Dieback of Pinus nigra Seedlings Caused by a Strain of Trichoderma viride

Four different fungi (Trichoderma viride, T. harzianum, Phomopsis sp., and Mortierella sp.) were isolated from 6-year-old Pinus nigra plants showing stunting and high incidence of mortality in a reforestation area of the National Park of Abruzzo, Lazio, and Molise (central Italy). Tests conducted on P. nigra revealed the pathogenic behavior of T. viride isolates with 30 to 80% mortality in artificially inoculated 2-year-old seedlings. The pathogenicity of these isolates was also observed in 10-year-old P. nigra trees and on lemon fruit. This result, in agreement with the constant isolation of T. viride from diseased plants, suggests the possible role of this fungus in the decline of P. nigra plants. T. harzianum and two reference isolates of T. viridarium and T. trixiae did not cause any symptoms, while Phomopsis sp. and Mortierella sp. caused limited necroses around the inoculation point in a few seedlings. Their role in the decline of P. nigra seedlings was considered irrelevant. According to phylogenetic analyses, pathogenic isolates of T. viride clustered in a very uniform group containing strains from different geographic origin and hosts, but none previously reported as a biocontrol agent.