higher viability after dispersal than larger ones, thereby spreading seedling emergence over two years. Differences of seed germination and longevities between seed morphs in Aegilops may have important implications for ex situ seed conservation and reinforce the hypothesis of a bet-hedging strategy in the germination ecology of this genus.

A new type of non-deep physiological dormancy: evidence from three annual Asteraceae species in the cold deserts of Central Asia

Although Asteraceae species are important in the cold deserts of Central Asia, little is known about their seed dormancy and germination. We determined dormancy breaking and germination requirements of three annual Asteraceae, Echinops gmelinii, Epilasia acrolasia and Koelpinia linearis. Achenes (seeds) were tested for germination in light and in darkness over a range of alternating temperatures after various periods of burial outdoors and of dry storage. Germination phenology was monitored for seeds sown in irrigated and non-irrigated sand, and temperature requirements for dormancy break were determined under wet and dry conditions. Effects of pericarp and phyllaries on germination of E. acrolasia and E. gmelinii, respectively, were determined. Low percentages of 20-day-old seeds of E. acrolasia and K. linearis were non-dormant and germinated to low percentages over the range of temperatures, whereas all seeds of E. gmelinii were dormant. As seeds of the three species afterripened, they germinated over the range of temperatures. Whether seeds germinated in autumn or spring depended on the amount of sand moisture. Mechanical resistance of the pericarp and phyllaries reduced germination of E. acrolasia and E. gmelinii, respectively. Temperature requirements for germination as seeds come out of dormancy do not correspond to any of the known five types of non-deep physiological dormancy (PD). Thus, a sixth type is recognized in which germination occurs over the same range of temperatures in the early and late stages of dormancy break. Type 6 allows seeds to germinate at high or at low temperatures, whenever sand moisture is non-limiting.

Intermediate morphophysiological dormancy allows for life-cycle diversity in the annual weed, Turgenia latifolia (Apiaceae)

Our aim was to determine the seed dormancy-breaking requirements and type of life cycle of Turgenia latifolia in north-western China. At dispersal in July, only 0–9% of the seeds germinated at 5/2°C, 15/2°C, 20/10°C and 25/15°C; thus, 91% of the seeds exhibited physiological dormancy (PD) and 9% were non-dormant. Also, the embryo was underdeveloped and embryo length : seed length ratio increased from 0.38 in fresh seeds to 0.79 at germination. Seeds buried in dry soil at the four temperature regimes for 12 weeks germinated to ≥50% when tested in darkness at 5/2°C, and those buried at 15/2°C and 20/10°C germinated to ≥50% when tested at 15/2°C. Seeds have intermediate complex morphophysiological dormancy (MPD). PD was broken at high and/or low temperatures, but embryo growth was completed only at low temperatures; gibberellic acid (GA3) promoted germination. Seeds buried under natural conditions during summer germinated to ~70% and ~55% at 5/2°C and 15/2°C, respectively, in darkness in autumn. In a germination-phenology study, cumulative germination was ~20% and ~80% in autumn and spring, respectively. Intermediate complex MPD allows the species to behave as a winter annual and as a short-lived summer annual.

Species-specific environmental requirements to break seed dormancy: implications for selection of regeneration niches in three Lonicera (Caprifoliaceae) species

Environmental requirements for seed germination can operate as an important filter in determining the regeneration niche and ultimately the habitat preference of many plant species. We hypothesize that morphological and morphophysiological seed dormancy may play a major role in habitat selection, because underdeveloped embryos responsible for those dormancy types usually require strict species-specific environmental conditions to grow and to overcome dormancy, imposing marked constraints to recruitment and thus to species distribution. We analyzed the influence of temperature and light on embryo growth and seed germination, as well as germination phenology in three Lonicera (Caprifoliaceae) species. Lonicera xylosteum L. seeds had morphological dormancy. Those of Lonicera etrusca Santi had unusual within-species dormancy variability, with a fraction being able to show both morphological and morphophysiological dormancy. Seeds of Lonicera arborea had deep complex morphophysiological dormancy. The close correspondence between the environmental conditions that each Lonicera species requires to break seed dormancy and their altitudinal range suggests that morphological and morphophysiological dormancies act as important filters in determining the regeneration niches of species, probably because such dormancy mechanisms impose markedly specific environmental requirements during the earlier stages of recruitment.

Seed dormancy and germination phenology of grass weeds and implications for their control in cereals

Seeds of Italian ryegrass perennial ryegrass wild oat winter wild oat phalaris and barnyard grass collected during the 2005/06 season were tested for dormancy and germination phenology between April and December 2006 In laboratory and outdoor environments dormancy was widespread in grass weed but not in ryegrass seeds The seeds of grass weeds had better germination in the outdoor environment than the laboratory In the outdoor environment only 15 of wild oat and winter wild oat 1963 of phalaris and 39 of barnyard grass seed germinated Protracted germination varied between species in two to seven flushes The earliest timing for effective postemergence grass control under the experimental conditions appeared to be about 6 weeks after sowing for wild oats and ryegrasses 12 weeks for phalaris and 14 weeks for barnyard grass The extended germination periods of phalaris and barnyard grass are a challenge to growers in designing a costeffective herbicide programme