Previous reports of somatic embryogenesis on rose tissues involved an embryogenic callus stage with either a complicated multi-step process or low numbers of embryos being produced. We have produced somatic embryos without a callus stage from leaf explants of the cut rose cultivar `Golden Emblem' by using a two step process. Explants were obtained from microshoots of `Golden Emblem' that had been in culture for three years. All experiments were repeated twice. When explants were maintained on Murashige and Skoog (MS) with 0.4 μM NAA and 0.4 μM kinetin for 10 weeks, 10% or less of the explants produced somatic embryos. Keeping the explants on the NAA/kinetin medium for two weeks, then switching to medium with 0, 0.5, 1.0, or 10.0 μM kinetin for the remaining 8 weeks failed to increase embryo production. Decreasing the time the explants were on the NAA/kinetin medium to 8 or 12 days, and then placing explants on MS medium with 1.0 μM kinetin increased somatic embryo production to a maximum of 25%. By limiting the length of time the rose leaf explants were exposed to auxin, direct somatic embryo production was increased.
Mary W. George and Robert R. Tripepi
Robert R. Tripepi and Mary W. George
De-inked paper sludge from a newsprint mill was evaluated as a substitute for softwood bark in container media. Whips, 1.2 m tall, of `October Glory' red maple (Acer rubrum L.), European birch (Betula pendula Roth), and `Royalty' crabapple (Malus L.) were planted in 15-L plastic pots that contained potting media amended with 0%, 20%, 40%, 60%, 80%, or 90% paper sludge and 80%, 60%, 40%, 20%, 0%, or 0%, respectively, bark (by volume). All media contained 10% sand. After 22 weeks, plant heights, trunk diameters, and shoot dry weights were determined. Initial pH of media increased as the amount of paper sludge in the media increased, with the 90% sludge mix having pH 7.2. Paper sludge had a low initial CEC. Physical properties of all sludge-amended media were suitable for tree growth, but media containing 80% or more paper sludge shrank in volume by 10% to 12% by the end of the study. All maple and crabapple trees grown in all sludge-amended media grew as well as those in 80% bark (control mix). In fact, maple and crabapples trees in 40% sludge produced at least 10% and 36% more total shoot biomass, respectively, than trees in 80% bark. Although birch trees grown in 40% or 60% paper sludge grew as well as control plants, those grown in 80% or more sludge were at least 11% shorter and produced 24% less total shoot biomass (leaves, stems, and trunk dry weight) than control trees. These results demonstrated that de-inked paper sludge was a worthy substitute for up to 40% of the bark in a container medium for the three species tested.
Robert R. Tripepi and Mary W. George
Seedlings of several conifer species can be difficult to transplant, with the problem often related to poor root regeneration. The objective of this study was to determine if corkbark fir (Abies lasiocarpa arizonica) seedlings or pinyon pine (Pinus edulis) seedlings would produce more root growth when grown in a Missouri gravel bed growing system compared to field soil. The 3–0 fir seedlings and 4–0 pine seedlings were planted in a gravel bed in mid-April. The gravel bed was 3 m × 3.7 m and was filled with a mixture of 60% pea gravel (1 cm minus), 30% Turface®, and 10% silica sand (by volume). A field bed 3 m × 3.7 m in size was also prepared. Fir seedlings were harvested in September and October, but pinyon pine seedlings were harvested only in October due to their poor transplant survival. Plant heights, stem diameters, and root volumes, as well as root and shoot dry weights, were determined at harvest. Of all the measured growth parameters for both species, only root dry weights and root volumes were significantly different. In particular, fir seedlings grown in the gravel bed produced at least 30% more root dry weight and 74% more root volume than those planted in field soil whether plants were harvested in September or October. Likewise, pine seedlings grown in gravel produced at least 37% more root dry weight and 86% more root volume than those grown in soil. In addition, only 10.6% of the pine seedlings planted in soil survived transplanting, but 23.3% of those grown in the gravel bed survived. This study demonstrated that corkbark fir and pinyon pine seedlings grown in a gravel bed produced larger root systems than those planted into field soil, and the gravel bed also improved pinyon pine seedling survival after transplanting.
