Laura Mugnai

Esca (Black Measles) and Brown Wood-Streaking: Two Old and Elusive Diseases of Grapevines

“Esca” disease of grapevine has long been known wherever grapes are grown. The disease may be as old as vine cultivation itself. References to esca-like symptoms are found in several ancient Greek and Latin works. Greater descriptive accuracy is found in medieval works such as the Kitab al-Felahah by Ibn al-Awam, a Spanish Muslim who lived in Seville at the end of the twelfth century, and the Opus Ruralium Commodorum by Pietro de’ Crescenzi, born around 1233 in Bologna. Esca is a Latin word meaning food, aliment, or, figuratively, bait. The name indirectly refers to the fruiting bodies of certain wood-rotting fungi. For example, Fomes, which in Latin means “tinder,” is the name of a genus of basidiomycetes once used to make a dry, easily ignited material suitable to start fires when using flints. Wood decayed by these fungi, including rotted grapevine wood, burned slowly and was used to keep fires aglow without a flame. Esca is a complex disease that comprises an array of symptoms, some of which have locally given their own names to the disease. For example in California, the dark, tiny spotting of the grapes is called “black measles.” In many grapevine-growing areas of the world, the sudden wilting of esca-affected vines in summer has earned this form of the disease the name “apoplexy.” Research on the etiology of esca, which started at the end of the nineteenth century in France, can be divided into three periods. The first period began in 1898 with Ravaz (61) and ended in 1926 with Viala (79). The overall conclusion of this period was that two basidiomycetous fungi, Stereum hirsutum (Willd.) Pers. and Phellinus (Fomes) igniarius (L.:Fr.) Quél., were the causal agents, although this could not be shown by pathogenicity tests. However, in Italy in 1912, Petri (58) successfully reproduced some early internal esca symptoms with two undetermined species of Cephalosporium and one of Acremonium that had also been associated with the disease. The second period in esca research started in California in 1957 with Hewitt (35) and lasted until 1959, when Chiarappa (9) detected the relationship between internal wood decay and black measles. He also showed how a Cephalosporium sp. reproduced in vivo some of the symptoms observed in the wood of diseased vines, and how P. igniarius caused wood decay in vitro. The third period, initiated by Larignon and Dubos in 1987 (39) and still underway, is directed at understanding the role of the mitosporic (asexually reproducing) fungi that act alone or together with the basidiomycetes to cause esca and related diseases. In the 1990s, studies on esca and its etiology have intensified. This came after a dramatic upsurge in the disease, especially in Germany, Italy, and Greece, where the arsenites, traditionally used to keep esca under control, have been banned and were replaced by less effective fungicides. However, even in France, Portugal, and Spain, where restricted use of sodium arsenite is still permitted, esca is widespread in all vine-growing regions. This paper refers mostly to conditions in the Mediterranean area and focuses on the progress achieved in our understanding of esca over the last few years. Reference is also made to a decline of young grapevines caused by some of the same mitosporic fungi as those commonly associated with esca in adult vines. Finally, the relations between esca and related syndromes or diseases are also discussed.

A chemotaxonomic evaluation of the genus Beauveria

Intra- and interspecific variation of thirty-two isolates assignable to the genus Beauveria was evaluated using 64 morphological and biochemical characters. Two isolates of Tolypocladium cylindrosporum were included to test generic concepts. Seventeen cluster groups were obtained following a numerical taxonomic analysis, each group being separated by at least one character. Cultural characters were highly variable and could not be used reliably for species determination. Spore form was the most useful criterion to distinguish between species. Biochemical data generally supported species concepts based purely on morphology, with the exception of B. bassiana which comprised a heterogeneous assemblage of strains. There is evidence from API ZYM and esterase patterns that this variability is determined by host (substrate) and geographical origins. B. alba , although morphologically close to B. bassiana , could be separated readily on biochemical characters using principal component analysis. The following species of Beauveria are recognized: B. alba, B. amorpha, B. bassiana, B. brongniartii, B. velata, B. vermiconia and an undescribed taxon close to B. amorpha but morphologically and biochemically distinct. Both isolates of T. cylindrosporum cluster in the same group and, on the basis of present evidence, particularly conidiogenesis, the synonymy of this genus with Beauveria is questioned.

Phytotoxins Produced by Fungi Associated with Grapevine Trunk Diseases

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.

Older and more recent observations on esca: a critical overview

The main research findings of studies in esca carried out over the last few years in a number of laboratories are discussed. The topics include: the disease model; the relationship between black dead arm and esca; the role of toxins and xylem cavitation in the development of leaf symptoms; the artificial reproduction of leaf symptoms and wood rot; the inoculum sources of the fungi Phaeomoniella chlamydospora, Phaeoacremonium aleophilum and Fomitiporia mediterranea, and the influence of climate on the incidence of esca. The purpose was to sum up the current state of esca research and where possible to present new suggestions and sometimes alternatives to the suggestions of other researchers. The ultimate aim was to draw attention to those questions in esca research that are open to differing and even opposing explanations because the hard data are still lacking.

The effect of nitric oxide generators on ischemia reperfusion injury and histamine release in isolated perfused guinea-pig heart.

