Interaction of Growth Retardants and Temperature in Growth, Flowering, Regeneration, and Auxin Activity of Begonia × cheimantha Everett

Soil application of CCC reduced stem and leaf growth in Begonia plants. This effect was evident with all concentrations tested at 18°C, whereas at 21 and 24°C no growth–retarding effect was observed with 2 × 10^?2 M CCC, and with 5 × 10^?3 M growth was even stimulated. Flowering was promoted by CCC in long day and neur–critical temperature, particularly under low light intensity in the winter. The formation of adventitious buds in leaves of plants grown at 21 and 24°C was stimulated when the plants received 5 × 10^?2 and 2 × 10^?2 M CCC, while 8 7times; 10^?2 M was inhibitory. In plants grown at 18°C bud formation was inhibited by all CCC concentrations. Root formation in the the leaves was usually stimulated by high CCC concentrations, while root elongation was reduced. The level of ether–extractable. acidic auxin (presumably IAA) in the leaves was lowered by CCC treatment of the plants, hut this required higher CCC concentrations at higt than at low temperature. When applied to detached leaves CCC stimulated bud formation at concentrations ranging from 10^?4 to 10^?2 M in leaves planted at 18 and 21°C. At 24°C budding was inhibited by 10^?2 M CCC, the lower concentrations being stimulatory also at this temperature. Root formation and growth were not much affected by CCC treatment of the leaves, but increased with the temperature. Soil application of Phosfon (4 × 10^?4 M) had no effect on growth and flowering, nov did it affect the subsequent regeneration of buds and roots in the leaves. In detached leaves Phosfon stimulated bud formation with au optimum at 10^?6 M. Root formation was stimulated by Phosfon at all temperatures, the optimal concentration being 10^?5 M, whereas root length was conversely affected. Foliar application of B-995 to intact plants and treatment of detached leaves greatly inhibited the formation of buds and had little effect on root formation. B-99D reduced the growth and delayed flowering in the plants.     

The Effects of Light and Temperature on Germination and Growth of Luffa aegyptiaca

The effects of light and temperature on the germination and growth of Luffa aegyptiaca were investigated both in the laboratory and in the field. The seeds germinated in both darkness and light but germination was better in the light. At constant temperatures germination was best at 21°C, while alternating temperatures of 21 and 31°C and 15 and 41°C caused higher germination than the most favourable constant temperature. Constant temperatures of 15 and 31°C and alternating temperatures of 21 and 41°C resulted in very low germination, whereas no germination occurred at 41°C and at alternating temperatures of 31 and 41°C. Soil depth caused only a delay in seed germination, as it did not affect the total germination. High temperature and high light intensity resulted in good seedling growth in terms of dry weight, leaf area and relative growth rate. High temperature and low light intensity caused increased plant height and high shoot weight ratio, both of which manifested in seedling etiolation. They also caused high leaf area ratio. Under low temperatures, irrespective of light intensity, growth was generally poor, but it was significantly poorer under low light intensity, which also caused high root weight ratio. High light intensity was principally responsible for high leaf weight ratio. The results help to explain the abundance of the species in newly cleared areas in Lagos and its environs.     

The effect of Sea Water and Temperature on the Germination Behaviour of Crithmum maritimum

The seeds of Crithmmm maritimum L. were germinated floating on various concentrations of sea water up to 50% at constant temperatures of 5, 10, 15, 20, and 25°C and at alternating temperatures of 5 and 15°C. 5 and 25°C. and 15 and 25°C. Significantly higher germination was obtained at alternating than at constant temperature. When two constant temperatures at which no germination occurred were alternated, good germination was obtained. There was reduced germination and increase in time of first germination as sea water concentration increased, in the absence of sea water, high temperature caused not only severe inhibition of germination but also permanent injury to the seeds. The results help to explain the germination behaviour of the species in nature.     

