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Endophytism in forest trees. (Monografia o trattato scientifico)

Type

Prodotto della ricerca (Classe)
Monografia o trattato scientifico (Classe)

Label

Endophytism in forest trees. (Monografia o trattato scientifico) (literal)

Anno

2004-01-01T00:00:00+01:00 (literal)

Alternative label

Ragazzi A., Moricca S., Dellavalle I. (2004)
Endophytism in forest trees.
Accademia Italiana Scienze Forestali, Firenze, 2004
(literal)

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Ragazzi A., Moricca S., Dellavalle I. (literal)

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Firenze (literal)

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Italian plant pathologists began to focus their attention on endophytic fungi in 1995- 1996, after many fungi were isolated both from healthy and from declining oak trees and found to be endophytes. Studies on oak decline since the 1980s had earlier led researchers in Italy and other countries in and outside Europe to the conclusion that, in accordance with the mode1 of MANION (1991), fungi were among the contributing causes of oak decline. Of the many fungal species isolated, on different types of stands, from various tree organs and tissues, a number thus were endophytes, and researchers proceeded to study them to understand the role these endophytes might have ecologically and in causing the decline. As a result, two Research projects were presented: l Weakness fungal parasites in oak-decline: enduphytism in their adaptation strategy (1999). 2 Role of fungal endophytes in oak decline (2001). These projects had the following aims: 1 To isolate and identify endophytic fungi on a range of sites, at different times of year, from trees varying in health condition and age, and from different tree organs and tissues. 2 To identify fungal populations. 3 To characterize fungal species at a molecular level. 4 To determine genetic variation in endophytic fungal populations. 5 To verify the pathogenicity of the fungal species isolated. 6 To ascertain the effect of water stresslnutrient deficiencies on the fungal species isolated. 7 To ascertain how penetration and colonisation occur. 8 To ascertain the models of inoculum transmission. The results of the first Project were presented at a national meeting organised by Prof. Francesco Marras and Prof. Antonio Franceschini, both from the Dipartimento di Protezione delle Piante, Sezione di Patologia vegetale, Università degli Studi di Sassari (Department of Plant protection, Plant pathology section, University of Sassari) at Sassari-Tempio Pausania, 19-2 1 May 2002. The findings of the experiments conducted in the second project, on the other hand, are gathered and presented to the national and international scientific community through the present book, which describes the research that has been and is being done in Italy in order to understand: l the ecological role of fungal endophytes in forest populations; 2 the role of endophytes in the onset and progression of oak decline. The chapters of the book begin with a historical overview exarnining the nature of endophytes in relation to plant pathogens, and asking various questions about the ecological role of fungal endophytes in forest populations, and the role of endophytes in the onset and progression of oak decline. In parallel with investigations on fungal endophytes, in the last 30 years studies were canied out on bacterial endophytes of forest trees and of woody plant species. Funga1 endophytes often occur in forest trees without causing visible symptoms. In addition, fungal taxa are not only numerous, but also distant from each other phylogenetically. As a result, traditional identification procedures (morphological, physiological, biochemicalj are not always completely reliable. This deficiency has recently been overcome by molecular techniques, which exploit the natura1 differences inside nucleic acids to detect, identify and characterize fungal taxa, to explore their diversity as well as to gain information on gene function. As an example of how molecular techniques can be used for the detection and diagnosis of fungal endophytes, another chapter deals with real-time PCR as a quantitative means to detect the occurrence in planta of Biscogniauxia mediterranea irrespective of the physiological state of a tree. The extensive geographical distribution in Italy of fungal endophytes most comrnonly associated with declining oaks is also described. These endophytes are shown to be asymptomatic as long as the trees they occur in are healthy, but to become pathogenic and start producing symptoms when the tree comes under stress. Endophytes have been isolated from oaks in more than 80 sites, from the north to the south of Italy and including the larger islands of Sicily and Sardinia. The most commonly isolated endophytes are: Biscogniauxia mediterranea, Cytospora sp., Colpoma sp., Coryneum sp., Discula quercina, Diplodia mutila, Phoma sp., Phomopsis sp., Tubakia dryina. At the same time, some fungal species that are known antagonists to many pathogens have also been found; they are: Acremonium sp., Aureobasidium sp., Cladosporium sp., Epicoccum sp., Gliocladium sp. and Trichoderma sp. B. mediterranea and D. mutila have been examined by optical and electronic microscopies to determine how these agents colonise the trees and what chanya they undergo histologically and cytologically during the colonisation process. On both the leaves and the wood of their hosts, B. mediterranea and D. mutila may switch to a parasitic state; the severity of their parasitism then depends on the tree species colonised. The occurrence of this widely varied assemblage of endophytes has been related in Italy to a phenomenon thought to be an inciting cause of oak decline, namely water stress, which is quantified on the basis of the midday water potential (MWP) and the predawn water potential (PWP). The bioactive metabolites that many fungal endophytes produce have also been studied. Bioactive metabolites have different biosynthetic pathways and chemically belong to different groups. Tubakia dryina, the agent of brown spot on many oak species, is especially common in northem Italy, where it is frequently isolated from the asymptomatic leaves, buds and shoots of Q. robur and Q. cerris. This fungus is strongly disadvantaged by a rapid-onset decline, so that the switch to the pathogenic state is probably connected with growing conditions that are not connected with water stress. A case study from Sicily is also reported. Since Sicily is an island, it may well contain assemblages of endophytes different from those on the Italian mainland, and indeed, besides some endophytes the island has in cornrnon with other parts of the country, some were also found that did not occur elsewhere: Coniochaeta tetraspora, Curvularia lunata, Munkovalsaria rubra, Seirnatosporium glandigenium. In parallel with the above mentioned studies on oaks, the effect of climate change on fungal endophytes was investigated in Fagus sylvatica by studying the assemblage of endophytes on the bark of twigs. The most common endophytes on this tree species were: Botryosphueria quercuum, Discula umbrinella, Neohendersonia kickxii, Aposphaeria sp. and Cryptosporiopsis sp. At the same time the effect of SDBS aerosol spray on endophytes in E. sylvatica seedlings was studied in the greenhouse. Endophytic fungi colonised twigs of SDBS-sprayed trees significantly more slowly than they did the twigs of unsprayed control trees. Some aspects of endophytic fungi in grasses are also dealt with: 1. the association of clavicipitaceous fungi; 2. the relationship between the reproductive system of the host tree and that of the endophyte; 3. the defensive mutualism of the symbiont; 4. the detection, distribution and incidence of seed-borne endophytes; 5. non-clavicipitaceous fungal endophytes in grasses. The purpose here was to explore parallels with forest trees, and to see whether some study models worked out long ago for herbaceous species might also be applicable to forest trees. Lastly, to round off the knowledge acquired in Italy about the relation between endophytes and forest trees, it seemed of interest to examine those insects that pass part of their life-cycle inside a tree host, during which time they act effectively like endophytes. (literal)

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-Ragazzi A., Dipartimento di Biotecnologie agrarie, Sez. Patologia vegetale, Università degli Studi di Firenze, Piazzale delle Cascine 28, I-50144 Firenze, Italy -Moricca S., Dellavalle I., Istituto per la Protezione delle Piante, CNR, Sez. di Firenze, Via Madonna del Piano 10, I-50019 Firenze, Italy (literal)

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