Search Results

You are looking at 71 - 80 of 3,687 items for :

  • light quality x
Clear All

Using spectral filters to reduce the amount of far-red (FR) light perceived by plants has been shown to effectively reduce internode elongation of many floriculture crops. It is theorized that gibberellin (GA) function is inhibited in some way by the increase in the red: far-red light ratio. Sex expression of flowers are effected by exogenous applications of gibberellin and cause a shift in flower sex expression towards maleness. The use of growth regulators (GA inhibitors) have demonstrated a shift towards femaleness. Flowering of spinach, a dioecious species, and cucumber (staminate and pistillate lines), a monoecious species, were surveyed for shifts in flower sex expression, indicating a suppression of GA. Male: female flower ratio decreased from 7.6:1 to 4.06:1 when comparing the controls and –FR for the staminate cucumber line and 1:13 to 1:40 for the gynecious cucumber line. The decrease in male flowers on plants grown in a –FR environment are an indication that the function of GA is inhibited. There was no significant effect on the male: female flower ratios of the spinach.

Free access

End-of-day (EOD) red (R) or far-red (FR) light treatments were used to study phytochrome-regulated growth and dry matter distribution in 2-week-old watermelon plants. Plants were exposed to low-intensity R or FR light for 15 min at the end of photoperiod for 9 consecutive days. End-of-day FR increased the petiole elongation in the first two leaves, which was accompanied by higher dry matter partitioning to the petioles after 3 days of treatments. However, total plant dry mass (above ground) in FR-treated plants increased significantly after 6 days of treatments. This indicates EOD FR regulated dry matter compensation among plant parts at the early stages of EOD light treatments, allowing plants to better adapt to the environment. Net CO2 assimilation rate in the second leaf of FR-treated plants also increased. Phytochrome involvement in these processes is suggested, since growth and dry matter distribution patterns were reversible when plants were treated with FR immediately followed by R.

Free access

Similarities exist between the effects of phytochrome and cytokinins on plant growth and development (e.g., chloroplast development, amaranthin synthesis, seed germination). It is unclear, however, if and how these two systems interact. The coaction between phytochrome and cytokinins was investigated by using Nicotiana plumbaginifolia plants transformed with the isopentenyl transferase (ipt) cytokinin gene and treated with end-of-day (EOD) red (R) and far-red (FR) light. The ipt gene was under control of either a constitutive cauliflower mosaic virus promoter (35S-plants) or an inducible, heat shock promoter (HS-plants). When treated with EOD FR light, whole plants were characterized by decreased chlorophyll concentrations and increased fresh weights. When treated with EOD R light, 35S-plants contained high concentrations of zeatin riboside (ZR) compared to plants treated with EOD FR light. When treated with EOD FR light, HS-plants contained high concentrations of ZR compared to plants treated with EOD R light. Both cytokinin responses were photoreversible. The reasons for the differences between the 35S- and HS-plant responses are not known. Results appear to implicate interactions between phytochrome and cytokinins in plant growth and development.

Free access

Pecan tree pruning is a standard cultural practice in commercial pecan farming operations. Pruning often promotes canopy light infiltration, air movement, and crop load management. Timing of pecan tree pruning is often during winter for labor and time management purposes, yet the most effective pruning time is not known for pecan. `Pawnee' trees were pruned during March (winter), May, June, July and August in a commercial orchard in Charlie, Texas during the 2003 and 2004 growing seasons. June pruning produced the greatest two year summed annual average yield (2447.7 kernel lb/acre), largest increase of kernel lb/acre (625%) and largest increase percent kernel (113%) between 2003 and 2004. Furthermore, June produced the largest nuts (39.8 nuts/lb) with the lowest yield (337.5 kernel lbs/acre) in 2003, and smallest nuts (59.4 nuts/lb) with the highest yield (2110.2 kernel lb/acre) in 2004. March pruning produced the least variable yield of kernel lb/acre (38% decrease) between 2003 and 2004. July pruning produced the most consistent percent kernel (1.3% increase) between 2003 and 2004. August pruning produced the lowest two year summed annual average yield (879.8 kernel lbs/acre). Percent light transmission and leaf area index data showed no correlation with pruning times and kernel yields. Data collection will continue for another 2 to 3 years to asses the continuous affects of varied pruning times.

