A gibberellic acid (GA) biosynthesis inhibitor, tetcyclacis, induced dormancy in nondormant seeds of lettuce (Lactuca sativa L.), tomato (Lycopersicon esculentum Mill.), pepper (Capsicum annuum L.), carrot [Daucus carota var. sativus (Hoffn.)], onion (Allium cepa L.), celery (Apium graveolens L.), and impatiens (Impatiens novette), as most of the seeds failed to germinate after washing under conditions that permitted germination before dormancy induction. In lettuce seeds, tetcyclacis and paclobutrazol were more effective in inhibiting germination in light than in darkness. A 16- to 24-h soak treatment with tetcyclacis was sufficient to induce dormancy in nearly all seeds. Tetcyclacis failed to induce dormancy if applied after 6 h presoak in water. Dormancy induced by tetcyclacis was released by GA4+7 (a mixture of gibberellin A4 and A7), light, and moist-chilling treatments. When GA4+7 was applied with tetcyclacis, dormancy induction was prevented under both favorable, e.g., 25C, and unfavorable, e.g., 5C, or low water potential (Ψ), germination conditions. Unlike tetcyclacis, abscisic acid (ABA) failed to induce dormancy in lettuce seeds. Thermodormancy induction in lettuce seeds at 35C was prevented by fluridone. However, neither ABA nor tetcyclacis countered its effect. Dormancy was also induced in lettuce seeds by ancymidol, flurprimidol, or paclobutrazol. Dormancy induced by tetcyclacis in pepper, tomato, carrot, and onion seeds was released by GA4+7, but not by irradiation or moist-chilling. Chemical names used: 5-(4-chlorophenyl)-3, 4, 5, 9, 10-pentaazatetracyclo [5.4.102,6.08,11]-dodeca-3, 9-diene (tetcyclacis); 1-(4-chlorophenyl)-4, 4-dimethyl-2-(1H-1, 2, 4-triazole-1-yl)-3-pentanol (paclobutrazol); α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidine methanol (ancymidol); α-(1-methyl)-α-[4-(trifluoromethoxy) phenyl]-5-pyrimidine-methanol (flurprimidol); 1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4 (1H)-pyridinone (fluridone).
ACC-derived ethylene production was used as an index of seed vigor of lettuce (Lactuca sativa L.), cabbage [Brassica oleracea (Capitata Group)], tomato (Lycopersicon esculentum Mill.), snap bean (Phaseolus vulgaris L.), and sweet corn (Zea mays L.) seeds. Seeds were aged at 40C and 93% relative humidity over saturated solution of KH2PO4 for various times to obtain seeds of differing vigor. Naturally aged lettuce seeds, differing in vigor, were also used. Depending on the seed type, 0.25 to 2 mm ACC (saturating dose) was needed to produce maximal amounts of ethylene. Seeds in the presence of ACC produced a much larger amount of ethylene than those in the absence of ACC, the ACC-derived ethylene could be detected before germination, and ACC had no adverse effect on germination. ACC-derived ethylene production paralleled vigor loss as determined by a decrease in percentage germination over a soak period required for complete germination of nonaged seeds (16 hours for lettuce, 24 hours for cabbage, and 48 hours for tomato and sweet corn), an increase in mean germination time (determined for lettuce only), and a decrease in seedling growth (determined for snap bean only). Second degree polynomial and logarithmic equations generated for the relationship of ACC-derived ethylene production to germination or growth parameters following seed aging, provided good to excellent fit. As a vigor test, the ACC-ethylene procedure has several advantages over the non-ACC ethylene procedure: It improves the sensitivity of the test by enhancing ethylene production, permits detection of small differences in vigor, and allows detection of ethylene before germination within a few hours of soaking. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).
Preconditioning `Mesa 659' lettuce (Lactuca sativa L.) seeds with the moist solid carrier Micro-Cel E at 15C for 20 hours removed thermoinhibition and allowed the seeds to germinate at 35C. Participation of 1-aminocyclopropane-1-carboxylic acid (ACC) and its use in the removal of thermoinhibition were indicated from the following: a) the ACC level in the preconditioned seeds peaked before germination at 35C; b) addition of aminoethoxyvinylglycine (AVG), an inhibitor of ACC synthesis, reduced the ACC level and inhibited germination at 35C; c) response of preconditioned seeds to ethylene at 35C preceded that of ACC; d) exogenous ACC, (2-chloroethyl) phosphonic acid (ETH, ethephon), or ethylene reversed the inhibitory effect of AVG and restored the capability of the seed to germinate at 35C; e) Co+2, an inhibitor of the ACC-to-ethylene step, partially inhibited germination of preconditioned seeds at 35C, and the effect was reversed by ETH. The major free polyamines in dry seed were spermidine (Spd) and putrescine (Put). An increase in polyamine level occurred following transfer of conditioned seeds to 35C. Of the various polyamine biosynthesis inhibitors, difluoromethylarginine and cyclohexylammonium sulfate inhibited an increase in Spd and Put levels only after germination, whereas difluoromethyorinthine had no effect on polyamine biosynthesis. None of these inhibitors affected the relief of thermoinhibition. Thus, the increase in polyamine level during germination at 35C does not appear to be associated with the alleviation of thermoinhibition.
