Grapevine Trunk Diseases---Esca

The first post related to grapvine trunk diseases was on Eutypa Dieback. Today, I'm writing about Esca.¹
Esca
General Information
The current understanding of Esca is that it is a disease complex with many fungi implicated as the causes of the disease. A number of the diseases manifested as "esca" are caused by the same fungi, but depending on the age of the vine and the duration of the infection can cause different symptoms.² Fungi Implicated¹

• Esca is a disease complex and the causative agents are considered to be the following:
  ⇾Tracheomycotic agents Phaeomoniella chlamydospora (Chaetothyriales, Herpotrichiellaceae) and Phaeoacremonium aleophilum (Diaporthales, Togniniaceae)
  ⇾Togninia minima was identified as the teleomorph of Pm. aleophilum
  ⇾Several basidiomycetes species the most common of which is Fomitiporia mediterranea (F. mediterranea)
  ⇾Eutypa lata and Stereum hirsutum could also play roles in the esca disease complex
  
• However, the main causal agents of Esca are considered to be the tracheomycotic agents Phaeomoniella chlamydospora (Pa. chlamydospora), Phaeoacremonium aleophilum (Pm. aleophilum) (teleomorph Togninia minima), and other Phaeoacremonium species
• Lifecycles of the major Esca complex agents are:
  ⇾Pa. chlamydospora and Pm. aleophilum are characterized by their aerial dispersal
  ⇾Spore liberation for Pa. chlamydospora is correlated to rainfall, while for Pm. aleophilum spore liberation occurs during the vegetative period without any link to rainfall
  ⇾Spores of Pa. chlamydospora and Pm. aleophilum penetrate the plant through pruning wounds
  ⇾Sources of inoculum and pycnidia for Pa. chlamydospora and perithecia for Pm. aleophilum have been observed on protected wood surfaces inside deep cracks
  ⇾Pa. chlamydospora and Pm. aleophilum can also be spread through vine propagation material
  ⇾F. mediterranea spreads by means of airborne basidiospores and regularly outcrosses in nature
  

Disease

• The five described syndromes of the esca complex are:
  (1) Brown/dark wood streaking (mostly affecting rooted cuttings)
  (2) Petri disease
  (3) Grapevine leaf stripe disease
  (4) White rot
  (5) Esca proper

• Brown/dark wood streaking
  ⇾Pa. chlamydospora and Pm. aleophilum are associated with brown wood streaking in young vines
  ⇾Brown vasculature observed when making a cross-section in very young plants (<2 years), is defined as dark wood streaking
  ⇾Can be observed as single or several xylem vessels and areas with darkened or brown necrosis around the pith
  ⇾The leaves do not yet show any symptoms of the fungal disease
  
• Petri disease
  ⇾Occurs in slightly older, but still young plantings (<7 years) and are caused by the fungi Phaeoacremonium minimum, Phaeomoniella chlamydospora, and by Cadophora luteo-olivacea
  ⇾The external symptoms of Petri disease affecting very young vines (from 1 year), include the complete cessation of growth, leaf chlorosis, loss of yield and a decline in vigour
  ⇾Shows the discolored vasculature
  ⇾The leaves may also show chlorosis and wither, and the vine can even die in its entirety

• Grape leaf stripe disease
  ⇾Mainly caused by Phaeoacremonium minimum and Pa. chlamydospora and can occur in both young and old vines
  ⇾Characteristic feature of this fungal disease is the tiger stripe pattern on the leaves
  ⇾This symptom is visible normally by the end of June, when high temperatures stress the vines
  ⇾ Reddish-brown patches on the leaves are observed in red cultivars, while yellow patches are more common on white grapes
  ⇾Grape leaf stripe affected vines produce grapes with less sugar and higher pH

• White rot
  ⇾Occurs in older vineyards
  ⇾Occurs in the trunk and branches of mature standing vines and is caused by F. mediterranea and⁄or other basidiomycetes
  ⇾The fungi break down lignin in the wood, leaving long white cellulose fibers and making the trunk brittle and fragile
  ⇾shows no external symptoms and is only perceptible when a cross-section of the wood is made
• Esca proper
  ⇾Is the combination of all fungi and symptoms that fall within the esca complex
  ⇾The trunk shows a discoloration of the wood as described for dark wood streaking and Petri disease, but also shows parts of the wood that are affected by white rot
  

• Other symptoms
  ⇾Characteristic spotting in the berry skin, described as "black measles" in the USA, is also observed
  ⇾Apoplexy characterized by the dieback of one or more shoots accompanied by leaf drop and the shrivelling and drying of fruit clusters
  
  

References:
1. C. Bertsch M. Ramírez‐Suero M. Magnin‐Robert P. Larignon J. Chong E. Abou‐Mansour A. Spagnolo C. Clément F. Fontaine, Grapevine trunk diseases: complex and still poorly understood, Plant Pathology, Volume62, Issue 2, April 2013, Pages 243-265.
2. WineSicence, Fungi in the grapevine, that’s rotten!, September 7, 2019.
3. WINETWORK, Grapevine Trunk Diseases, European Union Horizon 2020.
4. Gabriel Torres, UCCE farm advisor, Tulare County Grape Trunk Diseases and Management, Progressive Crop Consultant, October 3, 2019.