, and root sections of 14 sunn hemp accessions were evaluated for phytotoxicity in bioassays with the lettuce cultivar Green Ice. Bioassay for allelopathic potential. A lettuce bioassay for allelopathy using surface-sterilized seeds of cultivar Green Ice
Muhammad Mansoor Javaid, Manish Bhan, Jodie V. Johnson, Bala Rathinasabapathi and Carlene A. Chase
Andrew C. Schuerger and Philip D. Laible
`Yecora Rojo' Wheat (Triticum Aestivum L.) And `Florida Petite' Tomato (Lycoper-Sicon Esculentum Mill.) Plants Were Grown In Monocultured Or Intercropped Recirculating Hydroponic Systems To Determine Whether Plant Growth Or Yield Would Be Affected By Intercropping. Mean Fruit Weight Was Slightly Lower (12%) For Intercropped Than For Monocultured Tomato Plants. The Number Of Tillers Per Plant Was Slightly Lower (7%) For Wheat, And Grain Dry Weight Per Plant And Mean Seed Dry Weight Were Slightly Higher (14% And 15%, Respectively) For Intercropped Than For Monocultured Plants. A Lettuce Seedling Bioassay Showed No Evidence Of Allelopathic Compound Accumulation In Monocultured Or Intercropped Hydroponic Systems.
Iwanka Kozarewa, Daniel J. Cantliffe, Russell T. Nagata and Peter J. Stoffella
Ethylene synthesis and sensitivity, and their relation to germination at supraoptimal temperatures, were investigated in lettuce (Lactuca sativa L.) seeds matured at 30/20 °C [12-h day/night, high temperature matured (HTM)] or 20/10 °C [12-h day/night, low temperature matured (LTM)]. HTM seeds of both thermosensitive `Dark Green Boston' (DGB) and thermotolerant `Everglades' (EVE) had greater germination at a supraoptimal temperature (36 °C), in both light or dark, than LTM seeds of DGB and EVE. HTM seeds of DGB and EVE produced more ethylene during germination than LTM seeds, regardless of imbibition conditions. The ethylene action inhibitor, silver thiosulfate, led to reduced germination in both cultivars. The ethylene precursor, 1-aminocyclopropane-1-carboxylic acid at 10 mm increased germination of both cultivars at supraoptimal temperatures, whereas germination of HTM seeds was greater than that of LTM seeds. No differences in ethylene perception were detected between HTM and LTM germinating seeds using a triple response bioassay. This study demonstrated that at least one method through which seed maturation temperature influences lettuce germination is by affecting ethylene production.
Bala Rathinasabapathi, James Ferguson and Mark Gal
Shredded and chipped wood mulches are used for weed suppression in perennial fruit crops, in urban landscapes, and occasionally in vegetable crops. Wood chip mulches with weed-suppressing allelochemicals may be more effective for weed control, especially under sustainable and organic production systems, than mulches without such properties. The objective of this study was to test for the presence of water-soluble allelochemicals in wood chips derived from tree species, often found in wood resource recovery operations in the southeastern US. Presence of allelochemicals in water eluates of woodchips and leaves was evaluated in a lettuce bioassay. Eluates of wood chips from red maple (Acer rubrum L.), swamp chestnut oak (Quercus michauxii Nutt.), red cedar (Juniperus silicicola L.H. Bailey), neem (Azadirachta indica A. Juss.), and magnolia (Magnolia grandiflora L.) highly inhibited germinating lettuce seeds, as assessed by inhibition of hypocotyl and radicle growth. The effects of wood chip eluates from these five species were more than that found for eluates from wood chips of black walnut (Juglans nigra L.,) a species previously identified to have weed-suppressing allelochemicals. Tests on red cedar, red maple, and neem showed that water-soluble allelochemicals were present not only in the wood but also in the leaves. In greenhouse trials, red cedar wood chip mulch significantly inhibited the growth of florida beggarweed (Desmodium tortuosum DC.), compared to the gravel-mulched and no-mulch controls.
