Protection of pruning wounds on kiwifruit by Trichoderma harzianum and effects on the host plant

Decay of kiwifruit (Actinidia deliciosa var. deliciosa) is a recently discovered chronic wood disease, widespread in Italy, which causes reduced productivity and longevity of vineyards. The disease is highly dangerous, is usually underestimated and is difficult to eradicate once present. Different pathogenic fungi, above all Phaeoacremonium aleophilum and Fomitiporia mediterranea, are known to cause the disease. The main route for infection in plants appears to be through pruning wounds. In order to develop low-impact strategies for sustainable agriculture, we investigated the use of Trichoderma harzianum as a potential defence agent on summer and winter pruning wounds, to prevent disease development. During the summer, 1-year-old shoots from potted plants were cut and immediately treated with a T. harzianum suspension; the formation of healing callus on wounds was followed, and a better developed callus, together with a shorter callusing period, were observed in treated plants compared to the control. The physiological mechanisms involved in wound healing were investigated by measuring the concentration of the growth promoter hormone indole-3-acetic acid (IAA) in the pruned shoots, using gas chromatography-mass spectrometry (GC-MS). Changes in the level of endogenous free IAA were observed during the first 8 days after pruning, suggesting a possible implication in callus formation. Furthermore, the response of winter pruning wounds, treated with Trichoderma, to artificial infection with Phaeoacremonium aleophilum was investigated, through re-isolation of the pathogen from inoculated shoots. The results are discussed.