Dormancy-breaking Treatments Research Articles

Ethylene Evolution and Flowering of Cold- and GA-treated ‘Redwing’ Azaleas

Abstract Gibberellic acid (GA)-treated ‘Redwing’ azaleas (Rhododendron spp.) flowered in half the time required for cold-treated plants. Visual plant quality and flower uniformity were equal in both treatments. Ethylene evolution of buds was monitored in plants receiving cold treatment, receiving GA application, or remaining in the greenhouse without a dormancy-breaking treatment. Ethylene was not detectable in untreated plants or in cold-treated plants during cold treatment. Ethylene in buds was detected on the 4th day after removal from the cooler and was found to correspond to ethylene generation in GA-treated plants.

Studies of acid-soluble phosphorus compounds in genetically pure lines of Avena fatua with different dormancy characteristics

Seven genetically pure lines of wild oat selections of known dormancy characteristics were grown under uniform field conditions. Acid-soluble phosphorus components were determined in the dry seeds, in the imbibed seeds, and in imbibed seeds with dormancy-breaking treatments. No significant correlation between dormancy level and acid-soluble phosphorus composition was established for any component other than inorganic phosphorus (Pi). In dry caryopses Pi varied from 5 to 10% of the acid-soluble fraction. A highly significant inverse correlation was found between levels of Pi in the dry caryopsis and the relative depth of dormancy of the wild oat selection considered. The effect of imbibition on Pi level varied with depth of dormancy. Intact seeds of nondormant lines imbibed for 52 h showed a significant decline in Pi prior to coleorhiza protrusion from the dehulled caryopsis. More deeply dormant lines of Avena fatua (pure lines Anderson 51, Anderson 474, or Crop Science 40) required up to 10 days of incubation for significant drops in Pi to appear, while the most dormant lines (pure line Montana 73 and Idaho) did not evidence significant decline in Pi even after 10 days of incubation. The increase in Pi level associated with coleorhiza protrusion could be produced in the imbibed dormant lines by piercing them with a fine needle, by treating with gibberellic acid (GA3), or by a combination of the two treatments. The combination of piercing and GA3 treatment was much more effective than either treatment alone.

Poly(A) +RNA synthesis in cotyledons of dormant and non-dormant seeds of hazel ( Corylus avellana L.)

The incorporation of 32PO 4 3− into poly(A) +RNA in the cotyledon of hazel ( Corylus avellana L.) seeds is low and declines during dry storage. Imbibition results in increased poly(A) +RNA synthesis. Gibberellic acid (GA 3), cotyledon excision and testa removal (dormancy breaking) promote synthesis. The pattern of the stimulation of poly(A) +RNA synthesis by GA 3 in cotyledons differs from the pattern in axes. Poly(A) +RNA from dormant cotyledons is polydisperse with a peak maximum of 15.1 S, larger than that from dormant axes. Dormancy breaking treatments do not increase the size of the poly(A) +RNA synthesised in cotyledons, as they do in axes. These results support the suggestion that there are independent sites of action of gibberellin in the axis and in the cotyledon of hazel seeds. The poly(A) lengths in dormant and non-dormant cotyledons are similar and 32P is incorporated into both the poly(A) and the rest of the molecule. The results are discussed with respect to food mobilization, the hormonal interaction of axis and cotyledon and the breaking of dormancy.

Environmental and Hormonal Control of Turion Germination in Myriophyllum verticillatum

Germination, or outgrowth, of Myriophyllum verticillatum turions involves a series of visible changes starting with reflexing of leaves followed by extension and curving of the axis, and then by root formation. Before abscission, turions grow out in response to long days (16 hr) but not short days (8 hr). After abscission, turions show maximal dormancy which can be fully broken by a cold treatment (4 C). Turions are heterogeneous in degree of dormancy and ability to respond to less complete dormancy-breaking treatments, e.g., long days at 20 C. Cytokinins (10-6 m) break dormancy of non-cold-treated turions, whereas gibberellic acid (GA3) is ineffective except at high concentrations (10-3 m). Continuous treatment with cytokinins causes abnormal development after germination. GA3, on the other hand, induces apparently normal development even at high concentration. Indoleacetic acid (IAA) induces outgrowth only at high concentrations (10-3 - 10-4 m), but these concentrations also produce abnormal development. Abscisic acid (ABA, 10-5 m) retards outgrowth of cold-treated turions and can completely suppress it in non-cold-treated turions. The activity of ABA-like substances in turions remains about the same before and during germination, whereas other (unidentified) acidic inhibitors decrease markedly. The cytokinin activity changes in a complex pattern.

The Influence of Foliar Applications of GA3GA4,7and PBA on Breaking Flower Bud Dormancy on Azalea CVS Redwing and Dogwood

SummaryFoliar applications of gibberellins (GA3, GA4,7) and 6-benzylamino-9-(2-tetra- hydropyranyl)-9H-purine (PBA) were compared with untreated controls and the conventional low temperature treatment for breaking flower bud dormancy. GA3 and GA4, 7 were compared for their role in promoting flower development. Treatments were initiated when microscopic examination showed the flower buds had reached Stage 6 (style elongated and closed). Plants that did not receive a dormancy-breaking treatment failed to reach anthesis. Application of GA3 or GA4, 7 hastened flowering and increased flower size and pedicel length.

