SEED GERMINATION STUDIES IN MUSA. I. SCARIFICATION AND ASEPTIC GERMINATION OF MUSA BALBISIANA

Stotzky , G., Elsie A. Cox , and Roger D. Goos . (Central Research Labs., United Fruit Co., Norwood, Mass.) Seed germination studies in Musa. I. Scarification and aseptic germination of Musa balbisiana . Amer. Jour. Bot. 49(5): 515–520. Illus. 1962.—Methods for germinating seeds of Musa balbisiana Colla under aseptic conditions have been developed. Scarification was required for germination under these conditions, and mechanical was superior to chemical scarification. Various methods of mechanical scarification and cultural procedures were developed which facilitated the operation when large numbers of aseptic seedlings were required. Removing a chip from the lateral portion of the seed coat to expose the endosperm was the most effective method of scarification: germination percentages averaged 80%, and the time required for germination in sterile culture was shortened from the 3–6 weeks required for intact seeds in soil to 6–10 days. However, scarification did not shorten the time required for germination in soil, and seeds treated with some methods of mechanical scarification failed to germinate, as a result of their decomposition by microorganisms. The effectiveness of scarification in causing germination in aseptic culture is not presently understood, but, as the excised embryo exhibits no dormancy, the factors delaying germination apparently reside in other portions of the seed.     

林线树种太白红杉种子萌发的生理生态特性

 太白红杉(Larix chinensis)是太白山的高山林线树种。通过在人工气候室内的试验,研究了太白红杉种子在6种不同的光照与温度组合处理条件下的萌发特性。结果表明：在恒温和变温两种条件下,交替光照对于种子吸胀后的脱落酸（ABA）和赤霉素 (GA)有刺激作用。在恒温条件下,持续光照对于种子吸胀后的生长素 (IAA)有刺激作用,而变温条件下交替光照对生长素有刺激作用。细胞分裂素（CTK）的变化情况与IAA相反。光照条件相同时,恒温条件下的植物激素含量要高于变温条件下的含量,说明恒温对于各种激素有刺激作用。在25 ℃环境下种子的萌发率高于在12 ℃环境下的萌发率,说明温度对于种子的萌发有重要作用。太白红杉种子的萌发受交替光照（12 h光照/12 h黑暗）的刺激;恒温（25 ℃）条件下的种子萌发率高于变温（12 ℃/25 ℃）条件下的种子萌发率。实验结果反映了内源激素在太白红杉种子萌发过程中起着重要作用。     

THE EFFECT OF SALINITY AND TEMPERATURE ON THE GERMINATION OF POLYMORPHIC SEEDS AND GROWTH OF ATRIPLEX TRIANGULARIS WILLD.

Polymorphic seeds of Atriplex triangularis were germinated at various temperatures (5–15 C, 5–25 C, 10–20 C, 20–30 C) and salinity regimes (0 to 1.5% NaCl) in order to determine their germinability and early seedling growth under these conditions. Larger seeds generally had a higher germination percentage in saline medium. The rate and percentage of germination decreased with increased salinity stress. A thermoperiod of 25 C day and 5 C night, 12 hr/12 hr, temperature enhanced germination of seeds. Early seedling growth is promoted in larger seeds at lower salinity, and at high-day and low-night temperatures. Polymorphic seeds have different physiological requirements which provide alternative situations for seed germination in natural habitats.     

