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Douglas D. Archbold

Plants of a diverse collection of Fragaria clones from a range of native habitats representing F. chiloensis, F. virginiana, F. virginiana glauca, and F. vesca, were grown in a controlled environment at one of three day/night temperatures, 15/15, 23/15, or 31/15°C. Relative growth rate (RGR) and net assimilation rate (NAR) were estimated from plant leaf areas and total dry weights. At 23/15°C, the species mean RGR and NAR values were comparable although clones within species exhibited significant variation. At 15/15 and 31/15°C, RGR and NAR for species were lower than at 23/15°C. At 31/15°C, chiloensis and vesca mean values were reduced more than the others, to less than 50% the 23/15°C values. Also, NAR declined most for chiloensis, to 45% the 23/15°C value. At 15/15°C, virginiana had much higher RGR and NAR values than the other species, and its NAR mean value was greater than at 23/15°C. Although the species means would suggest that there are interspecific differences in temperature response, intraspecific variability was also large. Thus, classifying Fragaria species by temperature response may be an over-generalization.

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Pauline P. David, Audrey A. Trotman, and Desmond G. Mortley

One of the major objective of growth analysis data is to provide a basic understanding of some of the mechanisms that affect plant growth. This study was initiated to evaluate the effects on several growth parameters when plants are grown in an NFT system. Vine cuttings (15 cm length) of the sweetpotato cultivar ``Georgia Jet” was grown in a closed NFT system for a period of 120 days. Nutrient was supplied in a modified half-strength Hoagland's solution with a N:K ratio of 1:2.4. Destructive harvesting of plants occurred at 14 day intervals at which time plants were separated into their various component parts and analyzed for dry weight accumulation, leaf area index, crop growth rate, relative growth rate and net assimilation rate. Results showed dry weight distribution within the plant had a linear response for all component part evaluated. Greatest contributors to total plant dry weight was stem followed by leaves, fibrous roots, buds and flowers. However, once storage root production occurred it contributed the largest percentage to total plant dry weight. LAI was optimum at 80 days after planting (DAP) while CGR and RGR fluctuated throughout the growing season. Initially NAR was higher in foliage than storage roots but declined once storage root enlargement began, suggesting a translocation of assimilates to storage root.

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Marc van Iersel

Salvia splendens `Top burgundy' was grown in pots of different sizes (5, 50, 150, and 450 mL) to assess the effect of rooting volume on the growth and development of salvia. Seeds were planted in a peat-lite growing medium and plants grown in a greenhouse during the winter and spring of 1996. Plants were spaced far enough apart to minimize mutual shading and interplant light competition. Plants were harvested at weekly intervals and shoot and root dry mass and leaf area were measured. Relative growth rate (RGR) and net assimilation rate were calculated from these data. Differences in plant size became evident at 25 days after seeding. A small pot size (5 mL) decreased root and shoot dry mass, RGR, and NAR, while increasing the root:shoot ratio. Differences between the pot sizes became more apparent during the course of the experiment. The observation that root: shoot ratio decreased with increasing pot volume suggests that the decreased plant size in smaller pots was not the direct effect of reduced root size. Growth most likely was limited by the ability of the roots to supply the shoots with sufficient water and/or nutrients. Pot volume did not only affect the growth, but also the development of the plants. Salvia flowered faster in bigger pots (about 50 days after seeding in 450-mL pots), while the plants in 5-mL cells did not flower during the 9-week period of the experiment.

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Gina E. Fernandez and Marvin P. Pritts

Seasonal changes in growth, mean maximal photosynthetic rates, and the temperature and light response curves of `Titan' red raspberry (Rubus idaeus L.) were obtained from potted plants grown under field conditions. Primocane dry weight accumulation increased steadily at the beginning and the end of the season, but growth slowed midseason during fruiting. The slower midseason dry-weight accumulation rate coincided with an increase in root dry weight. Primocane net assimilation rate (NAR) was highest early in the season. Floricane photosynthetic rates (A) were highest during the fruiting period, while primocane A remained steady throughout the season. Primocane and floricane leaflets displayed a midday depression in A under field conditions, with a partial recovery in the late afternoon. Photosynthetic rates of primocane and floricane leaves were very sensitive to temperature, exhibiting a decline from 15 to 40C. Light-response curves differed depending on cane type and time of year. A temporal convergence of sink demand from fruit, primocanes, and roots occurs when plants experience high temperatures. These factors may account for low red raspberry yield.

