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- Author or Editor: Theodore W. Tibbitts x
Vapors of ethylene glycol, 1,2 ethanediol, were found to cause serious injury to cucumbers in controlled-environment rooms in which this chemical was utilized for heat transfer. A chlorotic injury, which later became necrotic, occurred at the leaf apices and progressed along the margins to cause stunting and cupping of the leaves. High concentrations caused cessation of shoot growth and produced florets with short petals and stunted sepals. The source of the contaminating vapors appeared to be residual ethylene glycol from leaks over the years that had impregnated the floors or walls of the rooms. Activated charcoal or potassium permanganate filters installed in the circulating air stream of the rooms effectively prevented injury.
The cotyledons of marigold, Tagetes erecta L., developed epinasty when reflective surfaces were maintained under the seedlings. Plain aluminum foil or white-painted foil induced up to 360° curvature as the cotyledons extended, whereas no epinasty occurred over the exposed surface of potting mix or black-painted foil. A gray-painted foil induced intermediate epinasty. Dry-weight accumulation of the seedlings was not significantly affected by the epinasty.
Chlorosis and necrotic spotting develop on the foliage of particular cultivars of potato (Solanum tuberosum L.) when grown under constant light. `Kennebec', a cultivar severely injured by constant light when propagated from tissue-cultured plantlets, also was injured when plants were propagated from small tuber pieces (≈1 g). However, plants did not develop injury when propagated from large tuber pieces (≈100 g). Plants from large tuber pieces grew more rapidly than plants from small tuber pieces. The role of plant vigor and carbohydrate translocation in controlling injury development is discussed.
Abstract
A system was developed for subjecting plants to elevated air ion levels. This system consisted of a rectangular Plexiglas chamber lined with a Faraday cage. Air ions were generated by corona discharge from frayed stainless steel fibers placed at one end of the chamber. This source was capable of producing varying levels of either positive or negative air ions. During plant exposures, environmental conditions were controlled by operating the unit in a growth chamber.
Plants of the potato (Solanum tuberosum L.) cultivars Denali, Norland, Haig, and Kennebec were grown for 42 days under three temperature cycling periods (thermoperiods) with continuous irradiation in two repeated experiments to help determine if temperature cycling might be varied to optimize tuber development of potatoes in controlled environments. Thermoperiods of 6/6 hours, 12/12 hours and 24/24 hours were established with the same temperature change of 22/14C and same controlled vapor pressure deficit of 0.60 kPa. The thermoperiod of 24/24 hours significantly promoted tuber initiation but slowed tuber enlargement in all four cultivars, compared to the thermoperiods of 6/6 hours and 12/12 hours. `Denali' produced the highest tuber and total dry weights under the 6/6 hours thermoperiod. `Kennebec' produced the highest tuber dry weight under the 12/12 hours thermoperiod. Thermoperiods had no significant effect on shoot and root dry weights of any cultivars. The major effect of thermoperiod was on initiation and enlargement of tubers.
Oedema, a physiological disorder, affects several cultivars of ivy geranium [Pelargonium peltatum (L.) L `Hér. ex Ait) when grown in greenhouses. This study investigated the regulation of oedema on this crop using far-red radiation because these wavelengths inhibited the injury on Solanaceous sp. Plants were exposed to far-red radiation from Sylvania #232 far-red lamps on abaxial and adaxial surfaces of leaves. A far-red photon flux of 15 to 20 μmol·m-2·s-1 (700-S00 nm) was not effective in preventing oedema injury. A far-red abaxial treatment during the light period tended to reduce the amount of injury that developed when photosynthetic photon flux was low (130-170 μmol·m-2·s-1), but this inhibition of the injury was absent with higher photon flux. The results from these studies indicate the use of supplemental far-red radiation treatments in greenhouses would not be justified because adequate and consistent control of the injury on ivy geraniums was not achieved.
An electron microprobe was used to determine tissue concentrations of Ca across 20-mm-long leaves of `Green Lakes' crisphead lettuce (Luctuca sativa L.) with and without tipburn injury. Concentrations within the fifth and 14th leaves, counted from the cotyledons, from plants grown under controlled-environment conditions were compared to concentrations within similar leaves obtained from plants grown under field conditions. Only the 14th leaf from plants grown under controlled-environment conditions developed tipburn. Injured areas on these leaves had Ca concentrations as low as 0.2 to 0.3 mg·g-1 dry weight. Uninjured areas of tipburned leaves contained from 0.4 to 0.5 mg·g-1 dry weight. Concentrations across the uninjured 14th leaf from field-grown plants averaged 1.0 mg·g-1 dry weight. Amounts across the uninjured fifth leaves from both environments averaged 1.6 mg·g-1 dry weight. In contrast, Mg concentrations were higher in injured leaves than in uninjured leaves and thus were negatively correlated with Ca concentrations. Magnesium concentrations averaged 4.7 mg·g-1 dry weight in injured leaves compared with 3.4 mg·g-1 dry weight in uninjured leaves from both environments. Magnesium concentrations were uniform across the leaf. Potassium concentrations were highest at the leaf apex and decreased toward the base and also decreased from the midrib to the margin. Potassium averaged 51 mg·g-1 dry weight in injured and uninjured leaves from both environments. No significant differences in K concentration were present between injured and uninjured leaves. This study documented that deficient concentrations of Ca were present in areas of leaf tissue developing tipburn symptoms and that concentrations were significantly higher in similar areas of other leaves that had no symptoms. This study also documented that Ca concentrations were significantly lower in enclosed leaves that exhibited tipburn symptoms than in exposed leaves that did not exhibit tipburn. Also, the amounts of Ca in plants that developed tipburn in controlled environments were lower than in plants of the same cultivar that did not develop tipburn in field plantings. The reduced levels of Ca in plants grown in controlled environments were associated with faster development rates compared with field-grown plants.
The physiological responses of four potato (Solanum tuberosum L.) cultivars to continuous irradiation were `determined in a controlled environment. Under a constant 18C and a constant photoperiod of 470 μmol·s-1·m-2 of photosynthetic photon flux, `Denali' and `Haig' grew well and produced large plant and tuber dry weights when harvested 56 days after transplanting. `Kennebec' and `Superior' were severely stunted, producing only 10% of the plant dry matter produced by `Denali' and `Haig'. The differences in leaf chlorophyll concentration and stomatal conductance were not consistent between these two groups of cultivars. The leaf net CO2 assimilation rates in `Kennebec' and `Superior' were lower, and intercellular CO2 partial pressures were higher than in `Denali' and `Haig'. These results indicate that inhibition of net CO2 assimilation in `Kennebec' and `Superior' was not due to a limiting amount of chlorophyll or to CO2 in the leaf tissues. Concentrations of starch in leaflets of `Kennebec' and `Superior' plants were only 10% of those in `Denali' and `Haig' plants, although soluble sugar concentrations were similar in the four cultivars. Therefore, the lower net CO2 assimilation rates in stunted `Kennebec' and `Superior' plants were not associated with an excess carbohydrate accumulation in the leaves.