Of all the plant processes examined, leaf growth and canopy development is the most sensitive to water stress. The consequent reduction in cumulative radiation interception by the plant leads to a smaller biomass as well as reduced transpiration, usually without altering radiation-use efficiency or water-use efficiency of the canopy. Sensitivity of leaf growth to the growth medium or aerial environment of the plant will be illustrated. A way to quantify the consequent and often marked impact on productivity will be discussed. In contrast with the high sensitivity of leaf growth to water stress, root growth is more resistant. This allows at least the partial maintenance of root growth as the stress intensifies. The result is a more thorough extraction of soil water while transpiration is restricted by the smaller leaf area. The possible mechanisms for the differential sensitivity of leaf and root growth to water stress will be evaluated. Emphasis will be placed on processes underlying cell enlargement. Recent data, obtained with the pressure microprobe that measures turgor pressure in individual cells, will be presented to illustrate the contrasting responses in growth, cell wall extending ability, and solute transport to the growing cells when the plant adjusts and accommodates to changes in water status.
Theodore C. Hsiao
Amy N. Wright, Stuart L. Warren, and Frank A. Blazich
Root growth is a critical factor in landscape establishment of container-grown woody ornamental species. Kalmia latifolia (mountain laurel) often does not survive transplanting from containers into the landscape. The objective of this experiment was to compare rate of root growth of mountain laurel to that of Ilex crenata `Compacta' (`Compacta' holly) and Oxydendrum arboreum (sourwood). Six-month-old tissue-cultured liners (substrate intact) of mountain laurel, 1-year-old rooted cutting liners (substrate intact) of `Compacta' holly (liner holly), 6-inch bare root seedling liners of sourwood, and 3-month-old bare-root rooted cuttings of `Compacta' holly were potted in containers in Turface™. Prior to potting, roots of all plants were dyed with a solution of 0.5% (w/v) methylene blue. Plants were greenhouse-grown. Destructive harvests were conducted every 2 to 3 weeks (six total harvests). Length, area, and dry weight of roots produced since the start of the experiment, leaf area, and dry weight of shoots were measured. Sourwood and liner holly had greater rate of increase in root length and root dry weight than mountain laurel and bare root holly. Rate of increase in root area was greatest for sourwood, followed by (in decreasing order) liner holly, mountain laurel, and bare-root holly. Increase in root length and root area per increase in leaf area was highest for liner holly, possibly indicating why this species routinely establishes successfully in the landscape. Increase in root dry weight per increase in shoot dry weight was lowest for mountain laurel. The slow rate of root growth of mountain laurel (compared to sourwood and liner holly) may suggest why this species often does not survive transplanting.
Rebecca Grumet, Mary Barczak, and Chris Tabaka
An above ground screening method to study cucumber root growth was developed using the herb icicle banding technique of Robertson et al. (Crop Sci 25:1084, 1985). Those roots that grow deeper or faster, sooner reach the herbicide, and sooner exhibit herbicide damage symptoms. Greenhouse pot trials showed that 1/4-1/2 lb/A atrazine could be used to produce distinctive symptoms, differentiate between depths of banding, and among different genotypes. Based on root washing experiments of a few cultivars, root length and/or mass correlated with herbicide symptom expression. One hundred diverse cucumber genotypes were tested in the greenhouse. Time to symptom expression was normally distributed among the genotypes; analysis of variance indicated significant genotypic differences. The herbicide banding technique was also useful for monitoring cucumber root growth in the field. Response time and severity varied with herbicide concentration, depth, and distance from the seed row. The diverse cucumber genotypes are now being tested in the field to further determine if there are significant genotypic differences and to compare greenhouse and field behavior.
Emily B. Merewitz, Thomas Gianfagna, and Bingru Huang
Drought is a detrimental abiotic stress for plant growth, including perennial turfgrass species. A typical drought stress symptom in turfgrass is a decline in turf quality (TQ) resulting from leaf senescence, slow shoot and root growth, and leaf
Guogiang Hou, Jack W. Buxton, and Donna Switzer
To prevent rooting into an irrigation mat, five water porous materials, perforated black plastic, perforated ground cover, polyester, woven polypropylene and porous plastic, were evaluated as mat covers. Only polyester, woven polypropylene and porous plastic prevented penetration of roots of marigold seedlings into the mat. Under high moisture stress, root tips were killed at the cell drainage hole; however, under low moisture stress the roots formed a mat on top of these mat covers. To prevent root penetration out the drainage hole, polyester and porous plastic were glued over the hole. No difference in shoot growth was observed between the control (only polyester mat cover) and seedlings produced in drainage hole covered cells. Total root growth of plug seedlings with drainage hole covered were greater than the control. Ten days after transplanting, seedlings that had been produced in plugs, with covered drainage holes, were larger.
