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- Author or Editor: Anwar A. Khan x
Papaya (Carica papaya L.) seeds germinated poorly at 25C in the presence of gibberellin (GA4+7) or following matriconditioning at 25C for 4 days. However, a combined treatment of matriconditioning and GA4+7 for 4 days synergistically promoted germination and seedling emergence. Drying the seeds after conditioning reduced the percentage of seedling emergence in the combined treatment involving 400 μm GA4+7 only. Combining matriconditioning with 100 or 200 μm GA4+7could effectively reduce germination time and improve seedling emergence and is recommended as a standard procedure for testing papaya seed germination.
The effects of various drying conditions on seed quality and performance of matriconditioned `Bush Blue Lake 47' snap bean (Phaseolus vulgaris L.) seeds were studied. An exponential model based on the Page equation provided a good fit (R2 = 0.9) to changes in moisture content during drying. Drying matriconditioned seeds with high initial moisture content (47.2%) for 5 to 6 hours at 35C, 30% to 35% relative humidity, and 0.7 to 1.4 m·s-1 air velocity (v) retained, and in some cases augmented, the benefits derived from conditioning. Matriconditioning greatly reduced electrolyte leakage (34.3 vs. 94.7 μS·cm-1·g-1 for nontreated seeds); drying to 15% moisture content at 0.7 or 1.4 m·s-1 v moderately increased the leakage rate (59.1 to 60.9 vs. 34.3 μS·cm-1·g-1), while drying at 0.02 m·s-1 v (ambient) increased the rate to that of nontreated seeds. The leakage rate remained low (43.6 to 50.8 μS·cm-1·g-1) in matriconditioned seeds dried to 22% moisture content at all air velocities. In growth-chamber studies, rapidly drying matriconditioned seeds to 15% moisture content at 1.4 m·s-1 v improved the emergence percentage over that of nontreated seeds, increased the shoot fresh and dry weight over that of nontreated and nondried matriconditioned seeds, and increased the shoot fresh weight over that of seeds dried at 0.02 or 0.7 m·s-1 v. Drying matriconditioned seeds to 15% moisture content at 0.7 m·s-1 v improved plant fresh weight over that produced by nontreated seeds. Rapid drying to 22% moisture content at 1.4 or 0.7 m·s-1 v improved only shoot fresh weight over that of nontreated seeds. In a 1992 field planting, percent emergence of matriconditioned seeds dried at 0.7 or 1.4 m·s-1 v was similar to that of nondried matriconditioned seeds and higher than that of nontreated seeds. No significant differences were noted in plant yield among the treatments.
The level of 1-aminocyclopropane-1-carboxylic acid (ACC) was 0.55 nmol.g-1 in dry lettuce (Lactuca sativa cv. Emperor) seeds. After 4h soak at 25°, 35° and 35°C+ KIN (kinetin, 50μM), the levels were 0, 0.2 and 1.14 nmol.g-1 seeds, respectively. The level of ACC was higher at 35°+KIN than at 35°C for up to 16h soak. No ACC was detectable at 25°C during 2 to 16h soak. In the presence of 50μM ABA, ACC level decreased to 0.2 nmol.g-1 at 4h soak and to zero level during 8 to 16h soak. The level of l-(malonylamino) cyclopropane-1-carboxylic acid (MACC), in dry seeds was 14 nmol.g-1. Exposure to 35°C in the presence or absence of KIN increased the level to 40-42 nmol.g-1 within 2h soaking, while at 25° only a slight increase (23 nmol.g-1) occurred. As in the case of ACC, the level of MACC was higher at 35°C+ KIN than at 35° or 25° for up to 16h soak.When seeds were soaked in ABA, the pattern of MACC produced was similar to that produced at 35°C. The results indicate that ACC synthase activity is enhanced by the addition of KIN at 35°C resulting in increased synthesis and/or accumulation of ACC and MACC. The relationship of ethylene biosynthesis to changes during stress imposition and alleviation by various factors will be discussed.
