Systematics, diagnostics and epidemiology of the fungal genus Armillaria
Species in the genus Armillaria (Fr.:Fr.) Staude are major root pathogens of woody
plants. A PCR-based technique was investigated aiming to develop a rapid and accurate
method for identification of Armillaria species. Armillaria taxonomy has been
extensively studied in Europe, North America and Australia. However, in Africa their
taxonomy remains uncertain. A. mellea and A. heimii are the main species described.
Morphological characteristics, somatic incompatibility, production of basidiomata in
vitro, amplified fragment length polymorphisms (AFLPs), DNA profiles generated by
polymerase chain reaction (PCR) amplification and restriction fragment length
polymorphisms (RFLPs) of the internal transcribed spacer (ITS) and the intergenic
spacer (lGS) regions of the ribosomal RNA (rRNA) gene cluster and phylogenetic
analyses were used for the characterization of Armillaria in Africa. Armillaria species
were successfully differentiated using PCR-RFLP-based techniques. A new Armillaria
species was found in tea plantations in Kenya with very distinct characteristics from A.
heimii and A. mellea. High variability within A. heimii was observed. The possibility of
this group being a complex of different species was investigated and it was concluded
that it was only one species, A. heimii.
The development of a suitable experimental system for the study of the pathogenicity of
A. mellea, the behaviour and growth of Armillaria in different types of soils and in
wood- and bark-chips were investigated. A successful experimental system was found to
work with Armillaria. New methods to study the growth and spread of Armillaria in
different substrates were successfully tested. There were no significant differences found
in the growth and spread of A. mellea between wood- and bark-chips. However, the
survival of A. mellea was more successful in deeper layers of wood-chip mulching.
Mulching had no effect on the A. mellea infection process, and the risk of healthy plants
being infected by colonised mulch was very low.