Inherent Dormancy Research Articles

Seed dormancy revisited: Dormancy‐release pathways and environmental interactions

Abstract Many internal (inherent) and environmental (imposed) factors control seed dormancy and germination that we divide into three basic dormancy‐release pathways: Maternal structures and embryo physiology control inherent dormancy that is broken by various types of scarification and physiological changes, followed by imposed‐dormancy release when the prevailing environment is replaced by certain ‘standard’ conditions that stimulate germination (Pathway 1); imposed dormancy prevails even if inherent dormancy is broken or not applicable that is released when replaced by certain ‘standard’ environmental conditions which stimulate germination (Pathway 2); and release from inherent dormancy by light/dark or cold stratification is contingent on the pre‐existence of certain environmental conditions that stimulate germination (Pathway 3). On‐plant seed storage (serotiny) and frugivorous seeds are recognized here as representing special types of physical dormancy, as their properties are consistent with those of hard diaspores. Warm stratification does not require seeds to be moist as it is just a physical response. Heat may promote germination of non‐hard, as well as hard, seeds as it may increase their permeability further. Levels of germination gauge the net effect of inherent‐ and imposed‐dormancy release so that it is only possible to identify the extent of inherent‐dormancy release when conditions for germination are optimal (imposed dormancy has been annulled). While imposed dormancy may be protracted after inherent dormancy is broken by heat or chilling during the dry or cold seasons, release from both states may effectively coincide if smoke chemicals or light are received during the (wet) growing season. We suggest reserving the term secondary dormancy for seeds that return to (inherent or imposed) dormancy due to changed environmental conditions. Under seasonal climates, fluctuations in environmental conditions can lead to secondary dormancy and even dormancy cycling. We recognize four types of functional interactions between any two environmental factors that induce inherent‐dormancy release: binary interactions are ineffective, only one stimulus is effective, both are effective but non‐additive, or both are additive/synergistic. Two environmental stimuli that individually break dormancy but have no additive effect must be affecting the same process; this was demonstrated here for some interactions between heat and smoke. The three dormancy‐release pathways, together with internal, seasonal and stochastic interactions, are coordinated by the non‐dormant seed to ensure maximum germination under optimal conditions. To ignore any aspect outlined here leads to an impoverished understanding of the disparate seed ecology of species adapted to different stressful and disturbance‐prone habitats. Read the free Plain Language Summary for this article on the Journal blog.

Hyphaene petersiana dormancy and germination

Hyphaene petersiana is a naturally occurring palm tree in Zimbabwe. The tree provides an important supplementary source of income to the communities where it is found, with a high demand for foliage for making baskets and sap for wine making. Propagation is both by vegetative and sexual methods, however, sexual propagation is constrained by the inherent dormancy of the seeds. Breaking seed dormancy is also the first step towards developing a conservation programme for the tree. The effect of water soaking (for 12, 24 and 48 hours), chemical scarification (sulphuric acid for 10 minutes), de-husking (tegument removal), sand papering as well as chemical treatment (thiourea and potassium nitrate) were compared with untreated seeds (control). No germination was observed for seeds treated with sulphuric acid. Water soaking for 12 hours gave the highest germination (71.7%) although not significantly different to other treatments.

Germination Biology of Picralima nitida(Stapf) under Pretreatments

Viable seed sometimes fails to germinate under favourable conditions. The study assessed the germination of Picralima nitida (Stapf) seeds following pretreatments. Fruits were collected from Benin, Southern Nigeria (lat. 6 0 23 1 N and long. 5 0 13 1 E). The seeds were extracted manually and processed for sowing. Seeds were pretreated using ten pretreatment methods: control; soaking in water at 90 0 C and allowing to cool overnight; soaking in water at room temperature; seeds which coats were manually removed; soaking in concentrated sulphuric acid (H 2SO 4) for 1min; 2mins; and 5mins; and soaking in primarily recycled H 2SO 4 for 2mins, 5mins and 10mins. One hundred seeds were assigned to each treatment and replicated in two locations of Akungba (lat. 7 0 28 1 N and long. 5 0 46 1 E) and Ibadan (lat. 7 0 24 1 N and long. 3 0 49 1 E). Seeds were sown in germination trays containing washed-sterilized river sand in the screen house. Germination counts were taken daily. P. nitida exhibited “durian-epigeal” germination, seeds which coats were manually removed were the first batch to germinate 17 and 22 days after sowing (DAS) in Ibadan and Akungba respectively. The highest germination percentage of 100 in Ibadan and 84 in Akungba were obtained among this batch. Seeds soaked in water at room temperature gave 86% germination in Akungba and 63% in Ibadan. Seeds soaked in water at 90 0 C, and primarily recycled H2SO 4 acid for 10mins did not germinate for 106days. Analysis of variance revealed significant differences at P ≤0.05 in treatment and location effects. Mean germination percentage of seeds which coats were removed was significantly different from other treatments. The inherent dormancy in P. nitida seed can be treated by manually removing the seed coat before sowing.

