An investigation into the detection, identification, differentiation and pathogenicity of Fusarium oxysporum f.sp. narcissi.
Basal rot of Narcissus caused by Fusarium oxysporum f.sp. narcissi is the major limiting
factor for the increased export of ornamental bulbs from the United Kingdom. There is no
known resistance to the disease amongst commercial cultivars. The purpose of this study was
to develop techniques for the rapid detection and identification of the pathogen in bulbs,
culture and soil, and to develop serological and biochemical tests to investigate differences
amongst isolates of this forma specialis from a range of countries.
Significant differences in virulence were observed between the isolates tested, two being
identified as avirulent. Results suggest that there is wider morphological variation within this
forma specialis than previously recorded. Isolates stored at -80°C have remained viable over
a three year period. Thirty three species and varieties of Narcissus and seventeen cultivars
were screened for resistance to the pathogen. Accessions were either wholly resistant,
partially resistant (a variable portion of the bulbs infected) or susceptible. Accessions
identified as resistant are now being used as parents in a resistance breeding programme.
F. oxysporum Esp. narcissi isolates of low virulence and avirulence showed greater
agglutination of microconidia with Narcissus pseudonarcissus lectin. In addition increased
lectin levels were found in cultivars showing greater disease resistance; this suggests a
possible host pathogen interaction. Polyclonal antisera were elicited against extracts of
isolates and a specific and sensitive enzyme-linked immunosorbent assay was developed for
the detection of the pathogen in bulbs. Little cross-reactivity was shown by other bulb-rotting
fungi. A direct correlation was observed between positive results in the ELISA and recovery
of the pathogen on selective media. The ELISA which was developed will be field evaluated
with growers during the coming season. In indirect ELISA and Western blotting of fungal
extracts, all fungi outside the genus Fusariwn showed consistently low binding. Isolates of
F. oxysporum f.sp. narcissi could be discriminated from other Fusarium species and further
split into a series of sub-groups. Avirulent isolates or isolates of low virulence showed
differential binding to the PAbs. Other sub-groups were not related to virulence. Western
blotting allowed greater differentiation of isolates and bands specific to F. oxysporwn f.sp.
narcissi were identified. Serological detection of the pathogen in soil proved possible through
the inclusion of a soil enrichment stage with a selective medium.