As interest in issues such as seed source, provenance, genetic pollution, and threatened and endangered plant species grows, so does the need for an understanding of the relatedness and evolutionary history of plants. Appropriate taxonomy and nomenclature become much more important. Taxodium (L.) Rich. is a genus of landscape trees included in many plant materials courses across the country. It has been treated variously in the horticulture literature as having one, two, or three species. The most appropriate treatment is one species with three botanical varieties: baldcypress [Taxodium distichum (L.) Rich. var. distichum], pondcypress [T. distichum var. imbricarium (Nutt.) Croom], and montezuma cypress [T. distichum var. mexicanum Gordon].
Geoffrey C. Denny and Michael A. Arnold
Geoffrey Denny, Michael A. Arnold, and Donita Bryan
Seedlings from 15 open-pollinated families of Taxodium distichum (L.) Rich. native to the Gulf Coast, central and south Texas, and Mexico, were evaluated for growth and foliar chlorosis development on field sites in Texas with acidic to alkaline soils. Forty seedlings per family were rated for level of chlorosis, height, and trunk diameter after two growing seasons in the field. Families grown on acidic soils did not differ in chlorosis ratings. Families from Mexico and south Texas had the lowest levels of chlorosis in the field, followed by those from central Texas, and then those from the Gulf Coast. Additionally, eight of the families were subjected to a greenhouse screening experiment with four levels of KHCO3 (0, 4, 8, 12 mM). These were evaluated for height, trunk diameter, shoot and root dry mass, and level of chlorosis and leaf necrosis. Family differences were less apparent during greenhouse screening experiments than in the field. Mexican families were significantly less chlorotic than other families at higher levels of alkalinity in the greenhouse. There was also a trend for height and shoot dry masses of western populations to be less adversely affect by higher alkalinity levels than more eastern populations.
Geoffrey C. Denny* and Michael A. Arnold
An experiment was initiated to evaluate the effects of previously recommended seed treatments for baldcypress [Taxodium distichum (L.) Rich.] or pondcypress [Taxodium distichum (L.) Rich. var. imbricarium (Nutt.) Croom] on Montezuma cypress [Taxodium distichum (L.) Rich. var. mexicanum Gordon], and to determine which, if any, provided optimum germination. Factorial combinations of seed treatments and stratification (2 °C for 0, 45, or 90 d) were applied to seeds of Montezuma cypress. Treatments included: 1) 90% ethanol 5 min soak, 2) ethyl ether 5 min soak, 3) 100 mg·L-1 citric acid 48 h soak, 4) mechanical scarification, 5) five hot water baths (42 °C) allowing the water to cool to room temperature between baths, and 6) a non-treated control. Three more seed treatments consisted of water soaks at room temperature (25 °C) for 0, 45, or 90 d. Seeds were germinated on moist filter paper in a growth chamber with a 12-h day/night photoperiod at a constant 25 °C. Data was collected daily for 14 d and then weekly for the following 4 wks. Radicle elongation of 1 cm was considered germination. Without stratification, 100 mg·L-1 citric acid and the hot water bath treatments were significantly different from other treatments by 7 d, though not from each other, with a mean cumulative germination of 15.6% and 12.2%, respectively. By 14 d, the 100 mg·L-1 citric acid treatment differed only from the ethyl ether wash attaining 28.9% and 14.4% germination, respectively. There were no other statistically significant differences observed among any other treatments without stratification. Germination percentages were low,<30%, without stratification. Effects of additional stratification will also be discussed.
Geoffrey C. Denny and Michael A. Arnold
A study was conducted to determine the effects of substrate, phenological stage of cuttings, and auxin concentrations on the rooting of Texas smoke tree (Cotinus obovatus Raf.). Softwood, semi-hardwood, and hardwood cuttings were treated with either a 0, 5,000, 10,000, or 15,000 mg·L-1 (ppm) potassium salts of indolebutyric acid (K-IBA) and placed in either 50% peat: 50% perlite or 100% perlite rooting substrates. Cuttings were places under an intermittent mist system in a greenhouse for 8 weeks. Softwood cuttings rooted in both substrates, but the 50% peat: 50% perlite substrate produced better-quality rooted only in the 100% perlite substrate. In 100% perlite substrate, the optimal concentration for semi-hardwood cuttings was ≈12000 mg·L-1 (ppm) K-IBA, while hardwood rooting was maximized at 15000 mg·L-1 (ppm) K-IBA or more.
