Influencing Stock Production of Mojave Sage and Cape Daisy with the Application of Plant Growth Regulators

This study aimed to assess the effects of plant growth regulators (PGRs) on stock plant production of mojave sage (Salvia pachyphylla) and ‘Avalanche’ cape daisy (Osteospermum hybrid) that received foliar sprays of the following three PGRs: 200 and 400 ppm ethephon; 250 and 500 ppm benzyladenine; and 50 and 100 ppm gibberellic acid 4 and 7 (GA4+7) plus benzyladenine. Vegetative growth [height and width growth index (GI)], the number of vegetative cuttings, and fresh weight (FW) and dry weight (DW) of the harvested vegetative cuttings data were collected. A propagation study was conducted concurrently to determine the effects of the PGR treatments on rooting vegetative cuttings. GA4+7 plus benzyladenine (50 and 100 ppm) increased the production of both mojave sage and ‘Avalanche’ cape daisy cuttings by ≥18% more than the other treatments. The GI, FW, and DW results showed similar trends across experiments 1 and 2 for each perennial. In the propagation study, the rooting percentage did not differ after 4 weeks, indicating that the use of GA4+7 plus benzyladenine in production protocols could benefit producers of both perennials.

60Co gamma irradiation-induced mutation in vegetatively propagated Philodendron erubescens 'Gold'.

Philodendron erubescens 'Gold', an ornamental plant and a popular climber with brilliant greenish yellow leaves, is used in indoor gardening and landscaping. It is commonly propagated through vegetative cuttings, thus incorporation of new traits through conventional breeding is impracticable. As commercial floriculture always demands novel varieties, this study was carried out to induce mutation in P. erubescens 'Gold' leaves using gamma- ray irradiation. Rooted cuttings (n = 200) of P. erubescens 'Gold' were subjected to 70 Gy, 100 Gy and 150 Gy gamma-rays and recovered on a propagator. Surviving shoots were transferred to pots. Regenerated shoots were multiplied vegetatively and ten M1 lines were maintained as M1-1 to M1-10 for 12 generations (M1V12) to evaluate growth and morphological variations along with their genetic stability. Of all 70 Gy and 100 Gy treated cuttings, 24 and two, respectively, survived after 6 months. Most of the irradiated plants had lost regeneration ability except for two M1 plants, which also showed comparatively reduced growth (one leaf in 45 days). Only one regenerated M1 plant showed morphological variation in its leaves and it was multiplied and maintained as lines. Several variations, including characteristics of leaves (shape, size, colour), stems (internodal length and branching) and plant stature, were observed among M1 lines and in subsequent vegetative generations. Leaves had three different colour patches, but neither the colour nor its distribution pattern was uniform or stable. The M1-4 line showed the highest stability of colour distribution in leaves; the colour composition of its leaves ranged as 0-10% dark bluish green, 60-90% strong yellow green and 10-30% brilliant greenish yellow throughout the 12 generations. This study demonstrates that gamma irradiated P. erubescens 'Gold' line M1-4 can be a promising mutant to develop as a new Philodendron cultivar.

Viability of Red (Ribes rubrum L.) and Black (Ribes nigrum L.) Currant Cuttings in Field Conditions after Cryopreservation in Vapors of Liquid Nitrogen

One of the prospective ways to safely preserve the genetic resources of red and black currant for breeding needs is the cryopreservation of cuttings with dormant buds. Vegetative cuttings of 12 varieties of red and 11 varieties of black currant were harvested in various regions of Russia: North, Northwest, and Central. Their viability after cryopreservation in nitrogen vapors (about −184 °C) under field conditions was studied. For red currant samples, it ranged from 61.2 ± 1.2% to 72.3 ± 3.0%, black currant—from 58.9 ± 1.1% to 73.5 ± 1.9%. In the group of red currant varieties, there were no significant differences in viability between varieties after cryopreservation. In the group of black currant varieties, “Chereshneva” and “Georgiy” had lower viability after storage in liquid nitrogen vapors than the others, 61.1% and 58.9%, respectively. On red currant, dry growing conditions of the experiment year significantly decreased the viability after cryopreservation. Neither black nor red currants revealed the influence of the place of harvesting on the survival of cuttings after cryopreservation. These results indicate the possibility of using cryopreservation to preserve cuttings of red and black currant with dormant buds collected in regions with different climatic environments.