GERMINATION ECOLOGY OF PHACELIA DUBIA VAR. DUBIA IN TENNESSEE GLADES

The germination characteristics of a population of the winter annual Phacelia dubia (L.) Trel. var. dubia from the middle Tennessee cedar glades were investigated in an attempt to define the factor(s) regulating germination in nature. Factors considered were changes in physiological response of the seeds (after-ripening), temperature, age, light and darkness, and soil moisture. At seed dispersal (late May to early June), approximately 50 % of the seeds were non-dormant but, would germinate only at low temperatures (10–15 C). As the seeds aged from June to September, there was an increase in rate and total percent of germination at 10, 15, and 20 C, and the maximum temperature for germination increased to 25 C. Little or no germination occurred at the June, July, and August temperatures in 0- to 2-month-old seeds, even in seeds on soil that was kept continuously moist during this 3-month period. At the September, October, and November temperatures 3- to 5-month-old seeds germinated to high percentages. In all experiments seeds germinated better at a 14-hr photoperiod than in constant darkness. Inability of 0- to 2-month-old seeds to germinate at high summer temperatures allows P. dubia dubia to pass the dry summer in the seed stage, while increase in optimum and maximum temperatures for germination during the summer permits seeds to germinate in late summer and early fall when conditions are favorable for seedling survival and eventual maturation.     

GERMINATION ECOPHYSIOLOGY OF THE WOODLAND HERB OSMORHIZA LONGISTYLIS (UMBELLIFERAE)

Osmorhiza longistylis is an herbaceous perennial that grows in woodlands of eastern and central North America. In northcentral Kentucky seeds ripen in early to mid July, and dispersal begins in September and October. Although most of the seeds are shed during late autumn and winter, some remain on the dead shoots for up to 18 months. Seeds are dormant at maturity due to an underdeveloped embryo. Embryos grew at low (5 C) temperatures, but only after seeds were given a period of warm (30/15 C) stratification. With an increase in the length of the warm treatment, there was an increase in the number of embryos that grew to full length during a 12-wk period at 5 C and an increase in the percentage of seeds that germinated. Seeds given 12 wk of warm stratification required more than 8 wk at 5 C to overcome dormancy. Embryos in freshly-matured seeds averaged 0.60 mm long, but those in seeds given 12 wk warm plus 12 wk cold stratification averaged 8.86 mm. Lengths of embryos of seeds kept moist at 30/15 and 5 C for 24 wk averaged 0.63 and 0.89 mm, respectively. Regardless of age and dispersal time, imbibed seeds must be exposed to high (i.e., summer or autumn) and then to low (i.e., winter) temperatures before they will germinate. Consequently, germination occurs only in spring.     

GERMINATION ECOLOGY OF DANTHONIA SERICEA POPULATIONS

Seed were collected from nine populations of Danthonia sericea on either wet or well-drained, sandy sites ranging from Georgia to New Jersey. Germination tests were conducted in the laboratory and in field plots established on contrasting habitat types. Factors considered were temperature, light, prechilling, scarification, and after-ripening. The majority of freshly harvested seed from all nine populations exhibited innate dormancy the intensity of which decreased with age. Dormancy was removed by scarification and prechilling treatments of 60 days. Seed from wet habitats showed significantly greater germination in light (alternating night-day) than in dark, while seed from well-drained habitats had a higher germination percentage in dark than in light. Both responses are considered to be physiological adaptations of the populations to their respective habitats. Alternating night-day temperatures of 15–25 C produced the greatest overall germination for the nine populations; 15–20 and 10–25 C produced the next highest responses. Field observations confirmed that peak germination occurred in the spring, at the time soil temperatures were in the same range found to be optimum in the laboratory. A comparison of the germination responses obtained from six New Jersey populations in field plots on contrasting habitat types further revealed distinctive physiological adaptations for populations from differing habitats.     

Ethylene Inhibition of Phytochrome-Induced Germination in Potentilla norvegica L. Seeds

Germination of Potentilla norvegica L. (rough cinquefoil) seeds stimulated by fluorescent irradiations of nearly 24 hours was inhibited by ethylene at <1 microliter per liter. Sensitivity to ethylene inhibition was highest during and immediately after the irradiation. By delaying ethylene treatment until about a day after the light potentiation, seeds escaped the inhibition. Ethylene inhibition may be readily reversed upon release of the gas and reirradiation of the seeds. Imbibition of seeds at 10 or 15°C, or at high temperatures of 35 and 40°C, partially prevented subsequent inhibition by ethylene. Alternating temperatures during germination nearly overcame the inhibition from 1 microliter per liter ethylene, but not higher doses. With brief red-irradiation and alternating temperatures, 0.1 microliter per liter ethylene promoted germination about 2-fold. These data suggest that ethylene may loosely associate on a site required for phytochrome action. The effect of temperature that opposed the inhibition may be to deny the association of ethylene with the site. Loose association is supported by the reversal of inhibition by gas release and increased temperature during germination. A blocking effect was shown by the failure of phytochrome to act when ethylene was present.     