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Michael S. Dosmann, William R. Graves, and Jeffery K. Iles

The limited use of the katsura tree (Cercidiphyllum japonicum Sieb. & Zucc.) in the landscape may be due to its reputed, but uncharacterized, intolerance of drought. We examined the responses of katsura trees subjected to episodes of drought. Container-grown trees in a greenhouse were subjected to one of three irrigation treatments, each composed of four irrigation phases. Control plants were maintained under well-hydrated conditions in each phase. Plants in the multiple-drought treatment were subjected to two drought phases, each followed by a hydration phase. Plants in the single-drought treatment were exposed to an initial drought phase followed by three hydration phases. Trees avoided drought stress by drought-induced leaf abscission. Plants in the multiple- and single-drought treatments underwent a 63% and 34% reduction in leaf dry weight and a 60% and 31% reduction in leaf surface area, respectively. After leaf abscission, trees in the single-drought treatment recovered 112% of the lost leaf dry weight within 24 days. Leaf abscission and subsequent refoliation resulted in a temporary reduction in the leaf surface area: root dry weight ratio. After relief from drought, net assimilation rate and relative growth rate were maintained at least at the rates associated with plants in the control treatment. We conclude that katsura is a drought avoider that abscises leaves to reduce transpirational water loss. Although plants are capable of refoliation after water becomes available, to maintain the greatest ornamental value in the landscape, siting of katsura should be limited to areas not prone to drought.

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Nader Soltani, J. LaMar Anderson, and Alvin R. Hamson

`Crimson Sweet' watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] plants were grown with various mulches and rowcovers and analyzed for relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA), leaf area index (LAI), and crop growth rate (CGR). Spunbonded polyester fabric (SB-PF) and perforated polyethylene film (PCP) rowcovers generally showed greater mean RGR, SLA and CGR than spunbonded polypropylene polyamide net (SB-PP), black plus clear combination plastic mulch and black plastic mulch alone. Plants on mulches and under rowcovers showed significant increases in RGR, NAR, and SLA over plants grown in bare soil. Carbon dioxide concentration inside the transplanting mulch holes was nearly twice the ambient CO, concentration. Growth analysis of sampled watermelon plants during early stages of development under various treatments was predictive of crop yield. Plants under SB-PF and PCP rowcovers produced the earliest fruit and the greatest total yield. An asymmetrical curvilinear model for watermelon growth and development based on cardinal temperatures was developed. The model uses hourly averaged temperatures to predict growth and phenological development of `Crimson Sweet' watermelon plants grown with and without rowcovers. Early vegetative growth correlated well with accumulated heat units. Results indicate a consistent heat unit requirement for the `Crimson Sweet' watermelon plants to reach first male flower, first female flower and first harvest in uncovered plants and plants under rowcovers. Greater variability was observed in predicting date of first harvest than first bloom.

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Silvana Nicola, Luigi Basoccu, and Salvino Leoni