Sugars and polyols in sclerotia of Claviceps purpurea, C. nigricans and Sclerotinia curreyana during germination

Qualitative studies were made on the alcohol-soluble carbohydrates in sclerotia of C. purpurea and C. nigricans during dormancy, activation and germination. Trehalose and mannitol were the major carbohydrates present, and evidence was obtained that these were synthesized via a lipid-consuming system which was activated during low-temperature, dormancy-breaking treatments. Carbohydrates were consumed during germination and mannitol was translocated from the ergot through the stipe to the stroma. In S. curreyana trehalose and mannitol were the principal carbohydrates present. During germination carbohydrates were similarly consumed, and mannitol and trehalose were translocated from the sclerotium to the apothecium.

On the germination of perilla seed

Dormancy of perilla (Perilla ocymoides L. var. crispa BENTH.) seed was studied. 1. Dormany of perilla seed continues for about three to five months after harvest, and it is very deep for the first month after harvest. 2. Germination of perilla seed is light-favored. In some cases, however, it is dark-favored for some period after harvest, and turns to light-favored thereafter. Causes of this variability in photosensitivity are not known yet. The grade of photosensitivity does not vary after dormancy has disappeared. 3. Causes of dormancy of perilla seed exist mainly in seed coat and partially in embryo. 4. Effective dormancy breaking treatments are decoating, sulfuric acid treatment and prechilling. Prechilling is most useful in practice. 5. Perilla seed aquires germinating ability in high temperature through aging or prechilling. 6. Dry seeds in normal air-humidity, as well as wet ones, are affected by light condition. Germination percentage in darkness is higher when the seeds have been kept under light than when kept in darkness. 7. Germination rate of perilla seeds is low when sown in soil. The rate increases considerably when the seeds have been presoaked under light for about one day.

Effect of light on the germination of vegetable seeds

Effect of light on the germination of vegetable seed was studied in this report. In addition, dorm-ancy of shungiku (Chrysanthemum coronarium L.) and temperature relation to the germination of onion seed were investigated. Three grades of temperature of 20°, 25°, and 30°C were used in most cases. Light was supplied from fluorescent lamp. Effect of wave-length of radiation was studied by the same method as is the case reported by NAKAMURA 15) 1. In Cruciferae, the germination of radish seed is inhibited by light, and seed of Brassica vegeta-bles is favored by light. The former is inhibited by light strongly at low temperature for a while after harvest. This strong light-inhibiting action at low temperature disappears with aging of seed, but radish seed is inhibited by light to some degree for over many years. Brassica seed is forced by light only in the period of dormancy. Both of radish and Brassica seeds lose their photo-sensitivity by such dormancy-breaking treatment as prechilling, thiourea treatment, etc. 2. Germination of dormant seed of shungiku is promoted by thiourea. 3. Seed of mitsuba (Chryptotaenia japonica HASSK.) is favored by light at any temperature. By alternating temperatures, these seeds are ger-minated almost completely in darkness. Photosensi-tivity of mitsuba seed is indifferent to seed age. Celery seed is also favored by light indifferently to seed age. 4. Germination speed of onion and Welsh onion seeds is retarded by light to some extent, and this light-inhibiting action is more remarkable in Welsh onion. Temperature of over about 28°C supresses germination of onion seed. Alternating temperatures of 33° to 25°C is effective, but 33° to 28°C is not. 5. Germination of egg-plant and tomato seeds is retarded by light at every temperature. Germination rate is also often lowered at 20°C in egg-plant, at 20° and 30°C in tomato. Germination of pepper seed is retarded by electric light at every temperature, but not retarded by fluorescent light. Seed of egg-plant does not lose itt photo-sensitivity by the removal of seed coat. 6. Seeds of watermelon, squash, calabash gourd, wax gourd, and balsum pear are hindered by light at any temperature, and the degree is greater at low temperature. Seeds of cucumber, melon, and shirouri (Cucumis melo var. conomon MAKINO) are inhibited by light only at low temperature. Vegetable sponge falls in between the two groups. Photo-sensitivity of Cucurbitaceous vegetable seeds is indifferent to their seed age, and light condition is not replaced by such factors as chemical treatment, alternating temperatures, prechilling, etc.. In the case of decoated seeds, too, the photosensitivity does, not disappear, and sometimes it will even augment. 7. Seed of perilla is favored by light at every temperature. Ramie seed is also promoted by light at any temperature. Photo-sensitivity of perilla and ramie seeds is indifferent to their seed age. 8. In the case of shungiku, carrot, spinach, beet, and Leguminosous seeds, no light effect was observed in our study. 9. Concerning the relation to the wave-length of radiation, that of mitsuba, celery, perilla, and ramie seeds is about the same as in edible burdock. In Cucurbitaceae, germination is inhibited at infr-ared and blue region, but not at green region. Egg-plant, tomato, and pepper seeds are strongly inhibited only at short infrared region, and also Brassica seed was inhibited to some degree only at this region. Onion and Welsh onion seeds did not show any reaction to the spectrum. 10. It is interesting that in the seeds retaining their photosensitivity in seed coat, their photo-sensitivity is related closely to their dormancy, accordingly it disappears or diminishes accomp-anying to the breaking of dormancy. On the contrary in the seeds which retain their photo-sensitivity in their embryo,