M. Ongena et al., Systemic induction of phytoalexins in cucumber in response to treatments with fluorescent pseudomonads, PLANT PATH, 49(4), 2000, pp. 523-530
The Pseudomonas putida isolate BTP1 and its sid(-) mutant M3 were recently
reported to protect cucumber against Pythium aphanidermatum root rot. This
protection was mainly associated with an accumulation of antifungal phenoli
cs in the treated roots. In this study, analyses of root extracts from spli
t-root experiments showed that these phytoalexins were produced systemicall
y. Indeed, several antifungal molecules accumulated similarly in both treat
ed and nontreated root parts of plants protected against P. aphanidermatum
with BTP1 or M3. In addition, analyses of leaf samples also revealed increa
sed amounts of fungitoxic molecules in PGPR-treated plants, although the na
ture of these molecules appeared to be different from those detected in roo
ts. The antifungal compounds isolated both from roots and leaves were mainl
y detected in acid-hydrolyzed extracts containing aglycones. These results
suggest that PGPR can elicit phytoalexins systemically in cucumber and that
the overall defence response is not based on a single phytoalexin but is c
hemically complex and organ-specific.