Amy L. Shober, Geoffrey C. Denny, and Timothy K. Broschat
Rapid population growth and urbanization in Florida have increased the number of urban landscapes that receive fertilization and irrigation. Consequently, maintenance of these landscapes may contribute to water shortages and water quality degradation. This article 1) describes the current fertilizer and water use practices that are used by homeowners and landscape professionals; 2) summarizes the research related to nutrient and water use by landscape plants; and 3) provides an overview of the critical issues that should be considered as we evaluate the need for improved management of water and nutrients in urban landscapes.
Geoffrey C. Denny, Michael A. Arnold, and Wayne A. Mackay
Forty seedlings from each of 14 open-pollinated families of Taxodium distichum (L.) Rich. from the southeastern United States, central Texas, and south Texas/Mexico were evaluated in the summer of 2005 for foliar chlorosis in a field situation with alkaline soil. The families from Mexico and south Texas had the lowest levels of chlorosis followed by those from central Texas and then those from the gulf coast. Height growth and trunk diameter were inversely related to chlorosis levels. Open-pollinated families from the gulf coast also had a significantly lower foliar manganese content on an alkaline field site compared with the western families. When selecting plant material for an alkaline site, genotypes from Mexico and south Texas should be preferred followed by central Texas genotypes.
Tongyin Li, Guihong Bi, Richard L. Harkess, Geoffrey C. Denny, and Carolyn Scagel
Plant growth, water use, photosynthetic performance, and nitrogen (N) uptake of ‘Merritt’s Supreme’ hydrangea (Hydrangea macrophylla) were investigated. Plants were fertilized with one of five N rates (0, 5, 10, 15, or 20 mm from NH4NO3), irrigated once or twice per day with the same total daily amount of water, and grown in either a paper biodegradable container or a traditional plastic container. Greater N rate generally increased plant growth index (PGI) in both plastic and biocontainers. Leaf and total plant dry weight (DW) increased with increasing N rate from 0 to 20 mm and stem and root DW were greatest when fertilized with 15 mm and 20 mm N. Plants fertilized with 20 mm N had the greatest leaf area and chlorophyll content in terms of SPAD reading. Container type had no influence on DW accumulation or leaf area. N concentrations (%) in leaves, roots, and the entire plant increased with increasing N rate. N concentrations in roots and in the entire plant were lower in biocontainers compared with plastic containers. Greater N rate generally increased daily water use (DWU), and biocontainers had greater DWU than plastic containers. The 20 mm N rate resulted in the highest net photosynthetic rate measured on 11 Sept. and 22 Sept. (65 and 76 days after treatment). Net photosynthetic rate (measured on 8 Oct.) and stomatal conductance (g S) (measured on 27 Aug., 22 Sept., and 8 Oct.) were lower in biocontainers compared with plastic containers. Two irrigations per day resulted in higher substrate moisture at 5-cm depth than one irrigation per day, and slightly increased PGI on 19 Aug. However, irrigation frequency did not affect photosynthetic rate, g S, or N uptake of hydrangea plants except in stems. Considering the increased water use of hydrangea plants when grown in the paper biocontainer and lower plant photosynthesis and N uptake, the tested paper biocontainer may not serve as a satisfactory sustainable alternative to traditional plastic containers.
Tongyin Li, Guihong Bi, Richard L. Harkess, Geoffrey C. Denny, Eugene K. Blythe, and Xiaojie Zhao
One-year-old liners of Encore® azalea ‘Chiffon’ (Rhododendron sp.) were transplanted in Apr. 2013 into two types of one-gallon containers: black plastic container and paper biodegradable container. Azalea plants were fertilized with 250 mL of nitrogen (N) free fertilizer solution twice weekly plus N rate of 0, 5, 10, 15, or 20 mm from ammonium nitrate (NH4NO3). All plants were irrigated with the same total volume of water through one or two irrigations daily. Plant growth and N uptake in response to N fertilization, irrigation frequency, and container type were investigated. The feasibility of biodegradable paper containers was evaluated in 1-year production of Encore® azalea ‘Chiffon’. Paper biocontainers resulted in increased plant growth index (PGI), dry weights (leaf, stem, root, and total plant dry weight), leaf area, and root growth (root length and surface area) compared with plastic containers using N rates from 10 to 20 mm. Biocontainer-grown plant had more than twice of root length and surface area as plastic container–grown plant. Leaf SPAD reading increased with increasing N rate from 0 to 20 mm. One irrigation per day resulted in greater PGI, root dry weight, root length, root surface area, and root N content than two irrigations per day. Higher tissue N concentration was found in plants grown in plastic containers compared with those grown in biocontainers when fertilized with 15 or 20 mm N. However, N content was greater for plants grown in biocontainers, resulting from greater plant dry weight. The combinations of plastic container and one irrigation per day and that of 20 mm N and one irrigation per day resulted in best flower production, 21.9 and 32.2 flowers per plant, respectively. Biocontainers resulted in superior vegetative growth of azalea plant compared with plastic containers with sufficient N supply of 10, 15, and 20 mm.