STUDIES ON THE SEED OF BANANA. II. THE ANATOMY AND MORPHOLOGY OF THE SEEDLING OF MUSA BALBISIANA

Mc Gahan , Merritt W. (Central Research Labs., United Fruit Co., Norwood, Massachusetts.) Studies on the seed of banana. II. The anatomy and morphology of the seedling of Musa balbisiana. Amer. Jour. Bot. 48(7): 630–637. Illus. 1961.—The first external evidence of germination of the seed of Musa balbisiana is the displacement of the micropylar plug by the elongation of the hypocotyl-radicle axis. As the hypocotyl and epicotyl emerge from the micropylar collar, the seminal adventitious roots become apparent and the cotyledonary sheath surrounding the epicotyl emerges as a coleoptile-like structure. Subsequent growth results in the elongation of the first leaves beyond the cotyledonary sheath and the rapid elongation of the adventitious root system. The vascular transition occurs between the cotyledon and the radicle. The sheath is considered to be only analogous to the coleoptile of the grasses.     

FACTORS AFFECTING GERMINATION IN GREENHOUSE-PRODUCED SEEDS OF OXALIS CORNICULATA,A PERENNIAL WEED

A study was conducted to investigate the physiological responses of greenhouse-produced Oxalis corniculata seeds to light, temperature, moist heat treatment, aging, and season of production. Fresh seeds exhibited over 90% germination and required low levels of light (5 μmol m^-2 s^-1, 400–700 nm) to germinate. Seeds germinated over a broad, yet seasonally-dependent range of incubation temperatures. Seeds produced in winter had the narrowest temperature range of germination (15 to 25 C) and the lowest germination percent (44% at 2 wk) at optimum temperature (17 C); seeds produced in summer had the widest temperature range of germination (10 to 30 C) and the highest germination percent (93% at 2 wk) at optimum temperature (17 C). Incubation at non-optimum temperatures between 5 and 40 C suppressed or slowed the rate of germination until seeds were placed at optimum temperature, where full germination subsequently occurred. Moist heat treatment at temperatures over 40 C resulted in varying degrees of inhibition of subsequent germination. When seeds were stored dry in laboratory conditions, three of four seed lots examined retained over 80% germination capacity until ca. 8 months; 50% capacity remained after ca. 15 months. These results indicate that the seasonal temperature and daylength effects on maternal plants in the greenhouse environment are major determinants of seed germination characteristics of O. corniculata.     

THE GERMINATION STRATEGY OF OLDFIELD ASTER (ASTER PILOSUS)

At maturity in November, a high percentage of Aster pilosus Willd. seeds germinated in light at high temperatures (30/15, 35/20 and 40/25 C). Stratification during winter lowered the temperature requirement for germination, and high percentages of germination were obtained in light at 15/6 and 20/10 C., as well as at 30/15, 35/20 and 40/25 C. Stratification in darkness was completely ineffective, but stratification in light was partially effective in overcoming the light requirement for germination. Inability of seeds to germinate at low temperatures prevents germination after dispersal in late autumn and winter, when freezing temperatures could kill the seedlings. The lowering of the temperature requirement for germination during winter stratification allows the seeds to germinate and the resulting vegetative rosettes to become well established before the onset of the periodic summer droughts that occur in habitats occupied by A. pilosus.     

