Methyl jasmonate protects Norway spruce [Picea abies (L.) Karst.] seedlings against Pythium ultimum Trow.

The effect of methyl jasmonate (MeJA) was tested on the resistance of Picea abies seedlings against Pythium ultimum. Treatments with volatile MeJA dur ing 3 days (25 mu l 100 l(-1) air) protected seedlings up to 75%. This effe ct was unlikely to result from a direct fungitoxic effect of MeJA, as under the same conditions of treatment, growth in vitro of Pythium ultimum was n ot affected. Observations of possible changes on histological barriers such as lignin deposits showed no differences between control and treated plant s. MeJA induced the accumulation of free salicylic acid (SA) in all parts o f the seedlings, whereas bound SA only increased in hypocotyls and cotyledo ns. An increase in chitinase activity was detected in cotyledons already 2 days after exposure to MeJA. The results suggest that MeJA acts by stimulat ing defence responses of the host plant. No increase in endogenous jasmonic acid was found in spruce seedlings inoculated with Pythium nor MeJA. (C) 1 999 Academic Press.