Effects of Growth Substrate and Container Size on Cutting Production from Mojave Sage Stock Plants

Stock plant productivity is an important concern for growers of mojave sage (Salvia pachyphylla) because this species produces more woody growth as the plant ages. The objective of the study was to determine the best growth substrate and container size combination to maximize stock plant productivity. A secondary objective was to determine whether the stock plant treatments influenced the rooting of vegetative cuttings. Three different container sizes (3, 12, and 15.5 qt) and four soilless substrates composed primarily of bark, peat, and perlite (substrate 1); bark, peat, and vermiculite (substrate 2); bark, peat, and coarse perlite (substrate 3); and peat (substrate 4) were used. The stock plant experiment was conducted using 12 treatment combinations, and a subset of those stock plants was selected randomly for the rooting study that immediately followed the stock plant experiment. Stock plants responded to substrate treatments differently. The most successful stock plants, which produced more cuttings per plant and per square foot, as well as larger cuttings, were those grown in substrate 3. Regardless of substrate, the highest number of cuttings per square foot was obtained from stock plants grown in 3-qt containers, indicating that the smaller containers allow for the most efficient use of space when growing mojave sage stock plants for 4 to 6 months. The rooting of vegetative cuttings was successful (88% to 100% of cuttings rooted after 4 weeks under mist) for all treatment combinations.

Increasing Stock Production of Two Herbaceous Perennials with the Application of Plant Growth Regulators

The objective of these experiments was to evaluate the reaction of ‘Snow Angel’ coral bells (Heuchera sanguinea) and Orange Carpet hummingbird trumpet (Epilobium canum ssp. garrettii ‘PWWG01S’) to repeated foliar applications of three plant growth regulators at two application rates. The plant growth regulators applied during a stock plant study and followed by a propagation study were 200 and 400 ppm ethephon, 250 and 500 ppm benzyladenine, and 50 and 100 ppm gibberellic acid 4 and 7 (GA4+7) + benzyladenine. The stock plant study was conducted to assess the efficacy of plant growth regulators, vegetative growth (height and width growth index), the number of vegetative cuttings, as well as the fresh weight (FW) and dry weight (DW) of the harvested vegetative cuttings. The propagation study was conducted to determine the effects of the plant growth regulator treatments on the rooting of the vegetative cuttings. The stock plant study showed that GA4+7 + benzyladenine (50 and 100 ppm) significantly increased production of ‘Snow Angel’ coral bells cuttings compared with all other treatments. However, no significant differences in FW or DW were observed with ‘Snow Angel’ coral bells between treatments. In the propagation study, no significant difference in rooting percentage was observed after 4 weeks. The Orange Carpet hummingbird trumpet stock plant study resulted in a greater number of vegetative cuttings with GA4+7 + benzyladenine (50 and 100 ppm) and benzyladenine (250 ppm) treatments. Fresh weight of vegetative cuttings harvested from plants treated with GA4+7 + benzyladenine (50 or 100 ppm) were the lowest. The only treatment that showed increased vegetative cutting production with no effect on FW was benzyladenine (250 ppm) on Orange Carpet hummingbird trumpet.

