Evaluation of selective media for the isolation ofFusarium solanivar.coeruleumandFusarium sulphureumfrom soil and potato tuber tissue

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Abstract
SUMMARY: A new selective medium containing pentachloronitrobenzene and 2‐aminobutane (the PAB medium) was developed for soil‐dilution plate enumeration of fungal propagules ofFusarium solanivar.coeruleumandF. sulphureumfrom field soil. Growth of ‘weed‐fungi’ was less on the PAB medium than on the previously developedF. solanivar.coeruleumisolation medium (the PM70 medium) and significantly more propagules ofF. solanivar.coeruleumwere detected.Propagule counts (x) ofF. solanivar.coeruleumandF. sulphureumfrom the PAB medium, after log10(x/10 + 1) transformation, were linearly related to the angular transformation of measurements of soil infectivity from the tuber bait method using the susceptible cv. Catriona. Slopes from disease‐inoculum regressions forF. solanivar.coeruleumandF. sulphureumin November and May were similar and this suggests that the mode of pathogenic action ofF. solanivar.coeruleumandF. sulphureumwas similar. Recently harvested tubers, inoculated in November, however, were more resistant to infection by both pathogens than stored tubers inoculated in May. Storage of air dry soil at 4°C for 6 months reduced the population ofF. sulphureumbut not the population ofF. solanivar.coeruleum.Whereas the PAB medium is recommended primarily for use in the isolation ofF. solanivar.coeruleumandF. sulphureumfrom field soil, the PM70 medium appears to be more suitable for recovery of these pathogens and others, includingPhoma exiguavar.foveatafrom diseased tuber tissue.