Ki Sun Kim and Ji Ny Lee
There are many ground covers native to Korea. Liriope spicata is very promising for landscaping purposes due to its waxy and dark-green foliage fragrant and pink flowers, as well as fruit. However, seeds harvested during late fall do not germinate at all if they are sown in spring. Thus, series of experiments were conducted to undestand the physiological mechanism of dormancy breaking and germination of Liriope spicata Lour. seeds and to determine the effective methods for enhancing seed germination. Fruit were harvested in October through December. Depulped seeds germinated rapidly, indicating that one or more inhibitors may be present in the pulps of fruit and/or seeds. GA3, NaOCl, NaOH, and H2SO4 treatments and dry cold treatment had no effect on germination, whereas wet, cold seed treatment for at least 30 days promoted germination up to 75% within 15 days. Optimum conditions for germination was continuous dark and 25/20 °C alternate temperature conditions. Extracts from pulps and seeds showed a strong inhibition effects on the germination of lettuce seeds, indicating that germination inhibitors are present in pulp and seeds. Since extracts from naked seeds did not show inhibition, inhibitory substances are thought to be present in pulp and seedcoat. Pulp and seeds were extracted with water and methanol and autoclaved at 115 °C, followed by bioassay experiments. Germination inhibitors were found water soluble and heat stable by series of bioassay experiments. Diluted extracts 4 to 8 times still maintained inhibitory effects. Optimum seed harvesting time was from 22 Nov. to 1 Dec., where seed germination was high without additional seed treatments. Total phenolic compounds and ABA contents of pulp and seeds decreased by wet cold seed treatment. Changes in total phenolic compounds and ABA in from October through December were correlated with germination during the seed development. When contents of total phenolic compounds and ABA were high, seeds did not germinate at all, while low contents resulted in good seed germination.
Richard L. Hassell and Dale W. Kretchman
Seed from six species of the Apiaceae and six parsley (Petroselinum crispum L.) cultivars with three seed lots of each parsley cultivar were tested for the presence of germination inhibiting substances. Aqueous leachate from seed of all six species inhibited germination of lettuce (Lactuca sativa L.) and radish (Raphanus sativus L.). Leachate from root parsley seeds (P. crispum tuberosum) were least inhibitory, while leachate from celery and celeriac (both Apium graveolens L.) seeds were most inhibitory. Inhibitory concentrations in leachate varied by seed lot within a cultivar. Aqueous leachate of seeds from the primary umbels caused less inhibition of germination than did leachate from tertiary umbels. Washing parsley seeds in aerated water for 3 hours or more removed some of the germination inhibitory substance as indicated by the germination bioassay. An aqueous extract prepared from seedcoat tissue, removed during mechanical scarification, inhibited radish seed germination; inhibition was proportional to the duration of scarification and the amount of seedcoat tissue extracted. Parsley seeds scarified ≤60 minutes germinated at rates comparable to washed seeds, but longer scarification time reduced germination. Washing seeds of Apiaceae prior to commercial drying and cleaning may be a practical solution for removal of inhibitors.
Richard J. McAvoy and Paige Kishbaugh-Schmidt
Easter lilies, Lilium longiflorum Thumb. cv Nellie White, were grown in a commercial pine bark-based medium (25% by vol.), amended with 0.5 g Acrylamide Acrylate Gel (AAG) per 1.6 liter pot. Lilies were grown in media drenched with ancymidol, at 0, 0.25, 0.375 or 0.5mg a.i.pot-1 following shoot emergence, or grown in media containing ancymidol impregnated AAG at 0, 0.25, 0.375 or 0.5mg a.i.pot-1. AAG applied ancymidol treatments resulted in a significant linear decrease in both lily stem and internode length as the rate of ancymidol increased. Drench applied ancymidol had no affect on stem or internode length. Stem and internode lengths of drench treated lilies were not significantly shorter than lilies not exposed to ancymidol. Bud length, leaf and bud number, and days to anthesis were not affected (P≤0.05) by any treatment. Ancymidol activity in the top, middle and bottom strata of medium filled containers, and in the leachate from these containers, was measured using a lettuce hypocotyl length bioassay. Ancymidol activity was uniformly distributed throughout the bark medium when applied in AAG. With this treatment, 10-15% of the ancymidol activity was detected in the leachate. When ancymidol was applied as a drench, over 95% of the activity was detected in the top two strata, with 70% in the upper most stratum and the rest in the leachate.
Howard F. Harrison Jr, Amnon Levi and C.S. Kousik
against weeds. Yu and Matsui (1994) found that cucumber root exudates contained a number of simple and complex phenolic compounds and organic acids that were inhibitory in a lettuce ( Lactuca sativus ) seedling growth bioassay. Soil sickness observed
Yu-Wei Liu and Chen-Kang Huang
pumps on the ion concentrations in nutrient solutions and growth of butterhead lettuce were examined. The effect of a ultraviolet sterilization system on the ions in the solution was also investigated. Materials and methods Nutrient solution circulation
James Ferguson, Bala Rathinasabapathi and Clinton Warren
greenhouse and field tests within 2 weeks after they were cut. Seeds of large crabgrass and redroot pigweed were purchased from Valley Seed Service (Fresno, CA). Lettuce bioassay. Preparation of water leachates of wood chips and a lettuce ( Latuca sativa