Phaeomoniella chlamydospora (Petri disease)

Vitis vinifera is known to host 29 fungal diseases (Wilcox et al., 2015), including the so-called grapevine trunk diseases (GTDs) affecting the vascular system and, in consequence, the wood, leaves and berries of the host plant. Esca, as one of the most destructive diseases within GTDs, is a complex disease whose symptoms may develop from the concomitant action of several factors (Mugnai et al., 1999; Graniti et al., 1999; 2000; Chiarappa, 2000; Fontaine et al., 2016; Mondello et al., 2018; Fischer and Peighami-Ashnaei, 2019). Petri disease (Surico, 2001), a well-known disease of young grapevine worldwide, is now generally accepted as a major component of the esca disease complex. The consistent isolation of fungi from discoloured or decayed wood of affected grapevines indicates a close relationship between particular stages of wood deterioration and individual species of fungi (Larignon and Dubos, 1997; Scheck et al., 1998; Mugnai et al., 1999; Bertsch et al., 2013). Petri disease, thought to be caused by fungi such as P. chlamydospora (only the anamorph is known) and/or Phaeoacremonium minimum (Togninia minima as teleomorph), is distinct from esca proper which, in addition to wood discolouration, is characterized by a more or less intensive white rot evident inside the trunk and main branches (Graniti et al., 2000; Fischer, 2006).

The development of esca complex-related symptoms is evident in the wood, on the berries and on the leaves. External symptoms can be of two types, chronic or acute. In the wood, symptoms attributed to P. chlamydospora (and/or P. minimum, and/or other species, for instance belonging to the genus Cadophora) comprise small, dark spots in cross sections of the wood, which appear as deep brown or black streaks in longitudinal section (Mugnai et al., 1999; Mondello et al., 2018). In cross section, these spots are sparsely distributed or arranged in groups around an annual growth ring or close to the pith (Mugnai et al., 1999). Symptoms on the leaves consist of light-green or chlorotic spots between the veins, which spread out over time to the distal part of the shoots, become increasingly necrotic and resulting finally in a 'tiger-stripe' pattern. Wilt symptoms are also evident in the crown. Symptoms on the berries comprise minute, dark-brown or purple spots on the skin, which are scattered or distributed in bands. In the later stages of the disease, cracks may form.

In kiwifruit orchards, foliage becomes chlorotic, with spots increasing in size over the year. Leaves wilt and fall prematurely. Fruits are smaller than usual and/or do not reach full maturity. Wood symptoms include wood discolouration and decay (Marco et al., 2000a). In olive trees, branch canker and twig dieback have been described by Úrbez-Torres et al. (2013).

Differentiation between esca proper and Petri disease is only possible on the basis of wood symptoms. In summary, the following syndromes associated with wood discolouration are thought to be caused by P. chlamydospora (and/or P. minimum, and/or other species): brown wood-streaking, wood discolouration of rooted cuttings, slow dieback, black goo and decline of young grapevines (Mugnai et al., 1999; Mondello et al., 2018).

For a number of centuries, esca and related diseases such as Petri disease have accompanied the history of the vine (Mugnai et al., 1999; Surico, 2000). In recent years, these diseases have reappeared in vineyards all over the world in a more destructive manner than ever before. As a consequence, vineyards have experienced a dramatic shortening of their productive life and increased management costs.

No accurate data is available on the economic impact of esca and Petri diseases. In most European wine-growing countries, these diseases are estimated to have reached incidences of more than 10%. In southern Europe, these diseases are found in all wine-growing regions, affecting 90-100% of vineyards and increasing annually by approximately 5% (Mugnai et al., 1999). Symptoms of Petri disease, assignable to Phaeomoniella chlamydospora and/or Phaeoacremonium aleophilum [P. minimum], are now frequently reported on vines younger than 8-10 years. With the restructuring of vineyards in Europe and elsewhere, an increasing number of young vines have been found to be affected by the disease, often resulting in time-consuming and costly replantation. This has led to the suggestion that the problem is caused, at least partly, by introducing the pathogens to vineyards in pre-infected plant material (Ridgway et al., 2003; Whiteman et al., 2003). Additional measures may, therefore, be necessary to reduce the possible sources of inoculum during grapevine propagation.