The role of ethylene in the control of post-germination root growth of Lactuca sativa L. ‘Mesa 659’ was investigated in saline (0.1 m NaCl) and nonsaline media by the use of the ethylene absorbant Hg(ClO4)2 and the ethylene action inhibitors norbornadiene (NBD), silver thiosulfate (STS), and silver nitrate. Root growth was inhibited by 0.1 m NaCl, 0.32 to 1.6 µl·liter–1 ethylene, 0.35 mm ethephon, 0.05 mm kinetin, or 1mm ACC. Application of 1.0 to 4.0 ml NBD gas–air mixture or 0.001 to 1.0 mm STS enhanced the root growth in both saline and nonsaline media. The magnitude of response to NBD or STS under saline condition was greater or equal to that under nonsaline condition. NBD was most effective when applied at the time when the radicle was just protruding (1–2 mm). Kinetin or ACC inhibition of root growth was not reversed by NBD or AgNO3, indicating that such inhibition may not relate directly to ethylene action. We conclude that the sensitivity of lettuce roots to ethylene might be enhanced in saline medium even though growth may be reduced. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); 2,5-norbornadiene (NBD); N-(2-furfurylmethyl)-1H-purine-6-amine (kinetin); and (2-chloroethyl)phosphonic acid (ethephon).
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.
The emergence of lettuce (Lactuca sativa L. cvs. Grand Rapids and Mesa 659) seeds was enhanced by the pre-sowing permeation via acetone of growth regulators into the dry seeds. Emergence of photosensitive ‘Grand Rapids’ seeds from soil medium at moderate temperatures (20-18°C) was enhanced by permeation with gibberellic acid (GA3) alone. At supraoptimal soil temperatures, emergence of both cultivars was enhanced most effectively by a combination of GA3, kinetin and (2-chloroethyl phosphonic acid) ethephon).
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)].
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)