Search Results

You are looking at 71 - 80 of 208 items for :

  • "relative growth rate" x
  • Refine by Access: User-accessible Content x
Clear All
Free access

D.A.J. McArthur and N.R. Knowles

The growth response of potato to infection by vesicular-arbuscular mycorrhizal fungi (VAM) (Glomus dimorphicum, G. intraradices, and G. mosseae), at increasing levels of soil phosphorus (P), was related to VAM-altered mineral status of the plant. In addition, the morphological development of the VAM was characterized using light and scanning electron microscopy.

Four weeks after inoculation, arbuscules and coiled hyphae were the predominate fungal structures within the roots, however, vesicle development increased steadily over the remainder of the 12 week growth period. As expected, the percent infection of roots by VAM decreased with increasing soil-P level. Leaf area, relative growth rate (RGR), lateral branching and root dry weight were increased by VAM, although the relative-response diminished with increasing soil-P level. A similar response to VAM-infection was evident for the concentration of and total shoot N, P and K. Examination of the shoot N status indicated that VAM influenced the rates at which the plant was partitioning N into various N pools. But again, differences between non-VAM and VAM plants tended to decrease with increasing soil-P level. These results indicate that VAM modification of dry matter accumulation and nutrient uptake is mostly a consequence of the alleviation of P-deficiency of the plant and the improved growth of roots, allowing increased mineral absorption.

Free access

Anne K. Hurley and B. Greg Cobb

Cucumis sativus, L., `Poinsett' seedlings were grown under artificial light in 40% modified Hoagland's solution until an average plant plastochron index of 4.73 was reached. Plants were then placed in solutions of (1) 0 mM NaCl, (2) 80 mM NaCl (salt-shock), or (3) placed in a dropwise gradient solution of NaCl and Hoagland's until the final concentration of 80 mM NaCl was reached at 41 hours. Leaves of the 80 mM shock treatment wilted immediately, but recovered turgor within 6 hours. Leaves of 80 mM gradient did not wilt at anytime. The control and gradient treatments had relative growth rates which were similar to each other, but RGR decreased in the shock treatment. Invertase activity was measured in the roots at 24, 41, and 48 hours after initial treatment. Invertase activity of shock treatment increased significantly over the controls at 24 hours. The 80mM gradient was not significantly different than either treatment. Four isozymes of α– galactosidase were detected. The relative intensities of the bands varied with time and treatment. One invertase band was resolved in roots on 8% native acrylamide gels. SDS gels indicated increases in proteins in the gradient treatment compared to the control and the 80 mM shock treatment.

Free access

Yong-Zhan Ma and Martin P.N. Gent

How are C and N metabolites affected by a root-zone temperature (RZT) in phase or out of phase with the photoperiod? Tomato (Lycopersicon esculentum Mill.) was grown with an air temperature of 20C, and RZT that was in phase with a 12-h photoperiod, 28C in the light and 12C in the dark, or out of phase, 12C in the light and 28C in the dark. Seedlings were grown in flowing solution containing 200 μm NO3 and excess amount of other mineral elements. The flow rate increased with plant size. After 8 days, plants were harvested at the end of the day and at the end of the night. The relative growth rate (day–1) was slightly greater for in-phase (0.19) than out-of-phase RZT (0.17) and less than that at a constant air and RZT of 24C (0.22). RZT affected N accumulation and partitioning of C and N metabolites. Cool roots contained more NO3 and free sugars than warm roots. Leaves had less NO3 in the light than in the dark, and NO3 in leaves of plants with an out-of-phase RZT was depleted in the light. Concentration of free amino acids and protein was greater and the amount of starch was less in leaves of plants with in-phase RZT.

Free access

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.

Free access

Andres A. Estrada-Luna, Fred T. Davies Jr., and Jonathan N. Egilla

Micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plants were transferred to ex vitro conditions to study plantlet performance and selected physiological changes that occur during acclimatization and post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry mass. Measurements were taken at 0, 1, 2, 3, 6, 12, and 24 days after transplanting. After initial transplanting ex vitro to liner pots with soilless media, plantlet wilting was observed that correlated with reduced leaf relative water content (RWC). Water stress was partially alleviated by a reduction in stomatal conductance (gs), confirming that the in vitro formed stomata were functional and able to regulate transpiration (E) to minimize desiccation losses. Because of this stomatal control, plantlets had minimal transplant shock, recovered, and survived. Prior to transplanting, micropropagated plantlets showed heterotrophic/mixotrophic characteristics as indicated by low photosynthesis [(A) 4.74 μmol·m2·s-1]. During acclimatization, RWC, gs, E, and A were significantly lower 2 days after transplanting. However, within 6 days after transplanting, plantlets recovered and became autotrophic, attaining high A (16.3 μmol·m-2·s-1), gs, and E. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with dramatic increases in plantlet growth.

