Recalcitrance in clonal propagation, in particular of conifers

Abstract

Despite major advances in forest biotechnology, clonal regeneration by somatic embryogenesis or organogenesis is still difficult for many woody species and is often limited to the use of juvenile explants. Adventitious regeneration of plants from gymnosperms older than zygotic embryos, and frequently even from highly immature zygotic embryos, is often difficult or has not yet been achieved. A number of experimental approaches that could eventually lead to overcoming recalcitrance are suggested in this review. When cloning trees of various ages, it is important to determine first which part of the individual contains the most responsive cells and at what time of the year these cells are in the most responsive state. This allows selection of the most useful explants. In hardwood trees and a few gymnosperms, responsive tissues are found in root or stump sprouts and in tissues near the site of meiosis at about the time that meiosis takes place. Another potentially active area is the shoot apex with most or all of its leaf or needle primordia removed. Apomixis is a natural form of clonal regeneration but occurs naturally in only one gymnosperm species. As the genetic mechanism of apomixis has been in part elucidated, the induction of apomixis by experimental means may soon be possible. The cytoplasm plays a major role in the expression or repression of nuclear genes that control embryogenesis. Expression of nuclear genes can be manipulated by nuclear transfer into de-nucleated cells (e.g., the cytoplasm of egg cells). Cytoplasmic control also plays a role in regeneration by androgenesis, asymmetric cell division and cell isolation. A short overview is presented of the genetic mechanisms involved in embryo initiation, maturation and germination and how manipulation of these mechanisms by genetic transformation could help in overcoming recalcitrance. It is expected that rapid development in the fields of research areas discussed in this review will over time eliminate the problem of recalcitrance in many instances where it is currently prevalent.

Micropropagation of commercially cultivated Henna (Lawsonia inermis) using nodal explants

“…Phenolic exudation is one the major problem in culture establishment when explants taken from woody tissues (Rai et al 2010). Furthermore, old branches shoots carry recalcitrant microbes in the tissues and these affect the process of surface sterilization and subsequent culture, behavior and growth of shoots (Bonga et al 2010). Apical juvenile or below apical nodal segments were sensitive to surface sterilization (Fig.…”

Rapid multiplication of Dalbergia sissoo Roxb.: a timber yielding tree legume through axillary shoot proliferation and ex vitro rooting

“…Datta et al (1982) and Gulati and Jaiwal (1996) rooted the microshoots of D. sissoo under in vitro condition by two-step method. Generally, woody plant species are recalcitrant to adventitious regeneration during their maturation stage as the vigor for shoot production and competence for rooting declines (Singh et al 2002;Bonga et al 2010). D. sissoo reaches maturity after 20-25 years in the arid regions.…”

Somaclonal Variation in Tissue Culture: A Case Study with Olive

“…Perennial and woody plants generally are considered to be recalcitrant in culture and are difficult to regenerate [108]. In commercial regeneration systems, the two methods that are used most commonly for olive plants are micropropagation and somatic embryogenesis.…”