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Potting of bare-root spring divisions is a simplified approach to ornamental grass production. Large and small divisions of eight common ornamental grasses were directly potted into 7-L nursery containers and grown outdoors for 20 weeks to determine an appropriate division size for each grass. Response to division size was dependent on the grass species. Large divisions of Calamagrostis ×cutiflora `Karl Foerster' (Schräd.) produced twice as many inflorescences as small divisions. At harvest, large divisions of Miscanthus oligostachyus `Purpurascens' (Stapf.) had twice as many inflorescences and 1.5 times as many tillers as small divisions. However, new tiller production in large divisions was only 50% of that in small division plants. Large divisions of Miscanthus sinensis (Anderss.) cultivars produced more tillers and greater fresh and dry weights than did small divisions, but again, the differences were not proportional to the size difference between the initial divisions. Large divisions of Panicum virgatum (L.) produced 50 more tillers per plant than did small divisions, but plant weight, size, and number of inflorescences were not affected by division size. Plants from large divisions of Pennisetum alopecuroides (L.) Spreng. were 7 cm shorter than small divisions and produced 24% more inflorescences and 27% more tillers, but appeared nutrient and/or water stressed. For most grasses, smaller division size is recommended for direct spring potting.
The effect of shading during nursery production on the growth, foliage color, and foliar chlorophyll content of container-grown Kalmia latifolia cultivars was investigated. Five cultivars were grown under 40% shade, 60% shade, or full sunlight for a 2-year production cycle. During the first year of production, there were no significant differences in measured growth characteristics for most cultivars in response to light treatment. Shade improved foliar color by decreasing lightness (L*), decreasing chroma, and changing hue angle from a yellow-green to a darker green. Foliar chlorophyll concentration increased under shade. In the second year of the production cycle, the response of foliar color and chlorophyll concentration to shade was similar to that observed in year 1. Plant size, number of branches, leaf area, leaf dry mass, and stem dry mass decreased linearly with increasing shade in year 2. Although shading improves foliar color, it probably should not be employed for container production of Kalmia latifolia in cool, northern production areas due to reduced plant growth during year 2. Shade may be useful in the first year of production to enhance foliar color without reducing shoot growth.
To introduce desirable trait genes into Kalmia latifolia, efficient adventitious shoot regeneration methods are needed. Silver Dollar (S$) callus induction and growth in the dark was compared on Woody Plant (WP) medium containing 2,4-dichlorophenoxyacetic acid (2,4-D) (1, 5, 10, 20 μM) or naphthaleneacetic acid (NAA) (1, 10, 20, 40 μM) with and without 5 μM isopentenyladenine (2iP). Both 2,4-D and NAA produced >450 mg of callus from leaf explants in 8 weeks. The addition of 2iP tripled growth for 2,4-D and doubled growth for NAA. Greatest callus growth was obtained on 20-40 μM NAA or 5-20 μM 2,4-D. Shoot regeneration on callus was achieved on WP medium containing 30 μM 2iP or 1 μM thidiazuron (TDZ), but a combination of the two was best, with 68% of dark-grown calli regenerating shoots in 4 weeks. 26% more dark-grown calli regenerated shoots than light-grown calli. The type of auxin (2,4-D or NAA) used to grow the calli did not affect shoot regeneration. For direct shoot regeneration, S$ leaf explants were tested on WP medium containing 5, 15, 30, 45 and 60 μM 2iP. The addition of 1 μM indole-3-butyric acid (IBA) doubled the percentage of leaves that regenerated shoots. 2iP concentrations between 15 and 45 μM supported excellent shoot regeneration, but optimal regeneration (95% of explants, 5.1 shoots/leaf) occurred on 30 μM 2iP+1 μM IBA. Leaf explants of six cultivars were grown on optimal medium with shoot regeneration ranging from 17% to 93% of leaves and 1.8 to 8.2 shoots per leaf, depending on the cultivar.
Although it is commonly recommended that shoot tip cultures be initiated from actively growing shoots, it has been demonstrated that shoot tips collected during the period of rapid shoot extension fail to produce shoot proliferating cultures. Shoot tips of Halesia Carolina and Malus `Golden Delicious' were collected at 2 week intervals from budbreak to summer dormancy and placed on medium containing 0, 4.5, 11.0, 22.5 and 44.5 uM benzyladenine (BA) to determine if elevated BA concentrations could overcome seasonal patterns of shoot proliferation potential (SPP). Both species reached maximum SPP 4 weeks post-budbreak (PBB), and exhibited a second window of high SPP during weeks 10 and 12. Elevated BA concentrations failed to overcome poor SPP exhibited by shoot tips harvested 6 to 8 weeks PBB. Shoot tips collected at 10 to 12 weeks PBB responded more favorably to higher exogenous BA concentrations than shoot tips collected at 2, 4, 6, or 8 weeks PBB. It appears as though seasonal fluctuations in SPP involve other endogenous factors in addition to cytokinins.
