Dissertation committee:
Αμαλία Δ. Καραγκούνη Καθηγήτρια (Επιβλέπουσα), Γιώργος Διαλλινάς Καθηγητής, Δημήτρης Χατζηνικολάου Αναπληρωτής Καθηγητής
Summary:
The aim of the present thesis was to examine specifically the biocontrol
capacity of the phytopathogenic fungi Rhizoctonia solani and Fusarium
oxysporum f.sp. lycopersici via indigenous strains of Streptomycetes.
In order to achieve the goal mentioned above, a total of 606 Streptomycetes,
which were isolated from different habitats of Greece and belong to the
collection of the Microbiology Laboratory of the Faculty of Biology of the
University of Athens, have been examined in relation to their ability to
control the growth of the phytopathogenic fungi Rhizoctonia solani and
Fusarium oxysporum f.sp. lycopersici in vitro, in solid cultures. Under the
criterion of their high anti-fungal activity twelve micro-organisms were
selected for further examination.Culture extracts from the selected
Streptomycetes have been concentrated and fractionated based on both their
molecular weight and their polarity. The fractions occurred were examined in
relation to their anti-fungal activity and it was shown that the bioactive
metabolites are polar compounds. The results also showed that the same
Streptomycetes inhibit the growth of each of the two phytopathogenic fungi
differently, i.e. their anti-fungal activity is specialized, since some of
their micro-molecular metabolites inhibit the former and a combination of
micro- and mega-molecular metabolites the latter.The effectiveness of the
selected Streptomycetes in controlling both the symptoms of pathogenic
behaviour caused by the fungus Rhizoctonia solani in bean plants and cases of
wilting caused by the fungus Fusarium oxysporum f.sp. lycopersici in tomato
plants was also examined through in vivo experiments. Different application
methods of the examined biocontrol agents were tested in each infected plant,
in order to estimate the easiest and most effective use in the field; at the
same time the capability of the selected Streptomycetes to protect the plants
against the fungi, promoting their growth, was also examined via in vivo
trials. From the total evaluation of the results of the in vivo biocontrol
trials it has been concluded that the most effective biocontrol agent against
the phytopathogenic fungus Rhizoctonia solani DSM843 was Streptomyces GRE 25
(Streptomyces rochei), while against the phytopathogenic fungus Fusarium
oxysporum DSM62059 was Streptomyces GRE 25 (Streptomyces rochei) and OL 7
(Streptomyces sp.). Additionally, the most efficient way to use the
Streptomycetes was by covering the plant seeds with their spores prior
planting. The Streptomycetes GRE 25 and OL 7 promoted the sprouting of the
plants. They also promoted the rest growth parameters of tomato plants and,
therefore, they could be characterized as tomato growth promoters. However, the
Streptomyces GRE 25 could not promote the growth of bean plants. Subsequently,
the mechanism of its activity as an effective biocontrol agent against
Rhizoctonia solani in the field remains to be discussed.
Keywords:
Biocontrol, Streptomyces, Actinobacteria, Rhizoctonia solani, Fusarium oxysporum