Excessive nitrogen can be detrimental to transplant quality when supplied during the period of suboptimal photoperiod conditions. This investigation was made to determine the relationship between nitrogen and photoperiod on the growth rate of the transplants. The growth analysis included the determination of the net assimilation rate (NAR) and the nitrogen productivity (NP). `Camone' tomato (Lycopersicon esculentum Mill.) seedlings were grown in the greenhouse under two photoperiods 8 and 12 h) at a constant light intensity and fertilized with three different N concentrations (8, 15, and 30 mmol·liter–1) applied four times. Longer photoperiods enhanced plant growth by increasing the internode, LAR, SLA, and SWR. Root fresh weight, dry weight, stem dry matter, NAR, and RWR were minimal when 30 mmol·liter–1 N concentration was supplied, while LAR and SLA were at their maximum level. The interaction between N and photoperiod was significant. Increasing N supply during an 8-h photoperiod decreased growth. During a 12-h photoperiod, 15 mmol·liter–1 was the optimum N concentration for fresh growth and 8 mmol·liter–1 for shoot dry growth. The RGR had the lowest value, with 30 mmol·liter–1 N and 8-h photoperiod. PNC was highest when plants received 30 mmol·liter–1 N during an 8-h photoperiod, and when the plants received 15 and 30 mmol·liter–1 N during the 8-h photoperiod. LNC doubled in plants fertilized with 30 mmol·liter–1 N compared to those with 8 mmol·liter–1 when grown under a 12-h photoperiod. The NP was at the maximum in plants fertilized with 8 mmol·liter–1 N at the 12-h photoperiod. The lowest NP values occurred when plants were fertilized with 30 mmol·liter–1 N. When photoperiod is a limiting factor in growing seedlings, N supply must be limited to optimize the efficiency of its utilization by the plant.

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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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Leonardo Lombardini*, D. Michael Glenn, and Marvin K. Harris

Trials were established in Summer 2002 and 2003 to test the consequences of the application of a kaolin-based particle film (Surround WP, Engelhard Corp.) on gas exchange, nut quality, casebearer density and population of natural predators (insects and arachnids) on pecan (Carya illinoinensis, cv. `Pawnee') trees. Film application started immediately after bud break and was repeated every 7-10 days for seven (2002) or nine (2003) times during the season. On both years, treated trees frequently showed lower leaf temperature (up to 4 °C) than untreated trees. Leaf net assimilation rate, stomatal conductance and stem water potential were not affected by film application. Nut size and quality did not differ between the two treatments. In 2003, shellout (percentage of nut consisting of kernel) was in fact 54.2% and 55.5% for treated and control trees, respectively. Moreover, the two treatments yielded similar percentage of kernel crop grading as fancy, choice, standard and damaged. Similar were also the percentages of kernels that showed damage caused by stink bugs. Only on one date the number of adult yellow pecan aphids (Monelliopsis pecanis) counted on film-treated leaves was lower than in control leaves. In general, the density of common natural predators (lady beetles, green lacewings, spiders) of pecan pests did not differ between the two treatments; however, the number of green lacewing eggs was frequently lower on film-treated leaves. In film-treated trees the number of nutlets damaged by pecan nut casebearer (Acrobasis nuxvorella) was significantly higher than that observed on trees treated with conventional insecticide (24.2% infested nutlets vs. 9.3%, respectively) and did not differ from trees that did not receive either product (29.9%).

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Serge Yelle, Richard C. Beeson Jr., Marc J. Trudel, and André Gosselin

Lycopersicon esculentum Mill. cv. Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO2 concentrations (330 or 900 μmol·m-3) for 10 weeks. The elevated CO2 concentration increased the relative growth rate (RGR) of L. esculentum and L. chmielewskii by 18% and 30%, respectively, after 2 weeks of treatment. This increase was not maintained as the plant matured. Net assimilation rate (NAR) and specific leaf weight (SLW) were always higher in C02-enriched plants, suggesting that assimilates were preferentially accumulated in the leaves as reserves rather than contributing to leaf expansion. Carbon dioxide enrichment increased early and total yields of L. esculentum by 80% and 22%, respectively. Carbon exchange rates (CER) increased during the first few weeks, but thereafter decreased as tomato plants acclimated to high atmospheric CO2. The relatively constant concentration of internal C0 with time suggests that reduced stomatal conductance under high CO2 does not explain lower photosynthetic rates of tomato plants grown under high atmospheric CO2 concentrations. Leaves 5 and 9 responded equally to high CO2 enrichment throughout plant growth. Consequently, acclimation of CO2-enriched plants was not entirely due to the age of the tissue. After 10 weeks of treatment, leaf 5, which had been exposed to high CO2 for only 10 days, showed the greatest acclimation of the experiment. We conclude that the duration of exposure of the whole plant to elevated CO2 concentration, rather than the age of the tissue, governs the acclimation to high CO2 concentrations.