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Mark J. Bassett and Arie Blom

The white-seeded snap bean `Early Wax' (Phaseolus vulgaris L.) was crossed with a black-seeded breeding line 5-593. The F2 segregation data are consistent with a three-gene model, in which all three genes must be homozygous recessive to give white seed coat. One of the genes is t because of segregation in F2 for plants with white flowers and partial seed coat coloration. We hypothesize that the genes ers and ers2 in the presence of f block all seed color expression in all genes for partial coloration of seed. The hypothesis of three recessive genes was confirmed in a backcross test involving `Early Wax' x F1. The interaction of ers and ers2 was tested in progeny tests of partly colored BC-F1 plants. One of the erasure genes, ers2, blocks color expression in color zones close to the hilum, but only in the presence of ers. The other erasure gene, ers, blocks color expression only in color zones beyond those close to the hilum in a manner similar to the restr locus of Prakken (1972). The old hypothesis that partly colored seed phenotypes require the presence of a second factor e in addition to t, where the function of e is vague and unspecified, should be discarded for lack of supporting evidence, Under the new hypothesis, soldier series phenotypes (e.g., bipunctata, arcus, virgata, and virgarcus) may express in t ers Ers2 by action of ers or in t Ers Ers2 by action of various genes for partly colored seeds other than ers.

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M. Edelstein, H. Nerson, F. Corbineau, and J. Kigel

The involvement of the seed coat in low temperature germination of melon seeds was examined in two accessions differing in their ability to germinate at 14°C: `Noy Yizre'el' (NY) (a cold-sensitive cultivar) and `Persia 202' (P-202) (a cold-tolerant breeding line). Submerging the whole seed, or covering the hilum with lanolin, strongly depressed germination of NY, but not of P-202. Accessions differed in germination response to decreasing O2 concentration, with NY showing higher sensitivity to hypoxia. Intercellular spaces in the outer layer of the seed-coat were evident in the more tolerant P-202, while in the sensitive NY this layer is completely sealed. Sensitivity to hypoxia was greater at 15°C than at 25°C and was greater in NY than in P-202. It is proposed that the seed-coat imposed dormancy at low temperature in NY is the combined result of more restricted oxygen diffusion through the seed coat and a greater embryo sensitivity to hypoxia, rather than imbibition impairment or a physical constraint.

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Jana Murovec

Murovec, J. Draslar, K. Bohanec, B. 2012 Detailed analysis of Cucurbita pepo seed coat types and structures with scanning electron microscopy Botany-Botanique 90 1161 1169 Nei, M. 1973 The theory and estimation of genetic distance, p. 45–54. In: Morton

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Milton E. Tignor Jr. and Courtney A. Weber

Current efforts in the study of citrus freeze hardiness including gene mapping and elucidating early induction processes require large populations of uniform seedlings. Related genera and intergeneric hybrids are often used in these studies and little is known about factors effecting their seedling emergence. We tested a total of 8 genotypes including Poncirus trifoliata `Rubidoux', Citrus grandis, C. sinensis `Pineapple', C. jambhiri `Schaub', C. paradisi `Duncan', C. aurantium (Brazilian), Carrizo citrange (P. trifoliata × C. sinensis), and Troyer citrange. A total of seven pre-planting treatments were used to evaluate seedling emergence rates. Expanding on the work of previous researchers, treatments were seed coat removal, hydrating in water (96 hours) at either 4, 25, or 35°C, acid scarification, or boiling. Generally, seed coat removal resulted in the most uniform emergence as compared to untreated controls. Presoaking at each temperature enhanced emergence in most varieties tested and 25°C was the best hydrating temperature. Acid scarification greatly delayed emergence in all genotypes tested except Troyer citrange and `Pineapple' orange which had enhanced emergence rates as compared to controls. Preplanting treatment with 100°C water was lethal in all varieties. Pretreatment of citrus seeds can enhance uniformity of germination, although optimum treatments for individual genotypes vary.

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James Dunlap, Brian Scully, and Dawn Reyes

Poor germination of lettuce seeds exposed to heat and salinity is attributed to a reduction in the capacity for embryo expansion. Ethylene and kinetin are proposed to overcome these stresses by increasing the expansion force of the embryo which ruptures the seed coat barrier to growth. To better understand the physiological mechanism regulating thermodormancy in the embryo, germination was determined for intact and decoated seeds from thermosensitive and thermotolerant varieties subjected to a critical range of temperature and salt (NaCl) stress. Although more tolerant of stress, the response of decoated seeds to ACC and kinetin was similar to the response of intact seeds. No interaction between ACC and kinetin was detected in decoated seed except under the most severe stress and in the thermosensitive variety. Heat and salt tolerance appear to be governed by the same physiological mechanism. We propose that the seed coat plays no qualitative role in the expression of lettuce seed thermodormancy. The response occurs exclusively in the embryo and may result from an inability to generate sufficient turgor pressure at supraoptimal temperatures for cell expansion.

