Micropropagation, Characterization, and Conservation of Phytophthora cinnamomi-Tolerant Holm Oak Mature Trees

Abstract

Holm oak populations have deteriorated drastically due to oak decline syndrome. The first objective of the present study was to investigate the use of axillary budding and somatic embryogenesis (SE) to propagate asymptomatic holm oak genotypes identified in disease hotspots in Spain. Axillary budding was achieved in two out of six tolerant genotypes from the south-western region and in two out of four genotypes from the Mediterranean region. Rooting of shoots cultured on medium supplemented with 3 mg L−1 of indole-3-acetic acid plus 0.1 mg L−1 α-naphthalene acetic acid was achieved, with rates ranging from 8 to 36%. Shoot cultures remained viable after cold storage for 9–12 months; this procedure is therefore suitable for medium-term conservation of holm oak germplasm. SE was induced in two out of the three genotypes tested, by using nodes and shoot tips cultured in medium without plant growth regulators. In vitro cloned progenies of the tolerant genotypes PL-T2 and VA5 inhibited growth of Phytophthora cinnamomi mycelia when exposed to the oomycete in vitro. Significant differences in total phenol contents and in the expression profiles of genes regulating phenylpropanoid biosynthesis were observed between in vitro cultured shoots derived from tolerant trees and cultures established from control genotypes.

Genetic Transformation of Quercus ilex Somatic Embryos with a Gnk2-like Protein That Reveals a Putative Anti-Oomycete Action

“…Although plant conversion from somatic embryos in many hardwoods is considered an important bottleneck [ 15 ], in the present study plants from four independent transgenic lines were successfully recovered by applying the protocols previously described for holm oak somatic embryos [ 9 , 50 ]. The in vitro behaviour and growth of these transgenic plants were not affected by overexpression of the Cast_Gnk2-like gene.…”

“…P. cinnamomi is one of the most destructive and widely spread oomycetes throughout the world, and it has been associated with the death of numerous different plant species, including many woody species [ 8 ]. To date, there are no efficient chemical methods available for controlling this oomycete [ 9 ]. The most effective means appears to be the afforestation of affected zones with genotypes that are tolerant to P. cinnamomi .…”

Effect of Methyl Jasmonate in Gene Expression, and in Hormonal and Phenolic Profiles of Holm Oak Embryogenic Lines Before and After Infection With Phytophthora cinnamomi

“…Also, during pathogen attack the phenylpropanoid pathway genes were found to be overexpressed, resulting in increasing activities and accumulation of various phenolic compounds (Yadav et al, 2020 ). More recently, our group demonstrated that axillary shoots from tolerant holm oak genotypes established in vitro had higher total phenol content than other susceptible genotypes (Martínez et al, 2021 ).…”

“…Recently, a national program for breeding and conservation of cork-and holm oak genetic resources against the decline syndrome has also been established. For exploiting all the genetic variability existing in natural populations, superior genotypes should be vegetatively propagated, but this task is hampered by the low rooting capability of oak cuttings, which is even reduced with the aging of the trees (Martínez et al, 2020(Martínez et al, , 2021. In this context, biotechnological tools such as somatic embryogenesis constitute an interesting alternative allowing clonal propagation of holm oak adult trees (Blasco et al, 2013;Barra-Jiménez et al, 2014;Martínez et al, 2017Martínez et al, , 2020Martínez et al, , 2021, although acclimatization of generated plants needs to be improved.…”

“…For exploiting all the genetic variability existing in natural populations, superior genotypes should be vegetatively propagated, but this task is hampered by the low rooting capability of oak cuttings, which is even reduced with the aging of the trees (Martínez et al, 2020(Martínez et al, , 2021. In this context, biotechnological tools such as somatic embryogenesis constitute an interesting alternative allowing clonal propagation of holm oak adult trees (Blasco et al, 2013;Barra-Jiménez et al, 2014;Martínez et al, 2017Martínez et al, , 2020Martínez et al, , 2021, although acclimatization of generated plants needs to be improved. Furthermore, combining somatic embryogenesis with chemical elicitors it is possible to induce resistance triggering natural plant defenses, as a complementary strategy to breeding programs developed to obtain resilient plant material (Morcillo et al, 2020).…”