Effects of light, temperature and water stress on germination of Artemisia sphaerocephala

Artemisia sphaerocephala is widely used for vegetation rehabilitation, but its germination is very low after air seeding of achenes. We explored effects of light, temperature and water stress on germination. Results show that both final percent germination and germination rate were increased by temperature increment, with the highest values occurring at 15: 25°C (night: day) in dark and 20: 30°C under light. Light inhibited germination, especially at lower alternating temperatures (5: 15°C and 10: 20°C). The alternating temperature window for germination was slightly narrower under light than in dark, and germination was slower under light than in dark across the temperature range. Achenes incubated in the dark and at constant temperatures had over 80% germination at 10 to 25°C, with an optimum at 20°C. Under dark and 25μmol m^‐2 s^‐1 light flux density at 10: 20°C, final percent germination was over 94%, but if the light flux density was increased to 100 and 400 μmol m^‐2 s^‐1, final percent germination was significantly lower (64% and 38% respectively). However, achenes could keep their germination capacity for a long time (over 50 days) and germinate well after going back to the dark. Germination was also lower under water stress and few achenes germinated at ‐1.4 MPa. This was more pronounced at high and low temperatures. Given these findings and the prevailing climatic characteristics, the most suitable time for air seeding of achenes may be mid‐May.     

The effects of time of seed production on the germination response of Spergularia marina

Germination studies were carried out with seeds of Spergularia marina L. Griseb produced over an interval of six months (June-November). The response of the seeds to light and dark, various constant and alternating temperature regimes, and salinity were determined. In addition, the effects of soil moisture status at the time of seed production on the subsequent germination response of seeds were also determined. Light was an absolute requirement for germination. While a constant temperature regime did not generally favour germination of seed of any month, alternating temperature greatly enhanced germination with an optimum at 5/15°C in all seeds. When imbibed in solutions of different salinities, seeds collected in July and October behaved like true halophyte seeds whereas those collected in June. August, September and November behaved like glycophyte seeds.
High concentration of gibberellic acid (3 000 μ M ) stimulated dark germination in the June and November seed lots, but in light, low GA3 concentration (300 μ M ) stimulated germination most. The addition of kinetin (30 μ M ) plus gibberellic acid enhanced germination in the dark in contrast to GA3 alone; kinetin alone stimulated a very low percentage germination.
The moisture status of the soil at the time seeds were produced did not affect the germination response of an early seed crop (July) but affected that of the later seeds (August).
Judging from the different germination responses, it appears that the seeds belong to at least two physiological groups, one which appears to need either a dark-wet or cold-wet pretreatmem for high germination to occur; and the other group which does not need pretreatmem. The ecological significance of these varied responses is discussed in relation to the survival of the species in its habitat.     

The Influence of n-Propanol on the Growth and Conidiation of Pestalotia rhododendri

Pestalotia rhododendri was exposed to vapours from 1 ml propanol solution in water and linear growth, formation of aerial hyphae and production of conidia were determined. A special Petri dish technique was used and maximum stimulation of conidial formation was induced by the vapours from a propanol concentration of 3–4 % (v/v) at 25°C. When propanol was added directly to the medium, a concentration of 1.2 × 10^?2M was optimal for growth and sporulation at 30°C. Sporulation stimulated by propanol was observed at temperatures from 20–32°C, with an optimum at 30°C. Certain observations indicated that an exposure to propanol for 24 hours was enough to induce a stimulated spore production. The stimulation was noticed on different media at 25°C, and was more pronounced at 30°C. One exception was observed. Propanol did not promote sporulation when the fungus was grown on maltagar at 30°C. Propanol 3 ° (v/v) in combination with the standard medium containing (NH₄)₂-tartrate as sole nitrogen source, inhibited the linear growth at 15–20°C, was inactive at 22.5° and 25°C, and stimulated growth at 27.5–31°C. The stimulatory effect was maximal at 30°C. Other media were tested at 25° and 30°C. At both temperatures stimulations of linear growth caused by propanol were observed with a medium containing KNO₃ as sole nitrogen source, and inhibitions with maltagar and another medium containing l -asparaginc as sole nitrogen source. The linear growth could be either inhibited or stimulated while the sporulation was stimulated.     