Impacts of Growth Substrate and Container Size on Cutting Production from ‘Snow Angel’ Coral Bells Stock Plants

Stock plant productivity is an important concern for growers of ‘Snow Angel’ coral bells (Heuchera sanguinea) because this variety produces a limited number of basal cuttings. The objective of the study was to determine the best growth substrate and container size combination to maximize productivity of stock plants. A secondary objective was to determine if the stock plant treatments influenced the rooting of vegetative cuttings. The study used three different container sizes (2.8, 11.4, and 14.6 L) and four commercial soilless substrates that were primarily composed of the following: bark, peat, and perlite (substrate 1); bark, peat, and vermiculite (substrate 2); bark, peat, and coarse perlite (substrate 3); and peat (substrate 4). Two stock plant experiments were conducted using the same 12 treatment combinations, and a subset of those stock plants was randomly selected for the rooting studies that immediately followed each stock plant experiment. Stock plants responded to substrate treatments differently depending on the batch of substrate in which they were grown. The most successful stock plants, which produced more cuttings per plant and per square foot, as well as larger cuttings, were those grown in substrate 3 (Expt. 1) and substrate 2 (Expt. 2). Regardless of the substrate, the highest number of cuttings per square foot was obtained from stock plants grown in 2.8-L containers, indicating that the smaller containers allow for the most efficient use of space when growing ‘Snow Angel’ stock plants for 6 to 8 months. The rooting of vegetative cuttings was successful (98% to 100% of cuttings rooted after 4 weeks under mist) for all treatment combinations, although higher numbers of visible roots were produced during the second study and may be due to larger fresh weights of cuttings.

Effects of Light Quality on Vegetative Cutting and In Vitro Propagation of Coleus (Plectranthus scutellarioides)

Coleus (Plectranthus scutellarioides) is an attractive and popular ornamental plant with propagation mainly achieved through vegetative cuttings. For commercial purposes, it is of interest to enhance the speed of establishment while maintaining high quality. Light quality has been shown to influence adventitious root development, so these experiments examined the effect of narrow-bandwidth light treatments on root growth and overall plant quality for seven coleus cultivars with vegetative cuttings in potting soil and one cultivar with shoot tip in vitro cultures onto Murashige and Skoog (MS) agar medium. During the 28 days of the propagation period, the cuttings grown under narrow-bandwidth red light (R; 663.4 nm at peak) more than doubled in the adventitious root number compared with those under blue light (B; 445.7 nm at peak) and green light (G; 530.0 nm at peak) in five cultivars. R light also increased fresh weight of the cuttings by 55.6% more than G light. In comparison, the cuttings grown under G light yielded significantly lower root and shoot dry mass than other light treatments. R light cuttings showed more dry mass content (9.63%) than those under white light (W; 437.4 nm and 559.5 nm at peak) and G light (7.85% and 5.86%, respectively). A positive correlation (R2 = 0.598, P < 0.001) was found between the formation of adventitious roots and gained fresh weight of cuttings. R light made the reddish color of leaves significantly stronger in most cultivars, whereas the cuttings exposed to G light became less vivid compared with other light conditions. When the shoot tips were propagated in vitro onto MS medium, R light treatment initiated the root development more rapidly than other lights, with significantly greater rooting rate (20.0% and 63.6%, respectively) at day 5 and 10. The shoot tips under R light also formed significantly more roots (12.3 per cutting) than those grown under narrow-bandwidth B light (5.8 per cutting). The shoot tips showed browning at an early stage and newly emerged leaves grew very compactly under B light. The combination of red and green light (R+G) increased more than twice as much roots and dry mass compared with W light. In addition, the R+G light led to morphological changes, including larger leaves and longer petioles and internodes than those in other light treatments. The exposure to R+G+B and B light made the shoots very compact for the 28 days of in vitro culture period and significantly increased the chlorophyll contents resulting in dark green leaves.

Sugarcane seed composition and changes during artificial ageing

Sugarcane (Poaceae) has not undergone any commercial selection based upon seed characteristics. As the plant is grown from vegetative cuttings and the stalk harvested for its sucrose content, relatively little is known about its seed compared with other grass crops. The seeds of sugarcane were small, 1.8 × 0.8 mm, and the embryo comprised about one-third of the seed volume. Among the samples analysed, the seed contained on average 37%, 20% and 10% of the fresh weight as starch, protein and lipid, respectively. Histochemical staining showed that the starch was confined to the endosperm and the lipid to the embryo and aleurone layer. Protein was found in the embryo, endosperm and aleurone layer. There were small but significant differences between the sources of sugarcane seed. The wild relative S. spontaneum had significantly less starch than the commercial hybrid sugarcane seed. The lipid content was higher for sugarcane seed than for the seeds of many other grasses, possibly because of the high ratio of lipid-containing embryo to endosperm. Following artificial ageing, the observed decline in seed viability was not closely reflected by any significant changes in composition, although protein and sugars were reduced after 168 h. These results contribute to our understanding of the sexual reproductive biology of sugarcane, which is important for the science-based environmental risk evaluation of the release of genetically modified sugarcane.

