Grapevine trunk disease (GTD) is a phrase coined by Dr Chiarappa and colleagues in the early 1990s to describe a collection of diseases with symptoms observed in both foliage and vascular tissue of grapevines. It is caused by a diverse group of fungi, that primarily infect vines through wounds caused by pruning. However, this is not a new disease complex, symptoms have been observed as long as vines have been in commercial production; but at the start of the 20th Century pathologist around the world started isolating fungi and demonstrating that they were the cause of symptoms (thus satisfying Koch’s postulates to demonstrate pathogenicity). This is a key step in understanding which of the many different organisms that can be isolated from diseased wood are causing dieback, and which are opportunistic pathogens or saprotrobes which alone would not cause grapevine trunk diseases.
Unfortunately, grapevines can be affected by one or more GTDs at the same time, for example two of the common diseases on young vines (less than five years old) known as Petri Disease and Black foot can both result in overall stunting, delayed bud break, shortened internodes, yellowing or chlorotic foliage with brown or necrotic margins and wilting of leaves or entire shoots. In addition to Petri Disease and Black foot other GTDs include Eutypa dieback, Botryosphaeria dieback, Phomopsis dieback and Esca. To further complicate matters, the symptoms could also be due to the result of poor cultural or environmental factors (referred to as disorders) affecting the establishment of these young vines.
These diseases are mainly spread by airborne fungal spores infecting wounds caused by natural damage and pruning. However, some of these pathogens such as those that cause Black foot are known to be soilborne so different management strategies will be required to prevent the introduction and spread as part of good biosecurity practice. Therefore, it is not only important to understand whether the symptoms observed are result of one of the GTDs, but which of the different pathogens are involved.
Mycologists at Fera Science Ltd have been involved in the diagnosis of GTDs for many years building up an understanding and expertise in the best techniques to detect and identify this difficult group of fungal organisms. Diagnosis will include a thorough visual examination to check for the range of symptoms, incubation and isolation to identify the range of organisms involved and expert morphological and cultural analysis to identify whether any of the key fungal pathogens are present. Additional services using molecular techniques are also available to support growers in tackling these highly damaging diseases.