Daniel I. Leskovar and Mark C. Black
Effects of spinach crop management strategies on white rust (Albugo occidentalis), leaf chlorosis, root growth and yield were evaluated in winter 1991/92. Irrigation main plots were low (I-low), medium (I-med) and high (I-high). Fungicide split-plots were none (F0), metalaxyl at planting (F1), and metalaxyl at planting plus experimental CGA 2014 foliar (F2). Genotype split-split-plots were ACX 5044 and ARK 88-354. The Gompertz model best described the white rust disease progress. At all irrigation levels, ACX 5044 had the higher rate of disease increase (rG) and earlier disease onset than ARK 88-354. Metalaxyl delayed disease onset and rG in ACX 5044 only at I-low and I-med, but not at I-high. ARK 88-354 was the least sensitive to fungicides. Yellowness and chlorosis, estimated by spectrophotometric measurements, were higher at I-med and I-high, and with F0, while ARK 88-354 had less chlorosis than ACX 5044. Root diameter was increased with F1 compared to F0. Lateral and tap root fresh and dry weights were higher for ARK 88-354. Yields for ARK 88-354 were significantly higher than ACX 5044. No treatments influenced the number of live or aphids parasitized by Pandora neoaphidis.
Marc van Iersel
Transplanting often causes root damage, and rapid root growth following transplanting may help to minimize the effects of transplant shock. The objective of this study was to determine the effects of NAA and IAA on posttransplant growth of vinca (Catharanthus roseus L.). Bare-root seedlings were germinated in a peat-based growing mix and transplanted into diatomaceous earth 10 days after seeding. Immediately after transplanting, seedlings were drenched with several concentrations of IAA or NAA (62.5 mL/plant). Both auxins increased posttransplant root and shoot growth, but the response was dose-dependent. The maximum growth occurred at concentrations of 10 mg·L-1 (IAA) or 0.1 mg·L-1 (NAA). The growth-stimulating effect of these auxins decreased at higher rates and NAA was highly toxic at 100 mg·L-1, killing most of the plants. Unlike the growth of bare-root seedlings, plug seedling growth was not stimulated by drenching with NAA solutions. These results show that auxins have the ability to stimulate posttransplant growth of vinca, but their effects may depend on the application method, rate, and timing, and transplanting method. Chemical names used: 1-naphthaleneacetic acid (NAA); 1-indole-3-acetic acid (IAA).
James L. Green, R.G. Linderman, B. Blackburn, and K.A. Smith
Verticle gradients of moisture, salinity, specific fertilizer ions, and pH in the root zone in the closed, insulated pallet system (CIPS) are relatively stable compared with those in the open container system (OCS). Establishment of the VA mycorrhizal fungus Glomus intraradices and maintenance of the biocontrol fungus Trichoderma harzianum and the entomopathogenic nematode Steinernema carpocapsae were greater in CIPS than in control OCS. In CIPS, percent corn root length colonized by G. intraradices was greatest in roots in the top stratum of the root medium. Colonization was significantly greater in copper-coated root-containment pouches. Population maintenance in CIPS of T. harzianum, initially uniformly inoculated throughout the root medium, was highest in the top stratum of the root medium where K+ and
Rebecca Grumet and Robert Duvall
The determinate allele (de) of cucumber (Cucumis sativus L.) causes shorter vine length and fewer and shorter internodes and lateral branches than the indeterminate allele (De). Four sets of cucumber inbreds carrying determinate or indeterminate alleles were compared with respect to root growth rate in the field and greenhouse using an herbicide banding method. Although the lines exhibited the expected differences in shoot growth, differences in root growth were not correlated with the differences in shoot growth. These results indicate that root growth was independent of the determinate shoot growth allele.
Brian E. Jackson, Amy N. Wright, and Jeff L. Sibley
In the southeastern United States, inconsistent pine bark (PB) supplies and overabundance of cotton gin by-products warrant investigation about the feasibility of replacing PB with cotton gin compost (CGC) for container horticultural plant production. Most research on the use of composted organic substrates for horticultural plant production has focused on shoot growth responses, so there is a need to document the effect of these substrates on root growth. In 2004, `Blitz' tomato (Lycopersicon esculentum), `Hot Country' lantana (Lantana camara `Hot Country'), and weeping fig (Ficus benjamina) were placed in Horhizotrons to evaluate root growth in 100% PB and three PB:CGC substrates containing, by volume, 60:40 PB:CGC, 40:60 PB:CGC, and 0:100 PB:CGC. Horhizotrons were placed in a greenhouse, and root growth in all substrates was measured for each cultivar. Physical properties (total porosity, water holding capacity, air space, and bulk density) and chemical properties (electrical conductivity and pH) were determined for all substrates. Physical properties of 100% PB were within recommended guidelines and were either within or above recommended ranges for all PB:CGC substrate blends. Chemical properties of all substrates were within or above recommended guidelines. Root growth of all species in substrates containing CGC was similar to or more enhanced than root growth in 100% PB.