Control of chestnut blight by the use of hypovirulent strains of the fungus Cryphonectria parasitica in northwestern Spain P. Zamora a,c,d,⇑ , A.B. Martín a , R. San Martín b,d , P. Martínez-Álvarez c,d , J.J. Diez c,d a Centro de Sanidad Forestal de Calabazanos, Consejería de Fomento y Medio Ambiente, Dirección General del Medio Natural, JCyL, Polígono de Villamuriel, 34190 Villamuriel de Cerrato, Palencia, Spain b Departamento de Estadística ETSIIAA Palencia, U. De Valladolid, Avda. Madrid 57, 34004 Palencia, Spain c Departamento de Producción Vegetal y Recursos Forestales, ETSIIAA Palencia, U. De Valladolid, Avda. Madrid 57, 34004 Palencia, Spain d Sustainable Forest Management Research Institute, University of Valladolid – INIA, Avda. Madrid 57, 34004 Palencia, Spain highlights  Hypovirulent isolates of EU11 reduced canker lesions in dormant chestnut stems.  Hypovirulent isolates of EU1 had no effect reducing canker lesions in the stems assay.  Effective hypovirulent treatment of chestnut blight in León orchards.  In Zamora orchards one of the three treatments had effect reducing canker growth. graphical abstract Field and cut stems inoculation with hypovirulent isolates from Castilla y León corresponding to the hypovirus subtype CHV1-F1. article info Article history: Received 1 June 2014 Accepted 18 August 2014 Available online 26 August 2014 Keywords: Cryphonectria parasitica Hypovirus Chestnut blight Field inoculations abstract Chestnut blight is controlled in Europe by using Cryphonectria hypovirus CHV1, a non-encapsulated RNA virus. The chestnut blight fungus, Cryphonectria parasitica, is weakened by the virus, and healing tissue growth occurs in the host tree. Transmission of this cytoplasmic hypovirus is restricted by the incompat- ibility system of the fungus, so that the hypovirus can be transmitted only between isolates of the same or closely related vegetative compatibility (vc) types. Hypovirulent isolates of C. parasitica (all of the French subtype CHV1-F1) from Castilla y León (NW Spain) were compared with virulent isolates in both laboratory (cut stems) and field inoculations (in two orchards in the province of León and one orchard in the province of Zamora). The tests were performed with the most common vc types in the region, EU1 and EU11. The cut stem assay revealed that the hypovirulent isolates of vc type EU1 did not reduce the growth of virulent cankers. By contrast, four hypovirulent strains H1, H4, H5 and H6 (all vc type EU11) reduced the growth of virulent isolates in the cut stem assay. Field tests showed that hypovirulent isolates of EU1 and EU11 were effective in reducing canker in both orchards in León with all treatments tested; however, in Zamora, where only EU11 was tested, all the treatments failed except H1, which was able to reduce growth of the canker eighteen months after the inoculation. The development of hypovi- rulence suggests that hypovirus subtype F1 is well adapted in the province of León. Both naturally extended and inoculated hypoviruses appear to have reduced the incidence of the canker, thus improving http://dx.doi.org/10.1016/j.biocontrol.2014.08.005 1049-9644/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author at: Centro de Sanidad Forestal de Calabazanos, Consejería de Fomento y Medio Ambiente, Dirección General del Medio Natural, JCyL, Polígono de Villamuriel, 34190 Villamuriel de Cerrato, Palencia, Spain. Fax: +34 979770212. E-mail addresses: zambrapa@jcyl.es (P. Zamora), marheraa@jcyl.es (A.B. Martín), rsmartin@eio.uva.es (R. San Martín), pmtnez@pvs.uva.es (P. Martínez-Álvarez), jdcasero@pvs.uva.es (J.J. Diez). Biological Control 79 (2014) 58–66 Contents lists available at ScienceDirect Biological Control journal homepage: www.elsevier.com/locate/ybcon