A simple detached leaf assay provides rapid and inexpensive determination of pathogenicity of Pythium isolates to ‘all year round’ (AYR) chrysanthemum roots

Abstract

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 14AE6 mm per day, significantly (P < 0AE05) faster than the mean rate of spread, 1AE6 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.

Assessing the effectiveness of oxathiapiprolin towardsPhytophthora agathidicida, the causal agent of kauri dieback disease

“…Detached leaf assays provide a simple measure of infectivity on host plants (Goth and Keane 1997; Pettitt et al 2011). They can be used to assess whether test compounds are preventative and/or curative (Cohen et al 2018).…”

Fitness Evaluation of Phytophthora infestans Isolates Collected from Punjab, Pakistan During 2017-18

“…The possible restraint during detach leaf assay according to study of Pettitt et al, (2011) is the possibility of pathogenicity reactions and the probable descent of detached leave parts before the assay may be successfully concluded. Mainly, the plant resistance tends to be compact after excision and in bioassay that presented here might be given the impression that non-pathogenic isolates were pathogenic in nature.…”

Primer informe de Nodulosporium (Xylariaceae) en Theobroma cacao L. en Chiapas, México y pruebas de patogenicidad

“…La inoculación en follaje se realizó con la técnica de hoja desprendida (Pettitt et al, 2011) sobre una charola plástica de 25 cm, con una suspensión de 1x10 8 esporas mL -1 , colocando esta suspensión sobre la superficie adaxial (haz) en un total de 10 hojas, replicado tres veces. En ambas pruebas se consideró un testigo absoluto en el que solo se aplicó agua destilada estéril siguiendo la misma metodología.…”