Retardation of Fusarium wilt symptoms in tomato by pre- and post-inoculation treatments of the roots and aerial parts of the host in hot water

The effects of hot water treatments of the roots, aerial parts or entire plant of tomato on the severity of Fusarium wilt symptoms was investigated.

Symptoms developing following root inoculation were markedly delayed by treatment of the roots or of the entire plant at time-temperature combinations which caused some cell death to parts of the root system. Treatments at 48–49°C for 30 sec were the least severe of the treatments which gave protection. Protection was not effective against stem inoculations but was associated with a reduction in stem colonization. Plants showed some degree of systemic protection against a root inoculation following heat treatment of the aerial parts at 48–49°C for 30 s, but to a lesser extent than that induced by root treatments. The highest levels of protection were obtained when roots or aerial parts were treated 12–48 h before root inoculation. Only the root treatments were effective when applied 48 h after inoculation. Drastic pruning of roots did not reduce the effectiveness of the heat treatment and in fact root pruning itself induced some protection.

The protection induced by the hot water treatments seems to depend on a transient state of resistance, which is similar to that induced by some biotic elicitors.