Phytotoxins produced by fungi associated with grapevine trunk diseases

Abstract

Up to 60 species of fungi in the Botryosphaeriaceae family, genera Cadophora, Cryptovalsa, Cylindrocarpon, Diatrype, Diatrypella, Eutypa, Eutypella, Fomitiporella, Fomitiporia, Inocutis, Phaeoacremonium and Phaeomoniella have been isolated from decline-affected grapevines all around the World. The main grapevine trunk diseases of mature vines are Eutypa dieback, the esca complex and cankers caused by the Botryospheriaceae, while in young vines the main diseases are Petri and black foot diseases. To understand the mechanism of these decline-associated diseases and the symptoms associated with them, the toxins produced by the pathogens involved in these diseases were isolated and characterised chemically and biologically. So far the toxins of only a small number of these decline fungi have been studied. This paper presents an overview of the toxins produced by the most serious of these vine wood pathogens: Eutypa lata, Phaeomoniella chlamydospora, Phaeoacremonium aleophilum and some taxa in the Botryosphaeriaceae family, and examines how these toxins produce decline symptoms. The chemical structure of these metabolites and in some cases their vivotoxin nature are also discussed.

Keywords: black dead arm; Botryosphaeria canker; Eutypa dieback; Fomitiporia; Phaeoacremonium; Phaeomoniella; esca; eutypiosis; grapevine trunk diseases; phytotoxins.

Figure 1

Symptoms of Eutypa dieback in (A) vine leaves and (B) new vine shoots; (C) Characteristic V-shaped necrosis of a vine trunk.

Figure 2

Chemical structures of Eutypa lata metabolites and derivatives: eutypine, eutypinol, O-methyleutypine, O-methyleutypinol, eutypin carboxylic acid analogue (1-5), 3-(3,4-dihydroxy-3-methyl-1-butynyl)-4-hydroxy-benzaldehyde, 2-(3,4-dihydroxy-3-methyl-1-butynyl)-4-hydroxymethyl-phenol, 3-(3,4-dihydroxy-3-methyl-1-butynyl)-4-hydroxy-benzoic acid (6-8), 2-iso-propenyl-5-formylbenzofuran, siccayne, eulatinol (9-11), eulatachromene and its derivatives (12 and 17-19), epoxidised chromanones (13-14), eutypoxide B and allenic epoxycyclohexane (15-16).

Figure 3

(A) Comparison, after 24 h and at 50 μg/mL, of the toxicity of the methanol control (C) and of the primary metabolites eutypine 1, eutypinol 2, 2-iso-propenyl-5-formylbenzofuran 9, siccayene 10, eulatinol 11, and eulatachromene 12, in a grape leaf bioassay; (B) comparison, after 24 h and at 10, 25, 50 and 100 μg/mL, of phytotoxicity of the methanol control (C) and eulatachromene (12) (redrawn with modifications from Figure 5 in [28]).

Figure 4

Toxicity of metabolites of Eutypa lata and their synthetic analogues measured in the grapeleaf disk bioassay as a per-cent reduction in chlorophyll relative to the control. (A) E. lata metabolites eutypine, eutypinol, 2-iso-propenyl-5-formylbenzofuran, siccayne and eulatachromene (1, 2, 9, 10 and 12, Figure 2). (B) Eulatachromene and its synthetic analogues 6-carboxymethylchromene, 6-formylchromene, and 6-carboxychromene (12, 17-19, Figure 2) (redrawn with modifications from Figure 5 in [31]).

Figure 5

(A) Vine leaf showing leaf stripe disease (previously young esca) and an affected grape cluster; (B) leaves showing the initial interveinal chlorotic spots; (C) black gummy material from Phaeomoniella chlamydospora infected wood, brown red wood and white decay caused by Fomitiporia mediterranea.

Figure 6

Chemical structures of Phaeoacremonium aleophilum metabolites: scytalone, isosclerone, cis-4-hydroxyscytalone, 1,3,8-trihydroxynaphtalene, 2,4,8-trihydroxytetralone, 3,4,8-trihydroxytetralone, flavioline, 2-hydroyjuglone and 4-hydroxybenzaldehyde 20-28.

