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  • Author or Editor: Donglin Zhang x
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Stewartia pseudocamellia Maxim. (Japanese Stewartia), a member of Theaceae (tea family), is an excellent garden plant with ornamental features for all four seasons. Reproduction difficulty, however, limits its popularity. We conducted three experiments to ascertain the optimum conditions needed for rooting and subsequent overwintering of semihardwood Stewartia pseudocamellia cuttings. Cuttings were collected in July and prepared for rooting using two types of hormones (KIBA quick dip and Hormodin powder) and three media (Perlite + ProMix, Perlite + Perennial Mix, or Perlite + ProMix + Perennial Mix). Rooted cuttings were overwintered at four different temperatures. The best overwintering temperature was 5 °C, at which 65.6% of newly rooted cuttings survived. Temperatures lower than –12.2 °C were detrimental to the plants. Without cold treatment, only 21.9% of the rooted cuttings survived, which was three times lower than those that received 5 °C treatments. Plants rooted in Perlite + Perennial Mix had 61.8% overwintering survival, which is significantly higher than Perlite + ProMix. The quality of roots, indicated by total root length per cutting, was higher (104.3 cm) with Perlite + Perennial Mix, but not statistically significant. Cuttings treated with rooting hormones had higher rooting percentages (71.9% to 93.6%) as compared with the control (53%). For the same concentration (8000 mg·L−1), liquid (KIBA) and liquid + powder (KIBA + indole-3-butyric acid) rooting hormones resulted in better rooting percentages than powder (Hormodin) alone, although there was no statistical difference in rooting percentages among rooting hormone treatments. The best hormone for subsequent overwintering survival was the combination of quick dip (5000 mg·L−1 KIBA) and Hormodin #2 (0.3% a. i.; equivalent to 3000 mg·L−1). It resulted in 64.2% survival, significantly higher than for KIBA quick dip (8000 mg·L−1 a.i.) or Hormodin #3 (0.8% a. i.; equivalent to 8000 mg·L−1) alone. Our results suggest that reproduction (rooting and overwintering) of Stewartia was affected by many factors. We recommend rooting Stewartia in media that has good aeration and moderate water-holding capacity and overwintering them at ≈5 °C.

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Scaevola aemula R.Br. (fanflower), an ornamental plant native to Australia, produces stunted growth when fertilized with high concentrations of P. To determine optimum P concentration, rooted cuttings were transplanted into 15 cm standard pots and grown with a water soluble fertilizer, where P concentrations were 0, 14.5, 29.0, 43.5, 58.0, 72.5, 87.0 mg·L-1 and all plants received 200 mg·L-1 N and 166 mg·L-1 K. Shoot growth and flowering data were taken every 21 days until the experiment was terminated after 84 days. Shoot length, number and dry weight, and leaf size were reduced significantly at P concentrations higher than 14.5 mg·L-1 with severe reduction at P levels higher than 43.5 mg·L-1. Number of flowers per plant was not affected by P concentrations in the range of 0 to 43.5 mg·L-1, but decreased significantly at P levels higher than 43.5 mg·L-1. Medium pH decreased with increase in P rate due to the acidic nature of the P fertilizer. When P was applied in every irrigation, the optimum concentration was 14.5 mg·L-1 or less. P greater than 43.5 mg·L-1 was detrimental to vegetative growth and flowering, possibly due to above optimum P or to medium acidification.

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In commercial greenhouses, fan flower ‘Whirlwind Blue’ (Scaevola aemula R. Br.) plants are sensitive to phosphorus applications in the range typically applied to other floricultural crops. To quantify this response, fan flower plants were grown in Hoagland solutions containing 0, 20, 40, 60, or 80 mg·L−1 P. Plants fertilized with either the highest (80 mg·L−1) or lowest (0 mg·L−1) P concentrations had significantly shorter stems and smaller shoot dry weights and leaf areas than plants fertilized with 20 to 60 mg·L−1 P. Low or high P concentrations negatively impacted flower number; fan flower fertilized with 0, 60, or 80 mg·L−1 P had fewer flowering branches and flowers compared with plants fertilized with 20 to 40 mg·L−1 P. Plants receiving no P had longer roots than those receiving any P and had greater root dry weights than plants receiving all other P concentrations except 20 mg·L−1. Foliar nutrient analysis indicated that although P treatments significantly impacted foliar concentrations of at least some essential macro- and micronutrients, all essential elements were within or near recommended ranges except P. Foliar P concentrations exceeded 1 mg·g−1 in fan flower that received even the lowest concentration of supplemental P, but leaf chlorosis was only observed in plants grown in 60 to 80 mg·L−1 P. As a result of rapid accumulation of P in fan flower foliage and subsequent reductions in flower number and shoot elongation, fan flower should be fertilized with no more than 20 mg·L−1 P.

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Zelkova sinica Schneid. is a popular landscape plant in China because of its wide adaptation, strong disease resistance, large crown, and beautiful fall color. Immature embryos from Z. sinica seeds were cultured on woody plant medium (WPM) supplemented with 4.5 μM 6-Benzylaminopurine (BA) and 5.4 μM α-naphthaleneacetic acid (NAA) to induce callus, and 60% of immature embryos formed callus. The cream-white, friable, nodular callus with proembryogenic structures was then cultured on WPM containing 5.4 μM NAA in combination with 9.0 or 11.2 μM BA to regenerate shoots; approximately five shoots per explant were induced on 70% callus. Shoots were rooted on WPM containing 0.5 μM indole-3-butyric acid (IBA), on which 62.3% shoots developed roots with an average of 4.2 roots per shoot at 4 weeks. The regenerated plantlets were acclimatized and transplanted into the field. This protocol could be used for mass production for field plantation, genetic improvement, and germplasm exchange of Z. sinica.

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Winter injury to the root systems of fruit trees can cause significant tree losses and yield reductions in the northern regions of the United States and Canada. To compare the root and trunk cold temperature tolerance, a series of experiments were conducted using ungrafted apple rootstocks. ‘Geneva® 11’ (G.11), ‘Geneva® 30’ (G.30), ‘Geneva® 41’ (G.41), ‘P.2’, and ‘Budagovsky 9’ (B.9) apple (Malus ×domestica Borkh.) rootstocks had root tissue hardiness similar to ‘M.26’, but ‘Geneva® 935’ (G.935) had greater cold-hardiness than M.26 when based on shoot regrowth in ungrafted trees. The LT50 of M.26 and P.2 roots ranged from –12 to –14 °C. The LT50 was –13 °C for B.9, –13.4 to –14.6 °C for G.30, and –12 °C for G.11. The LT50 of G.41 was one of the highest in one experiment, –8 °C, and one of the lowest in another, colder than –15.0 °C. The LT50 of G.935 roots was the lowest and ranged from –16 to –19 °C. Compared with M.26, trunk cold-hardiness in December was greater in B.9 and P.2 and was similar in G.30. Cold-hardiness of G.11 in December was mixed with less injury in the xylem but more injury in the phloem compared with M.26. In October, M.26 and G.935 trunks had little injury after exposure to –24 °C.

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