Nursery production of many ornamental grasses involves potting of established liners into 8.5-L containers. Direct potting of bare root divisions into 8.5-L containers may represent a more efficient production method. Large and small divisions (based on number of tillers and volume) of eight ornamental grasses were potted directly into 8.5-L containers. The potting medium used was a 3 aged pine bark: 2 peat moss: 1 sand nursery mix (by volume), amended with dolomitic lime at 3 kg/yard3, and top dressed with Sierra 17-6-10 plus minors at 40 g/container, 8 to 9 month fertilizer. Plants were grown outdoors in a container nursery from May through September. All grasses tested performed well using the direct potting method, with 100% survival. Large divisions of Miscanthus sinensis cultivars produced plants with greater fresh weight, dry weight and number of tillers than did small divisions. Division size did not affect Miscanthus foliage or flower height but did affect number of flowers for `Graziella' and `Purpurascens'. Large divisions of Calamagrostis `Karl Foerster', a grass grown primarily for flowering, produced twice as many flowers as small divisions. Panicum virgatum and Pennisetum alopecuriodes showed signs of nutrient stress when grown from large divisions. Although a greater number of tillers was produced by large divisions of Panicum and Pennisetum, fresh weight, dry weight, flower height, and foliage height were similar to or less than that observed on plants from small divisions.
Information on fertility optimization for container-grown ornamental grasses is limited. For ornamental grasses, growers are concerned with the degree of flowering, number of tillers, and height and width of the plants as well as other growth or ornamental components. Pennisetum alopecuroides divisions potted into 8.5-L containers were grown outdoors in a container nursery from May through September. The potting medium used was a 3 aged pine bark: 2 peatmoss: 1 sand nursery mix (by volume), amended with dolomitic lime 3 kg/yard3. Sierra 17-6-10 plus minors, 8 to 9 month controlled-release fertilizer (CRF) was top dressed at 20, 30, 40, 50, or 60 g/container. Foliage height increased linearly with increasing CRF rate. Flower height increased to a maximum at 40 g of CRF per container and then decreased with higher levels of CRF. Basal plant width exhibited a quadratic response to CRF rate, reaching a maximum at 40 g of CRF per container. The greatest number of flowers and tillers were obtained using 50 g of CRF per container. Maximizing the number of flowers is important for marketing of Pennisetum, since this plant is grown primarily for its flowering.
Container production of recently-developed and popular Kalmia latifolia cultivars has not been fully optimized. A study was conducted using six cultivars grown in full sun, 40% shade or 60% shade. Under 60% shade, plant height was reduced slightly, but shading, at either 40% or 60%, had no significant effect on all other measured growth parameters. Plants were too young to set significant numbers of flower buds, so the study will be continued a second year to quantify the effects of shade on flower bud set. Foliage color was measured using a Minolta CR-200 Chroma Meter. As shading increased, hue angle increased and the chroma and value of the color decreased, indicating that shading produced greener (less yellow), darker and duller foliage colors. Foliar chlorophyll content increased with increasing shading. Higher foliar chlorophyll content correlates with greener leaves in shaded treatments and is likely contributing to the green color. Using moderate levels of shade over container-grown Kalmia could allow growers to produce greener, more marketable plants without sacrificing plant growth.
Shoot tips of Amelanchier were grown on Murashige & Skoog (MS) or Woody Plant (WP) medium containing 4.4 μM benzyladenine and 4, 6 or 8% Difco Bactoagar. Increasing agar concentration reduced culture fresh weight, dry weight, and vitrification, but increased tissue nitrate concentrations. The number of shoots produced per culture was unaffected by agar concentration. Overall, response to agar additions was similar for shoots on both WP and MS salts, although the magnitude of the response may have differed. Amelanchier shoots cultured on WP medium containing 4% agar and 10.5, 15.5, 20.9 or 25.5 mM nitrate showed a linear increase in culture fresh weight, culture dry weight, number of shoots per culture and number of vitrified shoots per culture as medium nitrate concentration increased. Nitrate and total nitrogen content of explants also increased linearly with increasing medium nitrate concentration. Although vitrification has been previously ascribed to elevated ammonium concentrations in culture media, it is possible that elevated medium and tissue nitrate levels may also play a role in vitrification.
Combinations of me auxins 2.4-dichlorophenoxyacetic acid (2.4-D). indolebutyric acid (IBA). and naphthaleneacetic acid (NAA), with isopentenylademne (2-iP) were studied in Woody Plant (WP) medium for callus induction and shoot organogenesis from leaves of Rhododendron `Besse Howells' (BH) and `Catawbiense Album' (CA). IBA was more effective than NAA and 2,4-D at inducing shoot organogenesis when combined with 2-iP. Addition of 1 uM IBA and 15 or 30 uM 2-iP to WP medium resulted in the highest percentage of explants producing shoots (90% in BH, 100% in CA), and the greatest number of shoots per explant (18.4 in CA, 10.1 in BH) after 12 weeks of culture. Shoot organogenesis also occurred using 1 uM NAA and 2-iP combinations, but me number of shoots produced was much less than for IBA treatments. 2,4-D and NAA were more productive than IBA for callus induction. Media containing l-10 uM 2,4-D plus 5 uM 2-iP. or 10 uM NAA plus 15 uM 2-iP. were me best for callus production. In studies using thidiazuron instead of 2-iP as the cytokinin, leafy buds and very short shoots developed.