abstracts - INCDCSZ Brasov

3. Pathogenicity tests
At the end of the pathogenicity test, the presence of the inoculated fungi in the soil could not
be confirmed for all the pots. In the inoculated soils, Fusarium isolates were found again in 50 % of
the cases, R. solani was found only in 12.5 % and the other isolates were found in 62.5 % of the cases.
On the other hand, Fusarium strains were isolated from harvested tuber in 19 % of the cases, R. solani
in 76 % of the cases and the other strains were isolated in 26 % of the cases. These results show that
the repartition of the fungi in the soil depends on the ecological fitness of the strain inoculated. For
example R. solani seems to be attracted by the host plant. It is also possible that some inoculum did
not survive into the soil. A more reliable sampling method could be used for the detection of the
inoculum into the soil.
Thirty-one fungi out of the 33 strains were able to reproduce the atypical symptoms described
earlier. However, only 10 out of 33 strains reproduced symptoms similar to the one from which they
were isolated. One fungal strain could cause various types of symptoms and a given type of symptoms
could be caused by fungi belonging to different taxa. The only clear relationship between a fungal
species and a type of symptom was between R. solani and the occurrence of sclerotia. Apart from this
obvious evidence, no particular relationship could be established.
The isolation and identification procedure combined with the bioassay confirmed the
microbial nature of the superficial alterations of the tubers but also the diversity of the causal agents.
In order to relate the different symptoms with fungal species, potato varieties, geographic origins and
types of soil, the global set of data will be analysed by correspondence analysis.
To test whether atypical symptoms are caused by single or combinations of strains, a new bioassay
will be carried out, including bacterial and fungal strains. Additional strains of R. solani, Fusarium
spp. and Alternaria spp. will be tested, both alone and in coinoculation tests. For this, a new bioassay
in hydroponic conditions will be developed to visualize the symptoms on the tubers all along the
culture.
Acknowledgments This work is supported by Germicopa and Bretagne-Plants and is partly funded by
the Regional Council of Brittany
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