Acta Univ Latv (2005) 691: 59–70

Ethylene is involved in Trichoderma-induced resistance of bean plants against Pseudomonas syringae

Abstract

Trichoderma strains are effective biocontrol agents against a wide range of fungal plant pathogens. Current findings suggest that, in addition to microbial antagonism, the beneficial effect of Trichoderma is related to activation of plant defense responses. The aim of the present investigation was to study the effect of Trichoderma harzianum on oxidative enzyme activities and resistance to Pseudomonas syringae pv. phaseolicola of bean (Phaseolus vulgaris L.) plants. Special attention was focused on the role of ethylene as a signal mediating Trichoderma-induced responses. Both active and denatured fungal preparations induced sharp and transient increase of ethylene formation in bean leaves. The activity of both peroxidase (EC 1.11.1.7) and polyphenol oxidase (EC 1.10.3.2) increased in bean leaves after the treatment of derooted plants with active or inactivated Trichoderma formulations. Treatment with Trichoderma resulted in blocking of disease symptoms arising from inoculation with P. syringae. To demonstrate if the changes in defense responses and resistance against Pseudomonas were ethylene-dependent, bean seedlings were pretreated with 1-methylcyclopropene, a competitive inhibitor of ethylene action. Pretreatment with 1-methylcyclopropene led to a drastic acceleration of disease development both in control and Trichoderma-treated plants. The activities of peroxidase and polyphenol oxidase were suppressed by 1-methylcyclopropene treatment, suggesting that ethylene acts as one of the signals in Trichoderma-enhanced resistance against P. syringae.