Improved organogenic capacity of shoot cultures from mature pedunculate oak trees through somatic embryogenesis as rejuvenation technique

Abstract

Theoretically, complete rejuvenation of mature trees should occur through somatic embryogenesis, however, this has not been extensively studied. The main objective of the present study was to increase the efficiency of in vitro clonal propagation for mature Quercus robur (100-300 years old), by induction of somatic embryogenesis as rejuvenation step prior to establishment of shoot culture through micropropagation of somatic embryo-derived plantlets. Shoot culture lines of ''mature'' origin were established from epicormic shoots of two centenarian oak genotypes (Sainza and CR-0) and maintained by axillary shoot proliferation. Embryogenic lines were also initiated from epicormic leaf explants of the same genotypes and maintained by secondary somatic embryogenesis. Although the frequency of somatic embryo conversion into plantlets was low in pedunculate oak, shoot culture lines could be established and maintained by axillary branching from several germinated somatic embryos. For each genotype and shoot culture line of the two origins (mature tree and somatic plantlets), shoot multiplication rate and elongation as well as rooting ability parameters were compared. Compared with ''mature-origin'' shoot cultures and after more than one year propagation in vitro, shoot lines established from somatic plantlets produced a significantly higher proportion of elongated, rootable shoots (from 26.0-31.6 to 36.8-40.5%) with increased rooting ability (from 3.3-45.6% to 23.2-89.8%). In the case of 300-year-old Sainza genotype such a high organogenic capacity was similar to shoot cultures initiated from basal sprouts. Basal sprouts are considered as ''mature'' material that retains juvenile characteristics compared with epicormic shoots forced from crown branches. Somatic embryogenesis only slightly improved plant regeneration of shoot cultures from basal sprouts, thus validating their use as ''juvenile control''. The present results provide evidence that some rejuvenation occurred during the process of somatic embryogenesis and resulted in improved shoot growth and rooting of somatic embryo-derived culture compared with ''mature'' shoot culture. The results reported in this study might be useful in embryogenic systems with low plant conversion rates. The proposed experimental model might also be useful in finding molecular markers of plant ontogeny.

Micropropagation of mature Quercus ilex L. trees by axillary budding

“…As human management of the dehesas usually involves removal of the shrub layer and clearance of the arboreal stratum (Mesías et al 2010), holm oak trees do not usually have basal shoots. In the absence of mature material with juvenile physiological characteristics, an alternative procedure based on forced flushing of branch segments can be used to produce epicormic shoots, which are a source of more reactive and reinvigorated explants (Martínez et al 2012). In the present study, this method enabled the establishment and proliferation of shoot cultures from material derived from the crowns of mature trees.…”

“…Although little is known about the rooting of axillary shoot cultures established from crown material obtained from woody plants, in general the rooting rates are lower than yielded by basal shoots. Martínez et al (2012) reported that shoot cultures derived from the crown of a Q. robur tree displayed a low rooting capacity (3.3%), whereas shoot cultures collected from the same mature tree, but derived from basal sprouts, displayed a much higher rooting capacity (71.5%). Similar results have been reported for chestnut (Sánchez and Vieitez 1991) and Sequoia sempervirens (Bon et al 1994).…”

Plant Regeneration via Somatic Embryogenesis in Mature Wild Olive Genotypes Resistant to the Defoliating Pathotype of Verticillium dahliae

“…Moreover, further molecular analysis as well as a study of true-to-type phenotype of regenerated plants would be recommended, especially if embryogenic callus were kept for a long time in culture. In any case, taking into account that commercial olive micropropagation shows a strong genotype effect (Zuccherelli and Zuccherelli, 2002), regeneration and genetic fidelity of adult plants derived from somatic embryos open new opportunities to propagate recalcitrant cultivars, i.e., obtained material could be used as revitalized mother plants and further multiplied either in vitro , through nodal segmentation of elongated shoots, or in vivo , by rooted minicuttings, as reported in other woody species (Martínez et al, 2012; Georget et al, 2017).…”

Integrated analysis of the physiology, RNA, and microRNA involved in black locust (Robinia pseudoacacia) rejuvenation

“…Somatic embryogenesis can cause rejuvenation in mature Quercus robur [6]. Huang et al reported that, after five instances of repeated grafting of adult shoot tips onto juvenile rootstock in vitro, a rejuvenation phenomenon occurred in S. sempervirens [4].…”