Figure 7

Chemical structures of Phaeomoniella chlamydospora metabolites: scytalone, isosclerone (20-21), 4-hydroxybenzaldeide, tyrosol, 1-O-methylemodine, 3-hydroxy-5-decanolide, (S)-4-hydroxyphenyllactic acid, 3-(3-methyl-2-butenyloxy)-4-hydroxybenzoic acid (28-33).

Figure 8

Absorption of (A) 3 mL of 0.05 mg mL⁻¹ scytalone and (B) 0.1 mg mL⁻¹ isoslerone by detached leaves of grapevine cv. Italia exposed to these solutions for a few hours .(Reproduced with permission from the authors of [54]).

Figure 9

Chemical structures of Fomitiporia mediterranea metabolites: 4-hydroxybenzaldeide (28), dihydroactinolide (34) and 6-formyl-2,2-methyl-4-chromanone (35).

Figure 10

The pentaketide pathway of melanin synthesis with flavioline and 2-hydroxyjuglone (2-HJ). 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN); 1,3,8-tri- hydroxynaphthalene (1,3,8-THN); 1,2,4,5,7-pentahydroxynaphthalene (1,2,4,5,7-PHN); 5-hydroxyscytalone (5-HS); cis-4-hydroxyscytalone (4-HS); 1,2,4,5-tetrahydroxy- naphthalene (1,2,4,5-THN); 3,4,8-trihydroxytetralone (3,4,8-THT); 2,4,8-trihydroxy- tetralone (2,4,8-THT). (Reproduced with permission from the authors of [56])

Figure 11

(A) Cytofluorimetric profiles of Phaeomoniella chlamydospora extracts from strains CBS 229.95, 7, 31, 135, 551 and 606. (B) Cytofluorimetric profile of leaf extracts of asymptomatic vine leaves from asymptomatic vine no. 61 (AAA) and from symptomatic vine no. 58. The position on the x-axis clearly indicates no recognition by the antibody-labelled beads of the extracts from leaves from asymptomatic vines, and from asymptomatic leaves from asymptomatic shoots (ADD), not even when the leaves were close (ACD) or distal (AFD) to a symptomatic leaf in a symptomatic shoot (ADD). In contrast when the extracts of leaves with incipient chlorotic symptoms or leaves with fully developed symptoms from a diseased vine were tested (samples D and S, respectively), the position of the profiles on the x-axis indicated there was strong recognition by the antibodies. Axis of abscissa is FL-1og height; axis of ordinate is number of particles. (Reproduced with permission from the authors of [103]).

Figure 12

Esca-diseased grapevine leaves with tiger-stripe discoloration: a shoot showing the acropetal symptom gradient. (Reproduced with permission from the authors of [103])

Figure 13

Symptoms of grapevine affected with various species of Botryosphaeriaceae. (A) Stunting early in the season; B) Foliar chlorosis; (C) wedge-shaped necrosis in a trunk cross-section.

Figure 14

Toxic activity of organic extracts and related acqueous phases obtained from culture filtrates of Botryosphaeria dothidea, Diplodia seriata, Dothiorella viticola, Neofusicoccum luteum and N. parvum assayed on tomato plants. (Reproduced with permission from the authors of [74])

Figure 15

Symptoms caused on grapevine leaves of the cv. Tempranillo by 14-day-old culture filtrates of Neofusicoccum parvum: (A) severe withering; (B) partial withering with necrotic spots (arrows); (C) symptomless leaf (control immersed in distilled water). (Reproduced with permission from the authors of [74])

Figure 16

Structures of (3R,4R)-(-)-4-hydroxymellein, (3R,4S)-(-)-4-hydroxymellein, isosclerone and tyrosol (36, 37, 21, 29).

Figure 17

Structures of mellein, of (3R,4R)-(-)-4-hydroxymellein, of (3R)-7-hydroxymellein and of (3R, 4R)-cis-4,7-dihydroxymellein (38, 36, 39, 40), produced by Botryosphaeria obtusa.