Journal of the American Society for Horticultural Science. American Society for Horticultural Science

Published by American Society for Horticultural Science
Online ISSN: 0003-1062
Publications
Effect of initial radicle length on the gravitropic curvature (A) and growth (B) of cucumber seedlings. (A) Seedlings with initial radicle lengths of 1, 3, 5, 7, or 9 mm were rotated 90° and their curvature periodically was recorded every 2 h at 25 °C. The vertical bar represents the 5% LSD value. (B) The net length of radicles with initial lengths of 1, 3, 5, 7, or 9 mm was measured after 12 h at 25 °C. The vertical bar atop each bar represents the standard deviation. 
Effect of temperature on the gravitropic curvature of cucumber radicles. (A) Seedlings with 5-mm-long radicles were rotated 90° when transferred to 2.5, 5.0, 10, 15, 20, or 25 °C. The degree of curvature was measured every 12 h for 48 h. The vertical bar represents the 5% LSD value. (B) Relationship between the degree of curvature and the accumulated thermal time calculated as [(T-Tb)x time], using Tb = 6.0 °C. (Insert) Correlation coefficients versus the base temperature for calculated values of termal time. 
Effect of prior temperature exposure on subsequent curvature. Seedlings with 5-mm-long radicles were held in a vertical orientation at 2.5, 5.0, 7.5, 10.0, or 12.5 °C for 0, 24, 48, or 72 h. They were then rotated 90° after transfer to 25 °C. The degree of curvature was measured after 12 (A), 24 (B), and 36 (C) h at 25 °C. The vertical bar represents the 5% LSD value. 
Effects of chilling on the subsequent growth and curvature of cucumber radicles. Seedlings with 5-mm-long radicles were held at 2.5 °C for 0, 6, 12, 18, 24, 30, 36, 42, or 48 h before being rotated 90° after transfer to 25 °C. The length of the radicle and the degree of curvature was measured at 12 (A), 24 (B), and 36 h (C). The vertical bar represents the 5% LSD value. 
Article
Germinating 'Poinsett 76' cucumber (Cucumis sativus) seeds are chilling sensitive, and subsequent radicle elongation is inhibited by exposure to nonfreezing temperatures below 10 degrees C. Reorienting germinated seeds with 5-mm-long radicles from a vertical to a horizontal position induced gravitropic curvature within 2 hours at 10 to 25 degrees C without significantly affecting the rate of radicle elongation. However, neither elongation nor curvature occurred in similar seeds held at 2.5 or 5 degrees C. Chilling seeds with 5-mm-long radicles at 2.5 degrees C for 18 hours significantly reduced the subsequent rate of radicle elongation at 25 degrees C by 47% compared with nonchilled control, while gravitropic curvature was reduced by only 34%. After 36 hours of recovery at 25 degrees C, the difference was even more pronounced; elongation was reduced by 26% while curvature was reduced by only 6%. Clearly, gravitropic curvature was less chilling sensitive than radicle elongation, despite the fact that differential elongation of cells in the radicle are needed to produce curvature. Exposing seeds with 5-mm-long radicles to a heat shock of 45 degrees C for 4 to 10 minutes significantly diminished the chilling-induced reduction in radicle elongation and gravitropic curvature.
 
Article
To investigate the effects of environment on plant volatile emissions, 'Waldmann's Green' leaf lettuce was cultivated under different levels of photosynthetic photon flux (PPF), photoperiod, and temperature. A modified growth chamber was used to sample plant volatile emissions nondestructively, over time, and under controlled conditions. Total volatile emission rates were significantly higher from lettuce cultivated under PPF of 360 or 200 micromoles m-2 s-1 compared to 105 micromoles m-2 s-1, and significantly higher under a 16-h photoperiod than an 8-h photoperiod. No differences were detected among emission rates from different temperature treatments. In controlled environments, emissions could be regulated by adjusting environmental conditions accordingly.
 
Article
A copolymer acrylamide acrylate gel was investigated as the sole root matrix for dark-grown seedlings of soybean (Glycine max Merr. 'Century 84'). Increasing Ca2+ in the hydrating solution of the hydrogel from 1 to 10 mM decreased its water-holding capacity from 97 to 46 mL g-1, yet water potential of the medium remained high, sufficient for normal plant growth at all Ca2+ concentrations tested. Elongation rate of dark-grown soybean seedlings over a 54-hour period was 0.9, 1.5, and 1.8 mm h-1 with 1.0, 2.5, or 5.0 mM Ca2+, respectively, but did not increase with further increases in Ca2+ concentration. Further study revealed that Na+ was released from the hydrogel medium and was taken up by the seedlings as Ca2+ increased in the medium. In dry hypocotyl tissue, sodium content correlated negatively with calcium content. Despite the presence of Na+ in the hydrogel, seedling growth was normal when adequate Ca2+ was added in the hydrating solution. Acrylamide hydrogels hold good potential as a sole growth matrix for short-term experiments with dark-grown seedlings without irrigation.
 
Article
Seeds of 'Rutgers California Supreme' tomato (Lycopersicon esculentum Mill.) were exposed to outer space conditions aboard the long duration exposure facility (LDEF) satellite in the space exposed experiment developed for students (SEEDS) project of the National Aeronautics and Space Administration (NASA). Seeds aboard the LDEF were packed in dacron bags forming four layers per sealed canister. Some of these seeds were used in Oklahoma and Florida for studies of germination, emergence, and fruit yield. Among all measured variables in three experiments, there was only one significant main effect of canister 2 versus canister 7 (for mean time to germination) and only one main effect of layer (for seedling shoot dry weight). There also were only two inconsistent canister x layer interactions in the germination tests. The contrast of Earth-based control seed versus space-exposed seed was significant four times: in Oklahoma in 1991 the mean time to germination of space-exposed seeds and the days to 50% of final germination were 0.7 days less than for Earth-based seeds, and in Florida in 1992 seedling percent emergence and shoot dry weight were increased by space exposure. Fruit yield and marketability were unaffected in plants grown from space-exposed seeds. These results support student findings from the SEEDS project, and provide evidence that tomato seeds can survive in space for several years without adverse effects on germination, emergence, and fruit yield.
 
Article
The effect of root-zone temperature on young tomato plants (Lycopersicon esculentum Mill. cv. Heinz 1350) was evaluated in controlled environments using a recirculating solution culture system. Growth rates were measured at root-zone temperatures of 15 degrees, 20 degrees, 25 degrees, and 30 degrees C in a near optimum foliar environment. Optimum growth occurred at 25 degrees to 30 degrees during the first 4 weeks of growth and 20 degrees to 25 degrees during the 5th and 6th weeks. Growth was severely restricted at 15 degrees. Four concentrations of gibberellic acid (GA3) and kinetin were added to the nutrient solution in a separate trial; root-zone temperature was maintained at 15 degrees and 25 degrees. Addition of 15 micromoles GA3 to solutions increased specific leaf area, total leaf area, and dry weight production of plants in both temperature treatments. GA3-induced growth stimulation was greater at 15 degrees than at 25 degrees. GA3 may promote growth by increasing leaf area, enhancing photosynthesis per unit leaf area, or both. Kinetic was not useful in promoting growth at either temperature.
 
Article
Baked ceramic aggregates (fritted clay, arcillite) have been used for plant research both on the ground and in microgravity. Optimal control of water and air within the root zone in any gravity environment depends on physical and hydraulic properties of the aggregate, which were evaluated for 0.25-1-mm and 1-2-mm particle size distributions. The maximum bulk densities obtained by any packing technique were 0.68 and 0.64 g cm-3 for 0.25-1-mm and 1-2-mm particles, respectively. Wettable porosity obtained by infiltration with water was approximately 65%, substantially lower than total porosity of approximately 74%. Aggregate of both particle sizes exhibited a bimodal pore size distribution consisting of inter-aggregate macropores and intra-aggregate micropores, with the transition from macro- to microporosity beginning at volumetric water content of approximately 36% to 39%. For inter-aggregate water contents that support optimal plant growth there is 45% change in water content that occurs over a relatively small matric suction range of 0-20 cm H2O for 0.25-1-mm and 0 to -10 cm H2O for 1-2-mm aggregate. Hysteresis is substantial between draining and wetting aggregate, which results in as much as a approximately 10% to 20% difference in volumetric water content for a given matric potential. Hydraulic conductivity was approximately an order of magnitude higher for 1-2-mm than for 0.25-1-mm aggregate until significant drainage of the inter-aggregate pore space occurred. The large change in water content for a relatively small change in matric potential suggests that significant differences in water retention may be observed in microgravity as compared to earth.
 
Effects of 6 d of mechanical stress treatments in two different growth environments on shoot dry weight and leaf area of Arabidopsis seedlings. 
Effects of different day/night temperature regimes and the resultant average daily temperature (ADT) on average plant hypocotyl length (top) and average leaf area per plant (bottom), as well as on plant responsivity to daily brush treatments. Second-order regression equations are as follows: Length/control: y = 0.054x2-0.098x + 0.45 Length/stress: y = 0.044x2-0.079x + 0.24 Leaf area/control: y =-0.016x2 + 0.033x + 0.30 Leaf area/stress: y =-0.013x2 + 0.086x + 0.0094 
Article
Obtaining uniform mechano-dwarfing of Arabidopsis thaliana (L.) Heynh. seedlings within dense plantings is problematic. Alternative forms of mechano-stimulation were applied to seedlings in effort to obtain uniform growth reduction compared with undisturbed controls in both greenhouse and controlled growth environments. Arabidopsis grown under low photosynthetic photon flux (PPF) artificial light grew upright with limited leaf expansion, which enhanced mechano-responsiveness compared to that of rosette-growing plants under filtered sunlight or high PPF artificial light Hypocotyls of seedlings grown at PPFs >60 μmol·m-2·s-1 elongated less and had 6% less sensitivity to mechanical stress than seedlings grown at PPFs <60 μmol·m-2·s-1. Fluorescent lamps alone (F) or fluorescent plus incandescent (F+I) lamps were compared for seedling responses to mechanical stress. Under F lighting, hypocotyl elongation was reduced 25% to 40% by twice-daily brush or plate treatments, and brushed seedlings exhibited more growth reduction than did plate treatments. Seedlings grown under F+I lamps exhibited similar stress-induced growth reduction compared to seedlings grown under F only, but stressed F+I seedlings lodged to a greater extent due to excessive hypocotyl elongation. Temperature-response studies using standardized F-only lighting indicated increased hypocotyl elongation but decreased leaf expansion, and decreased mechano-responsivity to brushing over the temperature range from 20 to 28°C. Daylength studies indicated similar degrees of mechano-inhibition of hypocotyl elongation over the daylength range of 12, 16, 20, and 24 hours, whereas fresh weight of stressed seedling shoots declined compared to controls. A combination of environmental growth parameters that give repeatable, visual mechanical dwarfing of Arabidopsis include low-PPF fluorescent lighting from 55 to 60 μmol·m-2·s -1, ambient temperatures from 22 to 25°C, and twice-daily brush treatments.
 
