Search Results

You are looking at 81 - 90 of 475 items for :

  • Refine by Access: All x
Clear All
Open access

D. F. Hamilton and P. L. Carpenter

Abstract

Both physical and metabolic events were found important in the dormancy-regulating mechanism of seed of Elaeagnus umbellata Thunb. Covering structures offered mechanical resistance to germination, but they did not restrict the flow of water to the embryo. Oxygen concentrations from 60 to 100% increased germination, indicating that the endocarp and seed coat may restrict gaseous exchange by the dormant embryo. Restricted gaseous exchange may compliment a germination-inhibiting substance found in dormant seed. Gibberellic acid decreased the stratification period, but kinetin and potassium nitrate were ineffective.

Free access

Judy Harrington and Scott Reid

Distichlis spicata var. stricta (Torrey) Beetle is a native grass that tolerates salt, high pH, and some heavy metals. It has been proposed for use in several challenging environments, including mine spoils and salt-impacted areas of golf courses, but its widespread use has been hindered by several factors, one of which is seed dormancy. Dormancy appears to be coat-imposed and can be overcome by scarification in relatively young seed lots. Thirteen-year-old seeds germinated better without scarification. Seeds were tested at several constant and alternating temperatures. Temperatures around 30 °C seemed to give the highest percentage germination, approaching the viability that was shown by tetrazolium chloride tests for each seed lot. Alternating temperatures increased the germination of unscarified seeds but not as much as scarification did. Light appears to be unnecessary for germination.

Free access

Alan G. Taylor

Oral Session 34—Seed and Stand Establishment Moderator: Gene M. Miyao 21 July 2005, 2:00–3:00 p.m. Room 105

Free access

Jung-Myung Lee and Du-Hyun Kim

Dry-heat (DH) treatment has been extensively used for inactivation of some seed-borne virus and Fusarium disease in many vegetable crops, especially in cucurbitaceous vegetables. Strains of tobamovirus (cucumber green mottle mosaic virus; CGMMV) could be successfully inactivated by treating the infected seeds at 75 °C for 72 h. However, DH-treated seeds frequently exhibit slow and poor germination and abnormal seedling characteristics, such as distorted, white streaked, and punctured cotyledons in the seedlings. The moisture content in seed coat and inner cotyledons fell down to below 1% in DH-treated seeds when treated at 75 °C or higher. However, when the seeds were treated at 65 °C, final moisture content in the DH-treated seeds were maintained at about 2.5% to 3.5%. Seeds absorbed moisture above 20% at 100% RH, 9% to 10% at 73% RH, and 4% to 5% at 28% RH, respectively. When the intact and DH-treated seeds were exposed to conditions of varying relative humidity, DH-treated seeds absorbed atmospheric moisture at a much slower rate than the intact seeds in all tested cultivars, and this is thought to be one of the major reasons for slower germination in DH-treated seeds. The inactivation of virus, comparison of respiration of seeds, and endogenous gibberellic acid contents will also be presented.

Free access

Dianne Oakley, Julie Laufmann, James Klett, and Harrison Hughes

Propagation of Winecups [Callirhoe involucrata (Torrey & A. Gray)] for use as a landscape ornamental has been impeded by a lack of understanding of the seed dormancy and a practical method for overcoming it. As with many members of the Malvaceae family, C. involucrata produces hard seed. In the populations tested, it accounted for 90% of an average sample. Impermeability, however, is not the only limiting factor to germination. Three disparate populations of seed, representing two different collection years have been investigated using moist pre-chilling, boiling water, leaching, gibberellic acid, hydrogen peroxide and mechanical and chemical scarification methods. Scarifying in concentrated sulfuric acid stimulates germination of some seed fractions and causes embryonic damage in others, suggesting variation in seed coat thickness. Similar results were obtained using a pressurized air-scarifier; the hard seed coat of some seed fractions were precisely scarified while others were physically damaged using the same psi/time treatment. Placing seed in boiling water increases germination from 4%, 7%, and 18 % to 23%, 25%, and 77% in the three populations, respectively. Leaching for 24/48 h in cold (18 °C) aerated water or for 24 h in warm (40 °C) aerated water showed only a minor increase over the control. Pre-chilling at 5 °C for 30, 60, and 90 days showed no improvement over the control. Gibberellic acid-soaked blotters improved germination at 400 ppm to 20%, 10%, and 41%; at 500 ppm germination was reduced. Soaking seed for 24 h in a 3% concentration of hydrogen peroxide did not effect germination; at a 30% concentration germination was reduced. The considerable variation in seed dormancy expression may be a function of differences in environmental factors during development or seed age.