Open access

M. H. Dickson and M. A. Boettger

Abstract

Lines and cultivars resistant to mechanical damage with white and colored seeds germinated 60–80% compared to under 20% for several major cultivars. Seed damage resistance was associated with transverse cotyledon cracking (TVC) resistance, r = .649, seed coat shattering (SH) resistance, r = .488, and seed coat weight, r = .373. The SH test indicates whether the seed coat is tightly or loosely adhered to the cotyledons. If % seed coat as a proportion of seed weight exceeded 10% and TVC and SH were under 10%, then damage resistance was almost always good. Weakness in any one character resulted in damage susceptibility. Damage resistant lines produced more vigorous seedlings than susceptible lines following seed maltreatment. Damage resistance was correlated, r = .722, with seedling vigor following seed impaction.

Open access

Keith Redenbaugh, David Slade, Peter Viss, and Jo Ann Fujii

Abstract

The importance of tissue culture for clonal propagation in agriculture continues to increase each year. In general, commercial use of tissue culture propagation has been limited to crops that have a high per-unit value, such as ornamentals and fruit and nut trees. A lowcost, high-volume propagation system is not available, but could be of significant value to medium per-unit value crops such as lettuce, celery, and many others (Table 1). For these crops, highvolume propagation potential of somatic embryogenesis combined with formation of synthetic seeds for low-cost delivery would open a new field for clonal propagation. Candidate crops for synthetic seed production can be classified into two categories: 1) those that have a strong technological basis, such that high quality somatic embryos can currently be produced, and 2) those with a strong commercial basis. The latter category of crops are those in which seed costs are high because of fertility problems, gamete instability, labor-intensive hybrid seed formation, or a number of other reasons. Currently, there are few crops (Table 1) that meet both requirements and are suitable for synthetic seed technology.

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Safi S. Korban, Dermot P. Coyne, and John L. Weihing

Abstract

Variations occurred in the rate of water uptake of seeds of different dry bean cultivars (Phaseolus vulgaris L). ‘Pinto UI11’ had a higher water uptake by 24 hours than the other 6 cultivars. The micropyle was the main site for water entry in white-seeded ‘Great Northern’ and it is inferred that the raphe and or hilum areas were mainly involved in water uptake in ‘Pinto UI11’. No water uptake through the seed coat of seeds of 7 cultivars occurred by 2, 4, or 8 hours and only a small amount by 24 hours, except ‘GN Star’ where no water uptake was noted indicating that it had an impermeable seed coat during that period.

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Jocelyn A. Ozga and F.G. Dennis Jr.

Exposure of stratified apple (Malus domestics Borkh. cv. Golden Delicious) seeds to 30C induces secondary dormancy. To determine if an increase in abscisic acid (ABA) content was associated with the loss in germination capacity, stratified seeds (3,- 6, or 9 weeks at 5C) were held at 30C for 0, 3, or 6 days. Stratification at 5C either had no effect or increased ABA content in embryonic axes, cotyledons, and seed coats. Exposure to 30C after stratification either did not affect or decreased ABA content of embryonic axes and seed coats; in contrast, cotyledonary ABA was increased. Seed coats, cotyledons, and embryonic axes stratified for 3, 6, or 9 weeks at 20C contained the same or higher levels of ABA in comparison with nonstratified seeds or seeds stratified at SC. Changes in ABA levels were not consistently correlated with changes in germination capacity during stratification or after exposure to 30C. These data suggest that changes in ABA are not related to changes in dormancy. Chemical names used: abscisic acid (ABA); butylated hydroxy-toluene (BHT); n-(trichloromethyl) thio-4-cyclohexene-1,2-dicarboximide(Captan).

Open access

Chia Ting Han, Yu Sung, and Ming-Tung Hsueh

fissure of the seed acts like a valve that allows water vapor to diffuse out of the seed under low surrounding relative humidity (RH), and it prevents water from entering the seed under high humidity ( Hyde, 1954 ). Seed coats of hardseeds can be made