Article
The young developing leaves of 20-day-old lettuce plants (Lactuca sativa L. 'Buttercrunch') were enclosed by aluminized polyethylene sheaths to decrease transpiration and reduce Ca transport. The plants were grown in recirculating solution culture system using a modified half-strength Hoagland's solution under cool-white fluorescent lamps with a photosynthetic photon flux of 350 micromoles s-1 m-2 in a 16:8-hr (light:dark) period. Air temperature and humidity were 20 degrees C and 65%, respectively. After 4 days of enclosure, 53% of the inner leavers (leaves one to 3 cm in length) were tipburned. After the same period, less than 1% of the inner leaves on control plants were tipburned. The concentration of Ca in enclosed inner leaves was 0.63 mg g-1 dry weight, compared to 1.48 mg g-1 dry weight in inner leaves that were not enclosed. The Ca concentration in transpiring outer leaves of all plants was 9.9 mg g-1 dry weight. The Mg concentration in enclosed inner leaves was 2.25 mg g-1 dry weight, compared to 2.34 mg g-1 dry weight in inner leaves that were not enclosed. This research documents that enclosures of leaves at the growing point, as would occur with normal head development, is sufficient to create a limiting concentration of Ca in the enclosed tissue and encourage tipburn development.
 
Effect of PPF on diurnal changes in net carbon assimation rate of newly mature 'Norland' potato leaves exposed to different photoperiods. The mean PPF values were 263 and 412 µmol·m-2 ·s-1 in the low and high light chambers, respectively.
Effect of CO 2 concentration on net carbon assimilation of newly mature 'Norland' potato leaves exposed to different photoperiods. The mean PPF values were 263 and 412 µmol·m-2 ·s-1 in the low and high light chambers, respectively. 
Effect of PPF on diurnal changes in leaf starch concentration of newly mature 'Norland' potato leaves exposed to different photoperiods. The mean PPF values were 263 and 412 µmol·m-2 ·s-1 in the low and high light chambers, respectively. 
Effect starch concentration on net carbon assimulation rate of newly mature 'Norland' potato leaves grown in either high or low light conditions. The mean PPF values were 263 and 412 µmol·m-2 ·s-1 in the low and high light chambers, respectively. 
Article
The effect of photoperiod (PP) on net carbon assimilation rate (Anet) and starch accumulation in newly mature canopy leaves of 'Norland' potato (Solanum tuberosum L.) was determined under high (412 varies as mol m-2s-1) and low (263 varies as mol m-2s-1) photosynthetic photon flux (PPF) conditions. The Anet decreased from 13.9 to 11.6 and 9.3 micromoles m-2s-1, and leaf starch increased from 70 to 129 and 118 mg g-1 drymass (DM) as photoperiod (PP) was increased from 12/12 to 18/6, and 24/0, respectively. Longer PP had a greater effect with high PPF conditions than with low PPF treatments, with high PPF showing greater decline in Anet. Photoperiod did not affect either the CO2 compensation point (50 micromoles mol-1) or CO2 saturation point (1100-1200 micromoles mol-1) for Anet. These results show an apparent limit to the amount of starch that can be stored (approximately 15% DM) in potato leaves. An apparent feedback mechanism exists for regulating Anet under high PPF, high CO2, and long PP, but there was no correlation between Anet and starch concentration in individual leaves. This suggests that maximum Anet cannot be sustained with elevated CO2 conditions under long PP (> or = 12 hours) and high PPF conditions. If a physiological limit exists for the fixation and transport of carbon,then increasing photoperiod and light intensity under high CO2 conditions is not the most appropriate means to maximize the yield of potatoes.
 
Carbon use efficiency (CUE), daily carbon gain (DCG), and cumulative carbon gain (CCG) of petunia (study 17) as affected by four fungicides. Data represent the mean of two gas-exchange chambers with 60 plants each. Both absolute values (A, C, E) and data expressed as a percentage of the control plants (B, D, F) are shown. Error bars represent selected LSD 0.05 s. 
The effect of different fungicides on the net photosynthesis of impatiens (AC) and petunia (D) under greenhouse conditions. Data represent the mean of two gas-exchange chambers with 60 plants each. Error bars represent LSD 0.05. Note: only five of the seven treatments in the legend (A) were used in each individual study. 
The effect of two different Benlate DF lots on net photosynthesis of petunia seedlings (study 3). Plants were drenched with a 1× rate (10 L·m-2 of fungicide solution with 1.2 g·L-1 of Benlate DF). Data were collected in gas-exchange chambers with 350 plants/chamber. Both absolute values (A) and data expressed as a percentage of the control plants (B) are shown. 
Article
Benzimidazoles are effective and widely used fungicides, but they may be phytotoxic. We studied the effects of a single drench application of six benzimidazoles and one acetanilide fungicide on photosynthetic gas exchange, growth, development, and nutrient levels of four species of bedding plants in twenty growth-chamber and four greenhouse studies. Daily carbon gain and carbon-use efficiency were calculated from continuous crop gas-exchange measurements in the growth chambers. The maximum labeled rate of Benlate DF caused a 7- to 10-day decrease in net photosynthesis and daily carbon gain in transplants of all species. It also caused pronounced interveinal chlorosis and a 2- to 3-day delay in flowering. Growth of Benlate DF-treated plants was reduced more at high (90%) than at low (60% to 80%) relative humidity. Benlate DF had severe effects on 2-week-old petunia (Petunia xhybrida) seedlings in plug flats, reducing photosynthesis 25% to 57%. Cleary's 3336 WP decreased photosynthesis in some trials. Benlate DF reduced photosynthesis within 24 hours, but 3336 WP effects did not become apparent until 1 week after the treatment. This suggests different modes of inhibition. 3336 WP also caused leaf-tip and marginal chlorosis in impatiens (Impatiens wallerana). Mertect 340-F was extremely phytotoxic but is not labeled for drench applications (it was included because of its chemical similarity to other benzimidazoles). The only benzimidazole fungicide that did not reduce photosynthesis was Derosal, but it caused slight interveinal chlorosis in some studies with petunia. Benlate DF and Derosal decreased leaf Ca levels. Subdue (or metalaxyl), an acetanilide fungicide, did not affect photosynthesis or cause any visual symptoms. Our results indicate that some benzimidazole fungicides can cause growth reductions and visual damage in bedding plants.
 
The 10-chamber gas-exchange system used in Study 1. There are fi ve chambers on each side of a walk-in growth chamber. Each chamber has a refl ective skirt wrapped around the outside to minimize side lighting. 
A single canopy of Buttercrunch lettuce grown at a PPF of 1000 µmol·m-2 ·s-1 with meristem aeration. The canopy has a refl ective metal barrier to minimize side-lighting, an infrared sensor to measure leaf temperature, and a fi ne-wire thermocouple positioned on the underside of the leaf for additional monitoring of leaf temperature. Plants are 13 d old. 
Article
The productivity of lettuce in a combination of high light, high temperature, and elevated CO2 has not been commonly studied because rapid growth usually causes a calcium deficiency in meristems called tipburn, which greatly reduces quality and marketability. We eliminated tipburn by blowing air directly onto the meristem, which allowed us to increase the photosynthetic photon flux (PPF) to 1000 micromoles m-2 s-1 (57.6 mol m-2 d-1); two to three times higher than normally used for lettuce. Eliminating tipburn doubled edible yield at the highest PPF level. In addition to high PPF, CO2 was elevated to 1200 micromoles m-2 mol-1, which increased the temperature optimum from 25 to 30 degrees C. The higher temperature increased leaf expansion rate, which improved radiation capture and more than doubled yield. Photosynthetic efficiency, measured as canopy quantum yield in a whole-plant gas exchange system, steadily increased up to the highest temperature of 32 degrees C in high CO2. The highest productivity was 19 g m-2 d-1 of dry biomass (380 g d-1 fresh mass) averaged over the 23 days the plants received light. Without the limitation of tipburn, the combination of high PPF, high temperature, and elevated CO2 resulted in a 4-fold increase in growth rate over productivity in conventional environments.
 
Article
The National Aeronautics and Space Administration (NASA) has been conducting controlled environment research with potatoes (Solanum tuberosum L.) in recirculating nutrient film technique (NFT)-hydroponic systems as a human life support component during long-duration spaceflight. Standard nutrient solution management approaches include constant pH regulation with nitric acid (HNO3) and daily adjustment of electrical conductivity (EC) equivalent to half-strength modified Hoagland's solution, where nitrate (NO3-) is the sole nitrogen (N) source. Although tuber yields have been excellent with such an approach, N use efficiency indices are expected to be low relative to tuber biomass production. Furthermore, the high amount of N used in NFT-hydroponics, typically results in high inedible biomass, which conflicts with the need to minimize system mass, volume, and expenditure of resources for long-duration missions. More effective strategies of N fertilization need to be developed to more closely match N supply with demand of the crop. Hence, the primary objective of this study was to identify the optimal N management regime and plant N requirement to achieve high yields and to avoid inefficient use of N and excess inedible biomass production. In separate 84-day cropping experiments, three N management protocols were tested. Treatments which decreased NO3(-)-N supply indirectly through lowering nutrient solution EC (Expt. I), or disabling pH control, and/or supplying NH4(+)-N (Expt. III) did not significantly benefit tuber yield, but did influence N use efficiency indices. When supplied with an external 7.5 mM NO3(-)-N for the first 42 days after planting (DAP), lowered to 1.0 mM NO3(-)-N during the final 42 days (Expt. II), plants were able to achieve yields on par with plants which received constant 7.5 mM NO3(-)-N (control). By abruptly decreasing N supply at tuber initiation in Expt. II, less N was taken up and accumulated by plants compared to those which received high constant N (control). However, proportionately more plant accumulated N was used (N use efficiency) to produce tuber biomass when N supply was abruptly lowered at tuber initiation in Expt. II. Hence, a hydroponic nutrient solution N management system may be modified to elicit greater plant N-use while maintaining overall high tuber yield as opposed to achieving high tuber yields through excess N supply and shoot growth.
 