Effects of waterlogging on chickpeas II. Possible causes of decreased tolerance of waterlogging at flowering

Waterlogging tolerance of chickpeas was found, in earlier work, to decrease sharply at flowering. Three experiments were performed to attempt to explain the mechanisms involved in this response. In the first, a range of treatments was imposed to modify the plant's source/sink relationships, as carbohydrate supply and partitioning were considered possible determinants of waterlogging tolerance. Plants from which buds were removed showed the most rapid recovery after waterlogging. Defoliation immediately before waterlogging reduced the rate of recovery. Application of benzyladenine plus gibberellic acid prior to waterlogging delayed stomatal closure and leaf senescence, inhibited apical growth and stimulated axillary growth. The second experiment aimed to confirm the influence of bud removal and to determine whether waterlogging tolerance is correlated with carbohydrate supply. Treatments comprised two sowing times, ten days apart, and two bud treatments (retained and removed). Waterlogging was imposed when older plants had been flowering for seven days and younger plants were in bud. Waterlogging caused soluble sugars to accumulate in the lower stem, suggesting that a deficiency of assimilates did not contribute to waterlogging injury. Similarly, waterlogging increased nitrogen concentration in the stem, through mobilisation from senescing leaves. Bud removal enhanced leaf survival and reduced mortality rate after waterlogging; it also increased starch concentration in the lower stem, indicating that storage of assimilates decreased in flowering plants. However, across all treatments, starch concentration was not correlated with waterlogging tolerance. In the third experiment, the effect of the senescence-promoting factor ethylene on preflowering and flowering plants was assessed, using the ethylene-releasing agent ethephon. Ethephon reduced growth to a slightly greater extent when applied prior to flowering than at flowering. There was no evidence that inadequate supply of carbohydrates or nitrogen in the stem, or increased sensitivity to ethylene, contributed to waterlogging intolerance in flowering chickpea plants.     

Response of in vitro pollen germination and pollen tube growth of almond (Prunus dulcis Mill.) to temperature,polyamines and polyamine synthesis inhibitor

Prunus dulcis L. ‘Mamaei’ is grown widely in souhtwest of Iran. It blooms in early spring when temperatures are still low. Based on our knowledge there are no reports in the literature regarding pollen behavior of this cultivar under specified condition. Thus, the possible factors for low germination percentage in this cultivar have not been reported. The effect of three different temperatures (10, 25, or 35 °C), polyamines (putrescine, spermidine, and spermine) and polyamine synthesis inhibitor, methylglyoxals-bis (guanyl-hydrazone) (MGBG) on in vitro pollen germination and pollen tube growth were investigated in P. dulcis L. ‘Mamaei’. All temperatures and chemicals significantly affected both pollen germination percentage and pollen tube growth. In general, different polyamines stimulated the pollen germination percentage compared to the control at all temperatures, but increasing the temperature, particularly to 35 °C, had demonstrated inhibitory effects on pollen germination. At a concentration of 0.05 mM putrescine and spermidine and 0.005 and 0.025 mM spermine revealed longer pollen tube growth than that of the control at 10 °C, while higher concentrations tended to inhibit pollen tube growth. At 25 °C, most of the treatments had an inhibitory effect on pollen tube growth except for 0.25 mM putrescine and 0.005 mM spermine, which slightly stimulated pollen tube growth. Pollen germination and pollen tube growth were inhibited by MGBG at all temperatures and in all concentrations.     

The Influence of Temperature on Floral Initiation in the Olive

Floral initiation is completely inhibited when the olive is grown in a glasshouse at a minimum temperature of 16°C and a maximum temperature of 27°–30°C but occurs when it is grown at natural winter conditions in California. This study was undertaken to determine more specifically the temperature requirements for flowering and to show the relation of temperature treatment to hud development and floral initiation. Results of experiments performed with trees in containers grown at constant temperatures in controlled environment growth rooms show that the optimum temperature for flowering is 10°–13°C. Either higher (18°C) or lower (4°C) temperatures inhibit flowering completely. Morphological studies show that axis elongation and floral initiation occur in buds during temperature treatment at 10°C and 13°C but fail to occur during 4°C or 18°C treatments, or following these treatments when the temperature is raised to 21°C. When plants were exposed to 13°C for varying durations, it was found that no inflorescences formed after a 7.5 week exposure but that many formed after an 11-week exposure. A subsequent experiment showed that many more inflorescences formed after a 10-week exposure at 13°C than after 9 weeks exposure. Morphological changes in the bud seem to be associated with this increase in flowering affected by duration of treatment.     

