Esca of Grapevine : A Disease Complex or a Complex of Diseases

Abstract

Over the last few years research on esca has led to considerable progress in our understanding of the aetiology, epidemiology and physiology of the disease and revealed its complexity. On the basis of the available information, esca can be considered: 1. a disease complex, in the sense that several interacting factors and microorganisms concur to produce the overall syndrome; 2. a complex of at least two distinct diseases: ‘white rot’ caused by Fomitiporia punctata or other wood-rotting fungi, and brown wood-streaking and gummosis, caused by one or more species of Phaeoacremonium infecting the woody tissue; 3. a real hadromycosis induced by one or more species of Phaeoacremonium or related genera, which in mature or old grapevines is further complicated by the white rot caused by F. punctata. Research has also shown that different syndromes are produced depending on the origin of the infections, the prevalence of the associated fungi and the order in which they become active, and environmental factors. Five syndromes can be distinguished: 1. “brown wood streaking” (Petri, 1912). This affects rooted cuttings, rootstocks, and grafted or mother plants and is caused by species of Phaeoacremonium or related genera, often without external symptoms; 2. “Petri grapevine decline”. This name has been proposed to designate a decline of young grapevines known under various local names (‘black goo’, ‘slow dieback’, ‘Phaeoacremonium grapevine decline’), which occurs when propagation material or young grapevines are infected, again by species of Phaeoacremonium or related genera; 3. “young esca”. This syndrome, which Petri thought would evolve in ‘esca proper’, is characterised by black or brown wood-streaking and xylem gummosis in actively growing grapevines, with or without external symptoms. It is also caused by species of Phaeoacremonium or related genera, like the brown wood-streaking of point 1 above; 4. “white rot”. When infection is through wounds and solely or mainly by F. punctata or other wood-rotting basidiomycetes, it is characterised by wood rot, which may or may not be accompanied by external (leaf and fruit) symptoms; 5. “esca proper”. This occurs when white rot develops in the trunks of mature or old vines together with, or after, the development of brown wood-streaking. This, the full-fledged esca syndrome, is caused by the combined or successive action of one or more species of Phaeoacremonium, occasionally accompanied by other fungi, and F. punctata.