Free access

Rosa ×hybrida `Samantha' plants were grown under high-pressure sodium (HPS) lamps, HPS lamps fitted with blue gel filters to reduce the red to far-red (R:FR) ratio, or metal halide lamps. R: FR ratios were 1:0.95, 1:2, and 1:0.26 for HPS; filtered HPS, and metal halide, respectively. Although the R: FR ratio for metal halide was 3.5 times higher than for HPS, the total energy from 630 to 750 nm was 2.8 times lower. At a nighttime supplemental photosynthetic photon flux of 70 to 75 μmol·m-2.s-1, plants under HPS and metal halide lamps produced 49 % and 64% more flowering shoots, respectively, than those under filtered HPS (averaged over two crop cycles). The quality index for flowers under HPS, metal halide, and filtered HPS was 25.0, 23.3, and 18.5, respectively. Vase life was 10 to 11 days, regardless of treatment.

Free access

Abstract

Ficus benjamina was held in light-and-temperature-controlled chambers for 12 weeks under 3 light sources of 20 μE m−2s−1 incandescent (INC) lamps, 20 μE m−2s−1 Cool White fluorescent (CWF) lamps, or 10 μE m−2s−1 INC + 10 μE m−2s−1 CWF light combination totaling 20 μE m−2s−1 photosynthetically active radiation (PAR). Plants also received 4 light durations (6, 12, 18, or 24 hr/day). Growth index was greater for plants held under INC. When plants were held under the light combination, leaf drop was reduced and plant grade was improved. Dry weight and plant grade increased and leaf drop decreased when plants were lighted for 24 hr/day. Chlorophyll content decreased under the light sources in the following order: CWF> light combination >INC.

Open Access

Abstract

Two-year-old peach trees [Prunus persica (L.) Batsch cv. Candor] on ‘Lovell’ rootstock were summer-pruned (selective thinning and heading of current season's growth) 23 days before harvest. Pruning did not affect fruit quality. Summer pruning increased yield the subsequent year, apparently by increasing fruiting wood in the center of the tree. Summer pruning vigorous 3-year-old ‘Loring’ peach trees 8 weeks before harvest increased PAR through the canopy, 1 m above the ground, immediately after pruning and when measured at harvest. Fruit from summer-pruned ‘Loring’ were firmer, with lower soluble solids than those not summer-pruned.

Open Access

The effects of supplementary irradiance (20 μmol·s-1·m-2 for 6 hours) with incandescent light (I) or fluorescent compact gas-discharge lamps (CF) vs. a basic irradiance (96 μmol·s-1·m-2 for 12 h) with fluorescent (F) light at 17 or 25C was studied for Achimenes hybrids `Flamenco', `Hilda', and `Rosenelfe'. The additional I increased leaf area (LA) and plant dry weight (DW) in `Hilda' and `Rosenelfe' and promoted stem elongation in all three cultivars. Additional F had no effect on DW. However, depending on cultivar, responses for LA varied. An increase in the number of flowers was promoted only in `Rosenelfe' by I and CF compared with the control. In all cultivars, the supplementary CF, when compared with the I, reduced LA and DW. LA was significantly larger and DW higher at higher temperature, except for `Rosenelfe', where DW was not influenced and LA was smaller at the higher temperature. All three cultivars produced a longer stem and more flowers at the higher temperature. Calculated growth responses were influenced by an interaction between temperature and cultivar.

Free access
Author:

Abstract

Fruit of tomato (Lycopersicon esculentum Mill.) illuminated with red, blue, green, and white lights at the same radiant energy level were compared with controls kept in the dark for texture, color and solids and acid content during the ripening period. Red light was the most effective of the various light sources in softening of the tissue and in lowering the reflectance value in the early stages of ripening. Blue light was most effective in producing the enhancement of red hue in the later stages of ripening. Little effect on solids and acid contents was noticed.

Open Access
Authors: and

A preliminary study suggested light distribution (400-700nm) did not change from terminal bud set (July) to harvest (9/9/88). Therefore, limbs of 5-year-old trees were shaded the last 90 days of the season in 1988 and 7-year-old trees were shaded the last 60 days in 1989 with 30, 63, 95% or no shadecloth. Medium (63%) and heavy (95%) shade decreased fruit weight both years. Fruit soluble solids (SSC) decreased with increasing shade in 1988 but not in 1989 until after 60 days of storage. Fruit peel chlorophyll (chl) declined with time for all treatments. Apples from full sun and heavy shade treatments had the lowest chl and visually appeared the lightest. Evidence from both years suggested there was an optimal light level between 37-70% full sun for maximum fruit color and chl. Link of 7-year-old trees were shaded at intervals, light all season, mid-season and late season. Fruit weight and firmness were not affected by time of shading. SSC was liner for mid-season shaded fruit. Chl was highest for late season shaded fruit but differences evaporated by 90 days of storage.

Free access