Dry weight of leaves, stems, and roots of 42-day-old pepper plants grown for 21 days under metal halide (MH) lamps then transplanted under red lightemiting diodes (LEDs) plus blue fluorescent lamps (660/BF), red LEDs (660), and red plus far-red LEDs (660/735), or maintained under MH lamps for an additional 21 days. Similarly shaded portions containing different letters are significantly different based on ANOVA and protected least-squares mean separation tests (P ≤ 0.05). The letters above the bars indicates the significance for the combined plant dry weight. 
Number of leaves (A) and stem length (B) of 42-day-old pepper plants grown for 21 days under metal halide (MH) lamps then transplanted under red lightemiting diodes (LEDs) plus blue fluorescent lamps (660/BF), red LEDs (660), and red plus far-red LEDs (660/735), or maintained under MH lamps for an additional 21 days. Data points followed by different letters are significantly different based on ANOVA and protected least-squares mean separation tests (P ≤ 0.05). 
Article
Light-emitting diodes (LEDs) are a potential irradiation source for intensive plant culture systems and photobiological research. They have small size, low mass, a long functional life, and narrow spectral output. In this study, we measured the growth and dry matter partitioning of 'Hungarian Wax' pepper (Capsicum annuum L.) plants grown under red LEDs compared with similar plants grown under red LEDs with supplemental blue or far-red radiation or under broad spectrum metal halide (MH) lamps. Additionally, we describe the thermal and spectral characteristics of these sources. The LEDs used in this study had a narrow bandwidth at half peak height (25 nm) and a focused maximum spectral output at 660 nm for the red and 735 nm for the far-red. Near infrared radiation (800 to 3000 nm) was below detection and thermal infrared radiation (3000 to 50,000 nm) was lower in the LEDs compared to the MH source. Although the red to far-red ratio varied considerably, the calculated phytochrome photostationary state (phi) was only slightly different between the radiation sources. Plant biomass was reduced when peppers were grown under red LEDs in the absence of blue wavelengths compared to plants grown under supplemental blue fluorescent lamps or MH lamps. The addition of far-red radiation resulted in taller plants with greater stem mass than red LEDs alone. There were fewer leaves under red or red plus far-red radiation than with lamps producing blue wavelengths. These results indicate that red LEDs may be suitable, in proper combination with other wavelengths of light, for the culture of plants in tightly controlled environments such as space-based plant culture systems.
 
Crop yield response models for hydroponically grown Brassica napus under ambient (nonsupplemented) CO 2 conditions. (A) Seed yield rate, (B) shoot biomass production rate, (C) seed oil content, and (D) shoot caloric harvest index. Mathematical equations for these responses are listed in Table 3. 
Mathematical models used to represent crop response variables of dwarf, rapid-cycling brassica grown hydroponically under controlled-environment conditions. 
Article
Effects of N level (15 to 30 mM), time of N increase (14 to 28 days after planting), and planting density (1163 to 2093 plants/m2) were determined for crop yield responses of dwarf, rapid-cycling brassica (Brassica napus L., CrGC 5-2, Genome: ACaacc). Crops were grown in solid-matrix hydroponic systems and under controlled-environment conditions, including nonsupplemented (ambient) or elevated CO2 concentrations (998 +/- 12 micromoles mol-1). The highest seed yield rate obtained (4.4 g m-2 day-1) occurred with the lowest N level (15 mM) applied at the latest treatment time (day 28). In all trials, CO2 enrichment reduced seed yield rate and harvest index by delaying the onset of flowering and senescence and stimulating vegetative shoot growth. The highest shoot biomass accumulation rate (55.5 g m-2 day-1) occurred with the highest N level (30 mM) applied at the earliest time (day 14). Seed oil content was not significantly affected by CO2 enrichment. Maximum seed oil content (30% to 34%, dry weight basis) was obtained using the lowest N level (15 mM) initiated at the latest treatment time (day 28). In general, an increase in seed oil content was accompanied by a decrease in seed protein. Seed carbohydrate, moisture, and ash contents did not vary significantly in response to experimental treatments. Effects of N level and time of N increase were consistently significant for most crop responses. Planting density was significant only under elevated CO2 conditions.
 
The effect of photoperiod on time to first flower for two cowpea breeding lines. Each point represents the average of six repetitions. Open circles represent the day-neutral breeding line IT82D-889. Closed circles represent the short-day breeding line IT84S-2246. Plotted lines are from regression analyses (R 2 = 0.96). Error bars equal half of the least significant difference at P = 0.05. Predicted values are significantly different where error bars do not overlap.  
The effect of photoperiod and harvest scenario on edible yield for two cowpea breeding lines. Each point represents an average of three repetitions. Open symbols represent the day-neutral breeding line IT82D-889. Closed symbols represent the short-day breeding line IT84S-2246. Plotted lines are from regression analyses (R 2 = 1.00). Error bars equal half of the least significant difference at P = 0.05. Predicted values are significantly different where error bars do not overlap.  
The effect of photoperiod and harvest scenario on shoot harvest index for two cowpea breeding lines. Each point represents an average of three repetitions. Open symbols represent the day-neutral breeding line IT82D-889. Closed symbols represent the short-day breeding line IT84S-2246. Plotted lines are from regression analyses (R 2 = 0.98). Error bars equal half of the least significant difference at P = 0.05. Predicted values are significantly different where error bars do not overlap.
The effect of harvest scenario on EYR. Lower case letters represent significant differences using a Student-Newman-Keuls' test, P = 0.05, after regression analysis revealed only main effects to be significant.  
The effect of photoperiod on yield efficiency rate for two cowpea breeding lines and three harvest scenarios. Each point represents an average of three repetitions. Open symbols represent the day-neutral breeding line IT82D-889. Closed symbols represent the short-day breeding line IT84S-2246. Plotted lines are from regression analyses (R 2 = 0.98). Error bars equal half of the least significant difference at P = 0.05. Predicted values are significantly different where error bars do not overlap.  
Article
Photoperiod and harvest scenario of cowpea (Vigna unguiculata L. Walp) canopies were manipulated to optimize productivity for use in future controlled ecological life-support systems. Productivity was measured by edible yield rate (EYR:g m-2 day-1), shoot harvest index (SHI: g edible biomass [g total shoot dry weight]), and yield-efficiency rate (YER:g edible biomass m-2 day-1 per[g nonedible shoot dry weight]). Breeding lines 'IT84S-2246' (S-2246) and "IT82D-889' (D-889) were grown in a greenhouse under 8-, 12-, or 24-h photoperiods. S-2246 was short-day and D-889 was day-neutral for flowering. Under each photoperiod, cowpeas were harvested either for leaves only, seeds only, or leaves plus seeds (mixed harvest). Photoperiod did not affect EYR of either breeding line for any harvest scenario tested. Averaged over both breeding lines, seed harvest gave the highest EYR at 6.7 g m-2 day-1. The highest SHI (65%) and YER (94 mg m-2 day-1 g-1) were achieved for leaf-only harvest of D-889 under an 8-h photoperiod. For leaf-only harvest of S-2246, both SHI and YER increased with increasing photoperiod, but declined for seed-only and mixed harvests. However, photoperiod had no effect on SHI or YER for D-889 for any harvest scenario. A second experiment utilized the short-day cowpea breeding line 'IT89KD-288' (D-288) and the day-neutral breeding line 'IT87D-941-1' (D-941) to compare yield parameters using photoperiod extension under differing lamp types. This experiment confirmed the photoperiod responses of D-889 and S-2246 to a mixed-harvest scenario and indicated that daylength extension with higher irradiance from high pressure sodium lamps further suppressed EYR, SHI, and YER of the short-day breeding line D-288.
 
Elongation of exposed and enclosed lettuce leaves of developing lettuce plants. Each symbol represents a leaf from separate plants harvested on the indicated days from seeding.  
Calcium concentrations, mg·g –1 dry weight, in enclosed and exposed lettuce leaves during enlargement. Concentrations are averages of two replicate leaves. The leaf length is indicated at the bottom of each leaf. Areas showing collapse and tipburn injury are shaded.  
Magnesium concentrations, mg·g –1 dry weight, in enclosed and exposed lettuce leaves during enlargement. Concentrations are averages of two replicate leaves. The leaf length is indicated at the bottom of each leaf. Areas showing collapse and tipburn injury are shaded.  
Potassium concentrations, mg·g –1 dry weight, in enclosed and exposed lettuce leaves during enlargement. Concentrations are averages of two replicate leaves. The leaf length is indicated at the bottom of each leaf. Areas showing collapse and tipburn injury are shaded.  
Article
Tissue concentrations of Ca, Mg, and K were determined across immature leaves of lettuce (Lactuca sativa L. 'Buttercrunch') at different stages of enlargement using electron microprobe x-ray analysis. The analysis was with a wavelength dispersive spectrometer to permit detection of low concentrations of Ca. Patterns of mineral accumulation in immature leaves that were exposed were compared to patterns of accumulation in leaves that were enclosed within a developing head. The leaves developing without enclosure were free to transpire and developed normally whereas leaves developing with enclosure were restricted in transpiration and developed an injury that was characteristic of Ca deficiency. In the exposed leaves, Ca concentrations increased from an average of 1.0 to 2.1 mg g-1 dry weight (DW) as the leaves enlarged from 5 to 30 mm in length. In the enclosed leaves, Ca concentrations decreased from 1.0 to 0.7 mg g-1 DW as the leaves enlarged from 5 to 30 mm in length. At the tips of these enclosed leaves a larger decrease was found, from 0.9 to 0.3 mg g-1 DW during enlargement. Necrotic injury first became apparent in this tip area when the concentration was approximate to 0.4 mg g-1 DW. Magnesium concentrations across the exposed leaves were similar to concentrations across the enclosed leaves, and did not change with enlargement. Magnesium concentrations averaged 3.5. mg g-1 DW in both enclosed and exposed leaves during enlargement from 5 to 30 mm. In both exposed and enclosed leaves, K concentrations increased during enlargement from 40 to approximate to 60 mg g-1 DW. Potassium concentrations were highest toward the leaf apex and upper margin where injury symptoms occurred, and this may have enhanced injury development. This research documents the critical low levels of Ca (0.2 to 0.4 mg g-1 DW) that can occur in enclosed leaves of plants and which apparently leads to the marginal apex necrosis of developing leaves seen frequently on lettuce and other crops.
 
Concentrations of K across 20-mm-long 'Green Lake' lettuce leaves expressed as mg K/g dry weight. Analysis of leaves 5 and 14, counted from the cotyledons, from plants grown in two environments. Concentrations are averaged for two separate leaves. Shaded area indicates region with tipburn injury. 
Article
An electron microprobe was used to determine tissue concentrations of Ca across 20-mm-long leaves of 'Green Lakes' crisphead lettuce (Lactuca 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.
 