Dormancy was induced in nondormant (germinate readily in light or darkness) seeds of several lettuce cultivars (Mesa 659, Emperor, Empress, Montello, Ithaca) by soaking in the dark in 5-100μM tetcyclacis (TCY) for 24h at 25°C as the seeds failed to germinate in the dark upon removal of TCY by washing. Higher concentrations of TCY was needed to induce dormancy in the light Paclobutrazol (PP 333) was relatively less effective. No dormancy was induced in nondormant lettuce seeds soaked for 24h in 100μM ABA as the seeds germinated readily in the dark upon removal of the inhibitor by washing. Thus, contrary to popular belief ABA does not appear to be a dormancy factor. Dormancy induced by TCY was released by soaking seeds in petri plates in water at 25°C in the light, in the presence of 0.001-1mM GA4+7, or by moist-chilling for 4-15d at 5°C. Dormancy was also released when dried dormant (dormancy induced by TCY) Mesa 659 or Emperor lettuce seeds were planted in a moist peat-lite mix in plastic containers and kept moist for 30d at 5°C, as indicated by emergence of normal, healthy seedlings upon transfer of the containers to 25°C. The significance of TCY induced dormancy in altering planting strategy in field plantings of lettuce and other crops will be discussed.
The effects of chemical or physical factors during pregermination imbibition phase, or on dry seeds, on embryo growth potential (EGP) was studied in lettuce (Grand Rapids and Mesa 659) and tomato (H-9889) seeds in relation to dormancy, invigoration, and vigor loss. Embryos were excised from treated seeds (washed if imbibed in chemical solutions) and their growth rate (a measure of EGP) followed at 25°C at high magnification (X55). Treated seeds were also germinated at 25°C. In lettuce seeds, dormancy inducing treatments, i.e., a 2-day dark soak at 25°C with 50–100 μM tetcyclacis (TCY) or a 2-day dark soak in water at 35°C, reduced the subsequent embryo growth and germination rate at 25°C. The reduction was prevented by 1 mM GA4+7 or irradiation applied during dormancy induction. A -d osmoconditioning (OC) at 15C with -1.2 MPa PEG-8000 solution in light or in dark with added GA4+7 enhanced the EGP; addition of TCY reduced the EGP and the TCY inhibition reversed by GA4+7. A progressive reduction in EGP occurred with increase in vigor loss. In tomato seeds, a soak with 100 μM TCY in light or dark for 2 days at 30°C induced a dormancy, but had little effect on EGP. Application of GA4+7 plus TCY prevented dormancy induction without affecting EGP. A 4-day matriconditioning (MC) at 25°C in light or dark with moist Micro-Cel E enhanced the EGP; TCY and/or GA added during MC, had little effect on EGP. EGP progressively decreased as the aging period increased. Thus, in lettuce, the EGP is coupled with the reversible –GA/+GA or phytochrome-controlled dormancy induction/release process, enabling germination, its inhibition, or its enhancement. In tomato, the EGP is not subject to light or GA control. Reduction in EGP, accompanying vigor loss in both seeds, is independent of light or GA action.
Recently we have shown that the performance of vegetable seeds can be enhanced by matriconditioning in the presence of fixed amounts of chemically inert carriers, such as Micro-Cel™E and Zonolite™ Vermiculite, and water (Khan et al. National Symp. Stand Estab. Hort. Crops, p.19, 1990). This procedure, however, does not allow separation of seeds from the carrier during seed conditioning. This problem has been overcome by enclosing the seed in a semi-permeable membrane and placing the seed-membrane system in contact with the carrier and water (or test solution). By this means, the equilibrium moisture content, needed for seed conditioning is attained readily. This procedure allows conditioning of large amounts of seeds and eliminates the contamination of seeds from the carrier. The application of this procedure in seed enhancement within the seed industry will be discussed.
