Abstract
The phyllosphere supports a large and complex bacterial community that varies both across plant species and geographical locations. Phyllosphere bacteria can have important effects on plant health. The sweet chestnut (Castanea sativa Mill.) is an economically important tree species affected worldwide by the fungal pathogens Cryphonectria parasitica and Phytophthora cinnamomi. We examined the culturable phyllosphere bacterial community of the sweet chestnut at two nearby locations in Central Spain in order to know its geographical variability and to explore its potential as source of biological control agents against these two pathogenic fungi. The bacterial diversity at strain level was high but it varied significantly between locations; however, phylotype richness and diversity were more comparable. The isolates were affiliated with the phyla Actinobacteria, Firmicutes and Proteobacteria. Most of them were members of recognized bacterial species, with a notable proportion of representative of the genera Dietzia and Lonsdalea, but a small fraction of the strains revealed the existence of several potential novel species or even genera. Antagonism tests showed the occurrence in the chestnut phyllosphere of bacterial strains potentially useful as biological control agents against the two pathogenic fungi, some of which belong to species never before described as fungal antagonists. Chestnut phyllosphere, therefore, contains a great diversity of culturable bacteria and may represent an untapped source of potential biocontrol agents against the fungi causing blight and ink diseases of this tree species.
Highlights
The sweet chestnut (Castanea sativa Mill.) has been systematically cultivated since the Middle Age throughout southern Europe [1], from the Caspian Sea to the Atlantic Ocean
TP-random amplified polymorphic DNA (RAPD) fingerprinting was used as shortcut technique for grouping the phyllosphere isolates in a taxonomically meaningful way
From chestnut trees growing at two different stands in the mountain range of “Sierra de Tamames-Las Quilamas” (Salamanca province, Spain), we obtained a total of 227 phyllospheric bacterial isolates that grew consistently after cryopreservation and their genetic variability was investigated using random amplified polymorphic DNA techniques
Summary
The sweet chestnut (Castanea sativa Mill.) has been systematically cultivated since the Middle Age throughout southern Europe [1], from the Caspian Sea to the Atlantic Ocean. It covers more than 1.7 million ha in a discontinuous, scattered range, occupying coppices and orchards on acid soils [2]. The oomycete Phytophthora cinnamomi causes the ink disease of chestnut that is characterized by obstruction of the xylem vessels and exudation of blackish sap (due to air oxidation of tannins), resulting in a progressive decline of the uppermost shoots and of the whole crown [5]. The predicted global climate warming would be favourable for these two pathogenic fungal species [11], worsening the perspectives for chestnut forestry worldwide
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