Stimulation of ex vitro growth of Rhododendron hybrids ‘Nova Zembla’ and ‘Alfred’ by inoculation of roots with Serendipita indica

Experiments were carried out to study the consequences of inoculating Rhododendron ‘Nova Zembla’ and ‘Alfred’ microcuttings and young plants with Serendipita indica (formerly Piriformospora indica), an endophytic fungus. The inoculation at the in vitro rooting stage decreased the in vitro root and shoot quality, but after planting microplants in a greenhouse in a non-fertilised peat substrate, the plants grew 33% taller, with 10% more leaves and with more abundant roots in comparison with the non-inoculated microplants. The young plants rooted in vitro, acclimated in a greenhouse in a peat substrate and inoculated with S. indica at the time of the transplantation to the pots displayed, after 15 months, an increase in the shoot lengths by 35% and 13%, depending on the cultivar, in the leaf number by 47% and in the chlorophyll content by 31% when compared with the non-inoculated plants. The beneficial effect of S. indica on the young Rhododendron plants indicates the possibility of its practical use in the nursery production of this plant.

Effects of auxin and urea derivatives on adventitious rooting in chestnut and oak microshoots

The present study investigated how auxin concentration and the method of application affected the formation of adventitious roots in microshoots of chestnut (Castanea sativa) and oak (Quercus robur). The activity of two urea derivatives (2, 3-MDPU and 3, 4-MDPU) was also evaluated. Microshoots were derived from basal sprouts of two mature chestnut trees (P1 and P2) and one adult oak genotype (Sainza). In chestnut, rooting percentage was positively affected by auxin in a dose-dependent manner, particularly in shoots treated with the hormone for 24 h. The effect of auxin on rooting also differed depending on the application method. In shoots treated for 24 h, the highest concentration of auxin produced the healthiest rooted plantlets, in terms of the root system and shoot quality. By contrast, in shoots treated by the basal quick-dip method, the shoot quality was best at the lowest auxin concentration. The effect of urea derivatives on the root system depended on the species as well as on the auxin concentration and application period. Use of the MDPUs improved the root system architecture of auxin-treated shoots by promoting lateral root development and triggering the synchronous initiation of root primordia at the base of the shoot. Shoot quality was also improved by MDPUs, which promoted resumption of growth and reduced shoot-tip necrosis.

Stub Length and Stub Angle Did Not Influence Renewal Shoot Number or Branch Angle of Tall Spindle ‘Gala’/Malling 9 Apple Trees

Renewal of limbs by pruning to leave a short, angled, upward-facing stub is common practice for spindle-type apple (Malus ×domestica) training systems. A short, beveled stub cut is thought to stimulate renewal growth from latent buds present underneath the base of the excised branch, and to stimulate smaller, more fruitful renewal limbs with wide crotch angles. We conducted trials over the course of 2 years that involved dormant pruning of ‘Buckeye Gala’ with renewal cuts to compare two stub lengths, 0.5 and 2 cm, and three stub orientations, upward facing, downward facing, and vertical facing, to determine the effects on renewal shoot number, position, angle, and length. We found no clear advantages with either stub length that we evaluated, and there was no improvement in renewal shoot quality with a bevel cut at any orientation. Stub length and stub angle did not influence limb renewal and may be unimportant for training orchard-pruning crews and for machine-learning and robotic pruning.

