Asparagus is considered a relatively drought tolerant plant, but few studies are available on the gas exchange response to soil moisture stress. Seedlings were grown in the greenhouse for six months before initiation of the water stress treatments. Soils were allowed to dry to matric potentials of -0.05, -0.3 and -0.5 MPa before rewatering to pot capacity. Gas exchange and fern water potentials were measured diurnally on asparagus plants when soil matric potentials reached their minima. Decreasing soil matric potentials decreased net carbon dioxide assimilation, stomatal conductance and fern water potential. Assimilation rates (6 am) were between 3 and 5 umols m-2 s-1 for all soil moisture treatments. Carbon assimilation rates of 10, 8, and 7 umols m-2 s-1 were recorded at 10 am for the -0.05, -0.3 and -0.5 MPa soil matric potentials, respectively. Assimilation rates decreased sharply over the remainder of the day. The diurnal pattern for conductance were similar to the assimilation rates. Fern water potentials were greater in the -0.05 MPa than in the -0.5 MPa treatment for all measurement periods with an intermediate response for soil matric potentials of -0.3 MPa. Fern water potentials were highest at 6 am (-0.2 to -0.6 MPa) before declining to their minima (-1.5 to -1.8 MPa) at 10 am. Water potentials remained at these low levels throughout the day before recovering slightly at 6 pm.
Daniel Drost and Darlene Wilcox-Lee
F.J. Keiper and R. McConchie
Umbrella fern [Sticherus flabellatus (R. Br.) St John] is a successful Australian native foliage product. Currently, all umbrella fern sold on the market is bush-harvested. To meet the growing demand for this product on local and international markets, a commercially viable method for its production must be developed, with effective management of the germplasm resource in terms of conservation and exploitation. To manage this resource, breeders require a detailed knowledge of the amount and distribution of genetic variability within the species. Traditionally, plant breeders focus on a combination of agronomic and morphological traits (phenotype) to measure genetic diversity. In umbrella fern there are a limited number of morphological traits, and these are influenced by environmental factors and therefore do not reflect true genetic diversity. To overcome these problems, molecular techniques such as PCR-based DNA markers are used to complement traditional strategies for genotype assessment. DNA markers have the advantages of being independent of environmental effects, as well as being fast, cost-effective, reproducible, and largely accessible to the nonmolecular geneticist. Amplified fragment length polymorphisms (AFLPs) fulfil many of the desirable features of molecular markers, as well as requiring little knowledge of the genome to be investigated. AFLPs have been used widely in the analysis of breeding systems, ecogeographical variation, and genetic variation within and between natural populations. To date there are no published accounts of DNA molecular marker research on umbrella fern. A DNA extraction protocol has been developed for this species, and AFLP markers have been used to analyse genetic diversity within and between natural populations sampled in the Sydney Basin. A large number of polymorphic loci were revealed using 11 primer combinations. The genetic variation detected was partitioned between rather than within populations, suggesting that the mating system in Sticherus is primarily inbreeding. Data will be presented illustrating AFLPs as useful molecular markers for assessing genetic diversity within and between populations of umbrella fern and providing insight on the breeding system used by the species.
Kathryn Hahne Schultz and Stephen Garton
Phyllitis scolopendrium var. americana is a rare North American fern species whose range is being threatened by habitat alteration. Research efforts were undertaken to ensure survival of the southern population by applying horticultural techniques to propagate new plants for reintroduction. Several techniques were used to induce spore germination. Aseptic techniques included direct plating of spores onto agar medium in petri dishes and dusting spores into test tubes filled with liquid medium. Spores were spread onto soil samples taken from the fern habitats and onto various other propagation media. Prothalli grown in nutrient solution were transferred onto various nonsterile conventional horticultural media. Results indicated that germination in the nutrient solution and subsequent transfer of prothalli was more efficient and promoted survival of propagules compared to subculture from solidified medium.
Robert H. Stamps, Terril A. Nell, and James E. Barrett
Leatherleaf fern [Rumohra adiantiformis (Forst.) Ching] fronds produced under a high-temperature regime (HTR, 30 day/25C night) grew faster and produced sori earlier than those in a low-temperature regime (LTR, 20 day/15C night). Abaxial diffusive conductance was lower for HTR-grown fronds. Light-saturated net CO2 assimilation rates (Pn) and dark respiration were lower for HTR fronds, but light-saturated Pn efficiencies (chlorophyll basis); light compensation points; and soluble sugars, starch, and nonstructural carbohydrate levels were similar for the two regimes. Transpiration and water-use efficiency (mass basis) at light saturation were similar for fronds from both temperature treatments. Comparison of physiological characteristics of fronds from the two temperature regimes revealed no differences that might account for reduced postharvest longevity of fronds produced at the higher temperatures.
Darlene Wilcox-Lee and Daniel T. Drost
Asparagus officinalis L. cv. Centennial established with transplants in 1983 was maintained with tillage or a no-till (NT) system to evaluate effects of tillage on yield and plant growth in a mature asparagus planting. Metribuzin or metribuzin + napropamide at 1.12 and 1.68 kg a.i./ha, respectively, were used for weed control in both tillage regimes. Marketable yields were assessed for 5 years. In 1989, in addition to yield data, destructive harvests of entire plants were made every 3 weeks from March to November to evaluate the effect of tillage on fern, crown, and bud growth, and carbohydrate status. Yields were reduced by tillage from 12% to 50% from 1985 to 1989. There were no herbicide effects nor was there an effect on yield due to an interaction between herbicides and tillage. All indices of growth measured for NT exceeded those in tilled plots, although seasonal patterns of growth were similar in both. Crown and fern weight, bud cluster, and bud and fern counts were higher by 178%, 175%, 152%, 161%, and 195%, respectively, in NT than in tilled plots. The metribuzin + napropamide combination did not reduce fern fresh weight or yield, but significantly reduced the number of bud clusters, buds, and ferns when compared to metribuzin alone. Chemical names used: 4-amino-(1,1-dimethylethyl)-3-(methylthio)-l (metribuzin); 2,4-triazin-5(4H) -one, N,N-diethyl-2-(naphthalenyloxy)-propanamide (napropamide).