Garry Vernon McDonald, Geoffrey C. Denny, Michael A. Arnold, Donita L. Bryan, and Larry Barnes
Seeds of Taxodium distichum (L.) Rich. were collected, germinated, and grown from native stands ranging from Mexico, Texas, Louisiana, Mississippi, and Alabama. Twenty-two provenance selections were planted in Summer 2004 in College Station, TX, in 36 replicated single-plant replications per block for a total of 792 trees. Below-average midsummer temperatures and above-average number of rainfall events were conducive to the development of a leaf blight associated with the presence of Cercosporidium sequoiae (Ellis and Everh.) W.A. Baker and Partridge. A survey conducted in Oct. 2007 rated differential defoliation responses among provenances. Selections of Taxodium distichum var. mexicanum (Gordon) from Mexico and south Texas showed defoliation rates from 89% to 96%, whereas T. distichum var. distichum from central Texas had defoliation ratings from 79% to 99%. With the exception of one family collected from the Sabinal River in Texas, the central Texas selections had similar defoliation compared with those from south Texas. Selections of T. distichum var. distichum and one selection of T. distichum var. imbricarium (Nutt.) Croom from southeastern regions (Alabama, Louisiana, Mississippi, and east Texas) showed greater tolerance to the presence of the leaf blight with 52% to 80% mean defoliation. A few individuals within these families exhibited little or no symptoms of the leaf blight. In general, those selections from high-rainfall, high-humidity areas had less defoliation associated with the presence of the leaf blight fungus, although defoliation was variable among provenances within all geographical regions. These results suggest that tolerance to defoliation from C. sequoiae could be included in selection criteria when choosing possible germplasm releases from Taxodium distichum.
Amy L. Shober, Christine Wiese, Geoffrey C. Denny, Craig D. Stanley, Brent K. Harbaugh, and Jianjun Chen
Recent concerns over the environmental impact of peat harvesting have led to restrictions on the production of peat in Florida and other areas. The objectives of this study were to evaluate the use of composted dairy manure solids as a substitute for sphagnum or reed-sedge peat in container substrates on the growth of Solenostemon scutellarioides L. Codd ‘Wizard Velvet’, Tagetes patula L. ‘Safari Queen’, and Begonia ×hybrida ‘Dragon Wing Red’ and to examine the nutrient content in leachate from pots. Plants were grown for 5 weeks in a greenhouse in 15-cm plastic pots with seven substrates containing various proportions of sphagnum peat (S) or reed-sedge peat (R) and composted dairy manure solids (C), each with 20% vermiculite and 20% perlite. Substrate composition had no effect on plant quality ratings, number of flowers, or root dry mass for any of the plant species evaluated. Substrate composition did not affect the growth index (GI) or shoot dry mass of S. scutellarioides ‘Wizard Velvet’ or the GI of T. patula ‘Safari Queen’. However, growth of B. ×hybrida ‘Dragon Wing Red’ (GI and shoot dry mass) and T. patula ‘Safari Queen’ (shoot dry mass only) was highest in the 3S:0R:0C substrate. The substrates containing sphagnum peat and/or composted dairy manure solids (3S:0R:0C, 2S:0R:1C and 1S:0R:2C) had the highest NH4-N losses through the first 7 d of production. The 0S:3R:0C substrate had the highest initial leachate NO3+NO2-N losses and this trend persisted throughout most of the production cycle. Significantly more dissolved reactive phosphorus was leached from substrate mixes containing composted dairy manure solids than mixes containing only sphagnum or reed-sedge peat materials through 19 d after planting. All substrates tested as part of this study appeared to be commercially acceptable for production of container-grown bedding plant species based on plant growth and quality. However, nutrient losses from the containers differed depending on the peat or peat substitute used to formulate the substrates.