Seed germination responses to salinity and temperature in Limonium supinum (Plumbaginaceae), an endemic halophyte from Iberian Peninsula

Limonium supinum, a perennial herb with interest for the restoration and gardening of arid zones, is widely distributed in saline areas from southeastern Iberian Peninsula. Laboratory experiments were carried out to assess the effects of temperature and salinity on seed germination and on germination recovery from the effects of saline conditions after transfer to distilled water. Seed germination responses were determined over a four temperature regimes (20/10, 25/15, 30/20 and 35/25 °C; 12 h light/12 h dark photoperiod) and six salinities (0, 100, 150, 200, 400 and 600 mM NaCl). The higher germination percentages were obtained in non-saline conditions, under all temperature regimes. An alternating temperature of 20 °C light and 10 °C dark yielded the maximum germination for any saline concentration. Increase in salinity delayed the beginning and end of germination and reduced the final percentage of germination, which becomes completely inhibited at 600 mM NaCl. The adverse effect of salinity is reinforced by high temperatures (30/20 and 35/25 °C). The germination rate was also negatively affected by the increase in salinity and temperature. The final recovery percentages in high salt treatments were near 100%, indicating that exposure to high concentration of NaCl did not inhibit germination permanently.     

The impact of temperature on the production and fitness of microsclerotia of the fungal bioherbicide Mycoleptodiscus terrestris

The impact of growth temperature was evaluated for the fungal plant pathogen Mycoleptodiscus terrestris over a range of temperatures (20–36°C). The effect of temperature on biomass accumulation, colony forming units (cfu), and microsclerotia production was determined. Culture temperatures of 24–30°C produced significantly higher biomass accumulations and 20–24°C resulted in a significantly higher cfu. The growth of M. terrestris was greatly reduced at temperatures above 30°C and was absent at 36°C. The highest microsclerotia concentrations were produced over a wide range of temperatures (20–30°C). These data suggest that a growth temperature of 24°C would optimize the parameters evaluated in this study. In addition to growth parameters, we also evaluated the desiccation tolerance and storage stability of air-dried microsclerotial preparations from these cultures during storage at 4°C. During 5 months storage, there was no significant difference in viability for air-dried microsclerotial preparations from cultures grown at 20–30°C (>72% hyphal germination) or in conidia production (sporogenic germination) for air-dried preparations from cultures grown at 20–32°C. When the effect of temperature on germination by air-dried microsclerotial preparations was evaluated, data showed that temperatures of 22–30°C were optimal for hyphal and sporogenic germination. Air-dried microsclerotial preparations did not germinate hyphally at 36°C or sporogenically at 20, 32, 34, or 36°C. These data show that temperature does impact the growth and germination of M. terrestris and suggest that water temperature may be a critical environmental consideration for the application of air-dried M. terrestris preparations for use in controlling hydrilla.     

The effect of soil drought on the composition of carbohydrates in yellow lupin seeds and triticale kernels

