Indagini sugli endofiti fungini, patogeni e non, riscontrati su Quercus spp. e sulle reciproche relazioni antagonistiche
Author(s)
Librandi, Immacolata
Date Issued
September 17, 2008
Type
Doctoral Thesis
Abstract
Forest decline is a typical complex disease in which trees, already weakened, are subjected to attack of weakness pathogen that leads the plants to death. Many of these weakness pathogens are agents of bark necrosis, even present in an asymptomatic, endophytic status in healthy trees and that can evolve into pathogenic colonization and trigger the decay.
In the healthy tissues of trees, together with the endophytic fungal pathogens, many others non-pathogens have been found. Among these, several species known to be antagonist against pathogens were reported. Sometimes, the increased incidence of the pathogens seemed to correspond to a decrease of non-pathogens species; this suggests a possible interdependence between pathogens and non-pathogens species.
In such sense we hypothesized that the antagonism between pathogens and non-pathogens species inside plant tissues, could have important implication on the ability of the endophytic pathogens in switching to their pathogenic status.
Asymptomatic plants of Quercus spp were studied in order to explain the influence on the association and on incidence of each pathogen and non-pathogen endophyte in relation with some organs of the tree (buds, branches of
different age), the host species (Quercus cerris, Q. ilex, Q. pubescens, Q. robur, Q. suber), the health status of the forest (with or without decline symptoms), and the environmental conditions of the site (especially the altitude).
Possible antagonism phenomena between the main species of two groups (pathogen and non pathogen) have been tested in vitro.
Particular attention has been addressed to Biscogniauxia mediterranea, one of the most important weakness pathogen on decline of Quercus spp. in the Mediterranean area.
Many pathogens and non-pathogens species of fungi in many organs of the healthy trees, without symptoms of decay, has been consistently isolated. The larger part of pathogenic species, mainly secondary pathogens (weakness pathogens), are agents of cortical necrosis.
The incidence of each single endophyte species, such as their association, resulted to be clearly influenced by the organ and, mainly, by the Quercus species, by the altitude, by the decline status of trees.
The forest decline seems to be somehow related to the increase of pathogenic species incidence and to the contemporaneous decrease of non-pathogenic species.
Many of non-pathogenic endophytes have shown clear antagonist behaviour against pathogens: by spatial competition (e.g. Aureobasidium pullulans and Cladosporium cladosporioides), by means of antagonistic substance (Epicoccum nigrum, Gliocladium roseum and Trichoderma viride), and by mycoparasitism (Gliocladium roseum and Trichoderma viride).
Additional information
Dottorato di ricerca in Protezione delle piante
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