Photoautotrophic shoot and root development for triploid melon

The aim of this investigation was to establish environmental factors which promote growth and photosynthesis of melon (Cucumis melo L.) shoot buds, in vitro, and determine if photoautotrophic shoots had superior root forming ability in photoautotrophic environments. Buds from the triploid melon clone ‘(L-14×B)×L-14’ were observed for 21 days after transfer from a multiplication MS medium with 3% sucrose and 10 μM benzyladenine (BA) to a shoot development medium with 1 μM BA at three levels of sucrose in the medium (0, 1 and 3%), and light (50, 100 and 150 PPF) and CO₂ (500, 1000 and 1500 ppm) in the culture chamber. More shoot buds were observed with 3% sucrose in the medium. Increased light and CO₂ had a positive interaction with shoot proliferation. Fresh and dry weights were greatest at 3% sucrose, 150 PPF light and 1500 ppm CO₂. Shoot buds grew more slowly in sugar-free medium, but fresh and dry weight still doubled over 21 days of culture. Net photosynthetic rates (NPR) of buds were negative after four days in treatment conditions, but became positive after transfer to fresh, sugar-free medium. Two triploid genotypes of melon were (1) grown in vitro with sugar (photomixotrophic) and without sugar (photoautotrophic), (2) rooted in sugar-free media, both in a laboratory controlled environment chamber (in vitro) and a greenhouse acclimatization unit (ex vitro), and (3) compared for subsequent nursery growth in the greenhouse unit. The genotype ‘(L-14×B)×L-14’ produced more shoots than ‘(L-14×B)×Mainstream’ in both photomixotrophic or photoautotrophic conditions. ‘(L-14×B)×L-14’ rooted as well from either photoautotrophic and photomixotrophic shoots but ‘(L-14×B)×Mainstream’ rooted less frequently from photoautotrophic shoots. Seventy-six percent of the shoots in the laboratory controlled environment chamber were able to root photoautotrophically, whereas 47% of the shoots in the greenhouse acclimatization unit were rooted. Between 77% and 88% of plantlets from all treatment combinations survived transfer to the nursery. After growth in the nursery, the sizes of plants (fresh weight, dry weight, leaf area) were the same for either genotype, from either photoautotrophic or photomixotrophic shoots. Nursery plants that had been rooted in the laboratory controlled environment chamber were larger than those rooted in the acclimatization greenhouse chamber. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of different macronutrient solutions and growth regulators on micropropagation of juvenile shape Acacia mangium and shape Paraserianthes falcataria explants

The influence of five different macronutrient formulations and various growth regulators on micropropagation of single node explants from Acacia mangium and Paraserianthes falcataria seedlings was examined after 4 weeks and 8 weeks in vitro. The experiment was repeated 4 months later. On media lacking growth regulators, growth and development were significantly influenced by the different macronutrient solutions tested, although morphogenic responses could vary according to the species. For instance, P. falcataria displayed a greater ability for adventitious rooting than A. mangium. Overall, Knop macronutrient solution induced the weakest responses. Explant responsiveness was significantly influenced by the addition of 2.2 or 4.4 μM 6-benzyladenine combined with either 1.4 or 2.3 μM kinetin, 1.5 or 2.5 μM indolebutyric acid or 1.6 or 2.7 μM naphthaleneacetic acid. The various combinations of growth regulators tested were shown to inhibit the rooting ability of the explants, while stimulating the production of basal shoots for both species, and of axillary shoots only for A. mangium. In such experimental conditions, A. mangium displayed overall a greater potential for micropropagation than P. falcataria. This revised version was published online in June 2006 with corrections to the Cover Date.     

Compared root system architectures in seedlings and in vitro plantlets of Hevea brasiliensis,in the initial years of growth in the field

In vitro culture of Hevea was undertaken to propagate selected clones on their own roots. The challenge was to overcome the failure of cuttings due to the poor conformity of regenerated root systems. Trees of several juvenile or mature genotypes were propagated either by in vitro microcutting, or by somatic embryogenesis, and planted in the field. Certain static and dynamic components of the root system were observed at different growth stages, from 0 to 3 years, and compared to those of seedlings of the same age used in the trial as a reference. A simple method was designed for measuring the vigour and balance of the root system. The in vitro plantlets had a well-developed taproot and lateral root system, with an architecture similar to that of plants obtained from seed. Moreover, clear differences occurred between selected clones for the relative vigour of the tap roots, lateral roots and trunk. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of auxins and darkness on in vitro rooting of micropropagated shoots from mature and juvenile Acacia mangium

The influence of total darkness versus a 16/8 photoperiod and of auxins added to the culture medium on the in vitro root formation capacity of Acacia mangium microshoots of juvenile and mature origin was examined. Rooting of the mature clone was significantly increased by exposing the microshoots to auxins (4 and 6 μM IAA or IBA) in darkness, while the promoting effect of darkness combined with 4 μM IAA was more time-restricted for the juvenile-origin microshoots. Overall, the latter rooted in greater proportions than those from the mature source. Maintaining the microshoots of both origins on auxin supplemented medium in darkness resulted in a greater number of adventitious roots formed than under the standard 16/8 lighting conditions. On the other hand, light stimulated root elongation. These results are discussed mainly from the viewpoint of auxin metabolism in relation to adventitious root formation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Encapsulation of micropropagated buds of six woody species

Regrowth after encapsulation in a sodium alginate matrix of micropropagated buds from six different in vitro proliferated woody species was evaluated. Actinidia deliciosa Liang & Ferguson (kiwifruit), Betula pendula Roth (birch), Crataegus oxyacantha L. (hawthorn), Malus spp. (apple), Rubus spp. (blackberry) and Rubus idaeus L. (raspberry) propagated in vitro were used as bud sources. Encapsulation with sodium alginate and subsequent regrowth on nutrient rich medium was compared to encapsulation with nutrient-enriched alginate capsules followed by regrowth on nutrientless medium. Apical and sub-apical buds of Malus (rootstock M. 27 and cultivar Starkspur Red) were also compared for encapsulation and regrowth ability. All species showed a regrowth after encapsulation, but only if cultured on enriched media. M.27 apical and sub-apical buds showed different regrowth ability after encapsulation with sodium alginate. Applicability of encapsulation of single micropropagated tree buds is discussed.