Open access

J. T. Watkins, D. J. Cantliffe, D. J. Huber, and T. A. Nell

Abstract

Capsicum annuum (‘Early Calwonder’) seeds germinated (radicle protrusion) in 8 days at 15°C and 4 days at 25°. The seeds have an endosperm 7 to 9 cells in thickness which lies directly in front of the radicle. The external appearance of the endosperm did not change until one day before radicle emergence, when the endosperm in front of the radicle enlarged and protruded outward. This change was accompanied by breakdown and loss of endosperm cellular integrity and reduction in endosperm thickness directly in front of the radicle, but not in other regions of the endosperm. Gibberellic acid (GA4+7) decreased the time for appearance of the protruding endosperm and radicle protrusion through the seed coat by one day. Cell wall degrading activity was detectable during the early stages of germination and became extremely high after radicle emergence. Seeds treated with 100 ppm GA4+7 showed slightly increased enzyme activity during early germination and differences became more pronounced as germination progressed. Cellulase activity was not found in the extracts, but seed enzyme preparations degraded a galactomannan substrate. The enzyme exhibited only endohydrolytic activity, indicating an enzyme which may participate in the weakening of cell wall. It was postulated that an endomannanase is needed for endosperm breakdown in front of the radicle in order for rapid germination of pepper to occur. A reduction in germination temperature from 25° to 15° reduced the rate of radicle movement through the seed coat by one half.

Free access

Gary R. Bachman and Ted Whitwell

Southern seaoats (Uniola particulata) are difficult to propagate from seed due to low seed numbers produced and cold dormancy effects. To efficiently produce southern seaoats in the nursery industry the dormancy must be effectively broken to assure quick and even germination. 24 hr soaks in gibberillic acid (100 and 500 ppm) or scarification of the seed coat combined with GA soaks were compared. Seeds were planted in 50/50 peat/perlite medium 2.5 cm deep. 21 DAT both the 100 and 500 ppm GA soaks had higher germination rates. The 100 ppm GA was determined to he most effective (56% germination) with the seedlings being 3 cm in length. The 500 ppm treated seeds were 6 cm in length hut twisted from the GA causing excessive cell elongation.

Open access

Orlando Balboa-Zavala and F. G. Dennis Jr.

Abstract

c,t-Abscisic acid (ABA) was identified in methanol extracts of mature apple (Malus domestica Borkh.) seeds by gas chromatography-mass spectrometry, and concentrations of both free and base-hydrolyzable (bound) ABA in immature and mature seeds were quantified by electron capture gas chromatography. Immature embryos failed to germinate regardless of time of sampling unless seed coats were removed. Germination of excised embryos reached a maximum in early August, then gradually declined to nil in mid-September. Although ABA content of the embryonic axes rose sharply at maturity, the rise occurred only after germination capacity declined. Premature defoliation reduced ABA content of the axes, but did not prevent the induction of embryo dormancy. ABA content of mature seeds declined during stratification at both 5° and 20°C, with maximum differences occurring in the embryonic axis, but dormancy was broken only at 5°. Induction of secondary dormancy by high temperature (27°) was accompanied by a slight decline in ABA content of whole seeds.

Open access

D. J. Gray

Abstract

Orthodox seeds enter an arrested growth phase during their final stages of development that follows closely after seed coat hardening, reduction of water content, and maturation of embryonic and storage tissues. This resting phase may last for a number of years, depending on species and environmental conditions (2), and is the major factor accounting for the efficient storage and handling qualities of seed. A similar resting phase induced in synthetic seed will be essential for propagation of many annual crop plants, especially those grown at high density over large areas (e.g., com, soybean, wheat, etc.) where planting efficiencies must be optimum. Additionally, a resting phase will be needed if synthetic seed is to be used for germplasm preservation.

Open access

Pamela J. Myers and Peter D. Ascher

Abstract

Dehiscence of a mature orchid fruit releases a multitude of seeds — more than a million per capsule in some species. Air currents carry the seeds, but few land on a site permitting germination; even fewer chance upon an environment suitable for development of a mature plant. The seed is microscopic and consists of the bare essentials: a seed coat modified for buoyancy, an embryo of from 8 to 100 cells, and, rarely, a small amount of undeveloped endosperm (2). All orchids require an external source of organic molecules for seed germination or seedling development. After germination, many exist for long periods, the entire life cycle in the case of true saprophytes, deriving carbohydrates and other organic molecules from exogenous sources. Various fungi, in mycorrhizal association with the orchid, provide these complex molecules.