Abstract
Improved emergence rate and final stand occurred when ‘Ruby Queen’ beet seed pellets, amended with 1.10 to 3.95 mg polyethylene glycol 8000 (PEG) per seedball, were field planted. The number of seedlings per seedball 17 days after planting ranged from 1.39 to 1.60 for PEG-amended pellets, compared to 0.71 plants for non-PEG pellets or dry seeds. The PEG-amended seed pellets yielded 16 to 18 marketable roots per meter of row compared to 11 roots from non-PEG pellets.
Abstract
A preplant acetone permeation of ‘Grand Rapids’ and ‘Mesa 659’ lettuce (Lactuca sativa L.) seeds with either cyclohexanecarboxamide 1-(3-chlorophthalimide) (phthalimide) or gibberellin A 4+7 (GA) in combination with kinetin (KIN) and/or (2-chloroethyl) phosphonic acid (ethephon) markedly relieved the adverse effect of high temperature (20°, 12 hr night/30°C day regime) on seedling emergence from soil. Permeation of GA in ‘Grand Rapids’ seeds increased seedling hypocotyl length by 121% compared to only 25% for phthalimide permeated seeds. In ‘Mesa 659’ seeds, the corresponding increases with GA and phthalimide permeation were 52% and 26%, respectively. Permeation of GA + ethephon + KIN and phthalimide + ethephon + KIN increased seedling hypocotyl elongation over the control by 126% and 60% in ‘Grand Rapids’ and 91% and 21% in ‘Mesa 659’, respectively. Seed permeation with phthalimide tended to increase the leaf chlorophyll content of emerging seedlings. Permeation of GA decreased leaf chlorophyll up to 28% in ‘Mesa 659’ and up to 13% in ‘Grand Rapids’. These findings indicate that phthalimide could be substituted for GA in seed treatments needed to alleviate the adverse effects of high temperatures on germination and seedling establishment and to improve growth characteristics of emerged seedlings.
Abstract
Permeation via acetone of fusicoccin (FC), or of a combination of the three growth regulators, kinetin (K), 2-chloroethyl(phosphonic acid) (ethephon) (E), and gibberellic acid (G) into dry lettuce (Lactuca sativa L. cvs. Grand Rapids and Mesa 659) seeds markedly relieved the inhibiting effects of stress on germination and seedling emergence. Permeation with FC or K+E+G increased dark germination by 80 to 90% at 30°C. At 35°, germination of ‘Grand Rapids’ seeds was enhanced much more by FC than by K+E+G. Both FC and K+E+G increased germination in solutions of NaCl (−4.95 bars) or polyethylene glycol-6000 (−3 bars). In saline medium at 30 and 35°, FC was more active than K+E+G. Hypocotyl and radicle elongation was greater for seeds treated with FC than for seeds treated with other materials in both aqueous and saline media. In soil moistened with water or 0.1 NaCl, emergence of unpermeated ‘Mesa 659’ seeds was 0 to 2% at 25°. Permeation with FC or K+E+G enhanced emergence 65–80% in water, 48–55% in NaCl. FC produced more vigorous seedlings in terms of fresh weight and size than any other treatment including K+E+G. Furthermore, FC generally shortened the emergence time more than K+E+G treatment, the difference being more marked in saline soil.
Seeds of six pepper (Capsicum Anuum L.) cultivars were treated with tetcyclacis (TCY), an inhibitor of the oxidative steps from ent-kaurene to ent -kaurenoic acid in the gibberellin biosynthetic pathway. Seeds were soaked in TCY solutions for 24h in darkness at 25° to 30°C, washed with water and then air-dried. Various concentrations of TCY were needed to induce dormancy in `Yolo Wonder', `Cayenne', `California Wonder', `Sweet Banana', `El Paso' and `Anaheim'. TCY-treated seeds were germinated in water and in various concentrations of GA4+7 in darkness. Dormancy induced by TCY was released with 10 μM GA4+7. The germination inhibitor, abscisic acid (ABA), failed to induce dormancy in pepper seeds even when treated at a concentration of 400 μM for up to 14 d. Similar results were obtained with tomato seeds and will be reported elsewhere. The results indicate that the absence or the unavailability of GA rather than the presence of ABA determines the dormant state in pepper seeds.