Seeds (intact or slit) of lettuce (Luctuca sativa L.) cultivars with greater ability to produce ethylene germinated better under stressful conditions. Highly significant correlations were found between ethylene production and germination in 0.1 m NaCI (- 0.49 MPa) solution at 25C (r = 0.95, intact seeds), in - 0.3 MPa PEG solution (r = 0.86, intact seeds; r = 0.81, slit seeds), and in water at 32C (r = 0.80, slit seeds) or 35C (r = 0.80, slit seeds). Slitting the seed coat increased the ethylene production and improved germination during osmotic restraint in most cultivars, particularly in `Mesa 659' and `Super 59'. The differing ability of cultivars to produce ethylene during stress generally corresponded with their ability to generate germination potential. Ethylene production and germination potential in untreated and ACC-treated `Mesa 659' seeds increased upon slitting under stressful conditions. Thus, the ability of seeds to produce ethylene and to generate high germination potential under stressful conditions may be used as criteria to select stress-tolerant lettuce cultivars. Chemical names used: polyethylene glycol 8000 (PEG), 1-aminocyclopropane-1-carboxylic acid (ACC), (2-chlorethyl) phosphoric acid (ethephon).
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.
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.
The effect of preplant conditioning on germination of three flower seeds, Bupleurum griffithii (Tourn.) L. (thorough-wax), Ammi majus L. (greater ammi), and Cirsium japonicum DC. Per. (Japanese thistle), were studied. Seeds were osmoconditioned with -1.2 MPa polyethylene glycol 8000 (PEG) solution and matriconditioned with moist Micro-Cel E (ratio of 2 seed: 0.6 carrier: 3 water by weight for Bupleurum and Cirsium; for Ammi the ratio was 2:1.4:6) and moist expanded vermiculite #5 (the ratio was of 2 seed: 0.6 carrier: 2 water for Bupleurum). In some treatments, water in the matriconditioning mixture was replaced with 1 mm gibberellin A4+7 (GA) or 0.2 % KNO3. In Bupleurum, matriconditioning with Micro-Cel E was generally superior to matriconditioning with vermiculite or osmoconditioning with PEG. A 4-day matriconditioning with Micro-Cel E and germination in the dark reduced the period required for 50% (T50 of final germination by 4 days and improved the percentage germination at 20C (73 % vs. 95%), compared to nonconditioned seeds germinated in the dark. The treatment also improved the percentage of germination at 15C (68% vs. 95%) and effectively removed the thermoinhibition of germination at 25 and 30C. Germination was inhibited to a greater extent for seeds kept in the light during matriconditioning and germination than for seeds conditioned in darkness and germinated in light or conditioned in light and germinated in darkness. Nitrate added during conditioning in light prevented inhibition of germination, provided seeds were kept in darkness during germination. In A. majus, germination in light after 4-day matriconditioning reduced the T50 by ≈2 days, but had little effect on percentage germination. Both GA and irradiance equally promoted germination when added during osmoconditioning, with nitrate having no effect. In C. japonicum, a 4-day matriconditioning or a 7-day osmoconditioning reduced the T50 of germination by -2 days and improved the percentage germination to some extent. Neither irradiance nor nitrate had any significant effect.
A matriconditioning procedure based on the matric properties of Micro-Cel E and expanded vermiculite #5 has proved effective in improving seedling emergence in growth chambers. The major objectives of this study were to examine some physical characteristics of the carriers and their effectiveness as preplant conditioning media in improving stand establishment of vegetable seeds in field plantings. Carrier characteristics included no detectable solute or osmotic potential, low electrical conductivity (0.48-0.04 mmho/cm), high water-retaining capacity (450% to 600%), a pH range of 7.0 to 8.4, and ability to effectively control seed hydration (conditioning) at low matric potential. The seed: carrier: water ratio for seed conditioning ranged from 1:0.3-0.5:1-2 (by weight). In a field trial, conditioning of `Long Imperator' and `Nantes' carrot (Daucus carota var. sativus Hoffm.) seeds reduced the time to 10% of final emergence (T10) by 2.6 to 2.8 days and to 50% of final emergence (T50) by 2.1 to 3.0 days. Conditioning increased the final emergence percentage by 39% in 1-year-old `Long Imperator' compared to 150% in 4-year-old `Nantes' seeds. In another field trial, the effect of conditioning on stand establishment was evaluated in `Jackpot' tomato (Lycopersicon esculentum Mill.), `California Wonder' pepper (Capsicum annuum L.), and `BBL 47' snap bean (Phaseolus vulgaris) seeds. In tomato, conditioning reduced the T10 by 0.9 day, had no effect on T50, and increased the emergence percentage by 86%. In pepper, conditioning reduced the T10 and T50 by 1.5 days and increased the percentage emergence by 30%. In snap bean seeds, conditioning in Micro-Ccl E reduced the T10 and T50 by 0.8 day but adversely affected the percentage emergence. Further reductions in T10 and T50 (1.2 and 1.6 days, respectively) and restoration of percentage emergence to control level occurred upon addition of 0.001 mM GA3 during conditioning. Fungicides added to carrot, tomato, and pepper seeds, with or without conditioning, showed no additional improvements and, in a few cases, adversely affected emergence. A preplant conditioning in Micro-Ccl E, alone or in combination with GA3, smears to be a viable alternative to conditioning! seeds in liquid carriers. Chemical name used: gibberellic acid (GA3)
Several chemicals applied to dry seeds by means of organic solvents were successful in preserving seed quality as determined by germinating capability of seeds or ATP content. The fungicide (pentachloronitrobenzene)-treated, injured or healthy pea (Pisum sativum L. cv. Alaska) seeds were highly resistant to infection by Aspergillus ruber (Konig, Spiekerman and Bremer) Thom and Church (NRRL 52), a storage fungus. The insecticide, Chlorpyrifos caused the lima bean (Phaseolus lunatus L. cv. Fordhook 242) seeds to produce seedlings with reduced levels of damage from the seed-corn maggot, Hylemya platura (Meigen). The antibiotics, chloramphenicol and puromycin, slowed down the rate of deterioration of lettuce (Lactuca sativa L. cv. Grand Rapids) seeds stored under accelerated aging conditions [43°C & 85% Relative Humidity (RH)].