Petri disease, a decline affecting young vines and named after Italian plant pathologist Lionello Petri (1875–1946), who in 1912 first reported brown wood streaking and dark gummy sap (see black goo) in declining American rootstock mother vines. However, it was not until the mid 1990s that the fungi Phaeomoniella (Pa.) chlamydospora and Phaeoacremonium spp. were identified as the primary causal agents. Affected vines (generally younger than six years old) appear stunted and weak and show greatly reduced tolerance of stress. Internal symptoms are primarily found in the rootstock and are characterized by dark brown and/or black streaking of the wood. It has been well documented that infections can originate during propagation but the progress and spread of the disease have been shown to depend on the health of the vine. Clean propagation planting material and careful planting help to minimize disease levels. See also trunk diseases.