Propagation of mature Quercus ilex L. (holm oak) trees by somatic embryogenesis

Abstract

Somatic embryogenesis from in vitro leaf and shoot apex explants excised from axillary shoot cultures established from two mature Quercus ilex trees has been developed. Somatic embryos (SE) were obtained from both explant types and genotypes evaluated, although embryogenic frequencies were influenced by the genotype, auxin concentration, and explant type. The explants were cultured on Murashige and Skoog salts and vitamins, supplemented with 500 mg L -1 casein hydrolysate (CH) and different concentrations of indole-3-acetic acid or α-naphthalene acetic acid (NAA) in combination with 2.22 µM 6-benzylaminopurine (BA). In both genotypes, shoot apex explants were more responsive than leaf explants. The best results were obtained with apex explants of clone Q3 (11%) cultured on medium with 21.48 µM NAA plus 2.22 µM BA. This combination was also effective for initiating SE from leaf explants, although the induction rates were lower (1-3%). Embryogenic lines were maintained by repetitive embryogenesis following culture of nodular embryogenic structures on Schenk and Hildebrand medium without plant growth regulators. Low embryo multiplication rates were obtained when torpedo or early cotyledonary SE were used as initial explant for embryo proliferation, or when glutamine or CH (500 mg L -1 ) was added to proliferation medium. For germination, cotyledonary-stage SE were isolated and stored at 4ºC for 2 months. After cold storage, SE were cultured on germination medium consisting of Gresshoff and Doy medium, supplemented with 0.44 μM BA and 20 μM silver thiosulphate. Under these conditions, plantlets were regenerated from 21-66.7% of the SE generated for both genotypes.

High-Efficiency Somatic Embryogenesis from Seedlings of Koelreuteria paniculata Laxm.

“…Moreover, as observed in other studies, the embryogenic potential of calluses declined with incubation time. The number of somatic embryos obtained from calluses and germination rates were inversely related to the length of the culture period, which is consistent with the findings of conifer and holm oak SE studies [30,35,54]. Thus, maintaining embryogenic potential and shortening the culture cycle remain key issues in K. paniculata tissue culture.…”

“…In addition, the genotype also has an effect on embryogenic callus induction rates. Park et al [35] determined that SE induction was under strong genetic control in white spruce, similar results were also obtained in the study about holm oak. Although the current study, involving seeds from a half-sibling family, attempted to eliminate the influence of genotypes, the effect of different seeds could not be ignored during the induction and development of somatic embryos.…”

“…The choice of plant materials also plays a crucial role in plant regeneration [47]. Past studies about SE have revealed that the development stage, explant site, and the genotype of explants affect SE [12,35,48]. In the current study, we obtained aseptic seedlings from immature seeds, and plantlet stems were then used to induce embryogenic calluses.…”

“…Similarly, NAA has been reported to influence somatic embryo development in holm oak and Eucalyptus camaldulensis Dehn. [28,35]. In the study about Elaeis guineensis, the ability of NAA to promote somatic embryo development is poor compared with other PGRs [27].…”

Effect of elicitors on holm oak somatic embryo development and efficacy inducing tolerance to Phytophthora cinnamomi

“…Recently, a holm- and cork-oaks genetic improvement program to alleviate the “seca” syndrome has been launched by the Spanish Government (National Rural Development Program 2014–2020) cofunded by the European Agricultural Fund for Rural Development (EAFRD). Biotechnological tools allowing clonal propagation of selected resistant genotypes such as axillary budding 15 or somatic embryogenesis 14 , 16 – 18 are available, although acclimazation of generated plants needs to be improved; also, the induction of systemic resistance, triggering natural plant defenses by the use of elicitors, may offer complementary strategies to breeding programs developed to obtain resilient plant material.…”