Carbohydrate analysis was made of yellow lupin seeds (cv. Juno) and triticale kernels (cv. Dagro), produced by plants exposed to drought stress for 21 days after the initial flowering of the first node of lupin and initial earing of triticale. The seeds of all experimental variants were harvest at full maturity, dried and stored in linen bags at 18–20 °C. Soluble carbohydrates were extracted and analysed as described by Horbowicz and Obendorf (1994). Gas chromatographic separation of carbohydrates showed that raffinose family oligosaccharides (RFO) were dominant in lupin seeds. The other carbohydrates present were sucrose (10 %), cyclitols and galactosyl cyclitols (12–13 %). Soil drought resulted in higher levels of verbascose, but decreased the quantities of the other carbohydrates in lupine seeds. In triticale kernels, over 50 % of soluble sugars were composed of sucrose and maltose, while 17.7 % were raffinose and stachyose. In response to drought the content of mono- and oligosaccharides declined. The decrease of soluble carbohydrates content in seeds of lupin and triticale kernels has no effect on the seed germination and vigour. It is assumed that the changes in the concentration of soluble sugars observed under drought may impair the storability of triticale kernels, but improve it for lupine seeds.     

Puccinellia festucaeformis (Host) Parl.: Germinazione e crescita iniziale in funzione della salinità del substrato

Abstract

Puccinellia festucaeformis (Host) Parl.: germination and early growth on different salt substrates. Germination behaviour of Puccinellia festucaeformis seeds and early growth of seedlings at different experimental conditions was analysed. The following growth substrates were utilized: NaCl, KCl, KNO₃, MgCl₂, MgSO₄, Na₂SO₄, NaNO₃, CaCl₂ at the decreasing concentrations of 0.50, 0.25, 0.12, 0.06M. Caryopses were allowed to imbibe and grow at alternating temperatures (10°-20°C or 20°-30°C) in the dark for 3 days. Seedling were grown for 15 days, at controlled light and temperature conditions, in the same nutrient substrates as those used for the germination experiments.

The germination experiments showed a high tolerance to salts up to 0.25M solution and for the whole range of MgSO₄ concentrations. High growth temperatures increased the depressive effects of salt concentrations. Seedling growth was highly reduced when salt concentration was higher than 0.12M. High salt tolerance - maximum shoot and root growth - was showed by seedling allowed to grow on 0.50M MgSO₄.

Germination and growth condition of Puccinellia festucaeformis is discussed in relation to the ecological features of this species and to its possible importance as bioindicator of MgSO₄ rich natural substrates.     

Viability and virulence of blastospores of Metarhizium anisopliae (Metch.) Sorokin after storage in various liquids at different temperatures

Blastospores of three strains of Metarhizium anisopliae were stored in 18 liquids at 4°C, 20°C and 35°C for 18 weeks, 12 weeks or 9 days respectively. Viability was quantified by determination of their germination. In bioassays the virulence of stored blastospores was studied using adults and third instars of Locusta migratoria migratorioides (R. & F.) and compared to those of freshly produced blastospores and conidia. Generally, there was great variability in the viability of blastospores, depending on the fungal strain and the liquids used. Blastospores survived best at 4°C in 10% hydroxyethyl starch; for example, germination of M. anisopliae strain 97 still amounted to more than 80% after storage for 18 weeks. Other suitable liquids were deionized water, 25% Ringer's solution and 1% sodium alginate. The viability of blastospores stored at 20°C was considerably shorter than at 4°C. During storage for 12 weeks at 20°C the best protective liquids for M. anisopliae strain 97 were 25% Ringer's solution (43% germination), deionized water (23%) and 10% hydroxyethyl starch (23%). At 35°C, 45% of M. anisopliae strain 97 blastospores still germinated after storage for 7 days in 25% glycerol. The bioassays revealed that the virulence of blastospores after storage was comparable to that of fresh ones and even better than that of fresh conidia. In general, the LT₅₀ was about 4–6 days at an alternating day/night temperature of 28/20°C.     

