Correlative Aspects of Imposition of Dormancy in Caryopses of Aegilops kotschyi

Abstract

Caryopses of Aegilops kotschyi Boiss. from different positions within the same spikelet differ greatly in their degree of dormancy. Imposition of this dormancy pattern is a correlative phenomenon within the spikelet, inasmuch as the uppermost developing caryopsis is least dormant and its development is associated with the dormancy status imposed on the lower (one or two) caryopses. Differences in pigmentation of the caryopses follow a corresponding pattern.Spikelets of Aegilops kotschyi Boiss. are normally composed of three florets, of which the terminal one is not fertile. Germinability of the two caryopses which are normally produced differs markedly. The upper one (from the subterminal floret) attains a high capacity for germination shortly after anthesis, while the lower one (from the basal floret) retains a high level of dormancy for a long time (6). The present study was made to investigate the endogenous phenomena involved in the imposition of this differential dormancy within the spikelet. MATERIALS AND METHODSPlants of Aegilops kotschyi Boiss. were grown from mature caryopses, collected as random samples from the natural habitat, near Be'er Sheva, in May 1971. We found that growth at low temperature or with improved mineral nutrition cause a marked increase in the fertility of the terminal floret in the spikelets.In one experiment, plants were grown from seed to full maturity (Dec. 1971-May 1972 in the phytotron of the Faculty of Agriculture of the Hebrew University at Rehovot (2) in 16-hr photoperiods , at day/night temperature regimes of 27/22, 22/22, 22/17, and 17/12 C (day = 0800-1600, night = 1600-0800). The drained plant containers were irrigated each morning with half-strength Hoagland nutrient solution (4), and each afternoon with tap water. In all but the 17/12 C temperature regimes, the plants almost exclusively produced the typical spikelets with two caryopses each. At 17/12 C, about one-third of the spikelets contained caryopses in all three florets.In another experiment, plants were grown from seed to full maturity outdoors, in the natural growing season for this species (Dec. 1971-May 1972 at Bar-Ilan University. A planting medium consisting of sandy loam-vermiculite-peat moss-compost (5:1:1:1) was used. The drained plant containers were irrigated three times each week. One group was irrigated with tap water, the other with half-strength Hoagland nutrient solution. The first group produced typical spikelets with two caryopses each. About one-third of the spikelets produced by the second group contained caryopses in all three florets. The three caryopses thus produced did not differ greatly in mature dry weight. This was true in both experiments, although weight of the phytotrongrown caryopses was almost double that of the ones grown in the open (Table I).Germinability of the different caryopses was tested at 20 C in darkness (interrupted for counting and removal of germinated seedlings) in 9-cm Petri dishes containing one layer Whatman No. 2 filter paper and 4 ml of distilled H20. ...

Seed heteromorphy influences seed longevity in Aegilops

“…and Ae. triuncialis L. dimorphic pairs of seeds are found in the lower fertile spikelets, with one seed larger and lighter coloured than the other one (Datta et al ., 1970; Wurzburger et al , 1976; Dyer, 2004; Marañon, 1989). In Ae .…”

The effects of the parent environment on seed germinability

“…The germination characteristics of grass grains can be altered by surgical abscision of neighbouring grains (Wurzburger and Koller, 1973;Wurzburger and Leshem, 1976), or even by the removal of the glumes alone (Richardson, 1979). The germination characteristics of grass grains can be altered by surgical abscision of neighbouring grains (Wurzburger and Koller, 1973;Wurzburger and Leshem, 1976), or even by the removal of the glumes alone (Richardson, 1979).…”

“…Differences in germinability ('heteroblasty') due to position relative to other seeds is well known in the grasses where proximal grains in spikelets are usually the least dormant, for example in Aegilops ovata (Datta et al, 1970), Avena ludoviciana (Morgan and Berrie, 1970), and Poa trivialis (Froud-Williams and Ferris, 1987). In Aegilops kotschyi, the lower grain is the more dormant one (Wurzburger and Leshem, 1976). Curiously, Wurzburger and Koller (1976) found that in Aegilops kotschyi only the basal caryopsis (but not the upper one) was influenced by the external conditions imposed on the plant during seed development.…”

“…These differences in germinability can sometimes be due to the presence of other seeds in the immediate vicinity. The germination characteristics of grass grains can be altered by surgical abscision of neighbouring grains (Wurzburger and Koller, 1973;Wurzburger and Leshem, 1976), or even by the removal of the glumes alone (Richardson, 1979).…”

Dormancy-Related Seed Positional Effect in Two Populations of an Annual Grass from Locations of Contrasting Aridity

“…Nevertheless, the present findings imply that most probably positional seed dormancy effect in A. sterilis is not a specific desert adaptation against unpredictability of rainfall events. Heteromorphism in A. sterilis appears to evolve initially as a by-product of developmental constraints on seed size within a spikelet with small seeds having higher dormancy because of lower success in competition for essential metabolites or growth regulators [40] . Then, when oat plants started experiencing desert environment as either result of climate changes or range expansion, the positional seed dormancy revealed its usefulness and even necessity in a new environment and became one of the traits conferring adaptation to the desert climate unpredictability.…”