<i>Setaria</i> <i>faberi</i> Seed HeteroblastyBlueprints Seedling Recruitment: III. Seedling Recruitment Behavior

Seedling recruit ment of heterogeneous Setaria faberi seed entering the soil post-abscission is elucidated herein. This is the third in a series of three articles providing evidence that weedy Setaria seedling recruit ment behavior is predicated on dormancy state heterogeneity at abscission (seed heteroblasty), as modulated by environmental signals. Co mplex oscillating patterns of seedling emergence were observed during the first half of the growing season in all 503 soil burial cores of the 39 populations studied. These patterns were attributed to six distinct dormancy phenotype cohorts arising fro m inherent somatic poly morphis m in seed dormancy states (canalized phenotypes). Early season cohorts were formalized using a mixtu re model consisting of four normal distributions. Two, numerically low, late season cohorts were also observed. Variation in emergence patterns among Setaria populations revealed a fine scale adaptation to local conditions. Seedling recruit ment patterns were influenced by both parental-genotypic (time of embryogenesis) and environmental (year, co mmon nursery location, seed age in the soil) parameters. The influence of seed heteroblasty on recruitment behavior was apparent in that S. faberi populations with higher dormancy at the time of dispersal had lower emergence numbers the follo wing spring, and in many instances occurred later, co mpared to those less dormant. Heteroblasty was thus the first determinant of behavior, most apparent in recruit ment nu mber, less so in pattern. Environ ment modulated seedling numbers, but mo re strongly influenced pattern. The resulting pattern of emergence revealed the actual hedge-bet structure for Setaria seedling recruit ment investment, its realized niche, an adaptation to the predictable mortality risks caused by agricultural production and interactions with neighbors. These comp lex patterns in seedling recru it ment behavior support the conjecture that the inherent dormancy capacities of S. faberi seeds provides a germinability 'memory' of successful historical exp loitation of local opportunity, the inherent starting condition that interacts in both a determin istic and plastic manner with environ mental signals to define the consequential heterogeneous life history trajectories.

Preharvest Sprouting Tolerance in Current Soft Red Winter Wheat Cultivars

Preharvest sprouting (PHS) results in unacceptable flour quality for a portion of the mid‐Atlantic soft red winter wheat (SRWW) (Triticum aestivum L.) crop annually. This research evaluates inherent dormancy in current mid‐Atlantic wheat cultivars using grain falling number after delayed harvest and the weighted germination index (WGI) to predict PHS. Individual spikes from 15 wheat cultivars grown in Virginia in 2007 and 2008 were harvested at physiological maturity and seeds germinated under controlled conditions. A WGI was calculated that gave greater weight to cultivars with seeds that germinated more quickly. The WGI effectively identified very high and low dormancy SRWW cultivars; however, the influence of environment during grain fill was important, especially for cultivars with moderate dormancy. To evaluate PHS tolerance by line under natural conditions, plots were left standing up to 6 wk after normal harvest date. Final harvest falling numbers were used to separate cultivars into PHS resistance groups. Strong relationships were found among PHS resistance groups, and WGI was determined at both 10 and 30°C. This indicates that PHS resistance groups were good predictors of dormancy and relative response of cultivars to delayed harvest. The morphological characteristics of head angle, glume tenacity, and awn length had no significant effect on PHS. Artificial wetting resulted in a major loss of quality after just one event, emphasizing the need for timely wheat harvest.