GEOGRAPHIC DIFFERENCES IN THE SEED GERMINATION OF PAPER BIRCH (BETULA PAPYRIFERA)

The effects of light and temperature on germination of paper birch (Betula papyrifera Marsh.) were examined in seeds from different geographic locations. Under continuous light at 14–18 C northern seed sources germinated more rapidly and achieved higher germination percentages than southern ones. Seed source influenced the range of temperatures over which germination occurred. Northern seeds had a wider temperature range than southern ones due to depression of the low temperature limit in northern seeds. At 15 C, seeds exhibited a photoperiodic-like response with progressive increases in germination as daily photoperiod was increased. This was not a true photoperiodic effect because seeds responded to the total amount of light rather than to the relative length of light and dark periods. It is suggested that at temperatures near 15 C, this response may be important in preventing fall germination. Prechilling at 3 C promoted subsequent dark germination in most seed sources tested, and northern seeds were much more sensitive to the treatments than southern seeds. In some seeds the prechilling stimulus was lost with protracted storage at 3 C; this was observed in both northern and southern seeds. Prechilling enhanced the seeds’ sensitivity to subsequent light. Although acquisition of the prechilling stimulus does not serve to measure the length of winter in these seeds, the high light sensitivity induced by prechilling probably accelerates spring germination. Northern seeds typically had thinner, more translucent pericarps than their southern counterparts.     

SOME EFFECTS OF GAMMA IRRADIATION ON SEEDS AND RHIZOMES OF MUSA

The tolerance of Musa balbisiana Colla seeds to gamma irradiation was found to be considerably greater than that of rhizomes of the parthenocarpic variety ‘Gros Michel': e.g., 11.8 krad reduced the germination of rhizomes 92% and of seeds approximately 15%. Intact seeds exposed to doses higher than 48 krad did not germinate in non-sterile soil, but, when scarified and cultured axenically after irradiation, seeds which received doses as high as 70 krad germinated. Embryos excised from seeds exposed to doses as high as 285 krad formed callus, indicating that not all metabolic processes were inhibited by these extremely high doses. There was considerable variation in radiation tolerance between seed lots which was not related to their age, moisture content, or pre-exposure viability. Germination of intact seeds appeared to be stimulated by doses of 3 or 9 krad. No lasting differences attributable to the level of irradiation were apparent in the development of seedlings derived from either intact or scarified seeds nor of plantlets derived from excised embryos. Conversely, there was a significant reduction, proportional to irradiation dose, in the growth of plants developing from rhizomes, emphasizing the greater radiation sensitivity of the vegetative propagule. The radiation tolerance of seed-borne microorganisms was considerably higher than that of the plant materials, indicating that gamma irradiation is not effective as a means of obtaining pathogen-free rhizomes or surface-sterilizing seeds of M. balbisiana.     

EFFECT OF STRATIFICATION TEMPERATURE AND GERMINATION TEMPERATURE ON GERMINATION AND THE INDUCTION OF SECONDARY DORMANCY IN COMMON RAGWEED SEEDS

Stratification of common ragweed (Ambrosia artemisiifolia) seeds at 4 C was most successful for breaking dormancy, whereas -5 C was least effective and 10 C was intermediate. Germination in the light exceeded that in the dark at all stratification and germination temperatures. The optimum temperatures for germination in the light were 10/20, 15/25, and 20/30. Maximum germination in the dark occurred at 20/30 C for seeds stratified at 4 and 10 C but the optimum temperatures for seeds stratified at -5 C were 10/20, 15/25, and 20/30. Seeds stratified at -5 and 10 C germinated best after 15 weeks of stratification, whereas 12 weeks of stratification at 4 C resulted in maximum germination. Secondary dormancy was induced in seeds which did not germinate in the dark. This was affected by stratification temperature and duration and germination temperature. The ecological significance of these germination characteristics is discussed.     

FACTORS INFLUENCING SEED GERMINATION IN SALICORNIA PACIFICA VAR. UTAHENSIS

The halophyte, Salicornia pacifica var. utahensis (Tiderstorm) Munz produces seed under high salinity conditions, and deposits its seed on saline soil. Experiments were conducted to determine the effect of salinity, temperature and growth regulators on germination. Results indicate that the seeds can germinate at very high salt concentration (5% NaCl). Germination was sensitive to the changes in temperature regimes. At higher 30–20 C, light-dark sequence, no germination occurred at 3, 4 and 5% NaCl treatments. On the other hand, 30% germination did occur at 5% NaCl treatment at a temperature regime of 15–5 C. These seeds required light for germination. Only 50% germination occurred in the non-saline control in the dark and the addition of NaCl further reduced germination. The GA₃ partially alleviated the inhibitory effect of NaCl and darkness. Kinetin did not promote germination.     

