Abstract
Lavender species form the arbuscular mycorrhizal symbiosis and are at the same time highly susceptible to white root rot. In an attempt to evaluate the response of mycorrhizal Lavandula angustifolia L. to Armillaria mellea (Vahl:Fr) P. Kumm in a greenhouse experiment, plants were previously inoculated with an isolate of the arbuscular mycorrhizal fungus Rhizophagus irregularis (former Glomus intraradices BEG 72) and the influence of the pH growing medium on the plant-symbiont-pathogen interaction was tested in gnotobiotic autotrophic growth systems in which mycorrhizal inoculum was obtained from root organ cultures. After ten months growth dual-inoculated lavender plants grown in containers with a pasteurized substrate mixture produced a similar number of spikes than healthy plants and achieved equivalent plant diameter coverage. When the growing medium in the autotrophic systems was supplemented with calcium carbonate, the inoculation of lavender plantlets with R. irregularis at higher pH (7.0 and 8.5) media caused a significant decrease of A. mellea presence in plant roots, as detected by qPCR. Moreover, the observation of internal root mycorrhizal infection showed that the extent of mycorrhizal colonization increasedin plant rootsgrown at higher pH, indicating that tolerance to white root rot in lavender plants inoculated with R. irregularis could be associated to mycorrhizal establishment.
Highlights
Lavender species native of the western Mediterranean are the most economically important among herb crops due to their versatile use in phytochemical industries
Rhizophagus irregularis BEG 72 applied as bulk inoculum in container-grown lavender plants was very effective as plant growth stimulator, as reported before for other host plant species, both under controlled conditions and in field trials in which the fungus had been introduced in plant production systems (Estaún et al, 2003; Camprubi et al, 2008; Nogales et al, 2009)
Results obtained in the greenhouse experiment showed that mycorrhizal early inoculation with this selected Arbuscular mycorrhizal fungi (AMF) isolated from a high-pH soil in southern Catalonia (Camprubi & Calvet, 1996) alleviated the deleterious effect of the root rot fungus on container-grown lavender plants
Summary
Lavender species native of the western Mediterranean are the most economically important among herb crops due to their versatile use in phytochemical industries. They are commercially grown for essential oil extraction and as perennial drought-tolerant woody shrubs they are used in restoration and sustainable ornamental landscaping activities. Lavender forms the arbuscular mycorrhizal symbiosis, and benefits of plant inoculation with selected fungi have been reported by several authors (Azcón & Barea, 1997; Bakkali-Yakhlef et al, 2011; Karagiannidis et al, 2012). Arbuscular mycorrhizal fungi (AMF), present in natural soils and undisturbed ecosystems, develop their life cycle in association with the roots of most terrestrial plant species, being the most common symbiosis between plant and fungi.
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