Article
Growth chamber studies were undertaken with a tipburn-sensitive cultivar of romaine lettuce (Lactuca sativa L. cv. Lobjoits Green Cos) grown under a photosynthetic photon flux density of 320 micromoles s-1 m-2 for 16 hours; light and dark temperatures were 26.0 degrees and 12.5 degrees C, respectively. As the relative humidity (RH) during the light period was decreased from 74% to 51%, growth was retarded, Ca concentration increased, and the onset of tipburn delayed. Decreasing RH during the dark period from 95% to 90% reduced growth and resulted in lower Ca concentrations and earlier tipburn development. Further decreases from 90% to 65% caused no additional change in growth or tipburn response. Root temperatures of 23.5 degrees, compared with 15.0 degrees, slightly increased Ca concentration but induced earlier tipburn development. Ca concentrations were increased and tipburn delayed by humidity conditions which provided large diurnal fluctuations in water potential in the plant and which encouraged root pressure flow during the dark period. Elevated root temperatures did not provide expected increases in Ca accumulation in young leaves.
 
Diagrammatic representation of a multiple chamber system for semicontinuous CO2 exchange measurements of crops or canopies. Double lines indicate tubing for air flow, thick lines indicate water lines, and thin lines indicate electrical and electronic connections. Arrows indicate the direction of the air flow. For clarity, the heater and thermocouple are shown in only one of the gas exchange chambers. A detailed view of the gas exchange chambers is illustrated in Fig. 2. ACA (absolute CO2 analyzer), AOM (analog output module), BJ (buffer jar), C (condensor), DCA (differential CO2 analyzer), DL (datalogger), DPH (dew point hygrometer), GXC (gas exchange chamber), H (heater), MFC (mass flow controller), MFM (mass flow meter), MP (multiplexer), NV (needle valve), P (pump), RM (rotometer), RVB (rotary vane blower), SV (solenoid valve), WB (water bath), RD (relay driver), and TC (thermocouple). 
Exchange rate of CO 2 of a petunia crop in a gas exchange chamber. The (A) raw data show the diurnal changes in gas exchange, while (B) daily means of net photosynthesis (P net ) and dark respiration (R dark ) are better suited to show long term changes. Gross photosynthesis (P gross ) was calculated as the sum of P net and R dark. All data are expressed per unit ground area. The first dark period was longer than subsequent ones due to a technical problem. In A arrows indicate the time of watering. 
(A) Cumulative carbon gain (CCG) and (B) daily carbon gain (DCG) of a petunia crop in a growth chamber. In A cumulative carbon gain was calculated as the cumulative value of DCG (solid line) and as the integral of the CO2 exchange data (broken line). Note the decrease in CCG that occurs at night due to respiration when CCG is calculated as the integral of the CO2 exchange data. All data are expressed per unit ground area. 
Carbon use efficiency of a petunia crop as determined from CO 2 exchange data. 
Article
Long-term, whole crop CO2 exchange measurements can be used to study factors affecting crop growth. These factors include daily carbon gain, cumulative carbon gain, and carbon use efficiency, which cannot be determined from short-term measurements. We describe a system that measures semicontinuously crop CO2 exchange in 10 chambers over a period of weeks or months. Exchange of CO2 in every chamber can be measured at 5 min intervals. The system was designed to be placed inside a growth chamber, with additional environmental control provided by the individual gas exchange chambers. The system was calibrated by generating CO2 from NaHCO3 inside the chambers, which indicated that accuracy of the measurements was good (102% and 98% recovery for two separate photosynthesis systems). Since the systems measure net photosynthesis (P-net, positive) and dark respiration(R-dark, negative), the data can be used to estimate gross photosynthesis, daily carbon gain, cumulative carbon gain, and carbon use efficiency. Continuous whole-crop measurements are a valuable tool that complements leaf photosynthesis measurements. Multiple chambers allow for replication and comparison among several environmental or cultural treatments that may affect crop growth. Example data from a 2 week study with petunia (Petunia x hybrida Hort. Vilm.-Andr.) are presented to illustrate some of the capabilities of this system.
 
Article
An artificial neural network (NN) and a statistical regression model were developed to predict canopy photosynthetic rates (Pn) for 'Waldman's Green' leaf lettuce (Latuca sativa L.). All data used to develop and test the models were collected for crop stands grown hydroponically and under controlled-environment conditions. In the NN and regression models, canopy Pn was predicted as a function of three independent variables: shootzone CO2 concentration (600 to 1500 micromoles mol-1), photosynthetic photon flux (PPF) (600 to 1100 micromoles m-2 s-1), and canopy age (10 to 20 days after planting). The models were used to determine the combinations of CO2 and PPF setpoints required each day to maintain maximum canopy Pn. The statistical model (a third-order polynomial) predicted Pn more accurately than the simple NN (a three-layer, fully connected net). Over an 11-day validation period, average percent difference between predicted and actual Pn was 12.3% and 24.6% for the statistical and NN models, respectively. Both models lost considerable accuracy when used to determine relatively long-range Pn predictions (> or = 6 days into the future).
 
Article
Two studies were conducted in which 'Waldmann's Green' lettuce (Lactuca sativa L.) was grown hydroponically from seed to harvest in a large (20-m2), atmospherically closed growth chamber for the National Aeronautics and Space Administration's controlled ecological life support system (CELSS) program. The first study used metal-halide (MH) lamps [280 micromoles m-2 s-1 photosynthetic photon flux (PPF)], whereas the second used high-pressure sodium (HPS) lamps (293 micromoles m-2 s-1). Both studies used a 16-hour photoperiod, a constant air temperature (22 to 23C), and 1000 micromoles mol-1 CO2 during the light period. In each study, canopy photosynthesis and evapotranspiration (ET) rates were highly correlated to canopy cover, with absolute rates peaking at harvest (28 days after planting ) at 17 micromoles CO2/m2 per sec and 4 liters m-2 day-1, respectively. When normalized for actual canopy cover, photosynthesis and ET rates per unit canopy area decreased with age (between 15 and 28 days after planting). Canopy cover increased earlier during the study with HPS lamps, and final shoot yields averaged 183 g fresh mass (FM)/plant 8.8 g dry mass (DM)/plant. Shoot yields in the first study with MH lamps averaged 129 g FM/plant and 6.8 g DM/plant. Analysis of leaf tissue showed that ash levels from both studies averaged 22% and K levels ranged from 15% to 17% of tissue DM. Results suggest that lettuce should be easily adaptable to a CELSS with moderate lighting and that plant spacing or transplant schemes are needed to maximize canopy light interception and sustained efficient CO2 removal and water production.
 
Method for collecting volatiles produced by lettuce under controlled environmental conditions. ( A ) Glass sampling jar placed over lettuce for volatile collection. ( B ) Dewar containing copper tubing in ice water slurry for precooling air entering sampling jar. ( C ) Volatile collector trap. 
Germination box for producing seedlings, with cut-out view showing nylon fabric hanging into reservoir.
Article
A system and methodology were developed for the nondestructive qualitative and quantitative analysis of volatile emissions from hydroponically grown 'Waldmann's Green' leaf lettuce (Lactuca sativa L.). Photosynthetic photon flux (PPF), photoperiod, and temperature were automatically controlled and monitored in a growth chamber modified for the collection of plant volatiles. The lipoxygenase pathway products (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate were emitted by lettuce plants after the transition from the light period to the dark period. The volatile collection system developed in this study enabled measurements of volatiles emitted by intact plants, from planting to harvest, under controlled environmental conditions.
 
Article
The role of ethylene in the development of constant-light injury of potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.) was investigated. In one study, silver thiosulfate (STS) was applied to the foliage of four potato cultivars growing under constant light. Leaf area and shoot dry mass of 'Kennebec' and 'Superior', cultivars normally injured by constant light, were greater (P < 0.05) than those of control plants given foliar applications of distilled water. Examination of STS-treated 'Kennebec' leaflets revealed significantly less injury (necrotic spotting and reduced starch content) than the water-treated controls. 'Norland' and 'Denali', cultivars tolerant of constant light, exhibited no differences in growth between treatments. In a second study, injury (necrotic spotting and reduced starch content) was induced in leaflets of 'Denali' when exposed to spray applications of 0.5 mmol L-1 ethephon or air containing 0.5 to 0.8 microL L-1 ethylene. In a third study, three genotypes of 'Ailsa Craig' tomato were grown under constant light. Leaves of the normal 'Ailsa Craig' exhibited epinasty, reduced chlorophyll concentration, and reduced starch content. Leaves of a mutant 'Ailsa Craig', containing the Never ripe mutation, did not exhibit epinasty but exhibited the same amount of reduced chlorophyll concentration and starch content as normal plants. Leaves of a transgenic 'Ailsa Craig', containing an antisense gene of 1-aminocyclopropane 1-carboxylate (ACC) oxidase, were epinastic, but chlorophyll concentration and starch content were greater than in leaves of normal and mutant plants. These results suggest that transgenic plants were more tolerant of constant light than the other genotypes. Evidence from these studies indicates that ethylene, combined with constant light, has an important role in the development of constant-light injury.
 
Plant dry weight and leaflet characteristics in potato cultivars exposed to continuous irradiation. 
Net CO 2 assimilation (A), stomatal conductance (B), and intercellular CO 2 partial pressure (C) in the leaflets of potato cultivars grown under continuous irradiation. Values are means of six replicate plants. Mean separation in each data set by Duncan's multiple range test, P = 0.05. leaf area in 'Kennebec' and 'Superior' than in 'Denali' and 'Haig'. Chlorophyll concentration. In leaflets of 'Kennebec' and 'Superior', chlorophyll concentrations on a dry-weight basis were greater than in those from'Denali' and 'Haig' (Fig. 1A). In contrast, chlorophyll concentrations on a leaf-area basis did not differ consistently between these four cultivars. The higher chlorophyll concentration per leaf dry weight for 'Kennebec' and 'Superior' apparently resulted from the higher SLA for these two cultivars. CO 2 assimilation. Net C0 2 assimilation rates per unit leaf area in 'Kennebec' and 'Superior' were ≈30% of rates in 'Denali' and 'Haig' (Fig. 2A). The pattern among cultivars was similar for CO 2 assimilation expressed on the basis of leaf chlorophyll concentration (Fig. 2A). Leaf stomatal conductance did not differ consistently between the four cultivars (Fig. 2B). It was highest for 'Kennebec', lowest for 'Haig', and intermediate for 'Denali' and 'Superior'. 'Kennebec' and 'Superior' maintained high stomatal conductance, while net CO 2 assimilation was very low in the leaves. 
Article
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 micromoles 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.
 
Article
Radiation in controlled environments was characterized using fluorescent and various high-intensity-discharge (HID) lamps, including metal halide, low-pressure sodium, and high-pressure sodium as the radiation source. The effects of water, glass, or Plexiglas filters on radiation were determined. Photosynthetic photon flux (PPF, 400 to 700 nm), spectra (400 to 1000 nm), shortwave radiation (285-2800 nm), and total radiation (300 to 100,000 nm) were measured, and photosynthetically active radiation (PAR, 400 to 700 nm) and longwave radiation (2800 to 100,000 nm) were calculated. Measurement of PPF alone was not an adequate characterization of the radiation environment. Total radiant flux varied among lamp types at equal PPF. HID lamps provided a lower percentage of longwave radiation than fluorescent lamps, but, when HID lamps provided PPF levels greater than that possible with fluorescent lamps, the amount of longwave radiation was high. Water was the most effective longwave radiation filter. Glass and Plexiglas similarly filtered longwave more than shortwave radiation, but transmission of nonphotosynthetic shortwave radiation was less with Plexiglas than glass. The filter materials tested would not be expected to influence photomorphogenesis because radiation in the action spectrum of phytochrome was not altered, but this may not be the only pigment involved.
 