Johnny Carter, Bharat P. Singh, and Wayne Whitehead
Two greenhouse studies (1990 and 1991) were conducted to evaluate the effect of dikegulac (Atrinal) and benzyladenine (ProShear) on frond initiation and vegetative growth of Boston fern (Nephrolepis exaltata L.). Four weeks after transplanting, fern liners were sprayed with aqueous solutions of dikegulac and benzyladenine (BA). Chemical concentrations of dikegulac were 0, 250, 500, or 750 mg·L–1 and those of BA were 0, 50, 100, or 150 mg·L–1. The effect of dikegulac and BA on number of shoots, frond length, leaf area, and dry weight were measured. Dikegulac stimulated shoot initiation and increased leaf area and dry weight without affecting frond length. BA reduced frond length and its effect on shoot initiation, leaf area and dry weight varied from one time to another. This study suggests the potential use for dikegulac in improving the appearance and aesthetic quality of Boston fern.
Johnny Carter, Bharat P. Singh, and Wayne Whitehead
Greenhouse studies conducted in 1990 and 1991 evaluated the influence of dikegulac and benzyladenine on frond initiation and vegetative growth of Boston fern [Nephrolepsis exaltata (L.) Schott `Compacta']. Four weeks after transplanting, fern liners were sprayed with aqueous solutions of dikegulac (0, 250, 500, or 750 mg·L–1) or benzyladenine (BA; 0, 50, 100, or 150 mg·L–1). The effect of dikegulac and BA on the number of shoots, frond length, leaf area, and dry weight was measured. Dikegulac stimulated shoot initiation and increased leaf area and dry weight without affecting frond length. BA reduced frond length and had no effect on shoot initiation and dry weight. This study suggests dikegulac has potential to improve the appearance and aesthetic quality of Boston fern. Chemical names used: 2,3:4,6-bis-0-(1-methylethylidene)-α-l-Xylo-2 hexulofuranosonic acid (dikegulac); N-(phenylmethyl)-1H-purine-6-amine (benzyladenine).
Clarence Johnson Jr.
Asparagus (Asparagus officinalis)plants were sprayed and drenched with different concentrations of Promalin (0, 250, and 500 ppm) The varieties for the spraying experiment were `Mary Washington', `Emeral', `UC-157-F1', and `UC157F2'. Six replications for each treatment were used in a randomized complete-block design. The drenching experiment used two varieties (Mary Washington and UC-157-F2) with six replications of each treatment in a randomized complete-block design. Pots were numbered and labeled for each experimental unit. Plants (ferns) were counted and recorded in order to obtain the initial number of ferns before or after the spraying or drenching. In the spraying experiment, the plants were sprayed to run-off using a hand sprayer whereas; in the drenching experiment, 1000 mL or 1 L of the solution was used to drench each plant. The response to the chemical was measured in two ways: weekly stimulation of emergence of new-shoots and percent increase in final number of shoots over the initial number. In the spraying treatments differences were not found among the treatments used. In the drenching experiment with `Mary Washington' variety, a lower initial number of ferns at 250 ppm as compared to the 0 ppm of Promalin (8.82 to13.00) was observed. Differences for `Mary Washington' variety was not found for cumulative number of ferns on weeks 1, 2, and 3. However, the percent increase in number of ferns was higher for the 250 ppm as compared to the 0 ppm (174.55% to 78.14%). `UC-157-F2' showed no difference among the different concentrations. This indicates a difference in varietal response.
Johnny Carter and Sauveur Mahotiere
Effects of BA, Promalin and Dikegulac-sodium on frond number and overall growth in Boston Fern (Nephrolepis exaltata L.) were studies. Four weeks after transplanting, fern liners were sprayed with aqueous solutions of BA, Promalin and dikegulac-sodium. Chemical concentrations of BA and promalin ranged from 0 to 150 mg. liter-1 at 50 mg. liter-1 increments. Chemical concentrations of dikegulac-sodium ranged for 0 to 750 mg.liter-1 at 250 mg.liter-1 increments. Chemical treatments were arranged in a randomized complete block design with 6 replications. BA and Promalin significantly increased the number of fronds, average frond length, leaf area and dry weight as the concentration of the chemicals increased. In contrast, dikegulac-sodium significantly suppressed the average frond length, leaf area and dry weight when compared to the control. Similarly to BA and Promalin, dikegulac-sodium increased the number of fronds as the concentration of the chemical increased.
F. Ponton, Y. Piché, S. Parent, and M. Caron
The horticultural Boston fern [Nephrolepis exaltata (L.) Schott cv. Verona] was micropropagated in vitro using commercial techniques. Rooted plantlets were transferred into pots containing one of three test substrates made of peat and vermiculite and subsequently inoculated with one of two species of Glomus. Survival of uninoculated control plants growing on a black peat-based mix was less than that on a brown peat-based mix. Vesicular-arbuscular mycorrhizal (VAM) inoculation significantly increased survival on the former, but not the latter, substrate. The growth of roots was enhanced in brown peatmoss, but VAM colonization was faster with black peatmoss. Compared to uninoculated controls growing under the same fertilization regime, inoculated plants had significantly higher frond P and N concentration and also showed better frond and root growth. On a growth-increment basis, our results suggested that the brown peat-based mixed was more suitable for fungal activity and fern growth.