The effects of in vitro and ex vitro root initiation on subsequent microcutting root quality in three woody plants

Abstract

In vitro-and ex vitro-rooted microcuttings of Acer rubrum L. 'Red Sunset', Betula nigra L., and Malus × -domestiea Borkh 'McIntosh' were distinguished by several important anatomical and morphological properties which continued to regulate both root system and whole plant quality in later stages of production. In vitro microcuttings formed adventitious roots in greater number and more quickly than ex vitro microcuttings. Roots produced in vitro were characterized by extremely enlarged cortical cells and, consequently, had a much greater diameter than ex vitro roots. However, the vascular system of in vitro roots was underdeveloped (primary vascular tissues only) as compared to ex vitro roots, which produced vascular cambium and secondary growth during the same early stage of production. At least 50% of the post-transplant in vitro adventitious roots either died immediately, or temporarily persisted during acclimatization without producing any further growth. For the surviving in vitro-produced roots, the cortex partially collapsed after transplant, and new root extensions with ex vitro-like structure were produced. Only then did the in vitro portion of the root begin to form secondary vascular tissues. Shoots from in vitro treatments continued to grow vigorously during adventitious root initiation and during acclimatization, so that the plants were significantly taller and had a greater shoot area than those receiving comparable ex vitro rooting treatment. In vitro rooting led to a horizontal root morphology which continued to distinguish these treatments from ex vitro rooted plants during later stages of production, when anatomical differences in the roots could no longer be detected.

Auxin Control in the Formation of Adventitious Roots

“…In 1918, Arpad Paal accumulated the first evidence showing that growth signal is chemical in nature (Moore et al, 1995). In 1926, Went showed that (Kim et al, 1998;McClelland et al, 1990). IAA was the first used to stimulate rooting of cuttings (Cooper, 1935) and soon after another auxin which also promoted rooting, IBA, was discovered and was considered even more effective (Zimmerman and Wilcoxon, 1935).…”

Adventitious rooting of conifers: influence of physical and chemical factors

“…Both McClelland et al (1990) and Corrêa et al (2005) have stressed the need for increased efficiency of the process and that rooting should be carried out in the dark for the first few days. However, rooting can be influenced by light intensities, as reported by Kunneman and Ruesink (1997) who showed better responses to 66-83 lmol s -1 m -2 in a few Juniperus cultivars, while 27-37 lmol s -1 m -2 were more suitable for the Chamaecyparis and Cupressocyparis cultivars.…”

Enraizamento de plântulas de mirtileiro em condição ex vitro com diferentes substratos

“…Uma das etapas realizadas na micropropagação é o enraizamento dos explantes que classicamente tem sido realizado in vitro. Porém, como no enraizamento in vitro as raízes formadas apresentam dificuldades de sobrevivência no estágio de aclimatização (McCLELLAND et al,1990), além do custo de produção ser maior (FERRI et al, 1998). Assim, o uso do enraizamento ex vitro se apresenta como uma alternativa, pois de acordo com Pedrotti e Voltolini (2001) esta técnica possibililita a redução em 50% dos custos finais de produção de uma nova planta.…”