Plant Performance and Metabolomic Profile of Loquat in Response to Mycorrhizal Inoculation, Armillaria mellea and Their Interaction

Amelia Camprubi,Francesc Garcia-Figueres,Fabrizio Colosimo,Luigi Lucini,Veronica Cirino,Paolo Bonini,Cinta Calvet,Jimena Solari

doi:10.3390/agronomy10060899

Abstract

A greenhouse experiment was established with loquat plants to investigate the role of arbuscular mycorrhizal fungi (AMF) in the control of the white root rot fungus Armillaria mellea and to determine the changes produced in the plant metabolome. Plants inoculated with two AMF, Rhizoglomus irregulare and a native AMF isolate from loquat soils, were infected with Armillaria. Although mycorrhization failed to control the Armillaria root infection, the increased growth of infected plants following inoculation with the native mycorrhizal isolate suggests an initial tolerance towards Armillaria. Overall, metabolomics allowed highlighting the molecular basis of the improved plant growth in the presence of Armillaria following AMF colonization. In this regard, a wide and diverse metabolic response was involved in the initial tolerance to the pathogen. The AMF-mediated elicitation altered the hormone balance and modulated the production of reactive oxygen species (mainly via the reduction of chlorophyll intermediates), possibly interfering with the reactive oxygen species (ROS) signaling cascade. A complex modulation of fucose, ADP-glucose and UDP-glucose, as well as the down-accumulation of lipids and fatty acids, were observed in Armillaria-infected plants following AMF colonization. Nonetheless, secondary metabolites directly involved in plant defense, such as DIMBOA and conjugated isoflavone phytoalexins, were also involved in the AMF-mediated plant response to infection.

Highlights

Loquat (Eriobotrya japonica (Thunb.) Lindl.) is a high-value crop mainly produced in EasternAsia and in the Mediterranean Basin, where the unusual phenology of the plant allows to collect the fruits in late winter
The plants inoculated with R. irregulare produced a slightly higher biomass than plants inoculated with the native loquat fungus (Table 1)
The results indicated that the mycorrhizal inoculation of loquat plants with both arbuscular mycorrhizal fungi (AMF) isolates significantly enhanced growth and development in low-nutrient soils

Summary

Introduction

Loquat (Eriobotrya japonica (Thunb.) Lindl.) is a high-value crop mainly produced in EasternAsia and in the Mediterranean Basin, where the unusual phenology of the plant allows to collect the fruits in late winter. During the last two decades, heavy decay symptoms in orchards located in the production areas of Southeastern Spain have been observed and associated to the replant disease syndrome known as soil fatigue Both abiotic and biotic factors can cause decay symptoms in trees. Armillaria mellea is a facultative necrotrophic pathogen, whose behavior is characterized by colonizing live radicular tissue in its parasitic phase and in its saprophytic phase, using dead tissue as a nutrient source The symptoms of this disease in the aerial part are typically nonspecific, such as wilting, chlorosis, loss of turgor in the leaves, which develop late and fall, and the gradual or sudden death of the tree [6]. When the environmental conditions and the amount of inoculum allow it, the honey-colored fruiting bodies can appear at the baseline of the affected plants, a characteristic that gives the common name to the species mellea, “honey fungus”

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Discussion

Conclusion