Winegrowers Supplies - Grapevine Trunk Diseases
Grapevine trunk diseases are a relatively new but growing concern for vine growers.
Here is a precy of a recent very interesting article:
What if esca disease of grapevine were not a fungal disease?
Valérie Hofstetter& Bart Buyck & Daniel Croll & Olivier Viret & Arnaud Couloux & Katia Gindro
20 March 2012. The full article is published with open access at www.springerlink.com
Grapevine trunk diseases are considered to be the most destructive diseases of grapevine of the past three decades and are of rapidly growing concern in all wine producing countries. The worldwide economical cost for the replacement of dead grapevine plants alone is roughly estimated to be in excess of 1.5 billion dollars per year.
In the literature, the term 'grapevine
trunk diseases' refers to a number of
different diseases that are inflicted by pathogenic fungi that deteriorate the perennial organs of grapevine. The most destructive among these diseases are esca and young vine decline ('young esca')
that develop respectively in established and newly planted vineyards.
Esca occurs in adult plants aged 10 years or more and can manifest itself in two ways: a slow evolving form that is recognizable by visible foliar symptoms or an apoplectic form that kills the plants within a few days. A plant may express foliar symptoms over a few years, consecutively or not, but will then generally die from apoplexy. Known since antiquity, esca was long considered as an almost negligible weakness disease that could be controlled with fungicides. During the past three decades however, and coinciding with the recent ban on the use of sodium arsenite, the incidence of esca increased drastically, infecting as many as 50% of vines in some Italian vineyards. At the same time, the broad establishment of new vineyards globally has been accompanied by a dramatic increase of young vine decline, a disease expressing similar foliar symptoms as esca, but occurring in grapevine plants 1 to 9 years old.
Esca (including black dead arm [BDA] also called black measles), young vine decline (0 Petri disease, young esca, including black foot disease), and eutypa dieback are considered fungal diseases of grapevine wood that lead generally to the death of the plant. If these diseases are present in all vineyards worldwide, their incidence is highly variable depending on the geographical area, the year, the grapevine cultivar, the rootstock used for grafting and environmental factors.
Esca diseased plants can exhibit foliar symptoms during several
years, consecutively or not, before dying, but in all cases part of the
yield will be lost.
Precise information concerning fungal diseases on grapevine is sparse and the data
are usually restricted to a particular wine-producing region or
country, or may apply only to a single specific fungal disease or to a
particular grapevine cultivar. For some Italian vineyards, the incidence of cumulated esca
diseases (up to 50 %) values has been estimated.
A six-year study of esca in Austria revealed an annual increase of 2.7 % for the appearance of the foliar symptoms in vineyards.
In the region of Alsace (France), esca and Eutypa dieback together have been reported to result in up to 10 % of plant replacement yearly. Young vine decline has been reported as widespread in California but is responsible for the replacement of only 1 to 5 % of the plants in newly established vineyards. Eutypa dieback alone has been estimated to cause production losses in Australia equivalent of 20.5 million US dollars for the sole Shiraz cultivar, while in California (USA) the cost to wine grape production alone by this same disease has been estimated to be in excess of 260 million dollars per year.
Studies on trunk diseases of grapevine have mainly focused on the description of the disease symptoms and on the isolation and identification of the fungi present in necrotic wood of symptomatic plants. The principal pathogenic taxa associated with esca are Eutypa lata, Phaeomoniella chlamydospora, and various species of the genera Botryosphaeria, Cylindrocarpon, Fomitiporia, Phaeoacremonium, Phellinus, Phomopsis, and Stereum. With the exception of basidiomycetous Fomitiporia, Stereum, and Phellinus species, all these pathogens have also been isolated from necrotic wood of plants suffering from young vine decline, although with a higher incidence for Cylindrocarpon species, Phaeomoniella chlamydospora, Phaeoacremonium aleophilum, and one additional genus, Cadophora.
The fungi that are held responsible for esca or young vine decline have also been associated individually with other grapevine diseases. As such, Eutypa lata is considered to be responsible for eutypa dieback, Phomopsis viticola for excoriosis, Botryosphaeria dothidea for cane blight, various Cylindrocarpon species for black foot disease and Botryosphaeria species for cankers. It is unclear whether esca and young vine decline are due to these different fungi acting jointly or in succession. These disease-associated fungi have also been isolated with variable incidence from nursery plants, rootstock mother vines as well as from apparently healthy young and adult grapevines, leading to the view that these fungi are latent pathogens.
Climatic and edaphic factors as well as host genotype (i.e. grapevine cultivar) have been reported to influence the incidence of these trunk diseases, thereby suggesting that these fungal pathogens are a prerequisite for the expression of the disease symptoms, but are themselves not always responsible for their appearance. In spite of an impressive number of phytopathological studies over the past years, the epidemiology and etiology of grapevine wood diseases remain poorly understood. The assumption that these fungi are latent pathogens implies that they may live asymptomatically for at least part of their life in a plant, but should then, at some point, modify their behaviour and become invasive, thereby leading to the expression of the disease symptoms. A first objective of the present study was to determine which fungal species modified their latent behaviour and became invasive when esca symptoms appear. Secondly, as the contamination of nursery plants is presently one of the major concerns of the wine industry, we also wanted to determine whether the esca-associated fungi were transmitted to nursery plants through grafting material. In order to achieve these objectives, we analyzed the cultivable part of the fungal community that inhabits the wood of both healthy and esca-symptomatic grapevine plants, as well as the cultivable part of the fungal community that is associated with the wood of nursery plants. In this respect, it is important that the latter were not hot water treated and were grafted on identical rootstock as adult plants using shoots of apparently healthy material sampled from the same experimental adult vineyard.
Other organisms, such as bacteria, may be involved in esca but eventual differences between the bacterial communities associated with diseased or healthy grapevines have never been studied. Environmental parameters may also play an important role in the emergence of grapevine trunk diseases, as may changes in vineyard management and cultural practices or differences between grapevine genotypes.