GERMINATION AND GROWTH OF CELOSIA CRISTATA L., UNDER VARIOUS LIGHT AND TEMPERATURE REGIMES

Continuous light or alternating light and dark appear to be necessary for good germination of Celosia cristata L. As temperature increased up to 31 C so did germination; thereafter, it decreased. There appears to be a preference for high constant or high alternating temperatures in germination. As light intensity decreased so did growth in terms of leaf area, dry weight and relative growth rate. Proportionally more leaf is also made and leaf:area ratio increased. However, root weight ratio decreased. Although both high light intensity and high temperature are required for the good growth of Celosia, temperature appeared to be more important than light. A reduction of less than one-third of full light may not cause a significant reduction in growth. The results explain the observed differences in the nature of C. cristata in the field as well as its distributional limits.     

The joint action of phytochrome and alternating temperatures in the control of seed germination in Dactylis glomerata

The promoting effect of light and alternating temperatures on the germination of seeds of three contrasting populations of Dactylis glomerata L. was studied. Irradiation treatments using broad band low irradiance light sources resulted in red/far-red reversible effects, demonstrating the involvement of phytochrome in germination control. Reduction of germination by far-red below the level of a dark control indicated the presence of high pre-existing levels of the active form of phytochrome (P_fr) in some individuals. The capacity for dark germination at 21/11°C (12 h/12 h) was shown to be dependent on P_fr. Although some individuals were capable of germination at constant temperatures following red irradiation, in most seeds germination was dependent on the presence of P_fr and alternating temperatures. Some individuals responded to a single red irradiation, although a large proportion of seeds required high levels of P_fr to be maintained for long periods. Previously published dose response curves for alternating temperatures and a measured dark reversion time of 48 h for P_fr established by a single 60 min red irradiation, provided firm evidence of a direct correlation between the requirements for repeated irradiation and number of alternating temperature cycles.     

Light Actions in the Germination of Cocklebur Seeds: III. EFFECTS OF PRE-TREATMENT TEMPERATURE ON GERMINATION RESPONSES TO FAR-RED LIGHT AND ON DARK GERMINATION IN THE RED LIGHT-REQUIRING UPPER SEEDS

Esashi, Y., Oota, H., Saitoh, H. and Kodama, H. 1985. Lightactions in the germination of cocklebur seeds. III. Effectsof pre-treatment temperature on germination responses to far-redlight and on dark germination in the red light-requiring upperseeds.—J. exp. Bot. 36: 1465-1477. Red light (R) responsiveness in R-requiring upper cocklebur(Xanthium pennsylvanicum Wallr.) seeds changed in differentpatterns during a soaking period at different temperatures.At temperatures above 23°C, the responsiveness increasedand then decreased. At lower temperatures (3–18°C),however, it continued to increase throughout an experimentalperiod. The lower temperatures caused germination in the subsequentdark at 33°C, regained the R responsiveness and acquiredthe dark germinability when subsequently exposed to 8°C,to an extent proportional to the duration of the chilling. Far-red (FR) was inhibitory to germination in an earlier soakingperiod at lower temperatures, but its effect gradually decresed,and finally turned promotive. The negative FR response was repeatedlycontrolled by the following R irradiation. However, the positiveFR response was enhanced by an immediate R irradiation, andFR/R reversibility occurred after the second FR. In contrastto the R responsiveness and dark germinability, the positivegermination response to FR was not induced by soaking at 3°C,in which the growth of the axial tissue as a photoreceptivesite did not occur at all. Similarly, it was not manifestedwhen the seeds soaked at 33°C were subsequently subjectedto 8°C. Key words: Cocklebur seeds, dark germination, far-red light, low temperature, red light, seed germination, Xanthium pennsylvanicum     

The Interactive Effects of Phytochrome, Nitrate and Thiourea on the Germination Response to Alternating Temperatures in Seeds of Ranunculus sceleratus L.: A Quantal Approach