Experiments were carried out to provide evidence of the effect ofl-arginine (l-Arg), its analogue NG-monomethyl-l-arginine (MeArg) and of some nitrovasodilators (sodium nitroprusside, NaNP; 3-morpholino-sydnonimine, SIN-1) which spontaneously release nitric oxide (NO) on ischemia-reperfusion injury, histamine release and mast cell degranulation, occurring after multiple ligature and release of the left anterior descending (LAD) coronary artery in isolated perfused guinea-pig hearts. The reopening of the LAD coronary artery leads to a release of histamine related to a decrease in microdensitometry of cardiac mast cells and to calcium overload. The perfusion of the heart with NO-donors significantly reduces either the release of histamine, the loss of mast cell metachromasia and the overload of calcium. These effects were potentiated by SOD. The results suggest that the endogenous formation of NO and molecules able to generate NO have a role in the prevention of post-ischemic tissue injury.

Epidemiology of esca in some vineyards in Tuscany (Italy).

The incidence of esca in 5 vineyards (SCFI, GTFI, CBSI-1, 2, 3) in Tuscany was monitored from 1992 to 1994 in SCFI, from 1993 to 1998 in GTFI, and from 1995 to 1998 in CBSI-1, 2 and 3. Disease incidence varied from vineyard to vineyard and from year to year. SCFI was the vineyard most affected with an incidence of 63% in 1993, 20% in 1994, and 46% in 1992. However, symptom expression in individual plants was characterized by very marked discontinuity from year to year. As a result, only 8% of diseased plants in SCFI had foliar symptoms in all 3 years of the survey period. The percentage of consistently diseased plants went down to less than 1% in GTFI and CBSI-3 and was nil in CBSI-1 and 2. The cumulative disease incidence, calculated by counting all the plants that showed foliar symptoms at least once in the years surveyed, was 82, 50, 19, 12, and 10% in SCFI, GTFI, CBSI-3, 1 and 2 respectively. An examination of rainfall and air temperature parameters in relation to esca incidence did not detect any weather conditions especially conducive to esca. However, it seemed that a fresh, rainy summer is more favorable to the chronic form of esca while a hot, dry summer is more conducive to the acute form.

Effects of nucleus basolateralis amygdalae neurotoxic lesions on aversive conditioning in the rat

After bilateral stereotaxic administration of ibotenic acid on the n. basolateralis amygdalae, male adult rats were tested in the light-dark box apparatus to measure the time-course of the acquisition and retention of passive and active avoidance responses. The results show that after the lesions both passive avoidance and active avoidance acquisition were impaired. Passive avoidance responses were retained quite well, while active avoidance responses disappeared quickly. Conditioned freezing was almost completely absent. Thus it appears that the n. basolateralis plays a facilitatory role in all the conditioned responses which were investigated.

CHEMICAL STRUCTURE OF TWO PHYTOTOXIC EXOPOLYSACCHARIDES PRODUCED BY PHOMOPSIS FOENICULI

The two main exocellular polysaccharides produced in vitro by Phomopsis foeniculi, a fungal pathogen of fennel, were isolated and characterized by chemical and spectroscopic methods as a galactan with the known structure [-->6)-beta-D-Galf-(1-->5)-beta-D- Galf-(1-->5)-beta-D-Galf-(1-->]n and a mannan. The latter consists of a backbone of alpha-(1-->6)-linked mannopyranose units. Almost all of these are branched at the 2 position with arms containing 2- and 3-linked mannopyranose units. The crude polysaccharide fraction and its components, galactan and mannan, showed phytotoxic effects, i.e. chlorosis, necrosis and/or wilting, on fennel and on two non-host plants, tobacco and tomato.

Phaeomoniella chlamydospora-Grapevine Interaction : Histochemical Reactions to Fungal Infection

Histochemical reactions of one-year-old potted micropropagated vines (rootstock 1103 Paulsen) to inoculation with Phaeomoniella chlamydospora were studied. Microscopic examination of the vine wood showed that the fungus spread through the wood tissue, albeit slowly. Starting from the roots it required nine months to colonise the first 20-25 cm of the grapevine stems. The slow spread of P. chlamydospora is thought to be due to the defence response initiated by the vines: production of tyloses, including accumulation of phenols in the vessels and adjacent tissue, and the deposition of unidentified defence-response substances, probably stilbene-like substances from the cell-wall surrounding the infection

The Esca Disease Complex

Esca is a grapevine wood disease that seriously affects vine yield and longevity. Our knowledge of this disease and its causes has changed profoundly in recent years, as it has become clear that esca in fact comprises a number of distinct diseases and that the main fungal agents (primarily vascular pathogens) invade the vines not only through wounds applied in the field but also as a result of nursery practices. When vines become infected in the nursery, the diseases that develop may vary, from Petri decline to full-blown esca, with or without white decay. With the banning of sodium arsenite no chemical control is now available and sanitary practices in the nursery are suggested as being the best approach to eliminate or at least reduce pre-planting infections from the tracheomycotic fungi. In the absence of chemical prevention, some preventive and curative action can also be taken in the field to reduce infections or to hamper symptom appearance in esca-infected vines, as will be described.