Article
The design and operation of a system is described in which small plants can be grown under controlled environment conditions. Important features of this "Minitron" system include precise control of temperature and CO2 concentration in a flowing atmosphere. Plants can be grown either hydroponically or in solid root support medium. For either culture method, nutrient solution or water is added from an external reservoir, altering neither atmospheric composition nor temperature equilibrium within a closed Minitron chamber.
 
Number and length of adventitious roots from flight and ground-based sweetpotato stem cuttings. Mean values with different letters are significantly different. Significant effects were determined by differences in least squares means at P ≤ 0.05.  
Carbon dioxide concentration in growth units of flight and ground-sweetpotato stem cuttings. Mean values with different letters are different. Significant effects were determined by differences in least squares means at P ≤ 0.05.  
Ethylene and oxygen levels in growth units of flight and ground-based sweetpotato stem cuttings. Mean values with different letters are significantly different. Significant effects were determined by differences in least squares means at P ≤ 0.05.  
Article
Because sweetpotato [Ipomoea batatas (L.) Lam.] stem cuttings regenerate very easily and quickly, a study of their early growth and development in microgravity could be useful to an understanding of morphological changes that might occur under such conditions for crops that are propagated vegetatively. An experiment was conducted aboard a U.S. Space Shuttle to investigate the impact of microgravity on root growth, distribution of amyloplasts in the root cells, and on the concentration of soluble sugars and starch in the stems of sweetpotatoes. Twelve stem cuttings of 'Whatley/Loretan' sweetpotato (5 cm long) with three to four nodes were grown in each of two plant growth units filled with a nutrient agarose medium impregnated with a half-strength Hoagland solution. One plant growth unit was flown on Space Shuttle Colombia for 5 days, whereas the other remained on the ground as a control. The cuttings were received within 2 h postflight and, along with ground controls, processed in approximately 45 min. Adventitious roots were counted, measured, and fixed for electron microscopy and stems frozen for starch and sugar assays. Air samples were collected from the headspace of each plant growth unit for postflight determination of carbon dioxide, oxygen, and ethylene levels. All stem cuttings produced adventitious roots and growth was quite vigorous in both ground-based and flight samples and, except for a slight browning of some root tips in the flight samples, all stem cuttings appeared normal. The roots on the flight cuttings tended to grow in random directions. Also, stem cuttings grown in microgravity had more roots and greater total root length than ground-based controls. Amyloplasts in root cap cells of ground-based controls were evenly sedimented toward one end compared with a more random distribution in the flight samples. The concentration of soluble sugars, glucose, fructose, and sucrose and total starch concentration were all substantially greater in the stems of flight samples than those found in the ground-based samples. Carbon dioxide levels were 50% greater and oxygen marginally lower in the flight plants, whereas ethylene levels were similar and averaged less than 10 nL.L (-1). Despite the greater accumulation of carbohydrates in the stems, and greater root growth in the flight cuttings, overall results showed minimal differences in cell development between space flight and ground-based tissues. This suggests that the space flight environment did not adversely impact sweetpotato metabolism and that vegetative cuttings should be an acceptable approach for propagating sweetpotato plants for space applications.
 
Article
Eggplant (Solanum melongena L. var. esculentum 'Burpee's Black Beauty') and soybean [Glycine max (L.) Merr. 'Wells II'] seedlings were assigned to a greenhouse or a windless or windy outdoor environment. Plants within each environment received either periodic seismic (shaking) or thigmic (flexing or rubbing) treatment, or were left undisturbed. Productivity (dry weight) and dimensional (leaf area and stem length) growth parameters generally were reduced more by mechanical stress in the greenhouse (soybean) or outdoor-windless environment (eggplant) than in the outdoor windy environment. Outdoor exposure enhanced both stem and leaf specific weights, whereas mechanical stress enhanced only leaf specific weight. Although both forms of controlled mechanical stress tended to reduce node and internode diameters of soybean, outdoor exposure increased stem diameter.
 
Article
Strawberries (Fragaria xananassa Duch. 'Osogrande') were grown hydroponically with three NO3-N concentrations (3.75, 7.5, or 15.0 mM) to determine effects of varying concentration on NO3-N uptake and reduction rates, and to relate these processes to growth and fruit yield. Plants were grown for 32 weeks, and NO3-N uptake and nitrate reductase (NR) activities in roots and shoots were measured during vegetative and reproductive growth. In general, NO3-N uptake rates increased as NO3-N concentration in the hydroponics system increased. Tissue NO3- concentration also increased as external NO3-N concentration increased, reflecting the differences in uptake rates. There was no effect of external NO3-N concentration on NR activities in leaves or roots during either stage of development. Leaf NR activity averaged approximately 360 nmol NO2 formed/g fresh weight (FW)/h over both developmental stages, while NR activity in roots was much lower, averaging approximately 115 nmol NO2 formed/g FW/h. Vegetative organ FW, dry weight (DW), and total fruit yield were unaffected by NO3-N concentration. These data suggest that the inability of strawberry to increase growth and fruit yield in response to increasing NO3-N concentrations is not due to limitations in NO3-N uptake rates, but rather to limitations in NO3- reduction and/or assimilation in both roots and leaves.
 
Dendrogram generated using unweighted pair group method with arithmetic mean cluster analysis based on the proportion of shared alleles (Bowcock et al., 1994) among 48 Juglans genotypes. 
Allele sizes (in base pairs) at 14 microsatellite loci for selected cultivars of Juglans regia and one hybrid. 
Article
One hundred and forty-seven primer pairs originally designed to amplify microsatellites, also known as simple sequence repeats (SSR), in black walnut (Juglans nigra L.) were screened for utility in persian walnut (J. regia L.). Based on scorability and number of informative polymorphisms, the best 14 loci were selected to analyze a diverse group of 47 persian walnut accessions and one J. hindsii (Jepson) Jepson ex R.E. Sm x J. regia hybrid (Paradox) rootstock. Among the 48 accessions, there were 44 unique multi-locus profiles; the accessions with identical profiles appeared to be synonyms. The pairwise genetic distance based on proportion of shared alleles was calculated for all accessions and a UPGMA (unweighted pair group method with arithmetic mean) dendrogram constructed. The results agree well with what is known about the pedigree and/or origins of the genotypes. The SSR markers distinguished pairs of closely related cultivars and should be able to uniquely characterize all walnut cultivars with the exception of budsports. They provide a more powerful and reliable system for the molecular characterization of walnut germplasm than those previously tested. These markers have numerous applications for the walnut industry, including cultivar identification, verification of pedigrees for cultivar and rootstock breeding programs, paternity analysis, and understanding the genetic diversity of germplasm collections.
 
Continued.
Article
Powdery mildew [Podosphaera xanthii (Castagne) Braun & Shishkoff (syn. Sphaerotheca fuliginea auct. p.p.)] is now a common disease on watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] in the United States. In this study, the entire available U.S. Plant Introduction collection of Citrullus Schrad. ex Eckl. & Zeyh. species was evaluated for resistance to P. xanthii race 1W. The collection consists of four Citrullus species and one Praecitrullus Pangalo species [C. lanatus var. citroides (L.H. Bailey) Mansf., C. colocynthis (L.) Schrad., C. rehmii De Winter, and P. fistulosus (Stocks) Pangalo]. Wild-type accessions tended to be more resistant more often than the cultivated species, C. lanatus var. lanatus. None were immune, eight of the 1573 accessions exhibited high levels of resistance, and another 86 demonstrated intermediate resistance. Stem and leaf disease severity were weakly correlated (r2 = 0.64, P = 0.001). The majority of accessions having resistance were collected in Zimbabwe. Resistance was found in four species.
 
Article
Small-fruited cherry tomato accession PI 270248 [Lycopersicon esculentum Mill. var. cerasiforme (Dunal) A. Gray] with high fruit sugars was crossed to large-fruited inbred line Fla.7833-1-1-1 (7833) (L. esculentum) that had normal (low) fruit sugars. The F1 was crossed to PI 270248 and 7833 to obtain BCP1 and BCP2, respectively, and self-pollinated to obtain F2 seed. The resulting population was used to study the inheritance of high sugars from PI 270248. Continuous sugar level frequency distributions of BCP1, BCP2, and F2 suggest that the trait is under polygenic control. Additive variation was significant, but dominance variation was not. There was a heterozygote x heterozygote type of epistasis present that likely caused the F1 sugar level to skew nearly to the level of the high sugar parent. The F2 mean sugar level was lower than the midparent level. Broad-sense heritability was 0.86. There was a significant line x season (fall, spring) interaction where lines with higher sugars were affected more by seasons than lines with lower sugars. Sugar level, in general, was higher in spring. Higher solar radiation in spring than in fall may explain the sugar level difference between the seasons.
 
Article
Selenium and sulfur have similar chemical structures. This allows Se to be absorbed and incorporated in the same assimilation pathways as S. Onions (Allium cepa L.) are a crop with unique S metabolism, responsible for growth and flavor intensity. Because of the antagonistic behavior of the two ions, the effects of Se on S and Se nutrient depletion and tissue accumulation were investigated. `Granex 33' onions were grown in nutrient solutions with one concentration of S and increasing Se concentrations. Selenium was applied as sodium selenate (Na2SeO4) at concentrations of 0, 0.5, 1.0, 1.5, and 2.0 mg·L-1. Selenium depletion from the nutrient solution increased linearly with increasing Na2SeO4 treatment concentrations. Sulfur depletion increased and then decreased with increasing Na2SeO4 treatment concentrations. Selenium and S accumulation were highest in leaf tissues, less in root tissues, and lowest in bulb tissues at plant maturity. Selenium accumulation increased linearly with increasing Na2SeO4 for all tissues analyzed. Sulfur accumulation in leaf and bulb tissues was quadratic in response to increasing SeO4-2, while S in root tissues decreased linearly with increasing Na2SeO4. Low concentrations of Na2SeO4 in our study enhanced S uptake and accumulation. Previously, Se was thought to competitively inhibit S uptake and metabolism.
 
