GRAPEVINE PATHOGENS SPREADING WITH PROPAGATING PLANT STOCK DETECTION AND METHODS FOR ELIMINATION

ABSTRACT
The use of healthy propagating material is a key factor in viticulture. Besides causing symptomatic diseases several grapevine pathogens occur in the host plant as systemic latent (symptomless) infections. This phenomenon frequently causes epidemic disease outbreaks in new plantations leading to significant economic losses and regulatory consequences. Therefore, the use of pathogen-free propagating material is a critical component of integrated strategies to manage plant diseases. At present, more than 70 virus- and virus-like diseases of grapevines are known. Some of them (e.g., grapevine degeneration, leaf roll) can cause significant economic losses or may even be lethal (e. g., Rugose wood). Eight phytoplasmas belonging to five different groups are known to cause severe diseases with the same or very similar symptoms of grapevine yellows worldwide. Flavescence doree induced by ’Candidatus
Phytoplasma vitis’ of the 16SrV-C group, and the diseases described under different names but caused by phytoplasmas belonging to the 16SrXII group play very important roles in grapevine production. Crown gall disease caused by Agrobacterium vitis occurs in nearly all grape growing countries of the world, while Pierce’s disease (Xylella fastidosa) and bacterial necrosis (Xylophilus ampelinus) have been described in North and Central America, in the Mediterranean region of Europe and South Africa, respectively. Fungal diseases (e. g., Petri disease, Esca) leading to death of canes and trunk have emerged as important factors in viticulture in recent decades worldwide. Several fungal pathogens were found to cause decline in young vines e. g., Phaeomoniella chlamydospora, Phaeoacremonium spp., Cylindrocarpon spp., while others can cause different trunk diseases in the field as canker agents (e. g., Eutypa lata, Botryosphaeria spp.) and decay agents such as Fomitiporia mediterranea.
Pathogen-free propagating stock material can be obtained by testing existing plant material to select healthy plants and produced by appropriate curative treatments or propagation methods. For identification of virus free plants, testing on woody plant indicators (grapevines that are
especially susceptible to a given virus) by tissue grafting is still a basic and important approach. In parallel, ELISA and reverse transcription PCR that provide more rapid results are also widely used. For diagnosis, detection and identification of phytoplasmas, bacteria and fungi various sophisticated PCR-based protocols are now available (e.g. quantitative real-time PCR, multiplex PCR, nested PCR, etc.). For the elimination of viruses, grape plants are heat-treated by growing at 38oC or shoot tips are frozen in liquid nitrogen prior to starting in vitro cultures from apical meristems. Hot water treatment of dormant woody canes kills phytoplasmas, X. fastidiosa and X. ampelinus but does not completely eliminate A. vitis and fungal pathogens, although it strongly reduces the infection rate. To produce bacterium-free plants in vitro shoot tip cultures or shoot tip propagation can be used. The pathogen-free plants obtained by either of the above protocols serve as a basic material to establish stock plantations for large scale production of propagating material in vineyards. Besides the pathogens described above, there are several pests which directly cause damage, contribute to the spreading of pathogens as vectors or promote their infections through causing wounds. The most common of such pests of grapes are nematodes, mites, phylloxera and insect vectors of viruses. They can be eliminated from dormant canes by hot water treatment.