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  • Author or Editor: Donald T. Krizek x
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Abstract

The human needs for food, fiber, and raw materials rapidly are outstripping supply (10). Worldwide losses of crops from plant diseases, insect pests, and adverse weather conditions total billions of dollars annually. It is axiomatic that improvements in crop productivity can be made only through 2 basic approaches: 1) by modifying plant genotypes to fit their environment better; and 2) by changing the environment to ameliorate the effects of environmental stresses.

Open Access

Abstract

The foil potential of horticultural and agronomic crops is seldom reached because of limitations on physiological and morphological processes imposed by environmental stresses. The single most important factor limiting productivity and crop yield on a worldwide basis is drought (10).

Open Access

Abstract

Recent droughts in the United States, Africa, and other parts of the world have focused attention on the fact that the world’s water supply is declining rapidly. Maximum potential of horticultural and agronomic crops seldom is attained under natural conditions because of limitations imposed by drought, flooding, cold, heat, acid soils, and other environmental stresses (85, 87, 172).

Open Access

Roots exposed to drying soil have been shown to generate non-hydraulic signals which can be communicated to the shoot. Such `root signals' can cause an inhibitory effect on leaf growth without causing detectable water deficits in the shoots. Plants grown in restricted root zone volumes also typically show a reduction in leaf and shoot growth. Although water stress and root restriction both impair growth, their effects on photosynthesis, leaf initiation, and C, N, and P metabolism may be quite different. Abscisic acid (ABA) has been shown to be produced in the roots after only mild dehydration and to play a major role in signal transduction from the roots to the shoots. Whether root-restricted plants are capable of generating `root signals' such as ABA or other plant hormones, which can be communicated to the shoot, remains to be determined. The application of new tools, such as gas chromatography/mass spectrography for hormone analysis, nuclear magnetic resonance imaging, and photoacoustic spectroscopy, should help to identify the nature of `root signals' generated during root restriction and clarify their regulatory role in shoot behavior.

Free access

Abstract

The ASHS Working Group on Controlled Environments will sponsor an informal Evening Discussion on “Growth Chamber Research” at the annual ASHS Meeting in Miami, Florida on Monday, November 2.

Open Access

Cellulose diacetate has been widely used in UV-B enhancement studies under field and controlled-environment conditions since the early 1970s to remove wavelengths below ≈290 nm, without any evidence of toxicity effects. However, while conducting UV-B exclusion studies in window boxes covered with cellulose diacetate (CA) or in Plexiglas chambers lined with CA, there was marginal chlorosis and cotyledon epinasty in `Ashley' cucumber, which is normally resistant to elevated UV-B, while seedlings exposed to open sunlight and those grown under polyester (PE) film to exclude UV-B were free of visible injury. These findings suggested that the CA filter itself may be causing toxicity. To test this hypothesis, a UV exclusion study was conducted in which CA or Teflon (T), both UV-B and UV-A transmitting films, were used to cover window boxes in the following four combinations (top/bottom): CA/CA, CA/T,T/CA, and T/T. When CA was used as the bottom filter (CA/CA and T/CA), the plants showed significantly greater leaf injury and a 2- to 3-fold reduction in growth than when T was used as the bottom filter (CA/T and T/T). These findings suggest that toxicity is caused by CA itself rather than by solar UV-B radiation, possibly as a result of outgassing of phthalates known to be used as plasticizers in the manufacture of CA. Further evidence that CA was responsible for leaf injury was provided by a companion study in which T was replaced by PE and damage was still observed, although no significant growth effects of CA position were observed.

Free access

Abstract

Recently Raulston (1) reported that photoperiod and nutrition were important in determining the earliness and no. of inflorescences in annual statice (Limonium sinuata L.). Our results, based on date of first visible flower stalk (flowering) (Table 1) are comparable to his findings. Plants under Long Day (LD = 16 hr) came into flower an average of 22 days earlier than under Short Day (SD = 8 hr) treatment. The time of appearance of the first visible flower stalk varied greatly depending upon the cultivar and the photoperiod. Under LD, ‘Iceberg’ and ‘Gold Coast’ flowered first (an average of 115 days) while ‘Blue Bonnet’ and ‘Midnight Blue’ flowered last (an average of 139-140 days). ‘Twilight Lavender’ and ‘American Beauty’ were intermediate (approx 126-128 days). The greatest influence of photoperiod, however, was on the % of plants flowering. An average of 98% of the plants flowered under LD while only 52% flowered under SD. Flowering in ‘Gold Coast’ and ‘Iceberg’ under SD was reduced by ca. 20% while ‘Blue Bonnet’ failed to flower (Table 1).

Open Access

Abstract

Comparative SO2 sensitivity was determined for red, pink, marble, and white cultivars of poinsettia, Euphorbia pulcherrima Willd. ex Klotzsch, belonging to 4 groups of sports: ‘Paul Mikkelsen’, ‘Annette Hegg’, ‘Eckespoint C-l’, and ‘Oakleaf’. Based on injury to the bracts, sports of the ‘Eckspoint C-l’ group were the most insensitive, whereas sports from the ‘Annette Hegg’ and ‘Paul Mikkelsen’ groups were the most sensitive. However, based on the number of leaves showing SO2 injury, sports from the ‘Oakleaf’ group were the most insensitive and those of the ‘Paul Mikkelsen’ group were the most sensitive. True leaves were generally much more sensitive to SO2 exposure than were corresponding bracts. There was no consistent relationship between bract color and extent of SO2 injury.

Open Access

Abstract

The influence of 3 germination temperature (16/13°, 21/18°, and 27/24°C day/night) and 2 growing temp (24/16° and 26/24°C day/night) on flowering in 6 cultivars of annual statice (Limonium cv.) grown under long days was determined over a 24-week period. When grown at 24/16°C nearly all of the plants produced a visible flower stalk irrespective of the germination temp. Flowering percentages at 26/24°C varied greatly, depending upon the cultivar and the germination temp. When grown at a temp of 26/24°C, the percentage of ‘Blue Bonnet’ flowering was low regardless of the germination temp. However, the percentage of ‘Midnight Blue’, ‘Iceberg’, and ‘Twilight Lavender’ plants flowering at a growing temp of 26/24°C was higher following germ temp of 16/13° or 21/18°C. ‘Gold Coast’ flowered irrespective of temp treatment. Except for ‘Gold Coast’, plants grown at 24/16°C generally had the earliest and greatest number of mature flower stalks, and the highest flower stage. Thus, growing temp appears to be the chief determinant of flowering in annual statice.

Open Access