Mutation type and observed frequencies in the common bean 
Article
Common bean (Phaseolus vulgaris) is the major food legume worldwide, making it an important target for novel approaches of genetic analysis. This study evaluated the use of ethyl methane sulfonate (EMS) for the generation of a mutant population for targeted induced local lesions in genomes (TILLING) in common bean. TILLING is a powerful reverse genetics approach that uses a large mutant population for identification of mutants in loci of interest. Based on overall survival, development, and yield of treated seed, 40 mM EMS was found to be an appropriate concentration for the generation of a mutant population in common bean genotype BAT 93. Higher concentrations of EMS resulted in survival rates of less than 10% and lower concentrations resulted in the generation of fewer mutants. Based on TILLING results from other species, a population of 5000 lines is estimated to be sufficient for saturation of the common bean genome. Phenotypic mutation frequencies and the isolation of targeted mutations in the BAT 93 mutant population indicate that mutagenesis was effective.
 
Article
Since the first report of the 'A72' semidwarf peach [Prunus persica (L.) Batsch] tree in 1975, no new information has become available on this genotype. We evaluated the growth habit and verified the inheritance of 'A72' in a population of 220 progeny derived from self-pollination. Detailed tree and branch measurements revealed a unique forked-branch (FBR) character of the 'A72' (Nn) phenotype. The progeny segregated into 1 NN:2 Nn:1 nn. NN trees were indistinguishable from standard peach trees, Nn were FBR, and nn were dwarf. Hybrids between 'A72' and columnar (brbr) peach trees confirmed that FBR is inherited as a monogenic trait that appears to express incomplete dominance. 'A72' (Nn) trees were later blooming than sibling NN trees. The relationship (linkage or pleiotropy) between the growth habit of 'A72' and late bloom is not known. The structure of 'A72' trees presents new opportunities to breeder/geneticists, physiologists, and horticulturists to further explore the plasticity of peach tree growth and architecture that can be achieved through breeding. Applications of the 'A72' growth habit for commercial fruit production and as an ornamental, particularly in the dwarf form (nn) and in combination with the columnar tree (brbr) form, present opportunities that await exploration.
 
Article
When compared with exposure to darkness, exposing Hibiscus rosa-sinensis L. 'Nairobi' plants to red light (635 to 685 nm, 2.9 μmol?m-2?s-1) delayed flower bud abscission, while exposure to far-red light (705 to 755 nm, μmol?m-2?s-1) accelerated this process. Flower bud abscission in response to light quality appears to be controlled partly by the presence of leaves. The delay of bud abscission was positively correlated to the number of leaves being exposed to red light. Excluding the flower buds from exposure to red or far-red light, while exposing the remaining parts of the plants to these light conditions, did not influence the effects of the light exposure on bud abscission. Exposing only the buds to red light by the use of red light-emitting diodes (0.8 μmol?m-2?s-1) did not prevent dark-induced flower bud abscission. Exposing the whole plants, darkness or far-red light could only induce flower bud abscission when leaves were present; bud abscission was totally absent when all leaves were removed. To prevent flower bud abscission, leaves had to be removed before, or at the start of, the far-red light treatment. These results suggest that in darkness or far-red light, a flower bud abscission-promoting signal from the leaves may be involved.
 
Article
Highbush blueberry (Vaccinium corymbosum) is susceptible to winter freezing injury and frost damage in the spring. As part of an ongoing project to understand the process of cold acclimation, we isolated a C-repeat binding factor (CBF) transcriptional activator gene-coding region from the highbush blueberry cultivar Bluecrop. Expression of the highbush blueberry CBF gene was compared in floral buds of the cold-tolerant northern highbush cultivar Bluecrop and the more cold-sensitive southern rabbiteye (V. virgatum) blueberry cultivar Tifblue. Relative gene expression was higher in 'Bluecrop' than in 'Tifblue'. Expression in both cultivars was highest at the earliest time point in the fall (coincident with the first stage of cold acclimation), declined during the later fall and winter, and, in 'Bluecrop', increased again as buds deacclimated, when temperatures tend to fluctuate. To confirm the putative identity of the gene as a member of the CBF gene family, and to determine if expression in a heterologous system could enhance freezing tolerance, the blueberry gene coding sequence was overexpressed in transgenic Arabidopsis thaliana under the control of the cauliflower mosaic virus 35S promoter. Transgenic plants expressing the putative blueberry CBF gene exhibited induced expression of the A. thaliana cold-regulated (COR) genes COR78 and COR6.6, under non-inducing conditions (i.e., 23 °C); however, expression of two other COR genes was unaffected. Transgenic plants also exhibited enhanced freezing tolerance under non-acclimated conditions, but not to the level of acclimated control plants. Thus, the expression pattern in floral buds and the ability of the isolated gene to turn on a subset of COR genes and increase freezing tolerance in a heterologous system suggest it is a functional member of the CBF gene family in blueberry.
 
Lettuce daily carbon gain (A), daily respiration (below zero) and photosynthesis (B), carbon use effi ciency (C), and tomato daily carbon gain (D), daily respiration and photosynthesis (E), and carbon use effi ciency of lettuce (F). The PPF before shade was applied was 600 μmol·m –2 ·s –1 in lettuce, and 650 μmol·m –2 ·s –1 in tomatoes. Data are expressed as moles of C (measured as CO 2 ) per m 2 of ground area per day. Only one replicate chamber is shown for simplicity. Closed circles (●) are control, open circles (o) are ≈20% shade, closed squares (■) are for ≈45% shade, open triangles (s) are for ≈65% shade and closed triangles (▼) are for ≈80% shade.  
Recovery of net photosynthesis for lettuce (A), night respiration of lettuce (B), and carbon use effi ciency (C), and recovery of tomato photosynthesis (D), night respiration (E), and carbon use effi ciency (F) after shading expressed as a percent of pretreatment and control level. Numbers before the lines indicate the PPF at which that treatment was grown. Closed circles (•) are control, open circles (o) are ≈20% shade, closed squares (■) are for ≈45% shade, open triangles (s) are for ≈65% shade and closed triangles (▼) are for ≈80% shade. Error bars are the standard deviation of two chambers of similar PPF. Error bars not seen are smaller than the symbol.
Quantum yield of lettuce (A) and tomato (B) canopies before (day 0) and after shade application (days 1 to 18). Numbers after each line indicate the PPF after shade was applied. Error bars are the standard deviation of two chambers of similar PPF. Closed circles (●) are control, open circles (o) are ≈20% shade, closed squares (■) are for ≈45% shade, open triangles (s) are for ≈65% shade and closed triangles (▼) are for ≈80% shade. Error bars not seen are smaller than the symbol.  
Final dry mass (A) and percent mass of roots and fruit (B) for lettuce and tomato. Each data point is from a single chamber. Closed squares (■) are for tomato shoot, open squares (❏) are for lettuce shoot, closed triangles (▼) with solid line is the tomato root, open triangles (s) with dotted line is for the lettuce root, and the closed diamond (u) with dashed line is for the tomato fruit.
Relative growth rate (RGR) of lettuce (A) and tomato (B) before and after shade treatment. The steep decrease in RGR indicates when treatments began. Only one replicate chamber is shown for simplicity. Closed circles (●) are control, open circles (o) are ≈20% shade, closed squares (■) are for ≈45% shade, open triangles (s) are for ≈65% shade and closed triangles (▼) are for ≈80% shade.  
Article
Cloudy days cause an abrupt reduction in daily photosynthetic photon flux (PPF), but we have a poor understanding of how plants acclimate to this change. We used a unique 10-chamber, steady-state, gas-exchange system to continuously measure daily photosynthesis and night respiration of populations of a starch accumulator [tomato (Lycopersicon esculentum Mill. cv. Micro-Tina)] and a sucrose accumulator [lettuce (Lactuca sativa L. cv. Grand Rapids)] over 42 days. All measurements were done at elevated CO2 (1200 micromol.mol(-1)) to avoid any CO2 limitations and included both shoots and roots. We integrated photosynthesis and respiration measurements separately to determine daily net carbon gain and carbon use efficiency (CUE) as the ratio of daily net C gain to total day-time C fixed over the 42-day period. After 16 to 20 days of growth in constant PPF, plants in some chambers were subjected to an abrupt PPF reduction to simulate shade or a series of cloudy days. The immediate effect and the long term acclimation rate were assessed from canopy quantum yield and carbon use efficiency. The effect of shade on carbon use efficiency and acclimation was much slower than predicted by widely used growth models. It took 12 days for tomato populations to recover their original CUE and lettuce CUE never completely acclimated. Tomatoes, the starch accumulator, acclimated to low light more rapidly than lettuce, the sucrose accumulator. Plant growth models should be modified to include the photosynthesis/respiration imbalance and resulting inefficiency of carbon gain associated with changing PPF conditions on cloudy days.
 
Effect of UV-C 254nm postharvest irradiation on peel color measurements of 'Washington Navel', 'Biondo Comune', 'Tarocco', and 'Valencia Late' oranges in relationship to harvest date.
Article
'Washington Navel', 'Biondo Comune', 'Tarocco', and 'Valencia Late' orange [ Citrus sinensis (L.) Obsek] fruit, harvested at various periods of time, were subjected to ultraviolet-C (UV-C) irradiation at 0.5, 1.5, or 3.0 kJ·m<sup>-2</sup> doses and then stored at 7 °C and 90% to 95% relative humidity (RH) for 4 weeks plus one additional week at 20 °C and 80% RH. Following UV-C treatment, there was varying amounts of rind browning and necrotic peel damage, depending on cultivar, treatment dose, and harvest date. 'Tarocco' fruit were damaged more easily by UV-C treatment than the other cultivars. 'Valencia L.' were the most resistant to UV-C irradiation, showing no adverse effects at the lowest dosage and having the lowest percentages of damaged fruit at higher dosages. 'Washington Navel' and 'Biondo Comune' oranges showed an intermediate susceptibility to UV-C treatment, with negligible differences between these cultivars. The percentage of damaged fruit after irradiation at the higher UV-C dosages decreased in most fruit samples as the season progressed. UV-C irradiation at 0.5 kJ·m<sup>-2</sup> effectively reduced decay development compared with nontreated fruit. Irradiation with 1.5 kJ·m<sup>-2</sup> was more effective compared with 0.5 kJ·m<sup>-2</sup> only in early harvested fruit. In 'Washington Navel' and 'Biondo Comune' oranges in the later harvests, treatment with 3.0 kJ·m<sup>-2</sup> improved decay control further, compared with 0.5 kJ·m<sup>-2</sup>. Following UV-C treatments the phytoalexins, scoparone and scopoletin, accumulated in flavedo tissue depending on the cultivar, fruit age, and UV-C treatment. Both phytoalexins displayed a similar accumulation pattern, however, the levels of scopoletin were very low compared with scoparone. Concentrations of phytoalexins rose as the irradiation dose increased. No scoparone and scopoletin could be detected in nontreated fruit. The highest concentration of phytoalexins among cultivars was recorded in 'Valencia Late' oranges, the lowest in 'Tarocco', with similar intermediate accumulations in 'Washington Navel' and 'Biondo Comune'. In 'Washington Navel', 'Biondo Comune', and 'Tarocco' oranges, the rate of scoparone accumulation was significantly higher in fruit harvested earlier in the season while 'Valencia late' oranges exhibited an opposite trend.
 