Robert R. Tripepi and Mary W. George
Mung bean (Vigna radiata (L.) R. Wilcz.) cuttings are used in rooting bioassays, and nonexperimental variability must be rigorously controlled to obtain meaningful results. This study was conducted to document bacterial disease problems of mung bean and identify the causal organisms. `Berken' seeds were surfaced sterilized and aerated 24 hr before sowing. Nine-day-old seedlings were used in rooting bioassays. Up to 10% of the seedlings and 17% of the cuttings had collapsed stems or wilted leaves. A white and two yellow (Y1 and Y2) bacteria were isolated from diseased cuttings and used in subsequent pathogenicity tests. The Y2 isolate was nonpathogenic. Stems of healthy mung beans inoculated with the white isolate turned brown and collapsed 2 days after inoculation, whereas leaves of plants inoculated with the yellow isolate wilted after 7 days. Standard biochemical and physiological tests revealed that the white isolate was Pseudomonas syringue pv. syringae van Hall and the yellow isolate was Curtobacterium flaccumfaciens subsp. flaccumfaciens (Hedges) Collins and Jones. This research is the first report of a disease in mung bean caused by P.s. pv. syringae. These results demonstrate the need or disease-free seeds being used in bioassays since both pathogens were seed-borne.
Robert R. Tripepi and Mary W. George
De-inked paper sludge from a newsprint mill was evaluated as a substitute for sofwood bark in container media. Rooted cuttings of `Youngstown' juniper (Juniperus horizonatlis), Fraser photinia (Photinia × fraseri), and `PJM' rhododendron (Rhododendron) were planted in 3-L plastic pots that contained potting media amended with 0%, 20%, 40%, 60%, 80%, or 90% paper sludge and 80%, 60%, 40%, 20%, or 0%, respectively, bark (by volume). All mixes contained 10% sand and 10% peatmoss except for the 90% mix, which lacked peatmoss. After 19 weeks, plant heights were measured for photinia and rhododendron, but average plant width was measured for juniper. Shoot dry weights were also determined for all species. Juniper and photinia seemed to be the most tolerant of media amended with up to 40% paper sludge, whereas rhododendron was the most intolerant species. Shoot dry weights of juniper or photinia were similar for plants grown in media containing 40% or less paper sludge. Shoot dry weights of rhododendron plants grown in 40% sludge were 23% lower than those grown in 0% or 20% paper sludge, which were similar to each other. Plant heights followed similar trends to those of the shoot dry weights. With the exception of juniper, shoot dry weights and heights were drastically reduced if the potting mixes contained more than 40% paper sludge. These results demonstrated that de-inked paper sludge could be substituted for up to 40% of the bark in a container medium for two of the three species tested.
Mary W. George and Robert R. Tripepi
Plant Preservative Mixture™ (PPM), a relatively new, broad-spectrum preservative and biocide for use in plant tissue culture, was evaluated as an alternative to the use of conventional antibiotics and fungicides in plant tissue culture. Concentrations of 0.5 to 4.0 mL·L-1 were tested with leaf explants of chrysanthemum (Dendranthem×grandiflora Kitam), European birch (Betula pendula Roth), and rhododendron (Rhododendron catawbiense Michx.). PPM had little effect on the percentage of explants forming shoots and the number of shoots formed per explant in birch and rhododendron, but dramatically reduced both responses in chrysanthemum. Therefore, the effects of PPM must be evaluated for each species of interest prior to use.
Robert R. Tripepi, Mary W. George, and John E. Lloyd
Field-grown conifers are usually discarded if their root balls break during digging, but using an alternative holding system until the root systems recover could reduce production losses. The objective of this study was to determine if a gravel bed could be used as a holding treatment for 1.5- to 1.8-m-tall Colorado spruce (Picea pungens) trees that had soil removed from their root systems in the spring. Root systems from 12 trees were washed free from pine bark mulch and soil before the trees were randomly assigned to a gravel bed. One bed held a mixture of 88% pea gravel (1-cm minus), 2% Turface®, and 10% silica sand (by volume). The other bed contained a mixture of 90% basalt gravel (1.2-cm) and 10% sand. Trees were grown in the gravel beds for 5 or 6 months before height increases were determined. If the terminal leader died on the tree, the next highest lateral branch was measured for its increase in length. All trees survived and actually grew a little during the summer after removing all the soil from their root systems. Several trees suffered slight needle burning at the ends of random branches, but the damage appeared minimal. Tips of several small branches randomly located around the canopies on several trees died back, and up to 10 cm of the terminal leaders on about half the trees died back. Height increases were similar among the different trees grown in the two types of gravel, with the mean increase in height being 8.9 cm. The trees regenerated many roots in both types of gravel. In fact, new roots formed all over the root systems and encased large amounts of gravel, making its removal difficult. This study demonstrated that gravel beds can be used to help 1.8-m tall Colorado spruce trees recover from severe root losses.
