Current situation of Verticillium albo-atrum hop strains in Slovenia
In Slovenia, Verticillium wilt of hop (EPPO A2 List) was first discovered in 1974 in its mild form which is associated with the less virulent strains of Verticillium albo-atrum and V. dahliae. Until 1997, the disease appeared only sporadically in some hop (Humulus lupulus) gardens, but in that year an outbreak of the lethal form was registered in the Western part of the Savinja valley. Virulence testing and AFLP molecular analysis identified the causal agent as the highly virulent hop pathotype PV1 of V. albo-atrum, and further studies showed that it corresponded to a new genotype of PV1 (genotype PG2). Until now the V. albo-atrum hop pathotypes with increased virulence are reported only from the United Kingdom (1933), Slovenia (1997) and Germany (2005). Since 1998, an official monitoring survey of hop gardens has been conducted by the Slovenian Institute for Hop Research and Brewing under the supervision of the NPPO. This survey included visual inspection of hop gardens, sampling, laboratory analysis and expert advice on measures to both growers and phytosanitary inspectors. Results showed that V. albo-atrum (highly virulent pathotype PV1) occurred in several hop gardens in the Savinja valley (200 ha). V. albo-atrum (mild pathotype M) was found in a few hop gardens, but in all hop-growing regions in Eastern Slovenia: Koroška region (administrative units of Dravograd, Radlje ob Dravi, Slovenj Gradec); Savinjska region (administrative units of Celje, Žalec, Mozirje), Štajerska region (administrative units of Brežice, Krško, Lenart, Ljutomer, Ormož, Ptuj, Šmarje pri Jelšah).
Phytosanitary control measures were initiated in 2001 in accordance with Slovenian legislation (‘Decree on protective measures for preventing the spread and for suppression of the hop wilt caused by fungi Verticillium albo-atrum Reinke ; Berthold and Verticillium dahliae Klebahn’. Official Gazette of the Republic of Slovenia, no. 45/01, 117/02, 31/2004, 35/2014). Until the year 2000, the aim was to progressively eradicate the disease and approximately 67 ha of hop gardens were completely destroyed and a 4-year quarantine period was imposed in infected fields where only non-host plants could be grown. Despite intensive official monitoring, training campaigns, quarantine and hygienic measures, the disease continued to spread. It was realized that this spread was related to the use of infected hop debris in healthy gardens, of contaminated machinery, and non-certified planting material. As a consequence, measures were modified in 2001 to focus on the elimination of local foci and individual diseased plants. In total, 147 ha of infected hop gardens were destroyed in Slovenia in the period from 1997 to 2013. Since 2014, Verticillium wilt is regulated only within a certification scheme for hop planting material (‘Rules for marketing of hop planting material’. Official Gazette of the Republic of Slovenia, no. 31/2004, 21/2007, 19/2008, 12/2010, 45/2013) and the general phytosanitary legislation concerning plant passports (EU Council Directive 2000/29/EC). Before being commercialized, standard and certified planting material is officially checked to verify the absence of V. albo-atrum hop strains.
The pest status of Verticillium albo-atrum hop strains in Slovenia is officially declared as: Present, subject to official control.
Sources
NPPO of Slovenia (2014-07).