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Joyce G. Latimer and Reuben B. Beverly

Brushing (40 strokes per 1.5 minutes, twice daily) or moisture stress conditioning (MSC) (daily nonlethal dry-down cycles) reduced seedling growth of two cucumber (Cucumis sativus L.) cultivars in 1991 and three squash (Cucurbita pepo L.) cultivars in 1991 and 1992. In both years, watermelon [Citrullus lanatus Thunb. (Matsum. & Nakai)] cultivars varied in responsiveness to brushing; brushing reduced stem length 0% to 44% over four cultivars in 1992. MSC reduced growth of all cultivars. Brushing increased the rate of water loss from detached leaves of cucumber, squash, and watermelon, whereas MSC decreased water loss from leaves of cucumber and squash. In 1991, under well-watered posttransplant conditions, MSC increased the mean relative growth rate (RGR) of cucumber and watermelon transplants in the greenhouse. Brushing increased the RGR of watermelon transplants. In 1992, MSC increased the RGR of squash and watermelon transplants grown under posttransplant drought-stressed conditions, while brushing had no effect. Both conditioning treatments controlled plant growth in the greenhouse without diminishing subsequent plant performance.

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John D. Lea-Cox, G.W. Stutte, and W.L. Berry

The maintenance of pH in unbuffered nutrient solutions has important consequences for the hydroponic industry and proposed nutrient delivery systems for plants in space. The requirement for charge balance by a model plant system, dwarf wheat (Triticum aestinum cv. Yecora rojo), is largely a function of the uptake ratio of four cation species (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}, Ca2+, and Mg2+) and two anion species (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{SO}_{4}^{2-}\) \end{document}) up to anthesis. The change in electrical conductivity (EC) and pH of the nutrient solution over time integrates the overall influx:efflux process of the plants. Solutions with three different NH4:NO3 ratios were sampled at 15-min intervals over a 12-h period at 9, 10, 16, 17, 23, 24, 37, and 38 days after planting. Exhaustion of N in the solution at all stages of ontogeny resulted in a 2- to 3-fold reduction in ΔpH/Δt, despite high plant tissue N and irrespective of the concentration of other charge balance ions in solution. These data, combined with a plant nutrient uptake database (normalized for plant relative growth rate per mole PPF), suggest that a system can be developed to control pH by direct supply of various alternative nutrient stock solutions, rather than by the addition of H+ or OH from acid or base.

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Puffy Soundy, Daniel J. Cantliffe, George J. Hochmuth, and Peter J. Stoffella

Several levels of P were supplied via floatation irrigation to `South Bay' lettuce (Lactuca sativa L.) transplants to determine the optimum P concentration necessary. Plants were propagated by floating flats (ebb and flow system) in a nutrient solution containing P at either 0, 15, 30, 45, or 60 mg·L-1 in summer and fall experiments, and either 0, 15, 30, 60, or 90 mg·L-1 P in a factorial combination with 60 or 100 mg·L-1 N in a winter experiment. Adding more than 15 mg·L-1 P had minimal effect on growth. Transplants produced with 0 P grew poorly, regardless of the level of N applied. Nitrogen at 100 mg·L-1 improved the response of shoot growth to any level of P, but adversely affected root growth compared with N applied at 60 mg·L-1. In general, relative growth rate was improved, while net assimilation rate was reduced at all levels of P. High-quality transplants had a root to shoot ratio of about 0.25, total root lengths between 276 and 306 cm, and total root area between 26 and 30 cm3 in a 10.9-cm3 cell volume. Only 30% of the plants produced without P could be pulled from the transplant flats, whereas 90% could be pulled when P was added. Pretransplant P hastened maturity and increased lettuce head weight at harvest in the field. This work suggested that at least 15 mg·L-1 P, supplied via floatation irrigation to a peat + vermiculite mix, was required to produce a transplant with sufficient roots for ease of pulling, rapid field establishment, and earlier harvest.

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B. Murillo-Amador, E. Troyo-Dieguez, and F. orrego-Escalante

The response of physiological traits of four genotypes of Opuntia spp (AN-V1, AN-V3, AN-V5, and AN-TV6) to organic fertilization with two levels of thickness and different plant densities (10, 20, 30, 40, and 50 plants/m2) under plastic tunnels were studied in the Universidad Autnoma Agraria “Antonio Narro” in 1995 and analyzed at CIBNOR, La Paz, Mexico. The main goal of this work was to screen Opuntia genotypes for yield and photosynthetical efficiency. The experiment was established as a randomized blocks design with three replicates. Response variables were dry weight (DW), crop growth ratio (CGR), rate of crop growth (RCG), relative growth rate (RGR), leaf area index (LAI), and net assimilation rate. The annual average temperature in the study site was 19.8°C. Hottest months were July and August, with temperature values as high as 39°C. The lowest temperatures were recorded in December and January, with temperatures as low as –13°C. Annual rainfall was 365 mm. Soils in the study region show a generalized low fertility. According to our results, genotype AN-V1 showed the best photosynthetical features with 30 plants/m2; genotype AN-TV6 showed no differences for 40 and 50 plants/m2. The highest values for CGR and RCG were observed under the highest level of organic fertilization (16-cm thickness). Genotypes AN-V3 and AN-V5 evidenced the highest RCG. Other results suggest that AN-V3 and AN-V5 showed the highest value for LAI, for a density 50 plants/m2, and genotypes AN-V1 and AN-V3, with a density 40 plants/m2, had the highest RGR. The studied Opuntia genotypes appeared to be promising crops for marginal semiarid regions.

