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A simple detached leaf assay provides rapid and inexpensive determination of pathogenicity of Pythium isolates to ‘all year round’ (AYR) chrysanthemum roots
Author(s) -
Pettitt T. R.,
Wainwright M. F.,
Wakeham A. J.,
White J. G.
Publication year - 2011
Publication title -
plant pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.928
H-Index - 85
eISSN - 1365-3059
pISSN - 0032-0862
DOI - 10.1111/j.1365-3059.2011.02451.x
Subject(s) - pythium aphanidermatum , biology , virulence , inoculation , root rot , pythium , mycelium , petiole (insect anatomy) , horticulture , spore , pathogenicity , botany , phycomycetes , oomycete , microbiology and biotechnology , veterinary medicine , biological pest control , pathogen , medicine , hymenoptera , biochemistry , gene
A detached leaf assay was developed to determine the pathogenicity of Pythium isolates to cut‐flower chrysanthemum roots. Leaves from young plants were excised and inoculated by insertion of a plug of mycelium into a slit cut in the excised petiole. After incubation leaves were assessed for presence and extent of necrosis. Necrosis indicated pathogenicity and was consistently confirmed by comparisons with whole plant inoculations. The rate of necrosis spread also gave some indication of virulence. Isolates of Pythium sylvaticum , P. ultimum and HS group were the most virulent, with a mean rate of spread of 14·6 mm per day, significantly ( P < 0·05) faster than the mean rate of spread, 1·6 mm per day, of less virulent isolates. Less virulent isolates included P. irregulare, P. oligandrum and P. aphanidermatum . The latter was unexpected, as P. aphanidermatum is an important species in pythium root rot epidemics in chrysanthemums elsewhere. The value of the detached leaf assay for screening large numbers of isolates was demonstrated in a survey of isolates from clinic samples from chrysanthemum nurseries and in a series of dilution‐plating experiments looking at numbers of Pythium propagules in commercial chrysanthemum beds showing root rot. In the survey, the predominant pathogenic species was identified as P. sylvaticum and the most likely source of infection was contaminated soil as opposed to blocking media or irrigation water, whilst in soil colonization studies the use of detached leaf assays demonstrated a relationship between pathogenic inoculum concentration in soil and the expression of root rot symptoms.