Hormonal regulation of tomato seed germination at a supraoptimal temperature

Germination of tomato cv. New Yorker seed is inhibited at 35°C. This thermoinhibition was partially counteracted by application of GA₄₊₇ alone, the compound applied in combination with ACC or ethephon markedly enhancing the process. The latter compound alone was not able to induce germination at 35 °C. Thermoinhibition of seeds at 35 °C was also counteracted by fluridone, an inhibitor of ABA biosynthesis. At 25 °C, an optimal temperature, ABA inhibited germination of New Yorker seeds. Although another known growth inhibitor MeJA, when applied at an optimal temperature (25 °C), had also a slightly inhibitory effect on germination of those seeds and clearly delayed the process, inhibitors of its biosynthetic pathway (ibuprofen, indoprofen, antypiryne and salicylic acid) did not remove thermoinhibition at 35 °C. An increase in endo-β-mannanase activity after 24 hours of incubation at 35 °C was observed in the seeds incubated in the presence of gibberellins, ACC, ethephon, fluridone used alone and in combinations, but it was not clearly correlated with the effects of these compounds on alleviation of seed germination. However, fluridone present in the same incubation medium at 35 °C with ABA was able to counteract the inhibitory effect of ABA on endo-β-mannanase activity. The results of our study suggest that gibberellins, ethylene (produced from ACC or ethephon) and ABA, but not jasmonates, regulate tomato seed germination at supraoptimal temperatures. Alleviation of thermoinhibition of New Yorker seed germination by plant growth regulators and fluridone is partially associated with their controlling endo-β-mannanase activity.     

Germination behaviour of Conyza bonariensis to constant and alternating temperatures across different populations

Conyza bonariensis is one of the most problematic weed species throughout the world. It is considered highly noxious due to its interference with human activities, and especially the competition it poses with economically important crops. This research investigated the temperature requirements for seed germination of four populations of C. bonariensis with distinct origin and the influence of daily alternating temperatures. For this, a set of germination tests were performed in growth chambers to explore the effect of constant and alternating temperatures. Seeds of the four populations (from Lleida, Badajoz and Seville, Spain and Bahía Blanca, Argentina) were maintained at constant temperatures ranging from 5 to 35°C. The final germination and cardinal temperatures (base, optimum and maximum) of each population were obtained. We also tested the influence of daily alternating temperatures on final germination. To do so, seeds were exposed to two temperature regimes: 5/15, 10/20, 15/25, 20/30 and 25/35°C night/day temperature (intervals increasing 5°C, with constant oscillation of 10°C) and to 18/22, 16/24, 14/26, 12/28 and 10/30°C night/day temperature (intervals with average of 20°C, but increasing the oscillation in 4°C between intervals). In general, all populations behaved similarly, with the highest germination percentages occurring in the optimum temperature range (between 21.7°C and 22.3°C) for both constant and alternating temperatures. In general, climatic origin affected germination response, where seeds obtained from the coldest origin exhibited the highest germination percentage at the lowest temperature assayed. In addition, we observed that the alternating temperatures can positively affect total germination, especially in oscillations that were further from the average optimum temperature (20°C), with high germination percentage for the oscillations of 15/25, 20/30, 18/22, 16/24, 14/26, 12/28 and 10/30°C in all populations. The cardinal temperatures obtained were significantly different across the populations. These results provide information that will facilitate a better understanding of the behaviour of Conyza and improve current field emergence models.     

Tomato pollen respiration in relation to in vitro germination and pollen tube growth under favourable and stress-inducing temperatures

Tomato pollen germination, pollen tube growth and respiratory activity were recorded during incubation in a liquid medium for 7 h over a temperature range of 15–35°C. Although the initial rate of respiration was highest at 30°C, both at 30°C and 35°C respiration decreased after the first hour of incubation due to high temperature impairment of germination and pollen tube growth. The total per cent germination of pollen over the 7-h period was maximal at 15°C whereas pollen tube length was maximal at 25°C. Although the production of CO₂ measured at hourly intervals throughout the incubation period did not correlate to a statistically significant level with either the per cent pollen germination or the length of the pollen tubes alone, nevertheless from 2 h after the start of incubation, it closely correlated with the values for germination × pollen tube length, indicating that the respiratory activity of tomato pollen at a given time is a function of both the per cent germination and the pollen tube growth. We suggest therefore that the rate of respiration might be preferable to a simple germination test for the assessment of pollen germination ability since it expresses not only the pollen germination potential but also the growth vigour of the pollen tubes. In addition, where in vitro tests are designed to assess pollen germination–temperature interactions, they should employ a long incubation period (e.g. 7 h) to permit differences in sensitivity to temperature to be observed.     