Manoj Singlachar, Robert R. Tripepi, and Mary W. George
Attempts to regenerate plants from leaf explants of Rosa xhybrida L. on Murashige and Skoog medium have met with limited success. We report improved regeneration of somatic embryos and adventitious shoots from leaves of `Golden Emblem' on N6 medium. Leaf explants were obtained from microshoots that had been in culture for 4 years. Leaves were placed on N6 medium containing various combinations of 0, 0.4, or 1.0 μM 2,4-D and kinetin for 20 days with an initial dark treatment of 12 days, then transferred to a medium without plant growth regulator. Adventitious shoots and somatic embryos were observed 3 weeks after transferring to medium without plant growth regulators. Leaf explants placed on media without 2,4-D failed to form embryos or shoots. The best combinations of 2,4-D and kinetin (0.4 and 0.4 μM, 0.4 and 1.0 μM, or 1.0 and 1.0 μM) induced regeneration percentages ranging from 21% to 39%. N6 appears to improve regeneration of somatic embryos and adventitious shoots from `Golden Emblem' leaf explants, but the interaction between media formulation and duration of exposure to 2,4-D and kinetin needs to be examined.
Robert R. Tripepi, Mary W. George, R. Kasten Dumroese, and David L. Wenny
European birch (Betula pendula Roth) seedlings (1+ 0 plugs) were planted in a container growth medium amended with 0, 1.2, 2.4, or 3.6 kg/m3 of a commercial hydrogel and watered either daily or once every 3 or 5 days. When hydrogel was incorporated in the growth medium, shoot and root dry weights and lea area were reduced by 19, 29 and 18%, respectively, compared to controls. Shoot height, stem diameter and shoot:root ratio were unaffected by hydrogel amendment rate. Compared to seedlings in polymer-amended media, plants growing in medium without hydrogel had significantly lower stomata1 conductance and transpiration on fewer than 25% of the measurement dates. Irrigation frequency significantly affected all plant growth Indices and stomata1 parameters; seedlings irrigated daily grew the most and had the highest stomata1 conductance and transpiration. Although polymer-amended media held more water than the medium without hydrogel at all measured tensions, this moisture was retained in the expanded gel rather than being available for plant uptake at higher tensions. The hydrogel appeared to have little benefit for container production of birch.
Robert R. Tripepi, Mary W. George, K. Amanda Linskey, John E. Lloyd, and Jennifer L. Van Wagoner
Holding practices for balled and burlapped conifers may inadvertently impact nutrient availability and tree growth. The objective of this study was to examine the effectiveness of several nutrient treatments to maintain or enhance the growth and foliar nutrition of Colorado spruce (Picea pungens Engelm.) trees while they were in a mulch-holding bed. Sixty 1.5 to 1.8-m tall Colorado spruce trees with 61-cm (24 inch) diameter root balls were heeled into a holding bed of fresh pine bark mulch during 2002 and 2003. The treatments applied to the root balls were a control (pine bark without fertilizer), 114.2 g Osmocote (Scotts, Marysville, OH) 15N–3.9P–10K distributed over the top of the ball, one Ross Gro-Stake (Easy Gardener, Waco, TX) 10N–4.3P–8.3K Evergreen fertilizer spike (113 g) per ball, one-half cartridge (≈8.5 g) of Ross Root Feeder (Weatherly Consumer Products, Lexington, KY) 10N–5.2P–10K evergreen fertilizer injected into the root ball at four points, or a 1:1 biosolids-based compost:pine bark mixture (by volume). Trunk diameters and tree heights were measured and foliar samples for nutrient analyses were collected before applying these treatments and at the end of the growing season 20 or 17 weeks later. The 2003 trees were transplanted to a landscape site in 2004, and the height growth of their terminal leaders were measured at the end of the next two growing seasons. Overall, Colorado spruce trees appeared normal while they were held in the mulch beds the first season after nursery harvest. Changes in tree height and trunk diameter by the end of the first season after harvest were unaffected by the nutrient treatments. By fall of both years, needles from trees treated with the mixture of 1:1 compost:bark had the highest levels of foliar N, Mg, Ca, S, and B. Trees treated with the fertilizer spike in 2002 had similar levels of N and S in their needles compared with compost:bark-treated trees, whereas in 2003, spike-treated trees had the second highest levels of foliar N and S, and these levels were significantly higher than those of trees receiving the control or other fertilizer treatments with the exception of N in needles from fertilizer-injected trees in 2002. Plant-available N, however, was highest in the root balls of Osmocote- and fertilizer spike-treated trees only in 2003. Leaders on the 2003 trees that received the compost:bark or fertilizer spike treatments grew at least 70% or 36% taller, respectively, than those trees receiving the other treatments by the end of the second growing season in a managed landscape. Although all nutrient treatments failed to promote increases in tree heights and trunk diameters while the trees were held in a mulch bed for the first growing season after digging, the compost:bark mixture and, to some extent, the fertilizer spike improved foliar nutrition during this time.