Proton nuclear magnetic resonance ( 1 H NMR) spectra of chiro-inositol, standard (A) and isolated from Limonium perezii (B), and Limonium sinuatum (C) leaves. Additional peaks in the isolated samples are sample noise peaks.  
Limonium perezii and Limonium sinuatum leaf soluble carbohydrate (A– F) and starch (G) concentrations, and the ratio of chiro-inositol over the sum of fructose + glucose + sucrose (RCOFGS) (H) in response to salinity (San Joaquin Valley drainage water salt composition). Total soluble carbohydrates are the sum of all the detected sugars and sugar alcohols. Vertical bars represent ± SE, n = 3 (tanks). Significant difference (P # 0.05) between the two species is marked with an asterisk at any given salinity level.  
Comparison of responses of Limonium perezii leaf soluble carbohydrates (A–F) and starch (G) concentrations, and ratio of chiro-inositol over the sum of fructose + glucose + sucrose (RCOFGS) (H) to two salt compositions, San Joaquin Valley (SJV) drainage waters versus saline tailwaters encountered in the inland valleys of southern California typically representing concentrations of Colorado River (CCR) water. Total soluble carbohydrates are the sum of the all detected sugars and sugar alcohols. Vertical bars represent ± SE, n = 3 (tanks). Significant difference (P # 0.05) between the two salt compositions is marked with an asterisk at any given salinity level.  
Cumulative phloem exudation of cyclitols (A and B) and sucrose (C) from fully expanded leaves of Limonium perezii under salt (20.0 dSÁm –1 ) and nonsalt stress (2.5 dSÁm –1 ). The two sources of saline water, San Joaquin Valley drainage waters versus saline tailwaters encountered in the southern inland valleys of California typically representing concentrations of Colorado River water, had the same effect on the carbohydrate exudation, and thus the data were pooled. Vertical bars represent ± SE, n = 8 (leaves). Significant salt effect at each exudation period (P # 0.05) is marked with an asterisk at any given salinity level.  
Article
Two statice cultivars, Limonium perezii cv. Blue Seas and L. sinuatum cv. American Beauty, were grown in greenhouse sand tanks to determine the effect of salt stress on carbohydrate accumulation and partitioning. For the first experiment, irrigation waters were prepared to simulate typical saline-sodic drainage effluent in the San Joaquin Valley of California with electrical conductivities of 2.5, 7, 11, 15, 20, 25, and 30 dS·m-1. A second experiment compared responses to two types of irrigation waters with salinity levels of 2.5, 6, 8, 10, 12, 16, and 20 dS·m-1: 1) San Joaquin Valley drainage waters, and 2) solutions mimicking concentrations of Colorado River water, a major irrigation water source for southern California. In addition to the presence of myo-inositol and three common sugars (fructose, glucose, and sucrose), chiro-inositol was for the first time isolated and identified in leaf and root tissues of both Limonium species. As salinity increased from 2.5 to 30 dS·m-1, leaf chiro-inositol concentration increased from 6.4 to 52.8 and from 2.6 to 72.9 μmol·g-1 dry weight for L. perezii and L. sinuatum, respectively, suggesting that chiro-inositol contributes substantially to osmotic adjustment in the stressed plants. Meanwhile, leaf myo-inositol concentration remained low in both species and showed little response to salinity. Before salt stress, the seedlings contained little chiro-inositol, indicating that salt enhanced chiro-inositol synthesis per unit of biomass formation. Significant (P <or= 0.05) increasing trends for fructose and glucose and a decreasing trend for sucrose with increasing salinity were observed in the leaves of L. perezii but not L. sinuatum. As a result, the leaves of L. perezii had higher glucose and fructose but lower sucrose levels than that of L. sinuatum. However, no significant (P > 0.05) salt effect was found on the sum of the three common sugar concentrations in either species. Therefore, the accumulation of chiro-inositol resulted in a change in carbon partitioning among the soluble carbohydrates (i.e., the ratio of leaf chiro-inositol over a sum of the three common sugars rose from 0.034 to 0.29 dS·m-1 and from 0.012 to 0.32 dS·m-1 for L. perezii and L. sinuatum, respectively, as salinity increased from 2.5 to 30 dS·m-1). Salt stress did not affect starch accumulation and caused no carbon reserve deficiency. Furthermore, it was observed that salinity increased chiro-inositol phloem transport. The chiro-inositol response might be a physiological process for Limonium salt adaptation. The types of saline irrigation waters (i.e., sodium sulfate-dominated waters vs. a sodium chloride system) appear to have little effect on carbohydrate accumulation and partitioning in L. perezii.
 
Effect of temperature treatment on shoot dry weight for 'Designer Dark Red' and 'Galleria Bright Violet' geraniums 63 d after transplanting in Expt. 1.
Number of irrigations applied to geranium plants in the extra- low, low, medium, and high temperature treatments in Expts. 1 and 2.
Article
Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1-2 weeks) cause the substrate pH to shift downward one to two units. 'Designer Dark Red' geraniums (Pelargonium xhortorum Bailey) were grown in three experiments to assess possible effects of temperature on SPD. The first experiment tested the effect of four day/night temperature regimes (14 °C day/10 °C night, 18 °C day/14 °C night, 22 °C day/18 °C night, and 26 °C day/22 °C night) on substrate acidification. At 63 days after transplanting (DAT), substrate pH declined from 6.8 to 4.6 as temperature increased. Tissue phosphorus (P) of plants grown at the highest three temperatures was extremely low (0.10%-0.14% of dry weight), and P stress has been reported to cause acidification. It was not possible to determine if the drop in substrate pH was a singular temperature effect or a combination of high temperature and low P. To resolve this, a second experiment tested a factorial combination of the three highest temperatures from the first experiment and five preplant P rates (0, 0.065, 0.13, 0.26, or 0.52 g·L-1 substrate). Regardless of tissue P concentrations, which ranged from deficient to above adequate, substrate pH decreased with increasing temperature. At 63 DAT, in the 0.065 and 0.13 P treatments, tissue P was deficient and pH decreased with increasing temperature from 5.6 to 4.7 and 5.9 to 4.7, respectively. In the 0.26 P treatment, tissue P was adequate at the lowest temperature and there was no acidification. At the mid- and highest temperatures, tissue P was deficient and statistically equivalent, yet pH decreased to 5.2 and 4.7, respectively. In the highest P treatment, tissue P levels were unaffected by temperature, above adequate, and pH declined with each increase in temperature from 6.5 to 5.0. The results at 63 DAT once more showed that temperature acted independent of tissue P and caused geraniums to acidify the substrate. In the third experiment, the amount of acidity produced by roots of plants grown at the two highest temperatures used in the first two experiments was quantified. Plants grown at the higher temperature produced 28% more acid per gram dry root. The results herein indicate that high temperature can induce SPD by geranium.
 
Article
Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1-2 weeks) cause the substrate pH to shift downward one to two units. 'Designer Dark Red' geraniums (Pelargonium xhortorum Bailey) were grown in three experiments to assess possible effects of light on SPD and phosphorous (P) uptake. The first experiment tested the effect of four light intensities (105, 210, 575, and 1020 +/- 25 μmol·m-2·s-1) on substrate acidification. At 63 days, substrate pH declined from 6.0 to 4.8 as light intensity increased. Tissue P of plants grown at the highest two light levels was extremely low (0.10%-0.14% of dry weight). P stress has been reported to cause acidification. Because plants in the two lowest light treatments had adequate P, it was not possible to determine if the drop in substrate pH was a direct light effect or a combination of light and P. The second experiment used a factorial combination of the three highest light levels from Expt. 1 and five preplant P rates (0, 0.065, 0.13, 0.26, or 0.52 g·L-1 substrate) to assess this question. When tissue P concentrations were deficient, pH decreased by 0.6 to 1.0 pH units within 2 weeks and deficiency occurred more often with high light intensity. These data indicated that P deficiency caused substrate acidification and indicated the possibility that P uptake was suppressed by high light intensity. The third experiment was conducted in hydroponics to determine the direct effect of high light intensity on P uptake. In this experiment, cumulative P uptake per gram root and the rate of P uptake per gram root per day both decreased 20% when light intensity increased from 500 to 1100 μmol·m-2·s-1. It is clear from this study that P deficiency causes geraniums to acidify the substrate and that high light suppresses P uptake.
 
Article
Heat stress is a limiting factor of plant productivity throughout the world and kaolin-based particle films (PF) have demonstrated that the reflective nature of the resulting plant surface can increase plant productivity primarily by reducing temperature in fruit, leaf, and canopy. The purpose of this study was to evaluate the environmental mechanisms and related physiological responses of 'Empire' apple (Malus xdomestica) gas exchange at the canopy level to PF treatments to identify those parameters key to plant response and increased plant productivity. Trees received either no treatment or season-long applications of a PF treatment and each treatment either received no supplemental irrigation or full replacement of evapotranspiration. Studies were begun in 1998 and continued to 2007. Fruit number and fruit weight were measured in all years. Whole canopy carbon dioxide assimilation rates (A) were measured in apple for a 4-year period to determine the relationship with incoming light and vapor pressure deficit (VPD) levels. The photosynthetic response to the irrigation and PF treatments varied between years as a result of environmental variation in VPD and photosynthetically active radiation (PAR) levels. There was a unique treatment response for PAR levels greater than 1600 μmol·m-2·s-1 in which the combination of PF and irrigation maintained midday A at maximum levels compared with other treatments although A was reduced by increasing VPD. This response indicated that although VPD limited A, the combination of PF and adequate water could maintain maximum A rates at full sun levels during the midday period and minimize the midday depression of A that is commonly observed and reduces the daily carbon accumulation. The increased carbon accumulation during the midday period was likely partitioned to the fruit. Increased fruit weight resulting from the PF treatment, compared with the control, was positively correlated with the growing season air temperature and VPD indicating that as the environment becomes hotter and/or drier, the magnitude of the PF response increased as a result of the reduced leaf and fruit temperature and the subsequent physiological effect. The PF treatments reduced radiation and heat load on exposed leaves enabling them to better regulate leaf temperature and improved the light distribution inside the canopy resulting in increased carbon gain at the whole plant scale. Fruit hue angle was reduced and red color improved by PF treatments in 5 of 10 years. The use of PF may be an effective substitute for evaporative cooling to reduce solar injury and to improve apple quality through increased fruit weight. The results indicate that benefits of PF treatments would occur in agroecosystems with large VPDs and high temperatures and that use of irrigation would further enhance the benefits at high PAR levels.
 
