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

Mª Teresa Martínez,Isabel Arrillaga,María Amparo Pérez-Oliver,Ester Sales,Mª Del Carmen González-Mas,Elena Corredoira

doi:10.3390/f12121634

Mª Teresa Martínez, Isabel Arrillaga + Show 4 more

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https://doi.org/10.3390/f12121634

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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.

Highlights

IntroductionHolm oak (Quercus ilex L.) is one of the most widely distributed tree species in the Mediterranean basin and is the dominant tree species in the dehesas
Large differences were observed in the flushing capacity of the branch segments of trees growing in different areas
It is worthy to note that PL-T2 had the lowest basal phenols content (21.2 ± 2.7 μg/g dry weight (DW)), while presented the highest levels when confronted with P. cinnamomi (43.3 ± 4.5 μg/g DW). This high phenols content contrasted (p = 0.013) to those determined in E2 and E00 shoots sampled in infected plates (33.0 ± 5.3 and 34.3 ± 2.2 μg/g DW, respectively) that did not differ from levels determined in VA5 shoots confronted with Phytophthora cinnamomi Rands (Pc) (35.1 ± 3.1 μg/g DW). These results indicate that the response to Pc infection of the in vitro growing holm oak shoots was substantially dependent on the genotype, since the phenols content did not significantly increase in the E2 and VA5 genotypes while it doubled in PL-T2 plant material (Figure 7)

Summary

Introduction

Holm oak (Quercus ilex L.) is one of the most widely distributed tree species in the Mediterranean basin and is the dominant tree species in the dehesas. Since the 1990s, and in recent years, dehesas have been seriously affected by oak decline disease or “la seca”, which jeopardizes the long-term survival of this valuable ecosystem. The etiology of the disease is multiple and usually results from the interaction of several factors [4], such as aging and low natural regeneration of trees [5], the appearance of extreme climate events promoted by climate change including increased temperatures and altered precipitation regimes [6,7,8], and the emergence of new diseases and outbreaks of soil pathogens, mainly

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