Differential adaptation of high- and low-chill dormant peaches in winter through aquaporin gene expression and soluble sugar content

Plants have their own mechanisms for overcoming various stresses. In cold regions, plants are subject to stress and must enter an inherent dormancy, through several complex mechanisms, if they are to continue to exist. In winter, regulation of tonoplast and plasma membrane aquaporin genes differed in the bud cushions of the high-chill peach (Prunus persica L. Batsch) cv. Kansuke Hakuto and the low-chill peach cv. Coral. In December and January, when the temperature was lowest (around 2 degrees C), the increased expression of Pp-gammaTIP1 and Pp-PIP1 seen in the bud cushions of Kansuke Hakuto may have been related to the concomitant high-soluble sugar content of the cushions of this cultivar. This relationship may have made the cells highly stable and relatively unaffected by low-temperature stress owing to the presence of "glasses" that prevented ice nucleation. However, a simpler form of cold protection regulation seemed to occur in Coral, in which there was no winter increase in Pp-gammaTIP1 and Pp-PIP1 mRNA and a slow decline in total soluble sugar content in December and January. These results suggested that Pp-gammaTIP1 and Pp-PIP1, respectively, play important roles in intra- and intercellular membrane transport, enhancing cold resistance in the bud cushions of high-chill cultivars. In addition, Pp-deltaTIP1 and Pp-PIP2 mRNA increased at the end of endodormancy in both cultivars. This change may be induced by endodormancy-release signals and the resumption of bud activity in both cultivars.

The Effect of Some Mediterranean Scrubland Frugivores Upon Germination Patterns

SUMMARY (1) The probabilty of germination, the length of seed dormancy, and the temporal pattern of germination of five bird-dispersed plant species of an eastern Mediterranean scrubland community varied depending on the plant species, on which of seven bird species they were experimentally fed to, on whether or not they remained covered by pulp, and on whether or not the pulp was experimentally removed before sowing. (2) It is proposed that, in order to withstand the passage through the gut, seeds are protected in a way that may delay their germination after defecation and alter the inherent dormancy, depending on the amount of wear the seeds go through while in the gut. The experimental results suggest that frugivory modifies the length of this dormancy so that the evenness of seedling emergence over time increases as more dispersers, each of which treats the seed in its gut differently, ingest the fruit. This may help to spread the risks encountered during germination, as an adaptation to a relatively mesic environment with an unpredictable rain pattern. (3) Rhamnus palaestinus seeds are encased in a sheath with unique features. It fully protects the seeds during passage through the gut of a disperser, and is shed immediately after defecation. Thus protection does not wear out in the gut, yet germination is not impaired and remains totally independent of gut characteristics of the various dispersers.

GERMINATION RESPONSES TO LIGHT AND ALTERNATING TEMPERATURES IN EUROPEAN POPULATIONS OF DACTYLIS GLOMERATA L.: V. THE PRINCIPLE COMPONENTS OF THE ALTERNATING TEMPERATURE REQUIREMENT.

Detailed germination responses to temperature and light in two populations of Dactylis glomerata L. originating from S.E. Denmark and W. France were defined using thermogradient bars. Despite quantitative differences patterns of response were broadly similar. In both cases seeds were sensitive to the relative periods spent at the warm and cool phases of alternating temperature cycles with germination markedly reduced in diurnal cycles involving a 16 h warm phase and an 8 h cool phase. Whereas the proportion of seeds capable of germination increased sharply as the amplitude of temperature alternation increased the optimum amplitude was dependent on both the period spent at each phase and the presence or absence of light. Even under optimum temperature conditions there was an overriding requirement for light in a high proportion of individuals. When five 21/11 °C cycles of reduced duration were applied at 24 h intervals, 1 h/2 h alternations were as effective in stimulating germination as diurnal cycles. Germination response was directly related to the logarithm of the number of diurnal 21/11 °C cycles applied in three different seed samples. Sensitivity was not related to inherent dormancy status (between populations) or to a degree of after-ripening.

Variation in Lemma Thickness in Indian Ricegrass: Implications for Dormancy, Scarification, and Breeding1

Indian ricegrass [Oryzopsis hymenoides (Roem. & Schult.) Ricker] has been of interest for revegetation of western mine lands, however, high seed dormancy restricts stand establishment. Breeding to improve Indian ricegrass is hampered by this inherent dormancy, often as high as 98%. Scarification to break dormancy using sulfuric acid has been successful but reduction of viability has occurred. This study examined whether the number of seeds damaged by scarification was related to the thickness of the indurate lemma possessed by Indian ricegrass. Twelve strains and cultivars of Indian ricegrass were examined with a range in lemma thickness of 42 to 76 μm. They differed significantly for this trait, which was not affected by environment. Acid scarification treatments of 20, 30, and 40 rain were followed by water rinses. Viability before and after scarification was determined by tetrazolium tests. Lemma thickness had a significant protectiveffect on seed viability after scarification for all three scarification durations. Coefficients of determination (R2) values were 0.56, 0.75, and 0.79 for 20, 30, and 40 min time, respectively. These results indicate that lemma thickness can be utilized to determine proper scarification duration to minimize seed damage while maximizing germination, resulting in uniform stand establishment and evaluation of Indian ricegrass germplasm.