Article
To study ripening-related chilling injury in pepper (Capsicum annuum L.), chilling-tolerant 'Buchon' and chilling-sensitive 'Nockgwang' fruit were harvested at mature green (MG), breaker (BR), and red-ripe (RR) stages and stored at 1, 5, and 10 °C for 21 d. 'Buchon' did not show surface pitting (SP) regardless of ripeness stage and storage temperature, whereas 'Nockgwang' at MG and BR exhibited SP at 1 and 5 °C. After 14 days of storage at 1 °C, chilling-sensitive 'Nockgwang' did not show SP when fruit were at the RR stage. Compared with 'Buchon', 'Nockgwang' at MG and BR had more electrolyte leakage increase during storage at 1 and 5 °C. 'Buchon' at all ripeness stages showed significantly higher ethylene production during storage regardless of storage temperatures. Contents of β-carotene and lycopene increased in both cultivars as ripening progressed. The contents of β-carotene and lycopene were similar between the two cultivars regardless of storage temperatures and ripeness stages. Susceptibility of pepper fruit to chilling appeared to be related to superoxide dismutase (SOD) and catalase (CAT). Activities of SOD and CAT were much higher in 'Buchon' than 'Nockgwang', more apparently at MG and BR. The results suggest that chilling-tolerant 'Buchon' and fruit at RR could have been equipped with a more efficient antioxidizing system, even if it was not clear whether oxidative stress is a cause or an effect of the CI in pepper.
 
Article
Fruit extracts from 17 to 18 representatives of three strawberry species [Fragaria virginiana Mill., F. chiloensis (L.) Mill., and F. xananassa Duchesne ex Rozier] were tested for the ability to inhibit proliferation of A549 human lung epithelial cancer cells. The fruit extracts also were tested for activities against free radicals, (peroxyl radicals, hydroxyl radicals, singlet oxygen, and superoxide radicals), the activities of antioxidant enzymes [glutathione peroxidase (EC 1.11.1.9), superoxide dismutase (EC 1.15.1.1), guaiacol peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.11), monodehydroascorbate reductase (EC 1.6.5.4), dehydroascorbate reductase (EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2)], and the activities of nonenzyme antioxidant components, ascorbic acid and glutathione. Correlations between the proliferation of cancer cells and these antioxidant activities were calculated. At the species level, F. virginiana fruit extract inhibited the proliferation of A549 human lung epithelial cancer cells to a significantly greater extent (34% inhibition) than the extracts from fruit of either F. chiloensis (26%) or F. xananassa (25%) (P < 0.0001). Extracts from fruit of F. virginiana also had significantly greater antioxidant activities and higher activities of antioxidant enzymes and nonenzyme components than did extracts from the other two species. Among individual genotypes, there was a high positive correlation between antiproliferation of A549 cancer cells, antioxidant activities against free radicals, activities of antioxidant enzymes, and activities of nonenzyme components. Although all fruit extracts from all the strawberry genotypes inhibited proliferation of A594 cancer cells, fruit extracts from seven F. virginiana genotypes showed significantly greater antiproliferative effects than any of the F. xananassa or F. chiloensis genotypes. These genotypes, CFRA 0982, JP 95-1-1, NC 95-19-1, RH 30, NC 96-48-1, JP 95-9-6, and LH 50-4, may be especially useful in developing cultivars with greater anticancer potential.
 
Article
This research was carried out to extend the postharvest storage of japanese plum (Prunus salicina Lindl. cv. Tegan Blue), which has a short shelf life limiting its export potential. The effects of 1.0 μL·L-1 1-methylcyclopropene (1-MCP) and modified atmosphere packaging (MAP), alone or in combination, on quality of mature japanese plum fruit during storage (0 ± 1°C and 90% ± 5% relative humidity) were investigated. The activities of enzymes of ethylene biosynthesis [1-aminocyclopropane-1-carboxylic acid synthase (ACS), 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), and 1-aminocyclopropane-1-carboxylic acid (ACC) content] and those of cell wall-associated enzymes [exo-polygalacturonase (exo-PG), endo-polygalacturonase (endo-PG), pectin esterase (PE), and endo-1,4-β-D-glucanase (EGase)] were also measured. 1-MCP-treated fruit stored in normal atmosphere or in MAP had lower ACC content and inhibited ethylene production with reduced ACS and ACO activities compared with fruit stored in MAP and in normal atmosphere. Similarly, 1-MCP-treated fruit, stored either in normal atmosphere or in MAP, were firmer with reduced exo-PG, endo-PG, PE, and EGase activities compared with fruit stored in MAP and in normal atmosphere. During storage as well as during ripening, fruit stored in MAP exhibited a higher rate of respiration compared with other treatments. MAP exacerbated the effect of 1-MCP in reduction of ethylene production and fruit softening. 1-MCP application in combination with MAP after 5 and 7 weeks of storage delayed the fruit ripening by 10 and 8 days in contrast with control fruit, respectively. During storage, and as well as in ripe fruit, weight loss was reduced in fruit stored in MAP either with or without 1-MCP application. Control fruit and 1-MCP-treated fruit, stored in a normal atmosphere or in MAP, had the same values for the following parameters: chromaticity value L*, C*, and hue angle, titratable acidity, and concentrations of soluble solids, ascorbic acid, and total antioxidants. In conclusion, 1-MCP application in combination with MAP can be used effectively to reduce the ethylene biosynthesis and fruit softening during cold storage and to extend the storage life up to 7 weeks followed by 8 d of ripening without any adverse effects on the quality of ripe fruit.
 
Soluble solids content (SSC) and titratable acidity (TA) of strawberry cultivars and selections over the two harvest seasons.
Article
The aim of this study was to understand the flavor components of eating quality of several strawberry (Fragaria xananassa Duch.) genotypes grown in Florida over two harvest seasons. Five selections and one cultivar of the University of Florida Breeding program as well as two new cultivars from Australia (Rubygem and Sugarbaby) harvested on different dates from the same grower were evaluated by sensory evaluation. Festival, the main strawberry cultivar grown in Florida, had low ratings for flavor and sweetness in January and March. Selection FL 00-51 and 'Rubygem' had relatively high and consistent ratings for flavor and sweetness compared with the other selections. Genotypes with low flavor ratings were always judged as "not sweet enough" by the panelists, thus linking flavor to sweetness preference. Instrumental analysis confirmed that typically these selections had low soluble solids content (SSC) and/or high titratable acidity (TA), thus explaining their lack of sweetness. Volatile compounds that varied only quantitatively did not seem to influence the flavor rating except for 'Sugarbaby'. This cultivar contained between seven and 40 times less total ester content than the other selections and was disliked by panelists despite its high sugar content and perceived sweetness. It was perceived as having an artificial peach- or blueberry-like flavor. A principal component analysis was performed with chemical parameters (SSC, TA, and volatile content) and selections over the two harvest seasons. Chemical composition was mainly influenced by harvest date, except for FL 00-51. This selection maintained high volatile content and SSC throughout the seasons, explaining consistently high flavor ratings.
 
Article
The influence of polyethylene mulch surface color on the plant light environment and tomato (Lycopersicon esculentum Mill) production was investigated. White- or silver-painted mulches reflected more total light, and a lower ratio of far-red relative to red light, than mulches painted black or red. Soil temperatures were warmer under the black and red mulches. Mulch color also affected the yield and growth of tomato. Tomato plants grown with red mulch generally had the greatest early marketable yields and produced the least amount of foliage. Plants grown with a white or silver-colored mulch had lower early marketable yields but produced more foliage. These results suggest that mulch surface color can induce changes in the plant microclimate (e.g., spectral balance and auantity of light, root zone temperatures) that can act through natural regulatory systems within the growing plant and affect tomato plant growth and fruit production.
 
Article
While nickel (Ni) deficiency occurs in certain agricultural crops, little is known regarding the influence of deficiency on metabolic or physiological processes. We studied the influence of Ni deficiency on the reduced-nitrogen (N) composition of early spring xylem sap of pecan [Carya illinoinensis (Wangenh.) C. Koch]. High-performance liquid chromatography (HPLC) analysis of sap composition found the presence of ureido-, amide-, and amino-N substances and that they are quantitatively influenced by tree Ni nutritional status. Ureido-N forms quantitatively dominated amide-N forms with respect to both molar concentration and the forms in which reduced N atoms are present; thus, pecan appears to be predominately a ureide-transporting species. The primary ureido-N substances in sap of Ni-sufficient trees are citrulline approximately equal to asparagine approximately equal to xanthine > ureidoglycolate > allantoic acid > allantoin approximately equal to uric acid approximately equal to urea. Asparagine is the primary amide-N form, while only traces of amino-N forms (e.g., tryptamine and ss-phenylethylamine) are found in xylem sap. Nickel deficiency substantially increased citrulline and allantoic acid in xylem sap while decreasing the asparagine, xanthine, and ss-phenylethylamine concentrations. These Ni-linked quantitative shifts in reduced-N forms indicate that Ni nutrition potentially affects intermediates of both the ureide catabolic pathway and the urea cycle as well as the nitrogen/carbon (N/C) economy of the tree. Xylem sap-associated urease-specific activity was also reduced as a consequence of Ni deficiency. These results indicate that Ni deficiency potentially disrupts normal N-cycling via disruption of ureide metabolism.
 
Article
Seventy-one amplified fragment length polymorphism (AFLP), 93 sequence related amplified polymorphism (SRAP), and 14 simple sequence repeat (SSR) markers were used to extend an initial genetic linkage map for watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai]. The initial map was based on 151 randomly amplified polymorphic DNA (RAPD) and 30 and inter-simple sequence repeat (ISSR) markers. A testcross population previously used for mapping of RAPD and ISSR markers was used in this study: (plant accession Griffin 14113 [C. lanatus var. citroide (L.H. Bailey) Mansf.] x the watermelon cultivar New Hampshire Midget (C. lanatus var. lanatus)) x PI 386015 [C. colocynthis (L.) Schrad.]. The linkage map contains 360 DNA markers distributed on 19 linkage groups, and covers a genetic distance of 1976 cM with an average distance of 5.8 cM between two markers. A genomic DNA clone representing 1-amino-cyclopropane-1-carboxylic acid (ACC-) synthase gene, involved in ethylene biosynthesis, was also mapped. As in previous mapping studies for watermelon, a large number of AFLP and SRAP markers were skewed away from the 1:1 segregation ratio, and had to be excluded from the final mapping analysis. The stringent mapping criteria (JoinMap 3.0 mapping program) produced linkage groups with marker order consistent with those reported in previous mapping study for watermelon.
 
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Bingru Huang
  • Rutgers, The State University of New Jersey
Carl Sams
  • University of Tennessee
Mikal Saltveit
  • University of California, Davis
Randolph Beaudry
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