Probert, R. J., Gajjar, K. H. and Haslam, I. K. 1987. The interactiveeffects of phytochrome, nitrate and thiourea on the germinationresponse to alternating temperatures in seeds of Ranunculussceleratus L.: A quantal approach.—J. exp. Bot. 38: 1012–1025. The interactive effects of phytochrome, potassium nitrate andthiourea on the germination response to alternating temperaturesin achenes (seeds) of Ranunculus sceleratus L. were studied.Using thermogradient bars, high levels of germination were recordedover a broad range of alternating temperatures providing seedsreceived daily irradiations. Reduced germination in temperaturecycles with a relatively long warm phase was related to thelevel of the active form of phytochrome (Pfr). Dose-responseexperiments to red light (R) and temperature shifts showed thatthe actions of Pfr and alternating temperatures were interdependent.Maximum germination was recorded when intermittent pulses ofR were combined with daily 4 h temperature shifts from 16°Cto 26°C. Whilst probit analysis showed that potassium nitrateand thiourea both increased population sensitivity to temperatureshifts, thiourea was a more potent stimulant. Although the effectof both chemicals was dependent on phytochrome photo-equilibriumthe threshold level of Pfr required for thiourea action wasclearly much lower than that required for nitrate action. Thioureapotentiated a response to daily temperature shifts even whenPfr was at a low, normally inhibitory level. These results indicatedifferent mechanisms of action for potassium nitrate and thioureain relation to phytochrome controlled seed germination. Key words: Phytochrome, nitrate, thiourea, alternating temperatures, germination     

STUDIES ON THE SEED OF BANANA. I. ANATOMY OF THE SEED AND EMBRYO OF MUSA BALBISIANA

Mc Gahan , Merritt W. (United Fruit Co., Norwood, Mass.) Studies on the seed of banana. I. Anatomy of the seed and embryo of Musa balbisiana. Amer. Jour. Bot. 48(3): 230–238. Illus. 1961.—The seed coat of Musa balbisiana Colla consists of a relatively thick outer integument and a 2–cell-layered inner integument. The entire seed coat is sclerified, but routine tests for lignin are negative. Within the outer integument there is a zone of unusual sclereids tentatively termed “multiluminate.” Between the inner integument and the remnants of the nucellus is a cuticle 10–12 μ thick. The micropylar plug and collar are typical of the genus. The chalazal mass is an annular region of gelatinous cells. The mature embryo is comprised of a massive cotyledon, an epicotyl with 1 leaf primordium, a primary root primordium, and several adventitious root primordia. Procambium is well developed, but no mature vascular elements are present in the embryo.     

Germination responses of Discopodium penninervium Hochst. to temperature and light

The germination responses of Discopodium penninervium were tested at different constant and alternating temperature regimes as well as under various light conditions both in the laboratory and glasshouse. Seeds incubated at 10, 15, 20, 25 and 30 °C failed to germinate. When the seeds were incubated at alternating temperatures of 20/12 °C and 30/12 °C under continuous light, germination was 89 and 61%, indicating that the species requires alternating temperatures as a cue for germination. However, germination declined as the amplitude of alternating temperatures increased from 8 °C and was completely inhibited at an amplitude of 23 °C, suggesting that the optimum amplitude is around 8 °C. Germination was less than 10% in light and nil in darkness at 20 °C in the laboratory. In contrast, seeds incubated at 20/12 °C germinated to 96 and 86% in light and darkness, respectively. Seeds incubated under leaf shade in the glasshouse failed to germinate whereas those incubated under direct daylight and darkness germinated to 44 and 50%, respectively, 30 days after sowing. When seeds incubated under leaf shade and in darkness were exposed afterwards to light, final percent germination was 83% from seeds incubated initially under direct daylight, 79% from those incubated under leaf shade and 86% from those incubated in darkness. The requirement for alternating temperatures and light rich in red:far red ratio to break the dormancy of seeds of D. penninervium could restrict germination to gaps in the vegetation. The results conform with the ecology of the species.