Zamora P.,University of Valladolid |
San Martin R.,U. De Valladolid |
San Martin R.,University of Valladolid |
Martinez-Alvarez P.,ETSIIAA Palencia |
And 3 more authors.
Biological Control | Year: 2014
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 incompatibility 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 hypovirulence 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 chestnut stands. However, the inoculations were not as effective in the orchards in Zamora. This indicates that the disease could be controlled in Castilla y León by inoculation of trees with hypovirulent strains, but that more tests should be done in provinces where the hypovirus is still not present. © 2014 Elsevier Inc.
Zamora P.,University of Valladolid |
Martin R.S.,U. De Valladolid |
Martin R.S.,University of Valladolid |
Diez J.J.,U. De Valladolid |
Diez J.J.,University of Valladolid
European Journal of Plant Pathology | Year: 2015
Hypovirulent strains of the chestnut blight fungus Cryphonectria parasitica have not been registered in the autonomous region of Castilla y León (Spain), except in the province of León. In this laboratory-based study, we analyzed the rates of horizontal transmission of hypovirus CHV1 subtype F1, isolated from chestnut stands in León. We tested the conversion capacity of the six vegetative compatibility (vc) types of C. parasitica isolates most commonly distributed in Castilla y León (EU1, EU11, EU12, EU66, CL5 and CL6). We investigated conversion rates of virulent isolates into hypovirulent isolates between pairings of isolates of the same vc type (EU1, EU11 and CL6) and also tested cross conversion rates between isolates of different vc types (EU1, EU11 and CL6 as donors and EU12, EU66, CL5 and CL6 as recipients). We carried out the hypovirus transmission assay with 1700 pairings, of which 700 had donor and recipient isolates of the same vc type and 1000 pairings of isolates had different vc types. Our results show that the conversion frequency to hypovirulent isolates was significantly affected by the vc type, the genotype of isolates with the same origin (province) and the interaction between both factors. In the conversion between isolates of the same vc type, the conversion rates were better with EU1 (ranging between 56 and 94 %) than with EU11 (varying from 4 to 58 %). In the cross conversion between donor and recipient isolates of different vc types, only CL5 and CL6 recipients were converted and the conversion of recipient isolates of EU12 and EU66 failed in all cases. For CL5 as recipient isolate, the conversion rates were similar with EU11 and CL6 as the donor isolates. Recipient isolates of CL6 had good conversion with donor isolates from the same vc type (CL6) and in cross conversion the results were better with donor EU1. Fungal isolates from chestnut stands in León displayed the best conversion rates, followed by those from Zamora, Salamanca and Ávila when the donor and the recipient isolates were of the same vc type. The fungal isolates appear to have a strong influence on the transmission rate of the hypovirus, at least between strains isolated from chestnut stands in Castilla y León. EU1 isolates were more susceptible to conversion than the isolates from EU11. The results highlight the differences in hypovirus transmission, regarding vc types and the genotype of isolates from the same province, when donor and recipient isolates are of the same vc type. Further transmission assays would be useful to determine why hypovirus transmissions, when compared to the hypovirus transmission of other European assays, have different conversion rates with fungal isolates from Castilla y León. © 2015 Koninklijke Nederlandse Planteziektenkundige Vereniging