Free access

Martin M. Williams II, Rick A. Boydston, and Adam S. Davis

Research in dent corn has found significant variation in crop/weed competition for light among hybrids. However, little has been published on the extent of variation in sweet corn competitive ability. Field studies were conducted under weed-free conditions to quantify canopy development and light environment among three sweet corn hybrids and to determine associations among canopy characteristics to crop yield. An early-season hybrid (Spirit) and two midseason hybrids (WHT2801 and GH2547) were grown at experimental sites located near Urbana, Ill., and Prosser, Wash., in 2004 and 2005. Maximum leaf area index (LAI) and intercepted photosynthetically active radiation (PAR) was typically highest for GH2547 and lowest for Spirit. Most differences in vertical LAI among hybrids was observed above 60 and 150 cm in Illinois and Washington, respectively, with WHT2801 and GH2547 having leaf area distributed higher in the canopy than Spirit. Both number and mass of marketable ears were positively correlated with maximum relative growth rate (correlation coefficients 0.60–0.81), leaf area duration (0.68–0.79), total LAI (0.56–0.74) at R1, and intercepted PAR (0.74–0.83) at R1. Differences in canopy properties and interception of solar radiation among Spirit, WHT2801, and GH2547 lead us to hypothesize that variation in weed-suppressive ability exists among hybrids. Future testing of this hypothesis will provide knowledge of interactions specific to sweet corn useful for developing improved weed management systems.

Free access

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.

Free access

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

Although floatation irrigation has numerous advantages for vegetable transplant production, including improved seedling health, lettuce (Lactuca sativa L.) transplants grown with floatation (ebb and flow) irrigation can have poor root systems. Floatation fertigation of `South Bay' transplants with K at 15, 30, 45, or 60 mg·L-1 K applied every 2 to 4 days, increased fresh and dry root weight at 28 days. Higher K (24 mg·kg-1) in the medium did not affect root weight. Fresh and dry shoot weight, leaf area, relative shoot ratio (RSR), relative growth rate (RGR), leaf weight ratio (LMR), and root weight ratio (RMR) were unaffected by applied K, regardless of the initial K concentration in the medium. Available K in a vermiculite-containing medium may have supplied all the K required. When 60 was compared with 100 mg·L-1 N at various levels of K, the applied K again did not influence dry root weight; however, at 100 mg·L-1 N, root weight was reduced as compared with 60 mg·L-1 N, regardless of the level of applied K. In a field experiment, pretransplant K had no effect on growth. Transplants grown with no added K in a peat + vermiculite mix with at least 24 mg·L-1 water-extractable K produced yields equivalent to transplants supplied with 15, 30, 45, or 60 mg·L-1 K via floatation irrigation.

Free access

Michel Génard and Claude Bruchou

An approach to studying fruit growth is presented for peach fruit (Prunus persica L. Batsch). It combines a functional description of growth curves, multivariate exploratory data analysis, and graphical displays. This approach is useful for comparing growth curves fitted to a parametric model, and analysis is made easier by the choice of the model whose parameters have a meaning for the biologist. Growth curves were compared using principal component analysis (PCA) adapted to the table of estimated parameters. Growth curves of 120 fruits were fitted to a model that assumes two growth phases. The first one described the pit growth and the first part of the flesh growth. The second described the second part of the flesh growth. From PCA, firstly it was seen that fruit growth varied according to cumulated growth during both growth phases and to date of maximal absolute growth. Secondly, fruit growth varied according to cumulated growth and relative growth rates during each phase. Further examples are presented where growth curves were compared for varying fruit number per shoot and leaf: fruit ratio, and for different sources of variation (tree, shoot, and fruit). Growth of individual fruit was not related to fruit number per shoot or to leaf: fruit ratio. Growth variability was especially high between fruit within shoots.

Free access

Riccardo Lo Bianco, Brunella Morandi, and Mark Rieger

Along with sucrose, sorbitol represents the major photosynthetic product and the main form of translocated carbon in peach. The objective of the present study was to determine whether in peach fruit, sorbitol and sucrose enzyme activities are source-regulated, and more specifically modulated by sorbitol or sucrose availability. In two separate trials, peach fruit relative growth rate (RGR), enzyme activities, and carbohydrates were measured 1) at cell division stage before and after girdling of the shoot subtending the fruit; and 2) on 14 shoots with different leaf to fruit ratio (L:F) at cell division and cell expansion stages. Fruit RGR and sorbitol dehydrogenase (SDH) activity were significantly reduced by girdling, whereas sucrose synthase (SS), acid invertase (AI), and neutral invertase (NI) where equally active in girdled and control fruits on the fourth day after girdling. All major carbohydrates (sorbitol, sucrose, glucose, fructose and starch) were reduced on the fourth day after girdling. SDH activity was the only enzyme activity proportional to L:F in both fruit developmental stages. Peach fruit incubation in sorbitol for 24 hours also resulted in SDH activities higher than those of fruits incubated in buffer and similar to those of freshly extracted samples. Overall, our data provide some evidence for regulation of sorbitol metabolism, but not sucrose metabolism, by photoassimilate availability in peach fruit. In particular, sorbitol translocated to the fruit may function as a signal for modulating SDH activity.