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F.D. Moore III, S.R. Nath, and Y-C Wang

Duration of growth is dependent on morphological events or changes in growth rate. It is the latter that is associated with phasic development. The most productive phase of plant growth is the linear or constant rate phase, primarily because it endures longer than the exponential phase. The purpose of our research was to objectively determine the true tree-height growth pattern, the linear and stationary phases of height growth, and to mathematically derive the maximum slope (maximum growth rate) of the growth curve, its location (inflection point), and the maximum slope of the logarithmic form (maximum relative growth rate) of the growth curve. The data were composed of 333 tree-height records covering 240 years from 200 beechwoods in the U.K. Height-age data were fitted using a splined function (S) and the Chapman-Richards function (CR). The growth curve and critical points on the curve were derived from the CR model. The linear phase began when trees were 9 and lasted 43 years. However, the stationary phase did not begin until age 162. Anecdotal evidence suggests that very little fruiting occurs before age 50. Based on derived critical points and anticipated source-sink dynamics, the reproductive stage should have taken place during the progressive “deceleration phase” when trees were between 31 (location of the maximum slope, also inflection point) and 162 (from quadratic root). The linear phase ended at 52 years, (coinciding with minimum acceleration) and may prove a more accurate estimate than 31. Maximum slope was 1.2 m per year occurring at age 31. Maximum slope of the log curve was 0.14 m·m–1 per year. The advantage of the CR function and the importance of the derived quantities and growth phases will be discussed.

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Hiphil S. Clemente and Thomas E. Marler

Two studies were conducted with `Known You 1' and `Sunrise' papaya seedlings to determine the combined influence of wind and drought stress on growth. For each study, 4-week-old nursery plants were transplanted into 2.6-L containers and placed in a protected site with rain exclusion provided by polypropylene cover. Industrial fans were used to provide unidirectional wind of ≈2 m/s for 12 hours per day to half of the plants; the remaining half of the plants received no wind. One half of the plants for each cultivar and wind combination were designated as well-watered and received daily irrigation. The remaining half of the plants were designated as drought-stressed and received 25% to 50% of the water applied to the well-watered plants. Plants were grown for 3 weeks under these experimental conditions. There were no interactions between the drought and wind main effects. The reduction in height, trunk cross-sectional area, total plant dry weight, and relative growth rate below that for control plants was similar for drought stress or wind stress. Wind stress reduced growth of `Sunrise' plants more than `Known You 1' plants in both studies. Although the main effects did not interact, the combination of drought and wind stress reduced growth of papaya seedlings more than did either main effect alone. The greatest wind load from trade winds occurs on Guam during the annual dry season. These data indicate that chronic wind stress during the dry season may be more detrimental to growth of papaya seedlings than during the rainy season or under sufficient irrigation practices.

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T.K. Hartz, C. Giannini, E.M. Miyao, and J.G. Valencia

The effect of transplant production and handling practices on processing tomato growth, yield, and fruit quality were evaluated in five field trials in California. In 1999, processing tomato (Lycopersicon esculentum Mill. cv. Halley) transplants were obtained from a number of commercial transplant producers and taken to the Univ. of California-Davis (UCD) where treatments were imposed for 1 week prior to transplanting. Treatments included N and P fertilization, exposure to lath house or greenhouse temperature, withholding water, and storage in the dark for 2 days to simulate shipment from greenhouse to field. Nine treatments per site were compared in field trials at Yolo, Woodland, and Knights Landing. In 2000, transplants were grown at UCD under varying nutrient regimes, including P fertilization rates ranging from weekly application of 0 to 90 mg·L-1. Two commercial field trials comparing 8 treatments were conducted near Winters and Newman. Although transplant production and handling practices significantly influenced relative growth rate in the 3-4 weeks following transplanting in all 1999 trials, effects on fruit yield were minimal, with only one treatment at Woodland showing significantly lower yield and no treatment differences in crop maturity, fruit soluble solids, or juice color observed at any site. In 2000, plants receiving no weekly P fertilization showed slower growth in the 3 weeks after transplanting, but no treatment differences were observed after 6 weeks. Fruit yield, soluble solids content (°Brix) and juice color were unaffected by transplant treatment. We conclude that transplant production and handling practices tested had minimal differential effect on the subsequent field performance of processing tomato transplants in the Central Valley of California.

