2.2.49
DIVERSITY OF VEGETATIVE COMPATIBILITY GROUPS OF CRYPHONECTRIA PARASITICA IN EUROPE

U HEINIGER1, P CORTESI2, C COLINAS3, C PERLEROU4, D RIGLING1, C ROBIN5, K SOTIROVSKI6, M USCUPLIC7

1Swiss Federal Institute for Forest, Snow and Landscape Research, CH-8903 Birmensdorf, Switzerland; 2Istituto Patologia Vegetale, Universita, I-20133 Milano, Italy; 3University, SP-25198 Lleida, Spain; 4Forest Research Institute, NAGREF, GR-57006 Vassilika, Greece; 5INRA Pathologie végétale, BP 81, F-33 882 Villenave d'Ornon, France; 6Faculty of Forestry, RM-Skopje, Macedonia; 7 Faculty of Forestry, BH-Sarajevo, Bosnia-Herzegovina

Background and objectives
The chestnut blight fungus Cryphonectria parasitica was introduced into southern Europe around 1938 and led to great destruction of the European chestnut (Castanea sativa). The natural appearance of hypovirulence resulted in the recovery of many chestnut stands (reviewed in [1]). Hypovirulence is caused by double-stranded RNA hypoviruses which are transmitted between fungal strains via hyphal anastomosis . A major obstacle for hypovirus transmission - and thus biological control of the disease - is the vegetative incompatibility between C. parasitica strains. In Italy and Switzerland, 31 vegetative compatibility (vc) types were found, with certain vc types dominating at specific sites [2]. The objectives of this study were to compare vc types found throughout Europe with the European tester strains and to assess vc diversity in Italy, Switzerland, France, Macedonia, Greece, Bosnia, and Spain. The COST action G4 'Multidisciplinary Chestnut Research' made this cooperation possible.

Materials and methods
Vc testing was performed on PDA or PDAg or PDA with red food-colouring plates using the vc testers EU-1 to EU-31 from Italy and Switzerland [2]. More than 3000 C. ;parasitica isolates were sampled in Italy, Switzerland, France, Macedonia, Greece, Bosnia, and Spain.

Results and conclusions

A total of 33 vc types were identified. Twenty vc types were found in Italy, 28 in Switzerland, 28 in France, five in Macedonia, 17 in Bosnia, three in Greece, and 10 in Spain. Many vc types were rare. At all sites one or two vc types dominated. The diversity was greatest in northern Italy and southern Switzerland with a maximum of 16 vc types per site. In southern Italy, Macedonia, Greece, and Spain, only one to four vc types were identified per site. Vc types were not evenly distributed throughout Europe. EU-2 was the dominant vc type in northern Italy, Switzerland, and south-eastern France but was absent in southern Italy and Macedonia. EU-10 was not found in Switzerland and northern Italy. In contrast, it occurred at a frequency of about 25% in southern Italy, 0.3% in Macedonia and 2% in Greece. EU-12 accounted for 95% of the Macedonian isolates, 85% of the Greek isolates and for 86% of the isolates at a site in Sicily. In northern Italy and Switzerland, EU-12 never represented more than 8% of the isolates at the sites where it was present.

These results show that no equilibrium of vc types is established in Europe. This may be a consequence of multiple introductions, founder effects or restricted gene flow. Since the dissemination of hypovirulence is hampered by vc diversity, appropriate quarantine regulations are recommended to prevent the introduction of new vc types. Moreover, biological control must be carried out with hypovirulent strains belonging to the most common vc types at the site treated.

References
1. Heiniger U, Rigling D, 1994. Annual Review of Phytopathology 32, 581-599.
2. Cortesi P, Rigling D, Heiniger U, 1998. European Journal of Forest Pathology, in press.