Nitric oxide accelerates seed germination in warm-season grasses

The nitric oxide (NO) donor sodium nitroprusside (SNP) significantly promoted germination of switchgrass (Panicum virgatum L. cv Kanlow) in the light and in the dark at 25°C, across a broad range of concentrations. SNP also promoted seed germination in two other warm-season grasses. A chemical scavenger of NO inhibited germination and blocked SNP stimulation of seed germination. The phenolic (+)-catechin acted synergistically with SNP and nitrite in promoting seed germination. Acidified nitrite, an alternate NO donor also significantly stimulated seed germination. Interestingly, sodium cyanide, potassium ferricyanide and potassium ferrocyanide at 200 μM strongly enhanced seed germination as well, whereas potassium chloride was without effect. Ferrocyanide and cyanide stimulation of seed germination was blocked by an NO scavenger. Incubation of seeds with a fluorescent NO-specific probe provided evidence for NO production in germinating switchgrass seeds. Abscisic acid (ABA) at 10 μM depressed germination, inhibited root elongation and essentially abolished coleoptile emergence. SNP partially overcame ABA effects on radicle emergence but did not overcome the effects of ABA on coleoptile elongation. Light microscopy indicated extension of the radicle and coleoptiles in seeds maintained on water or on SNP after 2 days. In contrast, there was minimal growth of the radicle and coleoptile in ABA-treated seeds even after 3–4 days. These data indicate that seed germination of warm-season grasses is significantly influenced by NO signaling pathways and document that NO could be an endogenous trigger for release from dormancy in these species.     

Effect of temperature and cold stratification on seed germination of the Mediterranean wild aromatic Clinopodium sandalioticum (Lamiaceae)

A germination study was carried out on seeds of Clinopodium sandalioticum (Bacch. & Brullo) Bacch. & Brullo ex Peruzzi & Conti (Lamiaceae), a wild aromatic plant endemic to Sardinia. Seeds were incubated at a range of constant (5–25°C) and an alternating temperatures regime (25/10°C), with 12 hours of irradiance per day. The results achieved at 10°C were also compared with those obtained after a period of cold stratification at 5°C for three months. Final seed germination ranged from ca. 28% (5°C) to ca. 72% (25/10°C). A base temperature for germination (T_b) of ca. 5°C and a thermal constant for 50% germination (S) of 89.3°Cd were identified and an optimal temperature for germination (T_o) was estimated to be comprised between 20 and 25°C. Cold stratification negatively affected seed viability and germination at 10°C. Although a typical “Mediterranean germination syndrome”, could not be detected for C. sandalioticum seeds, these results were coherent with those previously reported for other Mediterranean Lamiaceae species.     

Seed germination of Pilosocereus arrabidae (Cactaceae) from a semiarid region of south‐east Brazil

We evaluated the effect of temperature regimes (six constant and four alternating temperatures), light qualities (five red : far red ratios) and water potentials (ΨW; seven NaCl and polyethylene glycol 6000 [PEG] solutions) on the percentage and germination rate, as well as the post‐seminal development morphology, that allow Pilosocereus arrabidae seeds to germinate in a hot semiarid climate on the south‐eastern Brazilian coast. The results showed that seeds germinated similarly between constant and alternating temperatures, with an optimal germination at 25/20°C and 20°C. Pilosocereus arrabidae seeds were photoblastic positive and the final germination percentage was inhibited at low red : far red ratios. Maximum germination was obtained in distilled water (0 MPa) and decreases of Ψ_W in the solutions reduced the germination, which was lower in NaCl than in iso‐osmotic PEG solutions. Germination inhibition appears to be osmotic because the recovery response was high when non‐germinated seeds from both iso‐osmotic solutions were transferred to water. Seeds of P. arrabidae are small and germination is phaneroepigeal. Despite the slow growth typically seen in seedlings and adults of Cactaceae, germination in this species depends on the ability of the seeds to appropriately sense and react to environmental cues that correlate with times and places under low‐risk growth conditions.