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Marc W. van Iersel*

Literature reports on the Q10 for respiration vary widely, both within and among species. Plant size and metabolic activity may be responsible for some of this variation. To test this, respiration of whole lettuce plants was measured at temperatures ranging from 6 to 31 °C during a 24-h period. Subsequently, plant growth rate (in moles of carbon per day) was determined by measuring the CO2 exchange rate of the same plants during a 24-h period. Environmental conditions during this 24-h period resembled those that the plants were exposed to in the greenhouse. The measured growth rate was then used to estimate the relative growth rate (RGR) of the plants. The respiratory Q10 ranged from 1.4 for small plants to 1.75 for large plants. The increase in Q10 with increasing plant size was highly significant, as was the decrease in Q10 with increasing RGR. However, growth rate had little or no effect on the respiratory Q10. One possible explanation for these findings is that the Q10 depends on the ratio of growth to maintenance respiration (which is directly related to RGR). The growth respiration coefficient generally is considered to be temperature-insensitive, while the maintenance respiration coefficient normally increases with increasing temperature. Based on this concept, the Q10 for the maintenance respiration coefficient can be estimated as the estimated Q10 at a RGR of zero (i.e. no growth and thus no growth respiration), which was 1.65 in this experiment. Although the concept of dividing respiration into growth and maintenance fractions remains controversial, it is useful for explaining changes in respiratory Q10 during plant development.

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Emad Bsoul* and Rolston St. Hilaire

Although valued for its fall foliage color, bigtooth maple (Acer grandidentatum Nutt.) is not widely used in managed landscapes. Furthermore, information on the tolerance of bigtooth maples to drought is scant. We studied water relations, plant development, and carbon isotope composition of bigtooth maples indigenous to New Mexico, Texas, and Utah. Plants were field grown in New Mexico using a pot-in-pot nursery production system. Plants were maintained as well-irrigated controls or irrigated after the weight of pots decreased by 35% due to evapotranspiration. Drought treatment lasted 71 days. Among the drought-stressed plants, plants native to Logan Canyon in Utah (designated UW2), had the greatest root: shoot dry weight ratio (3.0), while plants with the lowest root: shoot dry weight ratio (0.9) were half siblings from a tree native to the Lost Maples State Park in Texas (designated LMP5). Among the five sources we tested, LMP5 had the greatest (1242 cm2) leaf area, while UW2 plants had the smallest (216 cm2). Regardless of the treatment, plants from LMP5 had the highest shoot dry weight (25.7 g). Plants showed no differences neither among sources nor between treatments in relative water content, specific leaf weight, xylem diameter, root dry weight, plant dry weight, relative growth rate, and carbon isotope discrimination, which averaged - 26.53%. The lack of differences in these parameters might be due to selection of these sources from provenances we deemed to be the most drought tolerant. Our selection was based on the results of a previous greenhouse study of 15 bigtooth maple sources. We conclude that these sources, and in particular, plants from LMP5 in Texas, might hold promise for use in areas prone to drought.

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Md. Shahidul Islam and Tadashi Ito

Characterization of physico-chemical properties of ecologically sound unprocessed coconut (Cocos nucifera L.) coir and carbonated rice husk in relation to rockwool were investigated to examine the crop performance along with productivity of tomatoes (Lycopersicon esculentum Mill.). In all substrates, the water-filled pore space and water-holding capacity were larger and air-filled pore space was smaller. Bulk densities, water-holding capacity, and water-filled, air-filled, and total pore spaces were lower in carbonated rice husk than coconut coir and rockwool. These values in coconut coir and carbonated rice husk were increased by use. Most of the physical properties, EC, pH, and inorganic elements, of these natural organic substrates were within appropriate levels as growing media. There were little differences in plant height, stem diameter, percent fruit set, harvest index, ascorbic acid, total soluble solid, fruit pH, and leaf chlorophyll ratio. But, number of nodes, internode length, leaf number and area, days to first anthesis, flower number, and fruit number and weight differed significantly among treatments. There was smaller fluctuation in absolute growth rate, relative growth rate, net assimilate rate, and leaf area ratio among the treatments. It appeared that carbonated rice husk and the coconut coir gave better crop performance than rockwool under moderate high temperatures (30 and 35 °C compared to 25 °C). Furthermore, crop productivity from the organic substrate coconut coir and carbonated rice husk gave more profit than that of rockwool. Thus, carbonated rice husk and coconut coir substrates can be used successfully as a bag culture media amendment for producing vegetables, especially in tropical and subtropical areas.