Influence of Plant Age on Cold Hardiness of Three Container-Grown Herbaceous Perennials

Overwintering container-grown perennial plants is often necessary during their production. Rooted vegetative cuttings potted at the beginning of the growing season and rooted vegetative cuttings potted at the beginning of the previous growing season, were exposed to−2,−5,−8,−11, and−14C (28, 23, 18, 12, 7F) in January then returned to a greenhouse kept at 3 to 5C (37 to 41F). In June, plants were assessed using a visual rating scale (1 = dead, 3–5 = increasing salable quality) and dry weight of foliage regrowth. For Geranium × cantabrigiense ‘Karmina’, studied for one year, age did not affect either rating or dry weight. For Sedum ‘Matrona’, studied for two years, age had no effect on dry weight but ratings were higher for two-year-old plants than one-year-old plants in the first year and higher for one-year-old plants than two-year-old plants in the second year. For Leucanthemum × superbum ‘Becky’, studied for two years, age affected both rating and dry weight, which were higher for one-year-old plants. Of the cultivars studied, overwintering one-year-old, container-grown plants resulted in more growth and higher quality than overwintered two-year-old plants.

Substrates, Wounding, and Growth Regulator Concentrations Alter Adventitious Rooting of Baldcypress Cuttings

In previous studies, baldcypress [Taxodium distichum (L.) Rich.] clones were selected for tolerance to high pH soils, drought and salt exposures, and ornamental characteristics. The objective of the current research was to determine the treatment combinations that yielded optimum root quantity (percentage) and rooted cutting quality (root number, length, dry mass, and shoot dry mass) on vegetative cuttings for a representative clone. Cuttings were treated with factorial combinations of one of four potassium salt of indole-3-butyric acid (K-IBA) concentrations [0, 5,000, 10,000, 15,000 mg·L−1 (0, 20.72, 41.44, 62.16 mm, respectively)], wounded or not wounded (1-cm long basal incision), and rooted in one of three substrates (100% perlite, 100% peatmoss, or 50% perlite:50% peatmoss). Data indicated a tradeoff between potential rooting quantity and root quality measurements in response to different substrates. Although rooting percentages were affected by substrates only at P ≤ 0.10 (53% in 100% perlite versus 36% in 100% peatmoss), there were highly significant (P ≤ 0.0001) differences in rooted cutting potential among substrates as measured by the percentage of cuttings with basal callus. Cuttings placed in 100% perlite callused at 85%, whereas cuttings placed in 100% peatmoss callused at ≈53%. The 100% peatmoss treatment, however, yielded cuttings with significantly greater root quality for all measurements, except root number per cutting. Wounding cuttings proved to have deleterious effects on root quality measurements. Total root length was ≈14.5 cm for non-wounded cuttings and ≈10.8 cm for wounded cuttings. Increasing K-IBA concentrations did not significantly (P ≤ 0.05) affect rooting or callus percentages but did significantly affect root dry mass, total root length, and average root length per cutting. Total root length increased from 10.8 cm at 0 mg·L−1 K-IBA to 16 cm at 15,000 mg·L−1 K-IBA. Mean root number per cutting increased from ≈1.6 with wounded cuttings planted in 100% peatmoss to ≈3.1 with non-wounded cuttings planted in 100% perlite. Results suggested that high-quality softwood baldcypress cuttings should not be wounded, should be treated with 15,000 mg·L−1 K-IBA, and grown in a substrate with intermediate water-holding capacity to achieve an acceptable balance between rooting percentage and rooted cutting quality objectives.