Factors that influence dormancy in milkweed seeds

Seeds of Asclepias syriaca L. (milkweed) have an inherent dormancy and these seeds could be forced to germinate by various treatments including stratification, cutting or removal of the seed coat, gases, alternating temperature, and a number of chemicals. Of the various treatments, the growth regulators kinetin and gibberellic acid were most effective in overcoming dormancy and a combination of these two had a synergistic effect. The increased germination percentage after 5 weeks of stratification was not accompanied by an increase in endogenous gibberellin levels. Treatment of the seeds with abscisic acid after stratification resulted in a complete inhibition of germination whereas treatment with kinetin resulted in an increase in germination. It is concluded that dormancy in milkweed seeds could be broken by many factors and regulated by an intricate interplay between growth promoters and inhibitors.

Dormancy in Barley

WHEN applied to germination, ‘dormancy’ and ‘maturity’ are not precise terms, and their meaning therefore depends on the particular test which is used. The data in my communication1 relate to tests in which the conditions were optimal, in all respects, for the germination of barley grains. Complete germination was obtained immediately after the drying treatment, and must necessarily be attributed to the removal of inherent dormancy in the grains which would riot otherwise germinate. There is the further significant fact that this response was not only obtained during storage after harvest, but also when the grains were ripening, and at the harvest-ripe stage.

THE EFFECT OF MECHANICAL DE-WINGING OF PINUS PINASTER SEED

SUMMARY The 1951 work (Harding 1952) was continued in 1952 and in addition to corroborative work the effect of stratification was made clear. This paper shows firstly the danger of using unsuitable winnowers and secondly how inherent dormancy has clouded the issue, both in the past and in the early stages of the 1952 investigation. The project is technologically completed but it is postulated that fundamental reasons for seed phenomena dealt with might be worth investigation.

PHYSIOLOGICAL STUDIES OF WEED SEED GERMINATION

The persistence of many annual and winter annual weeds on the grain farms of Western Canada is closely related to the tendency of their seeds to remain viable in the soil under conditions favorable for the germination of most crop species. Irrespective of competing ability, prolific seeding, and other plant habits, it is only by the relatively narrow germinative responses of its seeds that an annual species can persist under frequent summer-fallowing, spring and fall cultivation, and the hazards of low winter temperatures, drought, and plant competition. Darlington (9) and Toole and Brown (23) have reported two of the classical experiments on the longevity of weed seeds. They showed that seeds of many species may live in a moist soil for several decades without germinating. Toole and Brown point out that while the seeds of many Leguminoseae had to be scarified at the completion of the test before they would germinate, seeds of a number of species that had remained in the soil for 39 years had seed coats which were pervious to and had taken in water during the test. A viable seed which is not in active growth is considered as being in a dormant condition. A seed may be in a state of dormancy because of the lack of one or more essential conditions for its development, a condition termed in this paper environmental'' dormancy. Or the seed may be under a satisfactory germinative environment but be in a state of dormancy because of some physiological condition. This is considered as inherent'' dormancy. The terms environmental and as applied to dormancy are synonymous with the terms induced and natural as used by Brenchley and Warington (3). They are preferable, however, since they are more descriptive of the condition. Also, the term induced was used previously by Kidd and West (16) in discussing the type of dormancy which developed in seeds of Brassica alba in high partial pressures of carbon dioxide. The two types of dormancy, inherent and environmental, are not always as distinct as they would at first appear, since the requirements for the germination of a particular seed may vary somewhat with its degree of inherent dormancy. Crocker (8) divides inherent dormancy into primary and secondary types. Primary dormancy usually exists from maturity of the seed until it is ready to germinate for the first time. This type of dormancy is reported as being due to a seed coat which interferes with water adsorption, gaseous exchange, or expansion by the embryo, or to a direct