Effect of cytokinins and amino acids on multiplication of Pelargonium cultivars

The effect of two cytokinins (BAP, m-Topolin) tested singly or in combination with a mixture of amino acids (glycine, glutamine, cysteine) on multiplication rate and quality of <em>Pelargonium</em> x <em>hederaefolium</em> and <em>Pelargonium</em> x <em>hortorum</em> shoots were investigated. For both <em>Pelargonium</em> cultivars, the application of cytokinins greatly increased the production of axillary and adventitious shoots compared with the shoots produced on the medium without growth regulators. In the case of <em>P</em>. x <em>hederaefolium</em> no significant differences it were found in the number of shoot formed for BAP and m-Topolin treatments. For <em>P</em>. x <em>hortorum</em> the most effective multiplication of shoots was obtained on the medium supplemented with m-Topolin (1.0 mg l^-1). Moreover, in the presence of m-Topolin an improvement of shoot quality of both genotypes has been observed (well developed shoots with soft green leaves). It was particularly apparent for <em>P</em>. x <em>hortorum</em> shoots. The addition of amino acids to a cytokinin medium increased slightly the number of formed shoots of <em>P</em>. x <em>hederaefolium</em> and influenced the shoot quality of both <em>Pelargonium cultivars</em> (well developed leaf blades, uniform growth of shoots in clumps, slower process of shoot senescence).

Effect of Meta-topolin on in vitro propagation of Pelargonium × hortorum and Pelargonium × hederaefolium cultivars

July and September. The most efficient regeneration and axillary multiplication were achieved on the medium supplemented with meta-topolin. The application of BAP caused a lower regeneration potency of explants and resulted in a decrease of shoot quality with every subculture. Four of the six cultivars showed growth inhibition after three months of growth on BAP-medium. The highest multiplication rate (2.7-4.7 depending on genotype) and the high quality of shoots were noted on the medium supplemented with mT (0.5-1.0 mg l^-1). It is also very important to note that mT had stimulating effect on organogenesis in <em>P.</em> × <em>hederaefolium</em> and <em>P.</em> × <em>hortorum</em> cultivars over the long term. Moreover, meta-topolin had no after-effect on the growth and inhibition of rooting. Only one cultivar ("Sofie Cascade") rooted better on control medium without auxin. In case of the other cultivars, IBA added in concentrations of 0.01-0.1 mg l^-1 had a stimulating effect on root production. The higher level of auxin inhibited root formation, stimulated senescence of shoots and had a negative after-effect on acclimatization in greenhouse conditions.

The Response of Three Ficus benjamina Clones to Stress Imposed by Complete Darkness or Reduced Frequency of Watering at Two Temperatures

Three clones of Ficus benjamina showed different responses to stress imposed by placing them in complete darkness for 2 weeks. `Natasha' was the most affected, showing 75% leaf abscission and a reduction of 25% of the chlorophyll content of the leaves. `Cleo' was the least affected. A general response of the three clones was the reduction in the quality of plants and in their shoot length. Withholding water for periods of 5, 9, and 14 days resulted in no stress response of the three clones at 22 ± 1C, and they only dropped their leaves at 30 ± 1C with the percentage of leaves abscising in∼creasing with longer periods between watering. `Natasha' was an exception, and showed an increase in shoot quality and leaf expansion under the high temperature and dropped only 4% of its leaves while the other two clones dropped 20% to 30% with watering at intervals of 9 days. `Cleo' dropped 90% of its leaves when watered at intervals of 14 days at 30C.

Container Medium and Slow-release Nitrogen Fertilizer Influence Growth and Quality of Salvia farinacea

We examined responses of Salvia farinacea Benth. (mealy blue sage, a water- and nutrient-efficient native landscape plant for the southern United States) to slow-release (8- to 9-month), resin-coated urea (39N-0P4K) preplant-incorporated at 0.5, 1, 2, or 3 kg N/m3 in 2 perlite: 1 vermiculite (PV) or 2 pine bark: 1 fine sand (BS) (both by volume). This slow-release fertilization was compared to weekly fertigation at 100 mg N/liter from ammonium nitrate (34N-0P4K). After 21 weeks of greenhouse culture in 3.8-liter containers, shoot dry weight was higher in BS than PV when these media received fertigation or contained slow-release fertilizer at 21 kg N/m3. Shoot dry weight and shoot quality were not increased by exceeding 1 kg N/m3 in PV or 2 kg N/m3 in BS. Fertigation resulted in shoot dry weight and shoot quality equal to the highest values achieved with slow-release fertilizer. Cate-Nelson analysis showed that shoot N concentration should be ≥ 4.0% for this element not to limit plant growth.